Free light chains of immunoglobulins in serum from patients with rheumatoid arthritis, sarcoidosis, chronic infections and pulmonary cancer

Serological Immunoglobulin-Free Light Chain Profile in Myasthenia Gravis Patients

Background

Serological levels of free immunoglobulin light chains (FLCs), produced in excess of heavy chains during synthesis of immunoglobulins by plasma cells, can be considered a direct marker of B cell activity in different systemic inflammatory-autoimmune conditions and may represent a useful predictor of rituximab (RTX) therapeutic efficacy, as reported for rheumatoid arthritis and systemic lupus erythematosus. Myasthenia gravis (MG) is an autoimmune disease of the neuromuscular junction with antibodies (abs) targeting the acetylcholine receptor (AChR) or the muscle-specific tyrosine kinase (MuSK), inducing muscle weakness and excessive fatigability. As MG course may be remarkably variable, we evaluated the possible use of FLCs as biomarkers of disease activity.

Subjects and Methods

We assessed FLC levels in 34 sera from 17 AChR-MG and from 13 MuSK-MG patients, in comparison with 20 sera from patients with systemic autoimmune rheumatic diseases and 18 from healthy blood donors, along with titers of specific auto-abs and IgG subclass distribution.

Results

We found a statistically significant increase in free κ chains in both AChR- and MuSK-MG patients, while free λ chain levels were increased only in AChR-MG. We also observed a significant reduction of both free κ and λ chains in 1/4 MuSK-MG patients along with specific abs titer, two months after RTX treatment.

Conclusions

From our data, FLCs appear to be a sensitive marker of B cell activation in MG. Further investigations are necessary to exploit their potential as reliable biomarkers of disease activity.

Free light chains: Eclectic multipurpose biomarker

The production of antibodies is accompanied by a slight excess of synthesis of κ and λ immunoglobulin light chains; small amounts of them are released in the peripheral blood and can also be found in various body fluids, such as synovial fluid, cerebrospinal fluid, urine and saliva. They are rapidly filtered by the glomerulus and >99% are reabsorbed from the cells of the proximal convoluted tubule, making them present in the urine in only trace amounts. The production of an excess of protein without a reason or a specific function in a biological system is rare. Free light chains, considered for years a waste product of Ig synthesis, are currently known to be very active molecules, able to bind antigens as well as whole immunoglobulin and helping to develop specific antibody affinity. The ability of free light chains to activate mast cells and then become an active part of the pathogenic mechanisms of chronic inflammatory diseases has increased interest in their clinical use, both as an attractive therapeutic target or as a biochemical marker of disease evolution or remission. This is an overview of relevant scientific interest that immunoglobulin light chains κ and λ have attracted over the years, a report on the progress in knowledge about their structure and function, with a special focus on their biological meaning and potential clinical utility in different diseases.

The association of serum-free light-chain levels with markers of renal function

BACKGROUND

The kidney is often affected in plasma cell dyscrasias, usually due to the effects of nephrotoxic monoclonal-free light chains. Renal failure due to a monoclonal gammopathy may be detected by the highly sensitive serum-free light-chain (sFLC) ratio yet missed by electrophoretic assays. The aim of this study was to assess sFLC levels in relation to markers of renal function.

METHODS

Five-hundred thirteen patients were included in this study. sFLC levels were measured by Freelite® (The Binding Site Group Ltd, Birmingham, UK) assay using the BNII nephelometer (Siemens Diagnostics, Germany). Kappa/lambda (κ/λ) sFLC ratio was calculated. Serum creatinine levels were analyzed by modified Jaffe method in Cobas 8000 analyser. GFR was estimated by the CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) equation. Patients were assigned to two groups depending on their eGFR values: ≤ 60 mL/min/1.73 m(2) (Group 1, n = 103) and > 60 mL/min/1.73 m(2) (Group 2, n = 410). Data were expressed as median and min-max. All the statistical analyses were done with SPSS version 20.0 and a significance level of 0.05 was considered.

RESULTS

Serum κ-FLC median value was 36.4 (5.62-16,000) mg/L, serum λ-FLC was 21.7 (4.91-8770) mg/L, κ/λ sFLC ratio was 1.33 (0.01-3258) and serum creatinine was 1.56 (0.63-7.21) mg/dL in Group 1. Both λ sFLC and κ/λ sFLC ratios were correlated with eGFR (r = -0.318, r = 0.198, p < 0.05, respectively). We did not find any significant correlation between κ/λ sFLC ratio and eGFR in Group 2.

CONCLUSIONS

We examined the association between sFLC concentrations and renal function. Our preliminary findings suggest that serum λ-FLC might be considered as a useful marker for predicting renal function. Prospective studies are needed to clarify the usefulness of these parameters for identifying renal failure due to a monoclonal gammopathy.

Association of serum TNF-α, IL-8 and free light chain with HLA-DR B alleles expression in pulmonary and extra-pulmonary sarcoidosis

Background

Sarcoidosis is a systemic disease of unknown etiology characterized histologically by the observation of non-caseating granulomas and several immunological abnormalities. Sarcoidosis is a multi-organ disorder which involves formation of granulomas in many tissues including the lungs (pulmonary) and others such as skin, bone, heart (extra pulmonary). Associations between human leukocyte antigens (HLA), the encoded cell surface receptor (HLA-DR) and sarcoidosis have been reported in several studies. Several HLA-DR alleles have been described as potential risk factors for sarcoidosis in distinct ethnic groups however evidence for a relationship between HLA-DR alleles and pulmonary and extra-pulmonary sarcoidosis (EPS) is still scarce. Although the etiology of the disease remains unclear, infectious and environmental factors have been postulated. Inflammatory cytokines and chemokines may play important roles in the pathogenesis of sarcoidosis and serum free light chain (FLC) numbers have been implicated in several immunologic disorders.

Purpose of the study

The aim of the present study was to investigate HLA associations with serum cytokines and FLC in Iranian patients with pulmonary (n = 86) and EPS (n = 46).

Results

We found that among the 16 HLA DRB alleles only *7 and *12 were different in sarcoidosis patients. The levels of TNF-α and IL-8 in pulmonary sarcoidosis patients were higher than in EPS (P < 0.05) whereas the levels of FLC subunits in EPS were higher than in pulmonary sarcoidosis.

Conclusion

This data may suggests a link between HLA-DRB *12 and sarcoidosis in Iranian population.

Elevation of serum immunoglobulin free light chains during the preclinical period of rheumatoid arthritis

OBJECTIVE

Immunoglobulin free light chains (FLC) represent biomarkers of B cell activity in rheumatoid arthritis (RA) and are associated with all-cause mortality in the general population. Our objective was to evaluate the relationships of serum FLC to preclinical disease, RA characteristics, and mortality in RA compared to non-RA subjects.

METHODS

A population-based study in Olmsted County, Minnesota, USA, was performed by crosslinking a large cohort in the general population having available serum FLC measurements with established RA incidence and prevalence cohorts. Serum κ, λ, and total FLC and their trends relative to RA incidence were compared between RA and non-RA subjects. Regression models were used to determine the associations between FLC, disease characteristics, and mortality, testing for differential effects of FLC on mortality in RA.

RESULTS

Among 16,609 subjects, 270 fulfilled the criteria for RA at the time of FLC measurement. Mean total FLC were significantly higher in RA compared to non-RA subjects (4.2 vs 3.3 mg/dl, p < 0.001). FLC became elevated 3-5 years before the clinical onset of RA and remained elevated during followup. Polyclonal FLC were found to predict higher mortality in persons with RA, though elevation to the highest decile had a relatively lower effect on mortality in RA compared to non-RA subjects.

CONCLUSION

Elevation of serum FLC precedes the development of RA and may be useful in monitoring B cell activity and disease progression. FLC are associated with mortality among patients with RA as well as the general population.

Circulating antibody free light chains and risk of posttransplant lymphoproliferative disorder

Posttransplant lymphoproliferative disorder (PTLD) is a major complication of solid-organ transplantation. With human immunodeficiency virus infection (an analogous immunosuppressive state), elevated kappa and lambda immunoglobulin free light chains (FLCs) in peripheral blood are associated with increased risk of lymphoma. To assess the role of B-cell dysfunction in PTLD, we measured circulating FLCs among Canadian transplant recipients, including 29 individuals with PTLD and 57 matched transplant recipients who were PTLD-free. Compared with controls, PTLD cases had higher kappa FLCs (median 1.53 vs. 1.07 times upper limit of normal) and lambda FLCs (1.03 vs. 0.68). Using samples obtained on average 3.5 months before PTLD diagnosis, cases were more likely to have polyclonal FLC elevations (i.e. elevated kappa and/or lambda with normal kappa/lambda ratio: odds ratio [OR] 4.2, 95%CI 1.1-15) or monoclonal elevations (elevated kappa and/or lambda with abnormal ratio: OR 3.0, 95%CI 0.5-18). Strong FLC-PTLD associations were also observed at diagnosis/selection. Among recipients with Epstein-Barr virus (EBV) DNA measured in blood, EBV DNAemia was associated with FLC abnormalities (ORs 6.2 and 3.2 for monoclonal and polyclonal elevations). FLC elevations are common in transplant recipients and associated with heightened PTLD risk. FLCs likely reflect B-cell dysfunction, perhaps related to EBV-driven lymphoproliferation.

Serum free light chains and the risk of ESRD and death in CKD

BACKGROUND AND OBJECTIVES

Associations between inflammation and ESRD and death in chronic kidney disease are well established. However, the potential role of the adaptive immune system is uncertain. We aimed to prospectively study the relevance of the adaptive immune system to ESRD and mortality by measuring monoclonal and polyclonal excesses of highly sensitive serum free light chains (sFLCs).

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Three hundred sixty-four patients selected from a nephrology outpatient clinic had kappa and lambda sFLCs concentrations and serum immunofixation electrophoresis measured. Cox regression was used to assess the relevance of monoclonal and polyclonal excess of sFLCs to the incidence of ESRD and death (mean follow-up for death 6.0 years).

RESULTS

After adjustment for baseline eGFR, there was no significant association between monoclonal excess of sFLCs and risk of ESRD or mortality. Baseline log κ and log λ concentrations were positively associated with ESRD risk, but these associations seemed to be due to correlations with eGFR (per 1 SD higher concentration: adjusted hazard ratio 1.05 [95% confidence interval 0.88 to 1.26] and 0.99 [0.83 to 1.19], respectively). For mortality, after adjustment for eGFR plus markers of cardiac damage, there was weak evidence of an association with λ, but not κ, sFLC concentration (fully adjusted hazard ratio 1.33 [95% confidence interval 1.05 to 1.67] per 1 SD higher concentration).

CONCLUSIONS

Associations between monoclonal and polyclonal excess of sFLCs and risk of ESRD are explained by the correlation between these measures and renal function. We found only weak evidence of an association between polyclonal excess of λ sFLC concentration and mortality.

Serum free light chains as biomarkers for systemic lupus erythematosus disease activity

OBJECTIVE

To evaluate serum free light chains (FLC) as a putative biomarker of systemic lupus erythematosus (SLE) activity.

METHODS

Seventy-five SLE patients and 41 age- and sex-matched rheumatoid arthritis (RA) controls were enrolled. Disease activity was assessed using the Safety of Estrogens in Lupus Erythematosus: National Assessment version of the Systemic Lupus Erythematosus Disease Activity Index (SLEDAI) definition and physician global assessments for SLE and the Disease Activity Score in 28 joints for RA. Serum FLC levels were compared against other biomarkers (IgG, C3, C4, double-stranded DNA [dsDNA] antibody). Nonparametric tests were used to compare 1) FLC and IgG in SLE versus RA and healthy controls, 2) FLC and IgG among different levels of activity in SLE, and 3) FLC in active versus nonactive RA. Correlation of FLC, C3, C4, dsDNA antibody, and IgG with the SLEDAI and modified SLEDAI (M-SLEDAI) were obtained.

RESULTS

FLC was higher in SLE than in RA; both were higher than referent healthy controls. Total FLC was significantly higher in subjects with greater SLE disease activity than lower/no activity. There were no significant differences in IgG, C4, or dsDNA antibody stratified by disease activity. Total FLC and C3 showed moderate to strong correlation with the SLEDAI and M-SLEDAI. In RA, no differences were seen in FLC levels for different levels of disease activity. Similar results were seen after controlling for renal function, age, and sex. In multiple linear regression, FLC significantly explained 50% variance of the SLEDAI after adjusting for renal function, age, and sex.

CONCLUSION

Serum FLC levels correlate strongly with disease activity in SLE, but not in RA. Serum FLC may be used as a biomarker of SLE disease activity.

Quantitative assessment of serum and urinary polyclonal free light chains in patients with chronic kidney disease

BACKGROUND AND OBJECTIVES

Monoclonal free light chains (FLC) frequently cause kidney disease in patients with plasma cell dyscrasias. Polyclonal FLC, however, have not been assessed in patients with chronic kidney disease (CKD) yet could potentially play an important pathologic role. This study describes for the first time polyclonal FLC in patients with CKD.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

A sensitive, quantitative immunoassay was used to analyze serum and urinary polyclonal FLC in 688 patients with CKD of various causes.

RESULTS

Serum kappa and lambda FLC concentrations increased progressively with CKD stage (both P < 0.001) and strongly correlated with markers of renal function, including cystatin-C (kappa: R = 0.8, P < 0.01; and lambda: R = 0.79, P < 0.01). Urinary FLC concentrations varied significantly between disease groups (kappa: P < 0.001; lambda: P < 0.005) and also rose significantly with increasing CKD stage (both FLC P < 0.0001). Urinary FLC concentrations were positively correlated with their corresponding serum concentration (kappa: R = 0.63; lambda: R = 0.65; both P < 0.001) and urinary albumin creatinine ratio (kappa: R = 0.58; lambda: R = 0.65; both P < 0.001). The proportion of patients with abnormally high urinary FLC concentrations rose with both the CKD stage and the severity of albuminuria.

CONCLUSIONS

This study demonstrates significant abnormalities of serum and urinary polyclonal FLC in patients with CKD. These data provide the basis for studies that assess the contribution of polyclonal FLC to progressive renal injury and systemic inflammation in patients with kidney disease.

Quantitative assessment of serum and urinary polyclonal free light chains in patients with type II diabetes: an early marker of diabetic kidney disease?

OBJECTIVE

Free light chains (FLCs) are bi-products of normal immunoglobulin synthesis and are predominately removed from the circulation by the kidneys. This study assessed polyclonal FLCs as a novel biomarker of early diabetic kidney disease.

RESEARCH DESIGN/METHODS

Serum and urinary FLCs were assessed by the immunoassay Freelite, in white and South-Asian patients with type II diabetes recruited from the United Kingdom Asian Diabetes Study.

RESULTS

The incidence of monoclonal proteins in this diabetic population was 1.9%. Type II diabetic patients had significantly raised concentrations of serum polyclonal FLCs before overt renal impairment developed (p < 0.001). Both kappa and lambda FLCs correlated with all tested markers of renal function; in particular cystatin-C: Spearman's coefficient (R) = 0.55 (p < 0.01) and R = 0.56 (p < 0.01), respectively. The South-Asian diabetic patients had higher serum polyclonal FLCs than Caucasian diabetic patients and this was independent of renal function. Urinary FLCs concentrations were raised in diabetic patients (p < 0.001). The majority (68%) of diabetic patients with normal urinary albumin:creatinine ratios (ACRs) had abnormal urinary FLC:creatinine ratios. Both kappa and lambda FLC concentrations correlated with urinary ACR: R = 0.32, p < 0.01 and R = 0.25, p < 0.01 respectively.

CONCLUSIONS

Type II diabetic patients can have significantly raised concentrations of serum and urinary polyclonal FLCs before overt renal disease occurs. These novel findings provide the basis for future studies to assess whether polyclonal FLCs could provide a useful tool for early diagnosis of diabetic kidney disease.

The Importance of Free Light Chains of Immunoglobulins Determination in Serum

For many years, Bence Jones proteinuria has been an important diagnostic marker for multiple myeloma. Relatively new serum tests for free kappa and free lambda light chains of immunoglobulins reflect the production of free light chains more accurately than urine tests. In this study, we examined the value of serum free light chains measurement in the diagnosis of some neoplastic diseases and the discrepance between the findings of serum protein electrophoresis and serum free light chains. Thirty one patients (f=19, m=12) were included in the study, most of them with blood malignant diseases. The results show that in six patients with normal gamma and beta electrophoresis fractions there are abnormal levels of free light chains and/or an abnormal κ/LD ratio. In 20 patients we found an abnormal κ/LD ratio, and in 21 patients we found an abnormal κ or LD level, or both. The obtained results show the important role of serum free light chains determination in identifying patients with monoclonal gammopathies.

Consequences of receptor editing at the lambda locus: multireactivity and light chain secretion

To investigate the manner in which B cells with lambda light (L) chains undergo receptor editing, we have studied hybridoma panels from 56R/kappa-deleted (kdel) mice. 56R/kdel mice only produce four L chains (lambda1, lambda2, lambda3, and lambdaX). They also have a simplified heavy (H) chain repertoire: All B cells start out with a 56R anti-DNA H chain. A few frankly autoreactive 56R lambda1 cells appear to escape into the periphery, but the majority of the peripheral B cell repertoire in 56R/kdel is made up of B cells expressing the 56R H chain with the lambdaX L chain. Surprisingly, 56R lambdaX B cells are multireactive, binding to a variety of self and nonself antigens, including dsDNA (albeit at reduced affinity compared with the other lambda L chains). Another significant population in the 56R/kdel mouse consists of allelically included B cells that express lambdaX along with another L chain. The multireactivity of both 56R lambdaX and 56R lambdaX/lambda1 receptors could contribute to autoimmunity if these B cells were to become activated. Also found among 56R/kdel hybridomas are clones that have inactivated the H chain and secrete only L chains. These clones may represent products of exhaustive rearrangement. Multireactivity, allelic inclusion, and L chain secretion are three consequences of editing at the lambda locus that may predispose toward the development of autoimmunity.

Serum immunoglobulin free light chain assessment in rheumatoid arthritis and primary Sjogren's syndrome

BACKGROUND

B cell activation may result in an increased secretion of immunoglobulin free light chains (FLCs) in autoimmune diseases.

OBJECTIVE

To analyse serum FLC levels in patients with rheumatoid arthritis and in those with primary Sjögren's syndrome (pSS).

PATIENTS AND METHODS

Blood samples were collected from 80 healthy blood donors, 50 patients with rheumatoid arthritis and 139 patients with pSS. Serum FLC level was measured using a new quantitative immunoassay.

RESULTS

Mean (standard error (SE)) serum kappa and lambda FLC levels were significantly higher in patients with rheumatoid arthritis and in those with pSS than in controls (kappa : 18.9 (1.1) and 16.3 (1.4) v 10.5 (0.4) mg/l, p<0.001 and p = 0.001, respectively; lambda: 16.7 (1.2) and 19.3 (1.5) v 11.6 (0.6) mg/l, p<0.001 for both). 18 (36%) patients with rheumatoid arthritis and 31 (22.3%) patients with pSS had abnormal serum FLC levels (increased kappa or lambda levels and abnormal ratio of kappa:lambda). Serum kappa and lambda levels were correlated with other B cell activation markers in both diseases. FLC levels increased with disease activity, because, unlike total gammaglobulin and immunoglobulin G levels, they were significantly correlated with Disease Activity Score 28 in patients with rheumatoid arthritis (p = 0.004 for kappa, p = 0.05 for lambda) and with extraglandular involvement in pSS (p = 0.01 for kappa, p = 0.04 for lambda).

CONCLUSION

FLC levels are increased and correlate with disease activity in patients with rheumatoid arthritis and in those with pSS, two diseases in which increased risk of lymphoma could result from persistent B cell activation and disease activity. Further studies are required to determine whether FLC assessment could represent a relevant biomarker for response to treatment (especially B cell depletion) and for the risk of lymphoma in autoimmune diseases.

Free immunoglobulin light chains as target in the treatment of chronic inflammatory diseases

Immunoglobulin free light chains were long considered irrelevant bystander products of immunoglobulin synthesis by B lymphocytes. To date, different studies suggest that free light chains may have important functional activities. For instance, it has been shown that immunoglobulin free light chains can elicit mast cell-driven hypersensitivity responses leading to asthma and contact sensitivity. Free light chains also show other biologic actions such as anti-angiogenic and proteolytic activities or can be used as specific targeting vehicles. Levels of free light chain levels in body fluids increase markedly in diseases such as multiple sclerosis, rheumatoid arthritis, and systemic lupus erythematosus. In this review, we will focus on the unexpected biological activities of immunoglobulin free light chains with special attention to its possible role in the induction of chronic inflammatory diseases.

Elicitation of allergic asthma by immunoglobulin free light chains

The observation that only 50% of patients with adult asthma manifest atopy indicates that other inflammatory mechanisms are likely involved in producing the characteristic features of this disorder; namely reversible airway obstruction, hyperresponsiveness, and pulmonary inflammation. Our recent discovery that antigen-specific Ig free light chains (LCs) mediate hypersensitivity-like responses suggests that these molecules may be of import in the pathophysiology of asthma. Using a murine experimental model of nonatopic asthma, we now have shown that an LC antagonist, the 9-mer peptide F991, can abrogate the development of airway obstruction, hyperresponsiveness, and pulmonary inflammation. Further, passive immunization with antigen-specific LCs and subsequent airway challenge can elicit a mast cell-dependent reaction leading to acute bronchoconstriction. These findings, and the demonstration that the concentration of free kappa LCs in the sera of patients with adult asthma were significantly increased (as compared with age-matched nonasthmatic individuals), provide previously undescribed insight into the pathogenesis of asthma. In addition, the ability to inhibit pharmacologically LC-induced mast cell activation provides a therapeutic means to prevent or ameliorate the adverse bronchopulmonary manifestations of this incapacitating disorder.

Immunoglobulin free light chains and mast cells: pivotal role in T-cell-mediated immune reactions?

Immunoglobulin (Ig) free light (L)-chains have long been considered as the meaningless remnants of a spillover in the regular Ig production by B cells. The recently discovered role for Ig free L-chains in mediating hypersensitivity-like responses sheds new light on their potential role in immune responses. Ig free L-chains can sensitize mast cells, such that a second encounter with the appropriate antigen results in mast-cell activation. The possible importance of this reaction for the induction of T-cell-mediated immune reactions, leading to contact sensitivity, multiple sclerosis and rheumatoid arthritis is discussed.

Immunoglobulin-free light chains elicit immediate hypersensitivity-like responses

Immunoglobulin (Ig)-free light chains IgLC are present in serum and their production is augmented under pathological conditions such as multiple sclerosis, rheumatoid arthritis and neurological disorders. Until now, no (patho)physiological function has been ascribed to circulating Ig light chains. Here we show that IgLCs can confer mast cell dependent hypersensitivity in mice. Antigenic stimulation results in plasma extravasation, cutaneous swelling and mast-cell degranulation. We show that IgLCs have a crucial role in development of contact sensitivity, which could be completely prevented by a novel IgLC antagonist. Although IgE and IgG(1) are central to the induction of immediate hypersensitivity reactions, our results show that IgLCs have similar activity. IgLCs may therefore be a novel factor in the humoral immune response to antigen exposure. Our findings open new avenues in investigating the pathogenesis of autoimmune diseases and their treatments.

Urine free light chains in SLE: clonal markers of B-cell activity and potential link to in vivo secreted Ig

As a marker of in vivo B-cell activity, urine levels of free light chain (FLC) were measured twice weekly by radioimmunoassay (RIA) and correlated with disease activity over periods of 5-10 months in seven patients with systemic lupus erythematosus (SLE). In addition, RIA-measured urine albumin was used to track glomerular injury, and alpha1-microglobulin (alpha1-M) levels, 28- to 32-kDa protein, provided control measurements on excretion of low-molecular-weight proteins. As controls, urine FLC levels were obtained from healthy normals and in subjects with acute pharyngitis, sickle-cell anemia, and acute sepsis or pneumonia. The control results showed that with acute sepsis/pneumonia had marked increases in urine FLC, while pharyngitis and sickle-cell controls had normal FLC levels. In SLE, active patients receiving intravenous cyclophosphamide and high-dose steroids exhibited highly increased urine FLC that fluctuated widely during therapy and fell to normal range levels with disease remission. During active SLE, urine albumin often was increased, while alpha1-M levels remained in normal range. In contrast to the increased FLC of active disease, inactive patients on low-dose maintenance therapy had predominantly normal FLC levels throughout the collection period. These results support our hypothesis that longitudinal levels of urine FLC can be used to track disease-related B-cell activity in SLE. Furthermore, we suggest that the urine FLC of active SLE would share LC idiotype with the clonal associated in vivo secreted Ig, and thus permit the identification of these antibodies that are targeted to the culprit immunogen(s) responsible for the pathogenesis of SLE.

Differences in kappa to lambda (kappa:lambda) ratios of serum and urinary free light chains

Free light chains (FLC) are a natural product of B lymphocytes and, as such, represent a quantifiable biomarker of cellular proliferation. Accurate measurement of the concentrations of these components in serum and urine provides a unique means of ascertaining B cell immunoglobulin synthesis during physiologic and, especially, pathologic states, where such information has important diagnostic and therapeutic implications. Previously, use of such quantitative assays has been limited due to the lack of potent serologic reagents specific for these components. We have immunized mice with kappa- and lambda-type monoclonal human light chains (Bence Jones proteins (BJP)) and have obtained monoclonal antibodies (MoAbs) that differentiate between unbound and bound light chains. These highly specific MoAbs were used to measure by ELISA the concentrations of FLC in the serum of 22 normal individuals and in urine from 16 of these subjects. The mean serum kappa and lambda FLC concentrations were found to be 16.6+/-6.1 microg/ml and 33.8+/-14.8 microg/ml, respectively. In contrast, the values for urinary kappa and lambda FLC were 2.96+/-1.84 microg/ml and 1.07+/-0.69 microg/ml, respectively. In each case studied, the serum kappa:lambda ratio was consistently less than that of urine (mean values, serum approximately 1:2; urine approximately 3:1). That the rate of synthesis of lambda-type FLC exceeded that of kappa was evidenced in assays of culture fluid supernatants of unstimulated normal peripheral blood mononuclear cells (PBMC), where the mean kappa:lambda ratio was determined to be 1:1.4. Metabolic studies in which mice were injected with pools of kappa- and lambda-type BJP prepared in ratios of 1:1, 1:2 and 1:4 demonstrated that, regardless of the proportion, kappa FLC were preferentially excreted. Our studies provide the first evidence that lambda FLC are secreted by normal PBMC at a greater rate than are kappa FLC, as evidenced in biosynthetic studies and by measurement of their serum concentrations. Further, we posit that quaternary structural differences between the two light-chain isotypes may account for the predominance of kappa versus lambda components in urine.

Clinical applications of immunoglobulin free light chain estimations

The relevance of free light chain assays to diagnosis, staging, treatment and prognosis assessment in B-cell disorders (including myeloma, chronic lymphocytic leukaemia, and lymphoma), multiple sclerosis and diabetes is discussed and their actual and potential use is examined.

Sarcoidosis. An updated review

Sarcoidosis, a multisystem disease of unknown cause characterized by the formation of noncaseating granulomas, may involve any organ of the body, but the commonest sites of predilection are the lungs, lymph nodes, skin, and eyes. Sarcoidosis can be associated with polyclonal hyperglobulinemia, hypercalcemia, hypercalciuria, circulating immune complexes, cutaneous anergy, and in vitro depressed cell-mediated immunity. Recent studies of the cellular composition and cellular interactions of sarcoid-involved tissue have resulted in some insight into the pathophysiology of the disease. In early stages the predominance of activated T-helper cells in affected sites may account for many of the immunologic aberrations. The production of macrophage chemotactic substances by these cells may be the initial stimulus for the formation of the granuloma. The natural history of the disease is highly variable; the acute forms tend to resolve spontaneously, whereas the chronic forms rarely involute. Although multiple therapeutic modalities have been used and some have reportedly been effective, systemic corticosteroids remain the most effective available therapeutic agents.

Free light chains of immunoglobulins in serum from patients with leukaemias and multiple myeloma

The serum concentration of free kappa and lambda light chains of immunoglobulins were measured in 114 patients with myelo- and lymphoproliferative disorders including multiple myeloma. Increased concentrations of a single light chain type, suggesting monoclonal origin, were found with high frequency in B-cell diseases only. Thus 6 out of 9 patients with chronic lymphatic leukaemia and 24 of 28 patients with multiple myeloma had increased concentrations of a single chain type. The highest values reported in chronic lymphatic leukaemia were approximately 10 and in multiple myeloma 1000 times normal mean. Cytostatic treatment of chronic lymphatic leukaemia was followed by a decrease in the light chain levels. The levels were, however, not correlated to the number of circulating lymphocytes, the lymphatic infiltration of tissue or clinical activity. Increased concentrations of both chain types, suggesting a polyclonal origin, were found in both of 2 patients with acute monocytic leukaemia, 6 of 7 with acute myelomonocytic leukaemia, 2 of 23 with acute myeloid leukaemia and 1 of 7 with acute lymphoblastic leukaemia. The highest levels of light chains in these groups were 5 times normal mean. All patients with myeloproliferative disorders revealed normal values of both light chain types.