Serum secretory IgA and secretory component in patients with non-cirrhotic alcoholic liver diseases

Extramucosal Formation and Prognostic Value of Secretory Antibodies in Rheumatoid Arthritis

OBJECTIVE

To investigate levels and possible extramucosal formation of secretory Ig, including anti-citrullinated protein antibodies (ACPAs), in rheumatoid arthritis (RA).

METHODS

Three patient groups were studied: 1) ACPA-positive patients with musculoskeletal pain without clinical arthritis, 2) patients with recent-onset RA, and 3) patients with established RA. In baseline serum samples (groups 1 and 2) and paired synovial fluid samples (group 3), we analyzed total secretory IgA, total secretory IgM, free secretory component (SC), and SC-containing ACPA. Extramucosal formation of SC-containing ACPA was investigated by preincubating RA sera and affinity-purified ACPA with recombinant free SC.

RESULTS

Compared to healthy controls, serum levels of total secretory IgA and total secretory IgM were increased both in patients with early RA and at-risk patients (P < 0.05). Patients with early RA with elevated total secretory Ig had significantly higher disease activity during the 3-year follow-up period compared to those without increased levels. At-risk patients who developed arthritis during follow-up (39 of 82) had higher baseline total secretory IgA levels compared to those who did not (P = 0.041). In established RA, total secretory IgA and total secretory IgM levels were higher in serum than in synovial fluid (P < 0.0001), but SC-containing ACPAs adjusted for total secretory Ig concentration were higher in synovial fluid (P < 0.0001). Preincubation with recombinant free SC yielded increased SC-containing ACPA reactivity in sera as well as in affinity-purified IgA and IgM ACPA preparations.

CONCLUSION

Circulating secretory Ig are elevated before and at RA onset. In the presence of free SC, secretory Ig may form outside the mucosa, and SC-containing ACPAs are enriched in RA joints. These findings shed important new light on the mucosal connection in RA development.

Localization and Regulation of Polymeric Ig Receptor in Healthy and Diseased Human Kidney

The polymeric Ig receptor (PIgR) constitutes an important part of the immune system by mediating transcytosis of dimeric IgA into mucosal fluids. Although well studied in organs such as the intestine, the regulation and localization of PIgR in human kidney are incompletely characterized. Herein, using immunohistochemistry, we show that in healthy human kidneys, PIgR is expressed by the progenitor-like tubular scattered cells of the proximal tubules and by parietal epithelial cells of glomeruli. We further show that proximal tubular expression of PIgR becomes widespread during kidney disease, correlating to elevated levels of urinary secretory IgA. Urinary secretory IgA levels also correlated to the degree of tubular fibrosis, plasma creatinine, and urea levels. In addition, primary tubular cells were cultured to study the function and regulation of PIgR in vitro. Cellular PIgR expression was induced by conditioned medium from activated human leukocytes, as well as by inflammatory cytokines, whereas transforming growth factor-β1 caused decreased expression. Furthermore, interferon-γ increased the transcytosis of dimeric IgA in cultured tubular cells. Finally, a correlation study of mRNA data from the Genotype-Tissue Expression portal indicated that PIGR mRNA expression in kidney correlates to the expression of TNFSF13, a cytokine involved in plasma cell class switching to IgA. These results indicate that PIgR induction is an integral part of the injury phenotype of renal tubular cells.

Higher Levels of Secretory IgA Are Associated with Low Disease Activity Index in Patients with Reactive Arthritis and Undifferentiated Spondyloarthritis

Introduction

Both reactive arthritis (ReA) and undifferentiated spondyloarthritis (uSpA) belong to the group of autoinflammatory diseases called spondyloarthritis (SpA). Hypotheses have been proposed about a relationship between the intestinal mucosa and inflammation of joint tissues. The role of immunoglobulin IgA or secretory immunoglobulin A (SIgA) in the inflammatory and/or clinical activity of patients with SpA remains poorly understood.

Objective

To evaluate the status of total IgA and SIgA, and the association among the levels of SIgA, IgA, IgA anti-Chlamydia trachomatis, and anti-Shigella spp. with the disease activity measures, erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) levels, was compared in a cohort of patients with ReA and uSpA and healthy subjects.

Methods

This was a cross-sectional study. The serum concentrations of SIgA, IgA anti-C. trachomatis, anti-Shigella spp., and total IgA were measured. Disease activity was measured in each patient by means of Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) and Ankylosing Spondylitis Disease Activity Score (ASDAS). Statistical analysis did include as bivariate evaluation, comparisons by Student’s t-test, Kruskal–Wallis test, and U Mann–Whitney test, with a multivariate evaluation by principal components analysis (PCA). A correlation analysis was carried out using the Pearson correlation coefficient and a linear regression models. All analysis were made using Stata version 11.2^® for Windows, R V3.3.21. Statistical significance was defined a p-value <0.05.

Results

In all, 46 patients (78.2% men; mean age, 34.8 ± 12.3 years) and 53 controls (41% men; mean age, 32 ± 11.4 years) were included in the study. The mean serum levels of SIgA were higher in SpA patients than in healthy subjects (p < 0.001). Only SIgA levels correlated with disease activity: BASDAI (r = −0.42, p = 0.0046), ASDAS-CRP (r = −0.37, p = 0.014), and ASDAS-ESR (r = −0.45, p = 0.0021). The negative correlation between SIgA and all activity indices was higher in HLA-B27-positive patients (BASDAI r = −0.70, p = 0.0009, ASDAS-CRP r = −0.58, p = 0.0093, and ASDAS-ESR r = −0.57, p = 0.0083). The PCA showed three factors: the first component was constituted by variables referred as clinical activity measures, the second did include the serological activity markers, and the last component was compounded by age and symptoms time.

Conclusion

Elevated serum levels of SIgA were found to be related with low disease activity in patients with ReA and uSpA.

Searching for biomarkers of comorbidities in sera of treated HIV-infected patients by isoelectric focusing

Based on their characteristics, we hypothesized that the following parameters, namely collagen IV, glutathione S-transferase, secretory component (SC), and AMP-activated protein kinase α1α2 may be useful serum markers in the detection of comorbidities in treated HIV-infected patients. These parameters were determined in 204 HIV-infected patients and 35 controls by using IEF and densitometry. Collagen IV was undetectable in controls and the majority of HIV-infected patients. Twenty-two HIV-infected patients presented significantly elevated levels of collagen IV, most of them were coinfected with hepatitis C virus and/or hepatitis B virus. SC was undetectable in controls. SC was significantly increased in 81 HIV-infected patients and significantly correlated with aspartate aminotransferase (r = 0.267, p = 0.0049), alkaline phosphatase (r = 0.309, p = 0.0011), and γ-glutamyl-transferase (r = 0.264, p = 0.0054). Glutathione S-transferase levels of HIV-infected patients were significantly higher than the controls (3779 ± 5860 vs. 785 ± 71 DU, p = 0.0007) and significantly correlated with serum urea (r = 0.204, p = 0.0038), triglycerides (r = 0.209, p = 0.0033), and lipase (r = 0.219, p = 0.0025). AMP-activated protein kinase α1α2 levels of HIV-infected patients were significantly higher than the controls (5676 ± 6248 vs. 1189 ± 6248 DU, p = 0.0009). Further studies are needed to demonstrate the relevance of these results to diagnose non-AIDS-related illnesses in HIV-infected patients.

Secretory IgA induces tolerogenic dendritic cells through SIGNR1 dampening autoimmunity in mice

IgA plays ambivalent roles in the immune system. The balance between inhibitory and activating responses relies on the multimerization status of IgA and interaction with their cognate receptors. In mucosal sites, secretory IgA (SIgA) protects the host through immune-exclusion mechanisms, but its function in the bloodstream remains unknown. Using bone marrow-derived dendritic cells, we found that both human and mouse SIgA induce tolerogenic dendritic cells (DCs) following binding to specific ICAM-3 grabbing nonintegrin receptor 1. This interaction was dependent on Ca(2+) and mannose residues. SIgA-primed DCs (SIgA-DCs) are resistant to TLR-dependent maturation. Although SIgA-DCs fail to induce efficient proliferation and Th1 differentiation of naive responder T cells, they generate the expansion of regulatory T cells through IL-10 production. SIgA-DCs are highly potent in inhibiting autoimmune responses in mouse models of type 1 diabetes and multiple sclerosis. This discovery may offer new insights about mucosal-derived DC immunoregulation through SIgA opening new therapeutic approaches to autoimmune diseases.

Possible mechanism of acute effect of ethanol on intestinal IgA expression in rat

The purpose of this study was to investigate the possible mechanism of acute effect of ethanol on IgA expression in rat intestine. To this end, adult female Wistar rats showing diestrus day 1 were treated with (a) ethanol (2 or 4 g/kg, i.p.); (b) N omega-nitro-L-arginine-methyl ester (L-NAME), which inhibits the activity of all isoforms of nitric oxide synthase, (30 mg/kg, s.c.) followed by ethanol 3 h later; and (c) L-NAME (30 mg/kg, s.c.) followed by saline 3 h later. Saline-injected and untreated rats were used as controls. The animals were sacrificed 0.5 h after ethanol administration. Intestinal expression of IgA was evaluated by both immunohistochemistry and Western immunoblotting. Morphometric analysis showed that acute ethanol treatment increased the number of IgA-immunoreactive cells in a dose-dependent manner. Pretreatment with L-NAME abolished this action of alcohol. Injection of L-NAME followed by saline had no influence on the number of IgA+cells. The results, obtained by Western immunoblotting, paralleled our immunohistochemical findings. Taken together, these data suggest that acute effect of ethanol on intestinal IgA might be mediated by endogenous nitric oxide.

Differential glycosylation of polymeric and monomeric IgA: a possible role in glomerular inflammation in IgA nephropathy

IgA nephropathy (IgAN) is characterized by mesangial deposition of polymeric IgA1 (pIgA1) and complement. Complement activation via mannose-binding lectin and the lectin pathway is associated with disease progression. Furthermore, recent studies have indicated a possible role for secretory IgA. IgAN is associated with abnormalities in circulating IgA, including aberrant O-linked glycosylation. This study characterized and compared functional properties and N-linked glycosylation of highly purified monomeric IgA (mIgA) and pIgA from patients with IgAN and control subjects. Total serum IgA was affinity-purified from patients (n = 11) and control subjects (n = 11) followed by size separation. pIgA but not mIgA contained secretory IgA, and its concentration was significantly higher in patients with IgAN than in control subjects. Both in patients with IgAN and in control subjects, IgA binding to the GalNAc-specific lectin Helix Aspersa and to mannose-binding lectin was much stronger for pIgA than for mIgA. Furthermore, binding of IgA to mesangial cells largely was restricted to polymeric IgA. Binding of pIgA to mesangial cells resulted in increased production of IL-8, predominantly with IgA from patients with IgAN. Quantitative analysis of N-linked glycosylation of IgA heavy chains showed significant differences in glycan composition between mIgA and pIgA, including the presence of oligomannose exclusively on pIgA. In conclusion, binding and activation of mesangial cells, as well as lectin pathway activation, is a predominant characteristic of pIgA as opposed to mIgA. Furthermore, pIgA has different N-glycans, which may recruit lectins of the inflammatory pathway. These results underscore the role of pIgA in glomerular inflammation in IgAN.

A pathogenic role for secretory IgA in IgA nephropathy

IgA nephropathy (IgAN) is characterized by deposits of IgA in the renal mesangium. It is thought that deposits of IgA mainly involve high molecular weight (HMW) IgA1. However, there is limited information on the exact composition of HMW IgA in these deposits. In this study, we investigated the presence of secretory IgA (SIgA) in human serum and in the glomerular deposits of a patient with IgAN. Furthermore, we analyzed the interaction of SIgA with mesangial cells. With enzyme-linked immunosorbent assay, SIgA concentrations in the serum of IgAN patients and healthy controls were measured. Both patients and controls had circulating SIgA that was restricted to the HMW fractions. Patients tended to have higher levels of SIgA, but this difference was not significant. However, in patients with IgAN, high serum SIgA concentrations were associated with hematuria. Binding of size-fractionated purified serum IgA and SIgA to mesangial cells was investigated with flow cytometry. These studies showed stronger binding of SIgA to primary mesangial cells compared to binding of serum IgA. Importantly, after isolation and elution of glomeruli from a nephrectomized transplanted kidney from a patient with recurrent IgAN, we demonstrated a 120-fold accumulation of SIgA compared to IgA1 in the eluate. In conclusion, we have demonstrated that SIgA strongly binds to human mesangial cells, and is present in significant amounts in serum. Furthermore, we showed that SIgA is accumulated in the glomeruli of an IgAN patient. These data suggest an important role for SIgA in the pathogenesis of IgAN.

The Pulpal Origin of Immunoglobulins in Dentin Beneath Caries: An Immunohistochemical Study

Immunoglobulins localized in uninfected dentin beneath caries are thought to be protective, but their origin remains controversial. We reasoned that the localization and dominance of serum IgG1 would support the pulpal origin of the immunoglobulins while a predominance of secretory component (SC) bearing IgA1 and IgA2 would support their salivary origin. The prevalence and staining intensity of IgG1, IgA1, IgA2, IgM, and SC in uninfected dentinal tubules beneath shallow, deep caries, and noncaries teeth were examined immunohistologically. SC was only localized in caries, and IgG1 was the predominant subclass in uninfected dentinal tubules beneath shallow and deep caries, followed by IgA1. In noncaries teeth, IgG1 was localized on the pulpal end. The intensity of IgG1 was significantly higher than either IgA1 or IgA2 in both shallow and deep caries. Our data support the serum origin of immunoglobulins in uninfected dentin beneath caries.

Alcohol-induced liver disease

Hepatic changes resulting from the regular ingestion of alcohol are many and include fat infiltration, alcoholic hepatitis, and cirrhosis. Only 10% to 15% of chronic alcoholics develop liver disease. Women are more susceptible. An area of considerable importance is the high prevalence of concomitant infection with hepatitis C virus in chronic alcoholics. Patients who have hepatitis C and alcohol-induced liver injury are much more likely to develop progressive liver disease and cirrhosis. Corticosteroid therapy has proven useful in the treatment of patients with severe acute alcoholic hepatitis.

Increased serum concentration of IgA2 subclass and IgA2/IgA1 ratio: specific markers of chronic alcoholic abuse?

Enhanced serum IgA concentrations are common in alcoholic liver cirrhosis, but functional differences between IgA subclasses and their relation with interleukin-6 (IL-6) have not been described. Distinct immunoregulatory mechanisms may exist that selectively affect one subclass. This possibility prompted us to investigate the distribution of IgA1 and IgA2 subclasses in the serum of 25 heavy alcohol drinkers (alcohol: 80 to 200 g per day) without clinical disorders, in comparison with 35 patients affected by alcoholic liver cirrhosis, 29 viral hepatitis patients and 33 social drinkers as a control group. Mean (+/- SD) IgA2 concentration (0.56 +/- 0.31 g/l) was significantly increased (p < 0.01) in heavy alcohol drinkers, with an IgA2/IgA1 ratio of 0.33 +/- 0.12, while the mean total IgA concentration was similar to the control group. Mean IgA1 and IgA2 concentrations were significantly increased (p < 0.001) in alcoholic liver cirrhosis patients (6.13 +/- 4.52 g/l and 1.83 +/- 1.93 g/l respectively, with an IgA2/IgA1 ratio of 0.32 +/- 0.19) and viral hepatitis patients (3.66 +/- 2.59 g/l and 0.69 +/- 0.67 g/l respectively, with an IgA2/IgA1 ratio of 0.21 +/- 0.14) High serum IL-6 concentrations (34 +/- 33 ng/l) were correlated with elevated IgA1 and IgA2 concentrations only in patients with alcoholic liver cirrhosis. IgA2 subclass and IgA2/IgA1 ratio could therefore be used as markers of chronic alcohol abuse directly related to the extent and duration of the alcohol abuse and the effectiveness of alcohol withdrawal.