EGFR-MEK1/2 cascade negatively regulates bactericidal function of bone marrow macrophages in mice with Staphylococcus aureus osteomyelitis.

The ability of Staphylococcus aureus (S. aureus) to survive within macrophages is a critical strategy for immune evasion, contributing to the pathogenesis and progression of osteomyelitis. However, the underlying mechanisms remain poorly characterized. This study discovered that inhibiting the MEK1/2 pathway reduced bacterial load and mitigated bone destruction in a mouse model of S. aureus osteomyelitis. Histological staining revealed increased phosphorylated MEK1/2 levels in bone marrow macrophages surrounding abscess in the mouse model of S. aureus osteomyelitis. Activation of MEK1/2 pathway and its roles in impairing macrophage bactericidal function were confirmed in primary mouse bone marrow-derived macrophages (BMDMs). Transcriptome analysis and in vitro experiments demonstrated that S. aureus activates the MEK1/2 pathway through EGFR signaling. Moreover, we found that excessive activation of EGFR-MEK1/2 cascade downregulates mitochondrial reactive oxygen species (mtROS) levels by suppressing Chek2 expression, thereby impairing macrophage bactericidal function. Furthermore, pharmacological inhibition of EGFR signaling prevented upregulation of phosphorylated MEK1/2 and restored Chek2 expression in macrophages, significantly enhancing S. aureus clearance and improving bone microstructure in vivo. These findings highlight the critical role of the EGFR-MEK1/2 cascade in host immune defense against S. aureus, suggesting that S. aureus may reduce mtROS levels by overactivating the EGFR-MEK1/2 cascade, thereby suppressing macrophage bactericidal function. Therefore, combining EGFR-MEK1/2 pathway blockade with antibiotics could represent an effective therapeutic approach for the treatment of S. aureus osteomyelitis.

Age-related dysregulation of CXCL9/10 in monocytes is linked to impaired innate immune responses in a mouse model of Staphylococcus aureus osteomyelitis.

BACKGROUND: Age-associated impairments in innate immunity are believed to be a causative factor responsible for severe pathogenesis of Staphylococcus aureus (S. aureus) infection in the bone tissue. However, the basis for age-associated decline in innate immune response upon S. aureus infection remains poorly understood. RESULTS: Our transcriptional data (GEO: GSE166522) from a mouse model of S. aureus osteomyelitis show up-regulated CXCL9 and CXCL10 (CXCL9/10), which is further confirmed in vitro and in vivo by the present study. Notably, monocytes are a main source for CXCL9/10 production in bone marrow upon S. aureus challenge, but this response declines in middle-aged mice. Interestingly, conditional medium of bone marrow monocytes from middle-aged mice has a strikingly decreased effect on bactericidal functions of neutrophils and macrophages compares with that from young mice. We further show that activation of CXCL9/10-CXCR3 axis between monocytes and macrophages/neutrophils promotes the bactericidal function of the cells, whereas blocking the axis impairs such function. Importantly, treatment with either exogenous CXCL9 or CXCL10 in a middle-aged mice model enhances, while pharmacological inhibition of CXCR3 in young mice model impairs, bacterial clearance and bone marrow structure. CONCLUSIONS: These findings demonstrate that bone marrow monocytes act as a critical promotor of innate immune response via the CXLCL9/10-CXCR3 axis upon S. aureus infection, and that the increased susceptibility to S. aureus infection in skeleton in an aged host may be largely attributable to the declined induction of CXCR9/10 in monocytes.

Anti-IL12p40 autoantibodies in a teenage girl with multiple recurrent abscesses.

More frequent among adults, phenocopies may be caused by somatic mutations or anti-cytokine autoantibodies, mimicking the phenotypes of primary immunodeficiencies. A fourteen-year-old girl was referred for a two-year history of weight loss and multiple recurrent abscesses, complicated recurrent pneumonia, pyelonephritis, osteomyelitis, and septic shock, without fever. She had started with nausea, hyporexia, and weight loss, then with abscesses in her hands, knee, ankle, and spleen. She also developed a rib fracture and left thoracic herpes zoster. The patient was cachectic, with normal vital signs, bilateral crackles on chest auscultation, tumefaction of the knee joint, and poorly healed wounds in hands and chest, oozing a yellowish fluid. Chest computed tomography revealed multiple bilateral bronchiectases. Laboratory workup reported chronic anemia, leukocytosis, neutrophilia, mild lymphopenia, thrombocytosis, pan-hypergammaglobulinemia, and elevated acute serum reactants. Lymphocyte subsets were low but present. Mycobacterium tuberculosis was detected via polymerase chain reaction in a bone biopsy specimen from ankle osteomyelitis. Whole-exome sequencing failed to identify a monogenic defect. Interleukin-12 was found markedly elevated in the serum of the patient. Phosphorylation of STAT4, induced by increasing doses of IL-12, was neutralized by patient serum, confirming the presence of anti-IL12 autoantibodies. IL-12 and IL-23 are crucial cytokines in the defense against intracellular microorganisms, the induction of interferon-gamma production by lymphocytes, and other inflammatory functions. Patients who develop neutralizing serum autoantibodies against IL12 manifest late in life with weight loss, multiple recurrent abscesses, poor wound healing, and fistulae. Treatment with anti-CD20 monoclonal antibodies was effective.

Osteomyelitis is associated with increased anti-inflammatory response and immune exhaustion.

Introduction: Osteomyelitis (OMS) is a bone infection causing bone pain and severe complications. A balanced immune response is critical to eradicate infection without harming the host, yet pathogens manipulate immunity to establish a chronic infection. Understanding OMS-driven inflammation is essential for disease management, but comprehensive data on immune profiles and immune cell activation during OMS are lacking. Methods: Using high-dimensional flow cytometry, we investigated the detailed innate and adaptive systemic immune cell populations in OMS and age- and sex-matched controls. Results: Our study revealed that OMS is associated with increased levels of immune regulatory cells, namely T regulatory cells, B regulatory cells, and T follicular regulatory cells. In addition, the expression of immune activation markers HLA-DR and CD86 was decreased in OMS, while the expression of immune exhaustion markers TIM-3, PD-1, PD-L1, and VISTA was increased. Members of the T follicular helper (Tfh) cell family as well as classical and typical memory B cells were significantly increased in OMS individuals. We also found a strong correlation between memory B cells and Tfh cells. Discussion: We conclude that OMS skews the host immune system towards the immunomodulatory arm and that the Tfh memory B cell axis is evident in OMS. Therefore, immune-directed therapies may be a promising alternative for eradication and recurrence of infection in OMS, particularly in individuals and areas where antibiotic resistance is a major concern.

Integrative gene expression analysis and animal model reveal immune- and autophagy-related biomarkers in osteomyelitis.

BACKGROUND: Osteomyelitis (OM) is recognized as a significant challenge in orthopedics due to its complex immune and inflammatory responses. The prognosis heavily depends on timely diagnosis, accurate classification, and assessment of severity. Thus, the identification of diagnostic and classification-related genes from an immunological standpoint is crucial for the early detection and tailored treatment of OM. METHODS: Transcriptomic data for OM was sourced from the Gene Expression Omnibus (GEO) database, leading to the identification of autophagy- and immune-related differentially expressed genes (AIR-DEGs) through differential expression analysis. Diagnostic and classification models were subsequently developed. The CIBERSORT algorithm was utilized to examine immune cell infiltration in OM, and the relationship between OM clusters and various immune cells was explored. Key AIR-DEGs were further validated through the creation of OM animal models. RESULTS: Analysis of the transcriptomic data revealed three AIR-DEGs that played a significant role in immune responses and pathways. Nomogram and receiver operating characteristic curve analyses were performed, demonstrating excellent diagnostic capability for differentiating between OM patients and healthy individuals, with an area under the curve of 0.814. An unsupervised clustering analysis discerned two unique patterns of autophagy- and immune-related genes, as well as gene patterns. Further exploration into immune infiltration exhibited notable variances across different subtypes, especially between OM cluster 1 and gene cluster A, highlighting their potential role in mitigating inflammatory responses by regulating immune activities. Moreover, the mRNA and protein expression levels of three AIR-DEGs in the animal model were aligned with those in the training and validation data sets. CONCLUSIONS: From an immunological perspective, a diagnostic model was successfully developed, and two distinct clustering patterns were identified. These contributions offer a significant resource for the early detection and personalized immunotherapy of patients with OM.

Inflammatory turmoil within: an exploration of autoinflammatory disease genetic underpinnings, clinical presentations, and therapeutic approaches.

Systemic autoinflammatory diseases (SAIDs) arise from dysregulated innate immune system activity, which leads to systemic inflammation. These disorders, encompassing a diverse array of genetic defects classified as inborn errors of immunity, are significant diagnostic challenges due to their genetic heterogeneity and varied clinical presentations. Although recent advances in genetic sequencing have facilitated pathogenic gene discovery, approximately 40% of SAIDs patients lack molecular diagnoses. SAIDs have distinct clinical phenotypes, and targeted therapeutic approaches are needed. This review aims to underscore the complexity and clinical significance of SAIDs, focusing on prototypical disorders grouped according to their pathophysiology as follows: (i) inflammasomopathies, characterized by excessive activation of inflammasomes, which induces notable IL-1ß release; (ii) relopathies, which are monogenic disorders characterized by dysregulation within the NF-κB signaling pathway; (iii) IL-18/IL-36 signaling pathway defect-induced SAIDs, autoinflammatory conditions defined by a dysregulated balance of IL-18/IL-36 cytokine signaling, leading to uncontrolled inflammation and tissue damage, mainly in the skin; (iv) type I interferonopathies, a diverse group of disorders characterized by uncontrolled production of type I interferons (IFNs), notably interferon α, ß, and ε; (v) anti-inflammatory signaling pathway impairment-induced SAIDs, a spectrum of conditions characterized by IL-10 and TGFß anti-inflammatory pathway disruption; and (vi) miscellaneous and polygenic SAIDs. The latter group includes VEXAS syndrome, chronic recurrent multifocal osteomyelitis/chronic nonbacterial osteomyelitis, Schnitzler syndrome, and Still's disease, among others, illustrating the heterogeneity of SAIDs and the difficulty in creating a comprehensive classification. Therapeutic strategies involving targeted agents, such as JAK inhibitors, IL-1 blockers, and TNF inhibitors, are tailored to the specific disease phenotypes.

Osteomielitis por Klebsiella pneumoniae BLEE. Reporte de un caso y revisión de la literatura. / OSTEOMYELITIS DUE TO KLEBSIELLA PNEUMONIAE ESBL. REPORT OF A CASE AND LITERATURE REVIEW

Las betalactamasas de espectro extendido (BLEE) son enzimas producidas por bacilos gram negativos capaces de hidrolizar las cefalosporinas de amplio espectro y los monobactámicos. La mayoría pertenece a la familia de Enterobacteriae, tales como Klebsiella pneumoniae y Escherichia coli: Sin embargo, se asocian también con otras bacterias como Proteus, Serratia, Salmonella, Pseudomonas aeruginosa y Acinetobacter. Las enterobacterias productoras de carbapenemasas no sólo han sido aisladas en el ambiente hospitalario, sino que también provienen de la comunidad. Se presenta una paciente de sexo femenino con antecedentes de sida y osteomielitis secundaria a artritis séptica producida por una Klebsiella pneumoniae BLEE de la comunidad. Un tratamiento oportuno y eficaz puede evitar la opción quirúrgica, disminuyendo la morbimortalidad asociada con esta afección

Extended-spectrum beta-lactamases (ESBL) are enzymes produced by gram-negative rods capable of hydrolyzing broad-spectrum cephalosporins and monobactams. Most belong to the Enterobacteriae family, such as Klebsiella pneumoniae and Escherichia coli. However, they are also associated with other bacteria such as Proteus, Serratia, Salmonella, Pseudomonas aeruginosa and Acinetobacter. Carbapenemase-producing Enterobacteriaceae have not only been isolated from the hospital environment, but also from the community. We present a female patient with a history of AIDS and secondary osteomyelitis to septic arthritis caused by a community Klebsiella pneumoniae ESBL. It is concluded that a timely and effective treatment can avoids the surgical option, reducing the morbidity and mortality of this condition.

Septic arthritis and atopic dermatitis: 2 cases and a review of the recent literature

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Distinct cytokine profiles of circulating mononuclear cells stimulated with Staphylococcus aureus enterotoxin A in vitro during early and late episodes of chronic osteomyelitis

We investigated the cytokine profile of peripheral mononuclear cells from chronic osteomyelitis (OST) patients following in vitro stimulation with staphylococcal enterotoxin A (SEA). We demonstrate that stimulation with SEA induced prominent lymphocyte proliferation and high levels of tumour necrosis factor (TNF)-α, interleukin (IL)-4 and IL-10 secretion in both OST and non-infected individuals (NI). Even though stimulation with SEA had no impact on IL-6 production in either patient group, the baseline level of IL-6 production by cells from OST patients was always significantly less than that produced by cells from NI. After classifying the osteomyelitic episodes based on the time after the last reactivation event as "early" (1-4 months) or "late" osteomyelitis (5-12 months), we found that increased levels of TNF-α and IL-4 in combination with decreased levels of IL-6 were observed in the early episodes. By contrast, increased levels of IL-10, IL-2 and IL-6 were hallmarks of late episodes. Our data demonstrate that early osteomyelitic episodes are accompanied by an increased frequency of "high producers" of TNF-α and IL-4, whereas late events are characterised by increased frequencies of "high producers" of IL-10, IL-6 and IL-2. These findings demonstrate the distinct cytokine profiles in chronic osteomyelitis, with a distinct regulation of IL-6 production during early and late episodes.

Osteomielitis aguda y crónica: 10 años de estudio en pacientes pediátricos: Hospital de Niños J.M. de Los Ríos Caracas Venezuela / Acute and chronic osteomyelitis: 10 years of study in pediatric patients: Hospital de Niños

La osteomielitis constituye un proceso inflamatorio común del hueso. Existen factores que influyen en la incidencia y etiología tales como: estado inmunologógico, edad, sexo, traumatismo locales o enfermedades de base. A pesar de su relativa baja frecuencia es una de las principales causas infecciosas de hospitalización prolongada. Describir las características de pacientes con diagnóstico de osteomielitis egresados del Hospital de Niños J.M. de Los Ríos (HJMR) y establacer prevalencia según egresos hospitalarios. Estudio retrospectivo mediante revisión de historias médicas, descriptivo en menores de 18 años con diagnóstico de osteomielitis del Hospital de Niños "J.M. de Los Ríos", período diciembre 1998 - diciembre 2008. Análisis estadístico: medidas tendencias central y Chi cuadrado. Se revisaron 72 historias, 65,3% (47/72) masculino y 34,7% (25/72) femenino. Prevalencia de 0,14 por cada 100 egresados. Según edad 8,33% (6/72) lactantes menores 5,56% (4/72) lactantes mayores, 29% (20/72) preescolares, 29% (20/72) escolares y 27,8% (20/72) adolescentes. Promedio días hospitalización fue 42,5 ± 20,75. El 27,8% (20/72) presentaba alguna patología de base. Sitios afectados 37,5% (27/72) fémur, 23% (17/72) tibia, 6,9% (5/72) calcáneo, 6,94% (5/72) cadera y otros lugares 25% (18/72). En 45,83% (33/72) se realizó limpieza quirúrgica, en promedio a los 26,% días del ingreso (DE ± 33). el 62,5% (45/72) fueron ostemielitis agudas y 37,5% (27/72) crónica. El aislamiento micronbiológicos se logró con mayor frecuencia en el grupo de pacientes con osteomielitis crónica (P < 0,05). Un 11,11% (8/72) presentó algún tipo de secuela y 12,5% (9/72) infección nosocomial. La osteomielitis en niños tiene una prevalencia relativamente baja, pero genera hospitalizaciones prolongadas con importantes complicaciones médicas y quirúrgicas.

Osteomyelitis represents a common inflammatory process of the bone. Immnologic status, age , sex, traumatic lesions and co morbidities influence the etiology and comorbidities influence the etiology and incidence of the disease. It is one of the most important infectious causing prolonged hospitalizations. Describe the characteristics of children with osteomyelitis from J.M. de Los Ríos Children`s Hospital and calculate its prevalence. Retrospective and descriptive study through medical charts revision, including patients less than 18 years old with osteomyelitis as discharged diagnostic at Children Hospital J.M. de Los Ríos between December 1998 - December 2008. Seventy two chart were revised, 65.3% (47/72) male and 34.7% (25/72) female. The prevalence by 100 dischages by age was 8.3% (6/72) infants, 5.6% (4/72) children, 29% (20/72) pre-school children, 29% (20/72) scholer children, and 27.8% (20/72) adolescents. The average hospitalization time was 42.63 ± 20.75. Twenty of 77 children (27.8%) presented with some co morbidities. The affected bones were: 37.5% (27/72) femur, 23% (17/72) tepid bone, 6.9% (5/72) calcaneus, 6.9% (5/72) hip and others 25% (18/72). In 45.8% (33/72) the resolution was surgery, with an average of 26.5 days of hospitak stay (DE ± 24.33); 62.5% (45/72) were acute osteomyelitis, and 37.5% (27/72) chronic. The microbiologic diagnostic was more frequent in the group of chronic (p < 0.05). Sequel were present in 11% (8/72), and nosocomial infection in 12.5% (9/72). Osteomyelitis children has a relative small prevalence, but it generates prolonged hospitalizations with important complications.

Utilidad de un anticuerpo monoclonal antigranulocitos marcado con tecnecio 99m en la identificación de enfermedades infecciosas de localización ósea y extraósea / The usefulness of an antigranulocyte monoclonal antibody marked with tecnesium 99m in identifying bone and estra-bone infectious diseases

Estudiamos 61 pacientes con sospecha clínica de enfermedad infecciosa localizada con el anticuerpo monoclonal antigranulocitos BW250/183 (AcAG). En 28 de 38 pacientes estudiaron por sospecha de osteomielitis se confirmó la afección infecciosa, los estudios con el AcAG fueron positivos en 27 de los 28 pacientes. En 14 de 23 sujetos estudiados por sospecha de infección extraósea se confirmó la enfermedad infecciosa, los estudios con el AcAG fueron positivos en 10 de los 14 pacientes. Se obtuvo un resultado falso positivo y cinco falsos negativos. Con prevalencia global (61 pacientes) de infección 68.8 por ciento, la sensibilidad fue 88 por ciento y la especificidad 94 por ciento. En el grupo de osteomielitis la sensibilidad fue 96 por ciento mientras que en el grupo de pacientes con infecciones extraóseas fue 71 por ciento. La especificidad fue 90 por ciento y 100 por ciento respectivamente