NLRP3 Inflammasome Involvement in Heart, Liver, and Lung Diseases-A Lesson from Cytokine Storm Syndrome.

Inflammation and inflammasomes have been proposed as important regulators of the host-microorganism interaction, playing a key role in morbidity and mortality due to the coronavirus disease 2019 (COVID-19) in subjects with chronic conditions and compromised immune system. The inflammasome consists of a multiprotein complex that finely regulates the activation of caspase-1 and the production and secretion of potent pro-inflammatory cytokines such as IL-1ß and IL-18. The pyrin containing NOD (nucleotide-binding oligomerization domain) like receptor (NLRP) is a family of intracellular receptors, sensing patterns associated to pathogens or danger signals and NLRP3 inflammasome is the most deeply analyzed for its involvement in the innate and adaptive immune system as well as its contribution to several autoinflammatory and autoimmune diseases. It is highly expressed in leukocytes and up-regulated in sentinel cells upon inflammatory stimuli. NLRP3 expression has also been reported in B and T lymphocytes, in epithelial cells of oral and genital mucosa, in specific parenchymal cells as cardiomyocytes, and keratinocytes, and chondrocytes. It is well known that a dysregulated activation of the inflammasome is involved in the pathogenesis of different disorders that share the common red line of inflammation in their pathogenetic fingerprint. Here, we review the potential roles of the NLRP3 inflammasome in cardiovascular events, liver damage, pulmonary diseases, and in that wide range of systemic inflammatory syndromes named as a cytokine storm.

Serological and Molecular Characterization of Hepatitis C Virus-Related Cryoglobulinemic Vasculitis in Patients without Cryoprecipitate.

Prolonged B cells stimulation due to the Hepatitis C virus (HCV) can result in autoimmunity, stigmatized by rising levels of cryoglobulins (CGs), the rheumatoid factor (RF), and free light chains (FLC) of immunoglobulins (Ig) associated with a range of symptoms, from their absence to severe cryoglobulinemic vasculitis and lymphoma. Here, we aimed to identify an immunological signature for the earliest stages of vasculitis when cryoprecipitate is still not detectable. We firstly analyzed the IgG subclasses, FLC, and RF in 120 HCV-RNA-positive patients divided into four groups according to the type of cryoprecipitate and symptoms: 30 asymptomatic without cryoprecipitate (No Cryo), 30 with vasculitis symptoms but without CGs that we supposed were circulating but still not detectable (Circulating), 30 type II and 30 type III mixed cryoglobulinemia (Cryo II and Cryo III, respectively). Our results revealed that patients with supposed circulating CGs displayed a pattern of serological parameters that closely resembled Cryo II and Cryo III, with a stronger similarity to Cryo II. Accordingly, we analyzed the groups of Circulating and Cryo II for their immunoglobulin heavy chain (IgH) and T-cell receptor (TCR) gene rearrangements, finding a similar mixed distribution of monoclonal, oligoclonal, and polyclonal responses compared to a control group of ten HCV-RNA-negative patients recovered from infection, who displayed a 100% polyclonal response. Our results strengthened the hypothesis that circulating CGs are the origin of symptoms in HCV-RNA-positive patients without cryoprecipitate and demonstrated that an analysis of clonal IGH and TCR rearrangements is the best option for the early diagnosis of extrahepatic complications.

Solving the mystery of HBV-related mixed cryoglobulinemia: potential biomarkers of disease progression.

OBJECTIVES: The biomarkers of an immunological dysregulation due to a chronic HBV infection are indeed understudied. If untreated, this condition may evolve into liver impairment co-occurring with extrahepatic involvements. Here, we aim to identify a new panel of biomarkers [including immunoglobulin G (IgG) subclasses, RF, and Free Light Chains (FLCs)] that may be useful and reliable for clinical evaluation of HBV-related cryoglobulinemia. METHODS: We retrospectively analysed clinical data from 44 HBV-positive patients. The patients were stratified (according to the presence/absence of mixed cryoglobulinemia) into two groups: 22 with cryoglobulins (CGs) and 22 without CGs. Samples from 20 healthy blood donors (HDs) were used as negative controls. Serum samples were tested for IgG subclasses, RF (-IgM, -IgG, and -IgA type), and FLCs. RESULTS: We detected a strikingly different distribution of serum IgG subclasses between HDs and HBV-positive patients, together with different RF isotypes; in addition, FLCs were significantly increased in HBV-positive patients compared with HDs, while no significant difference was shown between HBV-positive patients with/without mixed cryoglobulinemia. CONCLUSION: The immune-inflammatory response triggered by HBV may be monitored by a peculiar profile of biomarkers. Our results open a new perspective in the precision medicine era; in these challenging times, they could also be employed to monitor the clinical course of those COVID-19 patients who are at high risk of HBV reactivation due to liver impairment and/or immunosuppressive therapies.

COVID-19 and hepatic involvement: The liver as a main actor of the pandemic novel.

In the natural history of SARS-CoV-2 infection, liver injury is frequent but quite mild and it is defined as any liver damage occurring during disease progression and treatment of infection in patients with or without pre-existing liver diseases. The underlying mechanisms for hepatic injury in patients with COVID-19 are still unclear but the liver damage in SARS-CoV-2 infection seems to be directly caused by virus-induced cytopathic effects. In this review, we will summarize all data of updated literature, regarding the relationship between SARS-CoV-2 infection, acute response and liver involvement. An overview will be given on liver injury, liver transplant and the possible consequences of COVID-19 in patients with pre-existing liver diseases.

COVID-19, adaptative immune response and metabolic-associated liver disease.

Metabolic diseases are associated with a higher risk of a severer coronavirus disease 2019 (COVID-19) course, since fatty liver is commonly associated with metabolic disorders, fatty liver itself is considered as a major contributor to low-grade inflammation in obesity and diabetes. Recently a comprehensive term, metabolic (dysfunction) associated fatty liver disease (MAFLD), has been proposed. The hepatic inflammatory status observed in MAFLD patients is amplified in presence of severe acute respiratory syndrome coronavirus 2 infection. Intestinal dysbiosis is a powerful activator of inflammatory mediator production of liver macrophages. The intestinal microbiome plays a key role in MAFLD progression, which results in non-alcoholic steatohepatitis and liver fibrosis. Therefore, patients with metabolic disorders and COVID-19 can have a worse outcome of COVID-19. This literature review attempts to disentangle the mechanistic link of MAFLD from COVID-19 complexity and to improve knowledge on its pathophysiology.

Cryoglobulins: putative effectors of adaptive immune response.

Cryoglobulinaemia consists of circulating monoclonal and/or polyclonal immunoglobulins with rheumatoid factor (RF) activity that precipitate at temperatures <37°C. Cryoglobulinaemic syndrome, characterised by clinical signs of systemic vasculitis, is associated with chronic infection of hepatitis C virus (HCV) and might evolve in B-cell malignancies. In about one third of all HCV infection cases, serum autoantibodies are commonly found. This is probably due directly to the transformation of infected B cells but, also, indirectly, to the viral chronic stimulation of a pool of autoreactive B cells. The pattern of IgG subclasses seems to contribute to the worsening progression of HCV infection into lymphoproliferative and/or autoimmune diseases. Many evidences showed that B cells circulating in patients with HCV-associated mixed cryoglobulinaemia (MC) are profoundly abnormal; moreover, in most of cases, normal B cells are replaced by expanded clonal B cells characterized by the low expression of CD21. After viral eradication, these cells persist in circulation and their occurrence does not correlate with serum cryoglobulins nor with vasculitis response or relapse. It is probably due to the persistence of monoclonal B cells producing RF, that in course of MC can be reactivated by circulating immune complexes, highly produced during infections or tumours. Here, we aimed to review current literature focusing the pathogenesis of MC referring to specificity and immunochemical characteristics of the immunoglobulins involved in cryoprecipitation.

Immunological Role of IgG Subclasses.

The loss of tolerance to self-antigens is the unequivocal "red line" of autoimmunity: both development of autoreactive T and B cells and production of polyclonal autoantibodies represent seminal keys to the pathogenesis of protean autoimmune diseases. Most of these autoantibodies are immunoglobulins G (IgG), functionally distinguished in four subclasses named IgG1, IgG2, IgG3, and IgG4, due to structural differences in the hinge and heavy chain constant regions. Different studies analyzed serum levels of IgG subclasses in the course of different disorders, showing that they might have a pathogenic role by regulating interactions among immunoglobulins, Fc-gamma receptors, and complement. To date, the mechanisms promoting different IgG subclasses distribution during the natural history of most autoimmune diseases remain somewhat unclear. Evidence from the medical literature shows that the serum IgG profile is peculiar for many autoimmune diseases, suggesting that different subclasses could be specific for the underlying driving autoantigens. A better knowledge of IgG subsets may probably help to elucidate their pathological task, but also to define their relevance for diagnostic purposes, patients' personalized management, and prognosis assessment.

Biomarkers of minimal residual disease in rituximab-treated patients with mixed cryoglobulinemia.

Hepatitis C virus (HCV) represents the major risk factor for mixed cryoglobulinemia (MC), a small-vessel vasculitis that may evolve into an overt B-cell non-Hodgkin's lymphoma. Here, we aimed to identify a biomarker signature for the early diagnosis of minimal residual disease (MRD). We assessed free light chains (FLCs), IgM k,and IgM λ heavy/light chain (HLC) pairs, and vascular endothelial growth factor (VEGF) in sera from 34 patients with MC vasculitis (32 HCV- and 2 HBV-related), treated with low-dose rituximab (RTX). FLCs and IgM HLCs were measured by turbidimetric assay; VEGF by an enzyme-linked immunosorbent assay. After RTX, the positive (complete + partial) clinical and laboratory responses were of 85.29% and 50%, respectively; in contrast, the mean levels of FLCs, IgM HLCs, and VEGF were substantially unaffected in most patients and still above the normal range. In those achieving a reduction of FLCs and IgM k and λ chains values within the range of normality, we found that post-treatment free λ chains and IgM k values correlated with clinical and laboratory response. Our results suggest that high levels of FLCs, IgM HLCs, and VEGF could represent the signature of "dormant" B cell clones' activity that could be very useful to identify MRD indicative of possible relapse or worsening outcome.

Laboratory Investigation of Hybrid IgG4 k/λ in MuSK Positive Myasthenia Gravis.

Myasthenia gravis with antibodies (Abs) against the muscle-specific tyrosine kinase (MuSK) is a rare autoimmune disorder (AD) of the neuromuscular junction (NMJ) and represents a prototype of AD with proven IgG4-mediated pathogenicity. Thanks to the mechanism of Fab-arm exchange (FAE) occurring in vivo, resulting MuSK IgG4 k/λ Abs increase their interference on NMJ and pathogenicity. The characterization of hybrid MuSK IgG4 as a biomarker for MG management is poorly investigated. Here, we evaluated total IgG4, hybrid IgG4 k/λ, and the hybrid/total ratio in 14 MuSK-MG sera in comparison with 24 from MG with Abs against acetylcholine receptor (AChR) that represents the not IgG4-mediated MG form. In both subtypes of MG, we found that the hybrid/total ratio reflects distribution reported in normal individuals; instead, when we correlated the hybrid/total ratio with specific immune-reactivity we found a positive correlation only with anti-MuSK titer, with a progressive increase of hybrid/total mean values with increasing disease severity, indirectly confirming that most part of hybrid IgG4 molecules are engaged in the anti-MuSK pathogenetic immune-reactivity. Further analysis is necessary to strengthen the significance of this less unknown biomarker, but we retain it is full of a diagnostic-prognostic powerful potential for the management of MuSK-MG.

The Laboratory Role in anti-TNF Biological Therapy Era.

Along years, the advent of biological therapy widely modified treatment of rheumatic diseases and other disorders. However, many agents may elicit in anti-drug antibodies (ADAbs) upon consecutive infusions, with a loss of response. For the right strategy of a personalized medicine, the therapeutic monitoring of TNF-α inhibitors and ADAbs represents an important effort in diagnostic-therapeutic pathway, to improve overall patient management and favoring an appropriate clinical approach. A raising number of diagnostic tests have been designed to elucidate the efficacy and/or safety of a specific drug or class of drugs for a targeted patient's group. Our paper reviewed the current understanding of the immunogenicity of biological drugs employed in the treatment of inflammatory diseases underlying the laboratory role.

Fecal calprotectin and need of multiple microbiota trasplantation infusions in Clostridium difficile infection.

BACKGROUND AND AIM: Fecal microbiota transplantation (FMT) has proven to be very effective in recurrent Clostridium difficile infection (CDI) when compared with standard antibiotic therapy. However, given the lack of validated criteria, decision regarding number and timing of infusions is currently based on the clinician's experience, severity of infection, and clinical response. We performed a longitudinal assessment of fecal calprotectin concentration (FCC) in CDI patients undergoing FMT. FCCs were correlated with the need for multiple infusions and with the clinical status of the patient. METHODS: Fecal calprotectin concentration measurement was performed just before first procedure (T0 ) and 2 (T1 ) and 5 (T2 ) days later. The need for reinfusion was accounted for in the 8 weeks following procedure, and clinical status was evaluated at the end of the given period. Both outcomes were correlated with measured FCCs. RESULTS: A total of 28 CDI patients undergoing FMT were enrolled. Median FCCs at T0 were significantly higher in patients who needed repeat FMT, 540 µg/g versus patients who underwent single FMT, 290 µg/g (P < 0.05). Differences were not significant for FCC at T1 and T2 . Regarding correlation with clinical outcome, median FCC at T0 was found to be lower in responders compared with non-responders with a trend towards statistical significance (P = 0.07). Correlation at T1 and T2 was not significant. CONCLUSIONS: The use of an easily obtainable parameter such as fecal calprotectin could possibly optimize overall management of FMT procedural framework potentially being able to immediately identify patients who may benefit from repeat infusions.

Plasmatic free light chains in polycystic ovary syndrome.

Polycystic ovary syndrome (PCOS), as systemic disease, is accompanied by different indexes of inflammation. Free light chains of immunoglobulins (FLCs), produced by plasmacells, are released in slight excess for the immune requests, with still poorly defined physiological role but surely they represent a marker of inflammation. In order to evaluate their levels and correlate them with hyperandrogenism, we have studied a group of PCOS patients, age range 18-37 yrs, mean ± SEM body mass index (BMI) 24.1 ± 0.9 kg/m2), compared with age- and BMI-matched controls, with assay of k and λ FLCs, by turbidimetric method, and their ratio in blood plasma. PCOs exhibited higher levels vs. controls: (mean ± SEM λ: 10.0 ± 0.85 mg/L vs. 8.41 ± 0.45 mg/L; k: 12.45 ± 0.72 mg/L vs. 6.41 ± 0.34 mg/L; k/λ: 1.31 ± 0.07 vs. 0.78 ± 0.04). A significant direct correlation was observed between λ-FLCs and testosterone levels, no correlation was indeed found with HOMA-IR index. These data confirm high levels of FLCs in PCOS, suggesting systemic inflammatory state and a possible role in the pathophysiology of such complex syndrome.

Serum free light chain quantitative assays: Dilemma of a biomarker.

BACKGROUND: Serum free light chains detection assays are consistently meeting greater interest for the diagnosis and monitoring of monoclonal gammopathies and plasma cell dyscrasias. Nowadays, there are neither standardized methods nor reference material for the determination of free light chains; for this reason, it is important to compare two different assays used in clinical laboratory. METHODS: We evaluated 300 serum samples from patients with B-cell disorders and compared the analytical performances of both assay. Each test was assayed on both testing platforms (Siemens Dade Behring BN II Nephelometer and SPAPLUS by The Binding Site). κ/λ ratios were determined and compared. Results were analyzed by Passing-Bablok and Bland-Altman plots to evaluate comparability of the two techniques and to determine bias. RESULTS: The reproducibility of both assays is acceptable, reaching minimum and desirable analytical goals derived from biological variability. However, values are not interchangeable between systems. This study shows that the two systems do not allow results to be transferred from one method to the other even if they display good agreement. CONCLUSION: Our study highlights the importance of elaborating an international standard for free light chains quantification in order to offer homogeneous results as well as guarantee harmonization of values among laboratories. Moreover, the assays should be validated in specific patient groups to determine that they are clinically fit for purpose.

Comparison of Fully Automated and Semiautomated Systems for Protein Immunofixation Electrophoresis.

BACKGROUND: In order to establish a diagnosis of monoclonal gammopathy, it is necessary to detect and identify monoclonal components. To confirm the immunological nature of the proteins, the next step is to define their composition in heavy and light chains using immunofixation. The purpose of this study was to compare two different instruments, one semiautomated and the other fully automated for serum and urine immunofixation. METHODS: We selected 150 sera and 100 urines from patients admitted for routine analysis, which were analyzed by immunofixation to characterize monoclonal components. RESULTS AND CONCLUSION: Comparison study showed a difference in the identification of small monoclonal components and hypogammaglobulinemia, in serum and urine, between the two analyzers. We also observed a difference in the length of the electrophoretic pattern that is of considerable importance as it leads to a better resolution of the gamma region, allowing to identify even the smallest monoclonal component that can be easily hide in an oligoclonal pattern. For this reason, there is need to ameliorate commercial immunofixation assays. It is essential to improve data harmonization and standardize measurement procedures in order to guarantee a correct diagnosis for the right patient care.

Effect of prenatal steroidal inhibition of sPLA2 in a rat model of preterm lung.

INTRODUCTION: Secretory phospholipase A2 regulates surfactant catabolism and inflammatory cascade. This enzyme is correlated with compliance, oxygenation and major outcomes in various forms of acute respiratory failure. Steroids inhibit secretory phospholipase A2 in cell culture and are widely used to boost surfactant production before preterm delivery. No data are available about the effect of antenatal steroids on secretory phospholipase A2 in the offspring: we aimed to study this effect in a rat model of preterm lung. MATERIAL AND METHODS: Fifteen pregnant Wistar rats were randomized to receive betamethasone, dexamethasone or placebo at 20 and 21 days gestation. Newborn rats were supported for 8 h and then sacrificed: lung tissue was analysed for secretory phospholipase A2 expression and activity, inflammatory mediators and protein content. Lipidomics was analysed using liquid chromatography-mass spectrometry. RESULTS: Secretory phospholipase A2 expression was significantly reduced by antenatal steroids (p < 0.001). Secretory phospholipase A2 activity, TNFα and lysophosphatidylethanolamine, a product of phospholipase reaction, were lowest in betamethasone-treated rats (p < 0.001). There was a strong correlation between secretory phospholipase A2 activity and lysophosphatidylethanolamine (r = 0.75; p = 0.001) and this remained significant after adjustment for total proteins or phospholipids. CONCLUSIONS: Antenatal steroids decrease secretory phospholipase A2 in rat model of preterm lung.

Urinary Albumin Detection: Comparison of Two Different Methods.

BACKGROUND: Monitoring urinary albumin is a useful method in clinical practice for the management of diabetic nephropathy, chronic kidney disease, and hypertension. Currently there are neither standardized methods nor reference material for the determination of urinary albumin; for this reason it is useful to compare different assays used in clinical laboratory. OBJECTIVES: The aim of this study is to verify analytical performance of an immunoturbidimetric assay on Roche Cobas 8000 platform and to compare urinary albumin results with those obtained by immunonephelometry on Siemens Dade Behring BN II Nephelometer. RESULTS: The method comparison showed a good linear relationship, confirmed by Passing-Bablok and Bland-Altman plots. The turbidimetric assay meets the requirements of accuracy and precision for the practice of medical diagnostics and clinical use. CONCLUSIONS: The present study can contribute to the methods standardization and harmonization of urinary albumin assay.

Type 2 cytokines and scleroderma interstitial lung disease.

Interstitial lung disease (ILD) is a life-threatening complication of systemic sclerosis (SSc). Type 2 (Th2) cytokines play a pivotal role in airway disease. Study aim was to evaluate serum level of Th2 interleukin (IL) and chemokine in SSc-ILD. Serum levels of IL-4, IL-5, IL-11, IL-13, IL-21, IL-31 and CXCL-13 were measured by Bio-Plex Multiplex Immunoassays in 60 SSc patients and 20 healthy controls (HC). Pulmonary function tests with diffusion lung capacity for carbon monoxide (DLco) and high resolution computed tomography (HRCT) were performed in SSc patients. ILD is defined as fibrotic changes (ground glass, reticular and honeycombing), assessed by Computer-Aided Lung Informatics for Pathology Evaluation and Ratings (CALIPER) software, affecting at least 10% of the lungs. Serum levels of Th2 cytokines were higher in SSc patients than HC. A linear correlation was observed between ground glass and IL-13 (r = 0.342, p < 0.01), IL-21 (r = 0.345, p < 0.01), IL-31 (r = 0.473, p < 0.001), IL-4 (r = 0.863, p < 0.001), IL-5 (r = 0.249, p < 0.05) and peripheral blood eosinophils (r = 0.463, p < 0.001). We found a negative correlation between DLco and IL-4 (r = - 0.511, p < 0.001) and peripheral blood eosinophils (r = - 0.446, p < 0.001). In the logistic regression analysis, IL-4 is associated with DLco ≤ 60% of the predicted [OR 1.039 (CI 95%: 1.015-1.064), p < 0.001], whilst mRSS [OR 1.138 (CI 95%: 1.023-1.266), p < 0.05] and IL-4 [OR 1.017 (CI 95%: 1-1.034), p < 0.05] were associated with ILD. Th2 inflammation could play a key role in early phase of SSc-ILD.

Elevated serum polyclonal immunoglobulin free light chains in patients with severe asthma.

Background: Inflammation plays a pivotal role in the pathophysiology of asthma. Free light chains (FLC) can cause inflammation by mast cell antigen-activation. Serum immunoglobulin (Ig) FLC κ, but not λ, were shown elevated in adult males with asthma. We sought to investigate if serum Ig FLC concentrations are affected by asthma severity and their relationships with inflammatory outcomes. Methods: By using immunoassays, we measured serum κ and λ Ig FLCs in 24 severe persistent asthma patients, 15 patients with moderate persistent asthma, 15 steroid-naïve mild persistent asthma patients and 20 healthy control subjects in a cross-sectional observational study. Total and specific serum IgE concentrations, fractional exhaled nitric oxide (FENO), lung function, peripheral blood eosinophils and neutrophils, and C reactive protein (CRP) were also measured. Results: Serum κ FLC concentrations were elevated in severe asthma patients compared mild asthma patients (p < 0.05) and healthy subjects (p < 0.05). Serum λ FLCs were higher in severe asthma patients than in healthy subjects (p < 0.05) and correlated with blood eosinophil counts (percentage, κ: r = 0.51, p = 2.9678-6; λ: r = 0.42, p = 1.7377-4; absolute values, κ: r = 0.45, p = 6.1284-5; λ: r = 0.38, p = 7.8261-4), but not with total or specific serum IgE. In severe asthma patients, serum Ig FLC correlated with serum CRP (κ: r = 0.33; p = 0.003; λ: r = 0.38, p = 8.8305-4) and blood neutrophil cell counts (percentage, κ: r = 0.31; p = 0.008; λ: r = 0.29, p = 0.01; absolute values, κ: r = 0.40; p = 3.9176-4; λ: r = 0.40, p = 4.5479-4), were elevated in subjects with blood eosinophilia (≥300 cells/µL) (n = 13) compared with non-eosinophilic subjects (n = 10) (κ: 19.2 ± 1.2 mg/L versus 12.1 ± 1.3 mg/L, p < 0.001; λ: 27.2 ± 2.6 mg/L versus 16.8 ± 2.5 mg/L, p < 0.01), but were similar in atopic (n = 15) versus nonatopic subjects (n = 9) (κ: p = 0.20; λ: p = 0.80). Serum FLC were negatively correlated with lung function tests, including forced expiratory volume in one second (FEV1) (κ: r = -0.33; p = 0.0034; λ: r = -0.33; p = 0.0035), and FEV1/forced vital capacity ratio (κ: r = -0.33; p = 0.0034; λ: r = -0.33; p = 0.0036). Conclusion: Serum Ig FLCs are elevated in severe asthma adults and might represent new surrogate markers of inflammation. The pathophysiological implications of these findings require further research. This study was approved by the ethics committee of the University Hospital Agostino Gemelli Foundation and Catholic University of the Sacred Heart (approval number P/1034/CE2012).

Mono/polyclonal free light chains as challenging biomarkers for immunological abnormalities.

Free light chain (FLC) kappa (k) and lambda (λ) consist of low molecular weight proteins produced in excess during immunoglobulin synthesis and secreted into the circulation. In patients with normal renal function, over 99% of FLCs are filtered and reabsorbed. Thus, the presence of FLCs in the serum is directly related to plasma cell activity and the balance between production and renal clearance. FLCs are bioactive molecules that may exist as monoclonal (m) and polyclonal (p) FLCs. These have been detected in several body fluids and may be key indicators of ongoing damage and/or illness. International guidelines now recommend mFLC for screening, diagnosis and monitoring multiple myeloma and other plasma cell dyscrasias. In current clinical practice, FLCs in urine indicate cast nephropathy and other renal injury, whereas their presence in cerebrospinal fluid is important for identifying central nervous system inflammatory diseases such as multiple sclerosis. Increased pFLCs have also been detected in various conditions characterized by B cell activation, i.e., chronic inflammation, autoimmune disease and HCV infection. Monitoring the coronavirus (COVID-19) pandemic by analysis of salivary FLCs presents a significant opportunity in clinical immunology worthy of scientific pursuit.