Extrafollicular B cell responses correlate with neutralizing antibodies and morbidity in COVID-19.

A wide spectrum of clinical manifestations has become a hallmark of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) COVID-19 pandemic, although the immunological underpinnings of diverse disease outcomes remain to be defined. We performed detailed characterization of B cell responses through high-dimensional flow cytometry to reveal substantial heterogeneity in both effector and immature populations. More notably, critically ill patients displayed hallmarks of extrafollicular B cell activation and shared B cell repertoire features previously described in autoimmune settings. Extrafollicular activation correlated strongly with large antibody-secreting cell expansion and early production of high concentrations of SARS-CoV-2-specific neutralizing antibodies. Yet, these patients had severe disease with elevated inflammatory biomarkers, multiorgan failure and death. Overall, these findings strongly suggest a pathogenic role for immune activation in subsets of patients with COVID-19. Our study provides further evidence that targeted immunomodulatory therapy may be beneficial in specific patient subpopulations and can be informed by careful immune profiling.

Patients taking benralizumab, dupilumab, or mepolizumab have lower postvaccination SARS-CoV-2 immunity.

BACKGROUND: Biologic therapies inhibiting the IL-4 or IL-5 pathways are very effective in the treatment of asthma and other related conditions. However, the cytokines IL-4 and IL-5 also play a role in the generation of adaptive immune responses. Although these biologics do not cause overt immunosuppression, their effect in primary severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) immunization has not been studied completely. OBJECTIVE: Our aim was to evaluate the antibody and cellular immunity after SARS-CoV-2 mRNA vaccination in patients on biologics (PoBs). METHODS: Patients with severe asthma or atopic dermatitis who were taking benralizumab, dupilumab, or mepolizumab and had received the initial dose of the 2-dose adult SARS-CoV-2 mRNA vaccine were enrolled in a prospective, observational study. As our control group, we used a cohort of immunologically healthy subjects (with no significant immunosuppression) who were not taking biologics (NBs). We used a multiplexed immunoassay to measure antibody levels, neutralization assays to assess antibody function, and flow cytometry to quantitate Spike-specific lymphocytes. RESULTS: We analyzed blood from 57 patients in the PoB group and 46 control subjects from the NB group. The patients in the PoB group had lower levels of SARS-CoV-2 antibodies, pseudovirus neutralization, live virus neutralization, and frequencies of Spike-specific B and CD8 T cells at 6 months after vaccination. In subgroup analyses, patients with asthma who were taking biologics had significantly lower pseudovirus neutralization than did subjects with asthma who were not taking biologics. CONCLUSION: The patients in the PoB group had reduced SARS-CoV-2-specific antibody titers, neutralizing activity, and virus-specific B- and CD8 T-cell counts. These results have implications when considering development of a more individualized immunization strategy in patients who receive biologic medications blocking IL-4 or IL-5 pathways.

Detection of Newly Secreted Antibodies Predicts Nonrecurrence in Primary Clostridioides difficile Infection.

Within 8 weeks of primary Clostridioides difficile infection (CDI), as many as 30% of patients develop recurrent disease with the associated risks of multiple relapses, morbidity, and economic burden. There are no clear clinical correlates or validated biomarkers that can predict recurrence during primary infection. This study demonstrated the potential of a simple test for identifying hospitalized CDI patients at low risk for disease recurrence. Forty-six hospitalized CDI patients were enrolled at Emory University Hospitals. Samples of serum and a novel matrix from circulating plasmablasts called "medium-enriched for newly synthesized antibodies" (MENSA) were collected during weeks 1, 2, and 4. Antibodies specific for 10 C. difficile antigens were measured in each sample. Among the 46 C. difficile-infected patients, 9 (19.5%) experienced recurrence within 8 weeks of primary infection. Among the 37 nonrecurrent patients, 23 (62%; 23/37) had anti-C. difficile MENSA antibodies specific for any of the three toxin antigens: TcdB-CROP, TcdBvir-CROP, and/or CDTb. Positive MENSA responses occurred early (within the first 12 days post-symptom onset), including six patients who never seroconverted. A similar trend was observed in serum responses, but they peaked later and identified fewer patients (51%; 19/37). In contrast, none (0%; 0/9) of the patients who subsequently recurred after hospitalization produced antibodies specific for any of the three C. difficile toxin antigens. Thus, patients with a negative early MENSA response against all three C. difficile toxin antigens had a 19-fold greater relative risk of recurrence. MENSA and serum levels of immunoglobulin A (IgA) and/or IgG antibodies for three C. difficile toxins have prognostic potential. These immunoassays measure nascent immune responses that reduce the likelihood of recurrence thereby providing a biomarker of protection from recurrent CDI. Patients who are positive by this immunoassay are unlikely to suffer a recurrence. Early identification of patients at risk for recurrence by negative MENSA creates opportunities for targeted prophylactic strategies that can reduce the incidence, cost, and morbidity due to recurrent CDI.

StaphAIR: A Label-Free Antigen Microarray Approach to Detecting Anti-Staphylococcus aureus Antibody Responses in Orthopedic Infections.

Arrayed imaging reflectometry (AIR) is an optical biosensor platform for simple, multiplex measurement of antigen-specific antibody responses in patient blood samples. Here, we report the development of StaphAIR, an 8-plex Staphylococcus aureus antigen array on the AIR platform for profiling antigen-specific anti-S. aureus humoral immune responses. Initial validation experiments with mouse and humanized monoclonal antibodies against the S. aureus autolysin glucosaminidase (Gmd) domain, and subsequent testing with dilution series of pooled positive human serum confirmed analytically robust behavior of the array, with all antigens displaying Langmuir-type dose-response curves. Testing a cohort of 82 patients with S. aureus musculoskeletal infections (MSKI) and 30 healthy individuals enabled discrimination of individual patient responses to different S. aureus antigens, with statistical significance between osteomyelitis patients and controls obtained overall for four individual antigens (IsdA, IsdB, Gmd, and SCIN). Multivariate analyses of the antibody titers obtained from StaphAIR revealed its utility as a potential diagnostic tool for detecting S. aureus MSKI (area under the receiver operating characteristic curve (AUC) > 0.85). We conclude that StaphAIR has utility as a high-throughput immunoassay for studying and diagnosing osteomyelitis in patients.

Mechanisms of Immune Evasion and Bone Tissue Colonization That Make Staphylococcus aureus the Primary Pathogen in Osteomyelitis.

PURPOSE OF REVIEW: Staphylococcus aureus is the primary pathogen responsible for osteomyelitis, which remains a major healthcare burden. To understand its dominance, here we review the unique pathogenic mechanisms utilized by S. aureus that enable it to cause incurable osteomyelitis. RECENT FINDINGS: Using an arsenal of toxins and virulence proteins, S. aureus kills and usurps immune cells during infection, to produce non-neutralizing pathogenic antibodies that thwart adaptive immunity. S. aureus also has specific mechanisms for distinct biofilm formation on implants, necrotic bone tissue, bone marrow, and within the osteocyte lacuno-canicular networks (OLCN) of live bone. In vitro studies have also demonstrated potential for intracellular colonization of osteocytes, osteoblasts, and osteoclasts. S. aureus has evolved a multitude of virulence mechanisms to achieve life-long infection of the bone, most notably colonization of OLCN. Targeting S. aureus proteins involved in these pathways could provide new targets for antibiotics and immunotherapies.

Tracking Anti-Staphylococcus aureus Antibodies Produced In Vivo and Ex Vivo during Foot Salvage Therapy for Diabetic Foot Infections Reveals Prognostic Insights and Evidence of Diversified Humoral Immunity.

Management of foot salvage therapy (FST) for diabetic foot infections (DFI) is challenging due to the absence of reliable diagnostics to identify the etiologic agent and prognostics to justify aggressive treatments. As Staphylococcus aureus is the most common pathogen associated with DFI, we aimed to develop a multiplex immunoassay of IgG in serum and medium enriched for newly synthesized anti-S. aureus antibodies (MENSA) generated from cultured peripheral blood mononuclear cells of DFI patients undergoing FST. Wound samples were collected from 26 DFI patients to identify the infecting bacterial species via 16S rRNA sequencing. Blood was obtained over 12 weeks of FST to assess anti-S. aureus IgG levels in sera and MENSA. The results showed that 17 out of 26 infections were polymicrobial and 12 were positive for S. aureus While antibody titers in serum and MENSA displayed similar diagnostic potentials to detect S. aureus infection, MENSA showed a 2-fold-greater signal-to-background ratio. Multivariate analyses revealed increases in predictive power of diagnosing S. aureus infections (area under the receiver operating characteristic curve [AUC] > 0.85) only when combining titers against different classes of antigens, suggesting cross-functional antigenic diversity. Anti-S. aureus IgG levels in MENSA decreased with successful FST and rose with reinfection. In contrast, IgG levels in serum remained unchanged throughout the 12-week FST. Collectively, these results demonstrate the applicability of serum and MENSA for diagnosis of S. aureus DFI with increased power by combining functionally distinct titers. We also found that tracking MENSA has prognostic potential to guide clinical decisions during FST.

A humoral immune defect distinguishes the response to Staphylococcus aureus infections in mice with obesity and type 2 diabetes from that in mice with type 1 diabetes.

Obesity and diabetes are among the greatest risk factors for infection following total joint arthroplasty. However, the underlying mechanism of susceptibility is unclear. We compared orthopedic implant-associated Staphylococcus aureus infections in type 1 (T1D) versus type 2 (T2D) diabetic mouse models and in patients with S. aureus infections, focusing on the adaptive immune response. Mice were fed a high-fat diet to initiate obesity and T2D. T1D was initiated with streptozotocin. Mice were then given a trans-tibial implant that was precoated with bioluminescent Xen36 S. aureus. Although both mouse models of diabetes demonstrated worse infection severity than controls, infection in T2D mice was more severe, as indicated by increases in bioluminescence, S. aureus CFU in tissue, and death within the first 7 days. Furthermore, T2D mice had an impaired humoral immune response at day 14 with reduced total IgG, decreased S. aureus-specific IgG, and increased IgM. These changes were not present in T1D mice. Similarly, T2D patients and obese nondiabetics with active S. aureus infections had a blunted IgG response to S. aureus. In conclusion, we report the first evidence of a humoral immune deficit, possibly due to an immunoglobulin class switch defect, in obesity and T2D during exacerbated S. aureus infection which may contribute to the increased infection risk following arthroplasty in patients with T2D and obesity.

A Diagnostic Serum Antibody Test for Patients With Staphylococcus aureus Osteomyelitis.

BACKGROUND: Because immunity against Staphylococcus aureus has not been fully elucidated, there is no diagnostic test to gauge how robust a patient's host response is likely to be. Therefore, we aimed to develop a test for specific antibodies in serum with diagnostic and prognostic potential. QUESTIONS/PURPOSES: We describe the development and validation of a multiplex immunoassay for characterizing a patient's immune response against 14 known S aureus antigens, which we then used to answer four questions: (1) Do certain antigens predominate in the immune response against S aureus? (2) Is there a predominant pattern of antigens recognized by patients and mice with infections? (3) Is the immunoglobulin G (IgG) response to any single antigen a useful predictor of ongoing S aureus infection? (4) Does measurement of the combined response against all 14 antigens provide a better predictor of ongoing infection? METHODS: A case-control study was performed. Sera were collected from 35 consecutive patients with S aureus culture-confirmed (methicillin-sensitive S aureus or methicillin-resistant S aureus) musculoskeletal infections (deep implant-associated, osteomyelitis, and cases of established septic arthritis). Patients were excluded only if they did not give informed consent for participation. Twenty-four patients had implant infections after total joint replacements, five had fracture implant infections, four had native knee infections, and two had chronic osteomyelitis without an implant. Control patients were chosen from a group of healthy, medically optimized patients scheduled to undergo elective arthroplasty. Control patients were matched for age (± 3 years), BMI (± 3 kg/m(2)), and sex as closely as possible to patients with infections. Sera from patients with S aureus infections and murine S aureus tibial implant infections were used to evaluate a multiplex immunoassay for immunoglobulin titers against 14 recombinant S aureus antigens. All patients were treated with organism-targeted antibiotic therapy and appropriate, timely surgery. Treatment response was monitored with clinical examination, erythrocyte sedimentation rate, C-reactive protein, and resampling of the infection site for the pathogen as needed. Elevated inflammatory markers or persistent positive culture results were considered evidence of ongoing infection. Treatment provided was considered standard-of-care therapy in our medical center and all patients were treated jointly with a board-certified infectious disease specialist. RESULTS: Four antigens elicited more than 65% of the measurable IgG, the most dominant being against iron-regulated surface determinant protein B (IsdB). Patients with infections had different patterns of elevated IgG titers, so that no single titer was elevated in more than 50% of patients with infections (area under the curve [AUC] ≤ 0.80). Multivariate analysis of IgG titers yielded greater predictive power of S aureus infection (AUC = 0.896). Patients with infections who had high titers against IsdB (median of survivors, 7.28 [25%-75% range, 2.22-21.26] vs median of patients with infection-related death, 40.41 [25%-75% range, 23.57-51.37], difference of medians, 33.13; p = 0.043) and iron-regulated surface determinant protein A (IsdA) median of survivors, 2.21 [25%-75% range, 0.79-9.11] vs median of patients with infection-related death, 12.24 [25%-75% range, 8.85-15.95], difference of medians, 10.03; p = 0.043) were more likely to die from infections than those who did not have high titers of IsdB. CONCLUSIONS: Measurement of the host antibody response is a predictor of ongoing infection that may prove to have prognostic value. Future studies will seek to enlarge the patient population with infections to allow us to reduce the number of antigens required to achieve a stronger predictive power. CLINICAL RELEVANCE: Measurement of the immune response against S aureus with this diagnostic tool may help guide future studies on prophylaxis and therapy in an era of personalized medicine and pathogen-specific therapies.

Dilution of humoral immunity: Results from a natural history study of healthy total knee arthroplasty patients.

The incidence of prosthetic joint infection (PJI) following elective primary total knee arthroplasty (TKA) is very low but serious risk remains. To identify unknown risk factors, we completed a natural history study of IgG specific for Staphylococcus aureus antigens previously phenotyped as protective (anti-Atl) and pathogenic (anti-Isd). Twenty-five male and 25 female optimized patients 50-85 years of age and BMI 24-39 undergoing primary TKA were prospectively enrolled. Blood sampling was performed preoperatively, postoperative Day 1, and at 2, 6, and 12 weeks, to assess serum cytokine, anti-staphylococcal IgG levels and anti-tetanus toxoid IgG measured via custom Luminex assay. Clinical, demographic, and PROMIS-10 data were collected with outcomes to 2 years postop. All participants completed the study and 2-year follow-up. No patients were readmitted or noted to develop a surgical site infection or serious adverse event, and patient-reported outcomes were improved. Serology revealed a highly significant decrease in six out of eight antibody titers against specific S. aureus antigens on Day 1 (p < 0.0001), five of which normalized to preoperative levels within 2 weeks. These changes were commensurate with a decrease and recovery of anti-tetanus toxoid titers, and a 20% drop in hemoglobin 13.8 ± 1.7 at preop to 11.1 ± 1.8 mg/dL on Day 1 (p < 0.0001). After TKA, a significant decrease in humoral immunity commensurate with blood loss and hemodilution was recorded. This decrease in circulating anti-staphylococcal antibodies in the early postop period may represent a periprosthetic joint infection risk factor for patients.

The 2023 Orthopaedic Research Society's International Consensus Meeting on musculoskeletal infection: Summary from the host immunity section.

Musculoskeletal infections (MSKI), which are a major problem in orthopedics, occur when the pathogen eludes or overwhelms the host immune system. While effective vaccines and immunotherapies to prevent and treat MSKI should be possible, fundamental knowledge gaps in our understanding of protective, nonprotective, and pathogenic host immunity are prohibitive. We also lack critical knowledge of how host immunity is affected by the microbiome, implants, prior infection, nutrition, antibiotics, and concomitant therapies, autoimmunity, and other comorbidities. To define our current knowledge of these critical topics, a Host Immunity Section of the 2023 Orthopaedic Research Society MSKI International Consensus Meeting (ICM) proposed 78 questions. Systematic reviews were performed on 15 of these questions, upon which recommendations with level of evidence were voted on by the 72 ICM delegates, and another 12 questions were voted on with a recommendation of "Unknown" without systematic reviews. Two questions were transferred to another ICM Section, and the other 45 were tabled for future consideration due to limitations of available human resources. Here we report the results of the voting with internet access to the questions, recommendations, and rationale from the systematic reviews. Eighteen questions received a consensus vote of ≥90%, while nine recommendations failed to achieve this threshold. Commentary on why consensus was not achieved on these questions and potential ways forward are provided to stimulate specific funding mechanisms and research on these critical MSKI host defense questions.

MENSA, a Media Enriched with Newly Synthesized Antibodies, to Identify SARS-CoV-2 Persistence and Latent Viral Reactivation in Long-COVID.

Post-acute sequelae of SARS-CoV-2 (SARS2) infection (PASC) is a heterogeneous condition, but the main viral drivers are unknown. Here, we use MENSA, Media Enriched with Newly Synthesized Antibodies, secreted exclusively from circulating human plasmablasts, to provide an immune snapshot that defines the underlying viral triggers. We provide proof-of-concept testing that the MENSA technology can capture the new host immune response to accurately diagnose acute primary and breakthrough infections when known SARS2 virus or proteins are present. It is also positive after vaccination when spike proteins elicit an acute immune response. Applying the same principles for long-COVID patients, MENSA is positive for SARS2 in 40% of PASC vs none of the COVID recovered (CR) patients without any sequelae demonstrating ongoing SARS2 viral inflammation only in PASC. Additionally, in PASC patients, MENSAs are also positive for Epstein-Barr Virus (EBV) in 37%, Human Cytomegalovirus (CMV) in 23%, and herpes simplex virus 2 (HSV2) in 15% compared to 17%, 4%, and 4% in CR controls respectively. Combined, a total of 60% of PASC patients have a positive MENSA for SARS2, EBV, CMV, and/or HSV2. MENSA offers a unique antibody snapshot to reveal the underlying viral drivers in long-COVID thus demonstrating the persistence of SARS2 and reactivation of viral herpes in 60% of PASC patients.

Circulating antibody-secreting cells are a biomarker for early diagnosis in patients with Lyme disease.

BACKGROUND: Diagnostic immunoassays for Lyme disease have several limitations including: 1) not all patients seroconvert; 2) seroconversion occurs later than symptom onset; and 3) serum antibody levels remain elevated long after resolution of the infection. INTRODUCTION: MENSA (Medium Enriched for Newly Synthesized Antibodies) is a novel diagnostic fluid that contains antibodies produced in vitro by circulating antibody-secreting cells (ASC). It enables measurement of the active humoral immune response. METHODS: In this observational, case-control study, we developed the MicroB-plex Anti-C6/Anti-pepC10 Immunoassay to measure antibodies specific for the Borrelia burgdorferi peptide antigens C6 and pepC10 and validated it using a CDC serum sample collection. Then we examined serum and MENSA samples from 36 uninfected Control subjects and 12 Newly Diagnosed Lyme Disease Patients. RESULTS: Among the CDC samples, antibodies against C6 and/or pepC10 were detected in all seropositive Lyme patients (8/8), but not in sera from seronegative patients or healthy controls (0/24). Serum antibodies against C6 and pepC10 were detected in one of 36 uninfected control subjects (1/36); none were detected in the corresponding MENSA samples (0/36). In samples from newly diagnosed patients, serum antibodies identified 8/12 patients; MENSA antibodies also detected 8/12 patients. The two measures agreed on six positive individuals and differed on four others. In combination, the serum and MENSA tests identified 10/12 early Lyme patients. Typically, serum antibodies persisted 80 days or longer while MENSA antibodies declined to baseline within 40 days of successful treatment. DISCUSSION: MENSA-based immunoassays present a promising complement to serum immunoassays for diagnosis and tracking therapeutic success in Lyme infections.

Systemic IL-27 administration prevents abscess formation and osteolysis via local neutrophil recruitment and activation.

Interleukin-27 is a pleiotropic cytokine whose functions during bacterial infections remain controversial, and its role in patients with S. aureus osteomyelitis is unknown. To address this knowledge gap, we completed a clinical study and observed elevated serum IL-27 levels (20-fold higher, P < 0.05) in patients compared with healthy controls. Remarkably, IL-27 serum levels were 60-fold higher in patients immediately following septic death than in uninfected patients (P < 0.05), suggesting a pathogenic role of IL-27. To test this hypothesis, we evaluated S. aureus osteomyelitis in WT and IL-27Rα-/- mice with and without exogenous IL-27 induction by intramuscular injection of rAAV-IL-27p28 or rAAV-GFP, respectively. We found that IL-27 was induced at the surgical site within 1 day of S. aureus infection of bone and was expressed by M0, M1 and M2 macrophages and osteoblasts but not by osteoclasts. Unexpectedly, exogenous IL-27p28 (~2 ng·mL-1 in serum) delivery ameliorated soft tissue abscesses and peri-implant bone loss during infection, accompanied by enhanced local IL-27 expression, significant accumulation of RORγt+ neutrophils at the infection site, a decrease in RANK+ cells, and compromised osteoclast formation. These effects were not observed in IL-27Rα-/- mice compared with WT mice, suggesting that IL-27 is dispensable for immunity but mediates redundant immune and bone cell functions during infection. In vitro studies and bulk RNA-seq of infected tibiae showed that IL-27 increased nos1, nos2, il17a, il17f, and rorc expression but did not directly stimulate chemotaxis. Collectively, these results identify a novel phenomenon of IL-27 expression by osteoblasts immediately following S. aureus infection of bone and suggest a protective role of systemic IL-27 in osteomyelitis.

The Serological Sciences Network (SeroNet) for COVID-19: Depth and Breadth of Serology Assays and Plans for Assay Harmonization.

Background: In October 2020, the National Cancer Institute (NCI) Serological Sciences Network (SeroNet) was established to study the immune response to COVID-19, and "to develop, validate, improve, and implement serological testing and associated technologies." SeroNet is comprised of 25 participating research institutions partnering with the Frederick National Laboratory for Cancer Research (FNLCR) and the SeroNet Coordinating Center. Since its inception, SeroNet has supported collaborative development and sharing of COVID-19 serological assay procedures and has set forth plans for assay harmonization. Methods: To facilitate collaboration and procedure sharing, a detailed survey was sent to collate comprehensive assay details and performance metrics on COVID-19 serological assays within SeroNet. In addition, FNLCR established a protocol to calibrate SeroNet serological assays to reference standards, such as the U.S. SARS-CoV-2 serology standard reference material and First WHO International Standard (IS) for anti-SARS-CoV-2 immunoglobulin (20/136), to facilitate harmonization of assay reporting units and cross-comparison of study data. Results: SeroNet institutions reported development of a total of 27 ELISA methods, 13 multiplex assays, 9 neutralization assays, and use of 12 different commercial serological methods. FNLCR developed a standardized protocol for SeroNet institutions to calibrate these diverse serological assays to reference standards. Conclusions: SeroNet institutions have established a diverse array of COVID-19 serological assays to study the immune response to SARS-CoV-2 virus and vaccines. Calibration of SeroNet serological assays to harmonize results reporting will facilitate future pooled data analyses and study cross-comparisons.

The Serological Sciences Network (SeroNet) for COVID-19: Depth and Breadth of Serology Assays and Plans for Assay Harmonization.

In October 2020, the National Cancer Institute (NCI) Serological Sciences Network (SeroNet) was established to study the immune response to COVID-19, and "to develop, validate, improve, and implement serological testing and associated technologies" (https://www.cancer.gov/research/key-initiatives/covid-19/coronavirus-research-initiatives/serological-sciences-network). SeroNet is comprised of 25 participating research institutions partnering with the Frederick National Laboratory for Cancer Research (FNLCR) and the SeroNet Coordinating Center. Since its inception, SeroNet has supported collaborative development and sharing of COVID-19 serological assay procedures and has set forth plans for assay harmonization. To facilitate collaboration and procedure sharing, a detailed survey was sent to collate comprehensive assay details and performance metrics on COVID-19 serological assays within SeroNet. In addition, FNLCR established a protocol to calibrate SeroNet serological assays to reference standards, such as the U.S. severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) serology standard reference material and first WHO international standard (IS) for anti-SARS-CoV-2 immunoglobulin (20/136), to facilitate harmonization of assay reporting units and cross-comparison of study data. SeroNet institutions reported development of a total of 27 enzyme-linked immunosorbent assay (ELISA) methods, 13 multiplex assays, and 9 neutralization assays and use of 12 different commercial serological methods. FNLCR developed a standardized protocol for SeroNet institutions to calibrate these diverse serological assays to reference standards. In conclusion, SeroNet institutions have established a diverse array of COVID-19 serological assays to study the immune response to SARS-CoV-2 and vaccines. Calibration of SeroNet serological assays to harmonize results reporting will facilitate future pooled data analyses and study cross-comparisons. IMPORTANCE SeroNet institutions have developed or implemented 61 diverse COVID-19 serological assays and are collaboratively working to harmonize these assays using reference materials to establish standardized reporting units. This will facilitate clinical interpretation of serology results and cross-comparison of research data.

Serum antibodies against Staphylococcus aureus can prognose treatment success in patients with bone infections.

Prognosing life-threatening orthopedic infections caused by Staphylococcus aureus remains a major clinical challenge. To address this, we developed a multiplex assay to assess the humoral immune proteome against S. aureus in patients with musculoskeletal infections. We found initial evidence that antibodies against some antigens (autolysins: Amd, Gmd; secreted immunotoxins: CHIPS, SCIN, Hla) were associated with protection, whereas antibodies against the iron-regulated surface determinant (Isd) proteins (IsdA, IsdB, IsdH) were aligned with adverse outcomes. To formally test this, we analyzed antibody levels and 1-year clinical outcomes of 194 patients with confirmed S. aureus bone infections (AO Trauma Clinical Priority Program [CPP] Bone Infection Registry). A staggering 20.6% of the enrolled patients experienced adverse clinical outcomes (arthrodesis, reinfection, amputation, and septic death) after 1-year. At enrollment, anti-S. aureus immunoglobulin G (IgG) levels in patients with adverse outcomes were 1.35-fold lower than those in patients whose infections were successfully controlled (p < 0.0001). Overall, there was a 51%-69% reduction in adverse outcome risk for every 10-fold increase in initial IgG concentration against Gmd, Amd, IsdH, CHIPS, SCIN, and Hla (p < 0.05). Notably, anti-IsdB antibodies remained elevated in patients with adverse outcomes; for every 10-fold change in the ratio of circulating anti-Isd to anti-Atl IgG at enrollment, there was a trending 2.6-fold increased risk (odds ratio = 2.555) of an adverse event (p = 0.105). Moreover, antibody increases over time correlated with adverse outcomes and decreases with positive outcomes. These studies demonstrate the potential of the humoral immune response against S. aureus as a prognostic indicator for assessing treatment success and identifying patients requiring additional interventions.

Species-Specific Immunoassay Aids Identification of Pathogen and Tracks Infectivity in Foot Infection.

BACKGROUND: Conventional bacterial cultures frequently fail to identify the dominant pathogen in polymicrobial foot infections, in which Staphylococcus aureus is the most common infecting pathogen. Previous work has shown that species-specific immunoassays may be able to identify the main pathogen in musculoskeletal infections. We sought to investigate the clinical applicability of a S. aureus immunoassay to accurately identify the infecting pathogen and monitor its infectivity longitudinally in foot infection. We hypothesized that this species-specific immunoassay could aid in the diagnosis of S. aureus and track the therapeutic response in foot infections. METHODS: From July 2015 to July 2019, 83 infected foot ulcer patients undergoing surgical intervention (debridement or amputation) were recruited and blood was drawn at 0, 4, 8, and 12 weeks. Whole blood was analyzed for S. aureus-specific serum antibodies (mix of historic and new antibodies) and plasmablasts were isolated and cultured to quantify titers of newly synthesized antibodies (NSAs). Anti-S. aureus antibody titers were compared with culture results to assess their concordance in identifying S. aureus as the pathogen. The NSA titer changes at follow-ups were compared with wound healing status to evaluate concordance between evolving host immune response and clinically resolving or relapsing infection. RESULTS: Analysis of serum for anti-S. aureus antibodies showed significantly increased titers of 3 different anti-S. aureus antibodies, IsdH (P = .037), ClfB (P = .025), and SCIN (P = .005), in S. aureus culture-positive patients compared with culture-negative patients. Comparative analysis of combining antigens for S. aureus infection diagnosis increased the concordance further. During follow-up, changes of NSA titers against a single or combination of S. aureus antigens significantly correlated with clinically resolving or recurring infection represented by wound healing status. CONCLUSION: In the management of foot infection, the use of S. aureus-specific immunoassay may aid in diagnosis of the dominant pathogen and monitoring of the host immune response against a specific pathogen in response to treatment. Importantly, this immunoassay could detect recurrent foot infection, which may guide a surgeon's decision to intervene. LEVEL OF EVIDENCE: Level II, prospective comparative study.

Diagnosis of Streptococcus pneumoniae infection using circulating antibody secreting cells.

BACKGROUND: Streptococcus pneumoniae infections cause morbidity and mortality worldwide. A rapid, simple diagnostic method could reduce the time needed to introduce definitive therapy potentially improving patient outcomes. METHODS: We introduce two new methods for diagnosing S. pneumoniae infections by measuring the presence of newly activated, pathogen-specific, circulating Antibody Secreting Cells (ASC). First, ASC were detected by ELISpot assays that measure cells secreting antibodies specific for signature antigens. Second, the antibodies secreted by isolated ASC were collected in vitro in a novel matrix, MENSA (media enriched with newly synthesized antibodies) and antibodies against S. pneumoniae antigens were measured using Luminex immunoassays. Each assay was evaluated using blood from S. pneumoniae and non-S. pneumoniae-infected adult patients. RESULTS: We enrolled 23 patients with culture-confirmed S. pneumoniae infections and 24 controls consisting of 12 non-S. pneumoniae infections, 10 healthy donors and two colonized with S. pneumoniae. By ELISpot assays, twenty-one of 23 infected patients were positive, and all 24 controls were negative. Using MENSA samples, four of five S. pneumoniae-infected patients were positive by Luminex immunoassays while all five non-S. pneumoniae-infected patients were negative. CONCLUSION: Specific antibodies produced by activated ASC may provide a simple diagnostic for ongoing S. pneumoniae infections. This method has the potential to diagnose acute bacterial infections.

Clinical utilization of species-specific immunoassays for identification of Staphylococcus aureus and Streptococcus agalactiae in orthopedic infections.

Staphylococcus aureus and Streptococcus agalactiae (Group B streptococcus, GBS) are common causes of deep musculoskeletal infections (MSKI) and result in significant patient morbidity and cost to the healthcare system. One of the major challenges with MSKI is the lack of faithful diagnostics to correctly identify the primary pathogen, as standard culture-based assays are prone to false positives in the case of polymicrobial infections, and false negatives due to limitations in sample acquisition and antibiotic use before presentation. To improve upon our current diagnostic methods for MSKI, we developed a multiplex immunoassay for antigen-specific IgGs in serum (Luminex), and medium enriched for newly synthesized antibodies (MENSA) for anti-S. aureus and GBS generated from cultured peripheral blood mononuclear cells (PBMCs) of orthopedic infection patients undergoing surgical treatment. Samples were obtained from 110 MSKI patients: 80 diabetic foot ulcer, 21 periprosthetic joint infection, 5 septic arthritis, 2 spine, 1 hand, and 1 fracture-related infection (FRI). Anti-S. aureus and anti-GBS antibody titers were compared to culture results to assess their concordance in identifying the pathogens. Immunoassay, particularly MENSA, showed high diagnostic potential for monomicrobial S. aureus and GBS orthopedic infections (AUC > 0.95). MENSA also demonstrated diagnostic potential for GBS polymicrobial orthopedic infection and for GBS DFU (AUC > 0.83 for both). Serum showed high diagnostic potential for S. aureus PJI (AUC > 0.95). Taken together, these findings support the development of species-specific immunoassays for the identification of causal pathogens in active MSKI, especially in conjunction with standard culture.

Humanized Mice Exhibit Exacerbated Abscess Formation and Osteolysis During the Establishment of Implant-Associated Staphylococcus aureus Osteomyelitis.

Staphylococcus aureus is the predominant pathogen causing osteomyelitis. Unfortunately, no immunotherapy exists to treat these very challenging and costly infections despite decades of research, and numerous vaccine failures in clinical trials. This lack of success can partially be attributed to an overreliance on murine models where the immune correlates of protection often diverge from that of humans. Moreover, S. aureus secretes numerous immunotoxins with unique tropism to human leukocytes, which compromises the targeting of immune cells in murine models. To study the response of human immune cells during chronic S. aureus bone infections, we engrafted non-obese diabetic (NOD)-scid IL2Rγnull (NSG) mice with human hematopoietic stem cells (huNSG) and analyzed protection in an established model of implant-associated osteomyelitis. The results showed that huNSG mice have increases in weight loss, osteolysis, bacterial dissemination to internal organs, and numbers of Staphylococcal abscess communities (SACs), during the establishment of implant-associated MRSA osteomyelitis compared to NSG controls (p < 0.05). Flow cytometry and immunohistochemistry demonstrated greater human T cell numbers in infected versus uninfected huNSG mice (p < 0.05), and that T-bet+ human T cells clustered around the SACs, suggesting S. aureus-mediated activation and proliferation of human T cells in the infected bone. Collectively, these proof-of-concept studies underscore the utility of huNSG mice for studying an aggressive form of S. aureus osteomyelitis, which is more akin to that seen in humans. We have also established an experimental system to investigate the contribution of specific human T cells in controlling S. aureus infection and dissemination.