Increased excretion of soluble interleukin 2 receptors and free light chain immunoglobulins in the urine of patients with active lupus nephritis

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.

Immune-Related Urine Biomarkers for the Diagnosis of Lupus Nephritis

The kidney is one of the main organs affected by the autoimmune disease systemic lupus erythematosus. Lupus nephritis (LN) concerns 30-60% of adult SLE patients and it is significantly associated with an increase in the morbidity and mortality. The definitive diagnosis of LN can only be achieved by histological analysis of renal biopsies, but the invasiveness of this technique is an obstacle for early diagnosis of renal involvement and a proper follow-up of LN patients under treatment. The use of urine for the discovery of non-invasive biomarkers for renal disease in SLE patients is an attractive alternative to repeated renal biopsies, as several studies have described surrogate urinary cells or analytes reflecting the inflammatory state of the kidney, and/or the severity of the disease. Herein, we review the main findings in the field of urine immune-related biomarkers for LN patients, and discuss their prognostic and diagnostic value. This manuscript is focused on the complement system, antibodies and autoantibodies, chemokines, cytokines, and leukocytes, as they are the main effectors of LN pathogenesis.

Urinary soluble alpha chain of the interleukin-2 receptor as a biomarker of active lupus nephritis in Egyptian children with juvenile systemic lupus erythematosus

Objectives

This study aims to assess the urinary soluble alpha chain of the interleukin-2 receptor (sCD25) concentrations in patients with juvenile systemic lupus erythematosus (JSLE) and to evaluate its validity to be a possible marker of disease activity in patients with lupus nephritis (LN).

Patients and methods

We assessed sCD25 concentrations in urine samples obtained from 53 JSLE patients (15 males, 38 females; median age 11 years; range, 7 to 17 years) and 30 age- and sex-matched apparently healthy controls (10 males, 20 females; median age 10 years; range, 6 to 16 years). Concentrations were normalized according to urinary creatinine excretion. JSLE patients were subjected to clinical examination and assessment of overall disease activity by Systemic Lupus Erythematous Disease Activity Index (SLEDAI), while evaluation of LN activity was preformed using Systemic Lupus International Collaborating Clinics (SLICC) renal activity score.

Results

The JSLE patients had significantly higher normalized urinary sCD25 concentrations compared to the healthy controls (p=0.001). Patients with active LN had significantly higher normalized urinary sCD25 levels than active JSLE patients without LN (p=0.002) and JSLE patients with inactive disease (p<0.001). A significant positive correlation was found between normalized urinary sCD25 concentrations with different activity parameters such as proteinuria (p=0.004), SLEDAI (p<0.001), renal SLEDAI (p<0.001), and SLICC renal activity score (p<0.001). A significant negative correlation was found between urinary sCD25 and complement 3 (p<0.001).

Conclusion

Urinary concentrations of sCD25 were significantly elevated in JSLE patients, particularly in those with active LN. The remarkable association between urinary sCD25 concentrations and different renal disease activity parameters implies that urinary sCD25 can be a beneficial marker to monitor active nephritis in JSLE patients.

Free light chains and autoimmunity

The study of free light chains (FLCs) has grown as area of enormous interest for many clinicians with the aim of disclosing the exact biological role and potential use of FLCs in the clinical routine. Moreover, the attention given to immunological functions of FLCs has sparked a new light into their pathogenic contribution in different chronic autoimmune-based inflammatory diseases. The release of intracellular antigens following cell death or ineffective clearance of apoptotic debris, modification of self-antigens, and molecular mimicry may trigger the production of immunoglobulins after activation and polyclonal expansion of B cells, by which FLCs are released. The discovery of polyclonal FLCs as potential biomarkers started with the observation of their increased concentrations in a variety of biological fluids related to patients with autoimmune diseases. This review deals with the use of polyclonal FLCs for identifying severity and monitoring outcome after treatment in some autoimmune diseases, namely systemic lupus erythematosus, myasthenia gravis, systemic sclerosis, rheumatoid arthritis and Sjögren's syndrome, as supported by the fact that levels of FLCs correlate with both B cell activation markers and other specific markers of disease activity. In a near future, following the evidence shown, FLCs might probably work as early prognostic markers of severity and also as indicators of response to treatment or early assessment of relapse in selected autoimmune diseases.

Potential serum and urine biomarkers in patients with lupus nephritis and the unsolved problems

Lupus nephritis (LN) is one of the most frequent and serious complications in the patients with systemic lupus erythematosus. Autoimmune-mediated inflammation in both renal glomerular and tubulointerstitial tissues is the major pathological finding of LN. In clinical practice, the elevated anti-dsDNA antibody titer concomitant with reduced complement C3 and C4 levels has become the predictive and disease-activity surrogate biomarkers in LN. However, more and more evidences suggest that autoantibodies other than anti-dsDNA antibodies, such as anti-nucleosome, anti-C1q, anti-C3b, anti-cardiolipin, anti-endothelial cell, anti-ribonuclear proteins, and anti-glomerular matrix (anti-actinin) antibodies, may also involve in LN. Researchers have demonstrated that the circulating preformed and in situ-formed immune complexes as well as the direct cytotoxic effects by those cross-reactive autoantibodies mediated kidney damage. On the other hand, many efforts had been made to find useful urine biomarkers for LN activity via measurement of immune-related mediators, surface-enhanced laser desorption/ionization time-of-flight mass spectrometry proteomic signature, and assessment of mRNA and exosomal-derived microRNA from urine sediment cell. Our group had also devoted to this field with some novel findings. In this review, we briefly discuss the possible mechanisms of LN and try to figure out the potential serum and urine biomarkers in LN. Finally, some of the unsolved problems in this field are discussed.

Urinary sCD25 as a biomarker of lupus nephritis disease activity

OBJECTIVES

T cells play an important role in the pathogenesis of lupus nephritis (LN). We studied the role of urinary soluble CD25 (sCD25) as a biomarker of LN disease activity in a cross-sectional and longitudinal study.

METHODS

Patients with systemic lupus erythematosus were classified as active LN (AN), inactive disease (ID) and active non-renal (ANR) based on disease activity and renal involvement at the time of enrolment. Urine and serum samples were collected at baseline from all patients and at 3-monthly follow-up from patients with AN. SLE disease activity index (SLEDAI) was used for disease activity assessment at all visits. sCD25 was measured by ELISA and normalized to urinary creatinine excretion and is expressed as pg/mg. Urine samples from 10 healthy individuals (HC) served as controls.

RESULTS

There were 119 patients (111 females, median age 27 years, 57 AN, 43 ID, 19 ANR). Median SLEDAI was 18, 2 and 8 in AN, ID and ANR groups, respectively. Median renal SLEDAI in AN was 8. Mean (±SD) urinary sCD25 in the AN, ID, ANR and HC groups at baseline was 741.1 (±794.9), 407.8 (±511.1), 735.4 (±667.7) and 250.9 (±122.2) pg/mg respectively (p = 0.019). Mean (±SD) serum sCD25 in AN, ID and ANR was 8285.25 (±5922.2), 6044 (±3501.92) and 6568.72 (±4333.62) pg/ml, respectively. Urinary sCD25 correlated with SLEDAI (r = 0.22; p = 0.015) but did not correlate with serum sCD25 or proteinuria. Urinary sCD25 compares well with traditional markers of disease activity in differentiating active from inactive renal disease. On follow-up mean urinary sCD25 decreased to 470.0 (±449.6; p < 0.05) at 3 months, 496.7 (±465.8; p = 0.006) at 6 months, 471.9 (±303.2; p = 0.041) at 9 months and 358.6 (±496.9; p = 0.007) at 12 months from baseline value of 741.1 (±794.9). In four patients who either had relapse, persistent disease activity or developed chronic kidney disease, urinary sCD25 showed rise preceding traditional abnormalities on urine examination.

CONCLUSIONS

Urinary sCD25 is a good biomarker for follow-up of LN. It may also have the potential to predict poor response and relapse.

Association of urinary laminin G-like 3 and free K light chains with disease activity and histological injury in IgA nephropathy

BACKGROUND AND OBJECTIVES

IgA nephropathy has variable clinical presentation and progression. Its definitive diagnosis and prognosis require renal biopsy. The identification of new biomarkers allowing noninvasive diagnosis and monitoring of disease activity would be advantageous. This study analyzed the urine proteome of IgA nephropathy patients at an early stage of disease.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Urine from 49 IgA nephropathy patients, 42 CKD patients, and 40 healthy individuals was analyzed by surface-enhanced laser desorption/ionization time of flight/mass spectrometry. Differentially excreted proteins were identified by matrix-enhanced laser desorption/ionization time of flight/mass spectrometry, confirmed by immunologic methods, and validated in an independent set of patients (14 IgA nephropathy and 24 CKD). All patients were recruited at the Division of Nephrology of the University of Foggia from January of 2005 to March of 2007.

RESULTS

Two proteins, with 21,598 and 23,458 m/z, were significantly decreased in IgA nephropathy and identified as Perlecan laminin G-like 3 peptide and Ig κ light chains, respectively. Western blot analysis confirmed the lower urinary excretion of laminin G-like 3 in IgA nephropathy patients compared with CKD patients and healthy individuals. Immunonephelometry analysis confirmed the lower urinary excretion of free κ light chains in IgA nephropathy patients compared with CKD patients and healthy individuals. Immunohistochemistry analysis justified the urinary excretion profile of such proteins in IgA nephropathy. Finally, urinary free κ light chains and laminin G-like 3 concentration inversely correlated with severity of clinical and histologic features of our IgA nephropathy cohort.

CONCLUSIONS

Laminin G-like 3 and free κ light chains can contribute to the noninvasive assessment of IgA nephropathy disease activity.

Urinary free light chain is a potential biomarker for ISN/RPS class III/IV lupus nephritis

OBJECTIVES

To evaluate the use of urinary free light chains (FLCs) as a biomarker for proliferative LN and the potential association between the intensity of plasma cell infiltration of the kidney and urinary FLC levels in LN.

METHODS

Forty-three SLE patients were consecutively enrolled in the study. These patients were divided into an International Society of Nephrology and Renal Pathology Society (ISN/RPS) class III/IV LN subset (n = 18) and an ISN/RPS class I/II/V (class non-III/IV) LN subset (n = 25). The expression of κ-LCs, λ-LCs, CD19 and CD138 in kidney specimens was also evaluated with immunohistochemical staining. To measure FLC levels before and after treatment, an additional six patients with class III/IV LN were consecutively enrolled.

RESULTS

Urinary FLCs were significantly higher in the class III/IV LN subset than in the class non-III/IV LN subset. Urinary λ-FLC levels were significantly correlated with the urinary protein-creatinine ratio in the class III/IV LN subset (rs = 0.67, P < 0.01). Moreover, the LC-secreting CD19(-)/CD138(+) cell counts in the kidney specimens were higher in the class III/IV LN subset than in the class non-III/IV LN subset. Total urinary FLC levels were correlated with the numbers of CD138(+) cells in the kidney (r = 0.71, P = 0.03). Following treatment, urinary λ-FLCs could not be detected in any of the patients.

CONCLUSION

The intensity of plasma cell infiltration of the kidney is associated with urinary FLC levels. Urinary FLCs are potentially useful biomarkers in ISN/RPS class III/IV LN or proliferative LN.

Urine: An under-studied source of biomarkers in multiple sclerosis?

There remains a need for sensitive and reliable biomarkers that can be used longitudinally in multiple sclerosis. Whilst both CSF and MRI have been extensively studied, they remain invasive and expensive methods of investigation. On the contrary, urine provides a valuable fluid which is readily available for serial sampling. Some work has been done on urinary biomarkers in multiple sclerosis; however, urinary biomarkers have not been extensively studied and validated for use in routine clinical practice, and urine remains understudied and underutilised. In this review the use of neopterin, urinary free light chains, nitric oxide metabolites and urinary myelin basic protein-like protein as potential biomarkers that have been identified in urine are discussed, and avenues for future study are raised.

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.

Hepatitis B infection and changes in interferon-alpha and -gamma production in patients with systemic lupus erythematosus in Taiwan

According to previous reports, the prevalence of hepatitis B virus (HBV) infection in patients with systemic lupus erythematosus (SLE) is varied. There has been no report on Taiwan, a hyperendemic area for HBV infection. Furthermore, impaired production of interferon (IFN) in peripheral blood mononuclear cells (PBMC) has been reported to be potentially pathogenic to both chronic HBV infection and SLE. However, the production of IFN in patients with both diseases coexisting is unknown. The aims of this study were to evaluate the prevalence of HBV infection in lupus patients in Taiwan and to measure the production of IFN in patients with both diseases coexisting. One hundred and seventy-three consecutive lupus patients and a control group of 692 age- and sex-matched healthy subjects were included for evaluation of the prevalence of HBsAg. Four groups of subjects (patients with SLE and HbsAg, SLE, chronic hepatitis B and normal controls) were selected for evaluation of the in vitro production of IFN-alpha and -gamma. Six (3.5%) of the 173 SLE patients were positive for HBsAg, which was significantly lower than that of controls (14.7%; P < 0.0001). Patients with coexistent SLE and chronic HBV infection had less lupus activity, including less proteinuria (P = 0.02) and a lower serum titre of anti-double stranded DNA antibodies (anti-dsDNA; P = 0.04), than HBsAg-negative lupus patients. The in vitro production of IFN-alpha in patients with chronic hepatitis B was significantly lower than in those patients with SLE or in the normal control group (P < 0.01). The yields of IFN-alpha and -gamma in patients with coexistent SLE and chronic HBV infection were significantly different from those patients with SLE alone (P < 0.05), but close to those of patients with chronic HBV infection. In conclusion, the prevalence of HBsAg carriers is significantly lower in lupus patients in Taiwan. Patients with coexistent SLE and chronic HBV infection had less lupus activity. Interferon-alpha and -gamma may play a role in the above phenomenon.

Soluble interleukin-2 receptor in patients with glomerular diseases

In this study, we measured the soluble interleukin-2 receptor (sIL-2R) level to evaluate the cellular immune status in 61 patients with different types of glomerular diseases; 40 healthy volunteers were used as control. All patients with glomerular diseases had levels of serum sIL-2R significantly higher than those of the controls (766 +/- 59 vs 280 +/- 23 U/ml; p < 0.05). Even patients with normal renal function still had higher serum sIL-2R levels than the controls, no matter to which subgroups they belonged (primary glomerulonephritis, lupus nephritis or diabetic nephropathy). Serum sIL-2R levels were similar among the three subgroups. The serum levels of sIL-2R correlated well with age and were significantly higher in older patients, although this was not observed in the control group. Serum sIL-2R levels were significantly higher in patients with active urinary sediment and in patients with impaired renal function and showed a significant negative correlation with creatinine clearance (r = -0.56; p < 0.05). Although urinary and serum sIL-2R levels were quite well correlated, (r = 0.35; p < 0.05), the urinary levels of sIL-2R did not differ in patients with different disease activity or different renal functions although they had a significant correlation with 24-hour urinary protein (r = 0.39; p < 0.05). Patients with nephrotic syndrome also had higher urinary sIL-2R levels than other patients (529 +/- 106 vs 280 +/- 31 U/ml; p < 0.05). We conclude that greater T-cell activation might contribute to the pathogenesis of different glomerulonephritis entities, and serum levels of sIL-2R can serve as a useful clinical marker of glomerulonephritis activity. Renal function influenced the serum levels of sIL-2R significantly. This factor must be considered when we interpret the data. Urinary sIL-2R levels did not reflect the disease activity as well. This might be due to the secondary influence of the extent of the glomerular protein leak. Further investigation is needed to define the exact excretory pathway of this substance.

Abnormal splenic and thymic IL-4 and TNF-alpha expression in MRL-lpr/lpr mice

The MRL-lpr/lpr and MRL-(++) mice were studied for the expression of cytokines in the spleen, lymph node, thymus, kidney and brain through the reverse transcription-polymerase chain reaction (RT-PCR). The frequencies of IL-4 and TNF-alpha expression in the thymus and spleen were significantly higher in MRL-lpr/lpr mice than in MRL-(++) mice from the age of 17 to 32 weeks. More importantly, IL-4 transcript was demonstrated in the early rather than in the terminal stage of the lupus disease. At the 20th week, MRL-lpr/lpr mice with active disease exhibited higher concentrations of IL-1 alpha, IL-6 and TNF-alpha in serum than MRL-(++) mice. Interestingly, in MRL-lpr/lpr but not MRL-(++) mice, the IL-6 concentration in cultured supernatants of the thymic cells was significantly higher than that of the splenic or lymph node cells. On the other hand, IL-6 and IL-1 beta were expressed in the brain and kidney of MRL-lpr/lpr mice but not of MRL-(++) mice. Cultured MRL-lpr/lpr mesangial cells could also express IL-6 but to a lesser extent. These results suggest that the abnormal splenic and thymic IL-4 and TNF-alpha expression may predispose the development of autoimmune reactions. The expression of IL-1 beta and IL-6 in the brain and kidney may be implicated in the damage of these two organs in MRL-lpr/lpr mice.

Serum and urine soluble interleukin-2 receptor in idiopathic nephrotic syndrome

Although a cellular immune pathogenesis is suspected in idiopathic nephrotic syndrome of childhood (INS), there is scant direct evidence of in vivo immune activation. In order to investigate cytokine cascade activation in INS, soluble interleukin-2 receptor (sIL-2R) in plasma and urine was characterized and its levels measured in INS patients during relapse. Immunochemically detectable sIL-2R had a molecular mass of 35-46 kDa in both serum and urine and the molecule appears to be excreted intact; the pI was 5.05. INS patients had elevated serum sIL-2R levels compared with adult normal controls (845 +/- 97 vs. 373 +/- 47 U/ml, P = 0.001) and were significantly higher than previously published age-matched controls. Urinary excretion of sIL-2R was 47.2 +/- 13 U/mg creatinine in patients. Both the sIL-2R excretion rate and the fractional excretion of sIL-2R were positively correlated with the excretion of albumin (P = 0.02 and 0.002, respectively). These increased serum and urine levels occurred whether relapse was or was not associated with an intercurrent illness. We conclude that: (1) despite increased sIL-2R excretion during INS relapse, serum levels are significantly elevated; (2) while the elevated urinary levels could result from enhanced intrarenal production, they more likely reflect the increased serum levels; (3) the elevated sIL-2R levels support an immune pathogenesis in INS.