Does secretory component (SC) exist as free SC in human serum?

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.

The relationship of smoking, preeclampsia, and secretory component

OBJECTIVE

We sought to determine whether total secretory component in serum is increased in women in whom preeclampsia subsequently develops.

STUDY DESIGN

Serum samples were collected serially throughout pregnancy and post partum from nulliparous women (N = 1496). Serum concentrations of total secretory component were measured by an enzyme-linked immunosorbent assay in all women in whom preeclampsia developed (n = 71) and a randomly selected group of normotensive women (n = 83).

RESULTS

Secretory component increased with smoking (P =.0003) and with gestation (P =.0001). In the whole group secretory component was not different in women with preeclampsia (P =.10), but there was a significant interaction of smoking, gravidity, and preeclampsia (P =.04). Among the women who smoked, secretory component was lower in women in whom preeclampsia subsequently developed compared with those who remained normotensive (P =.02). This difference was significant from 15 to 19 weeks' gestation.

CONCLUSION

Very high serum concentrations of secretory component in smokers may protect against the development of preeclampsia and may indicate the involvement of mucosal tolerance.

Secretory component of immunoglobulin A in maternal serum and the prediction of preterm delivery

OBJECTIVE

Our purpose was to determine whether the secretory component of immunoglobulin A in maternal serum predicts delivery before 34 weeks' gestation.

STUDY DESIGN

Primigravid women of an urban population in New Zealand were recruited at booking into a prospective longitudinal nested case control study (n = 1651; after exclusions and withdrawals, n = 1511). Serum was collected at 8 to 12 weeks, 15 to 18 weeks, 21 to 24 weeks, 28 to 30 weeks, and 36 to 38 weeks of gestation and 6 weeks post partum. Concentrations of the secretory component of immunoglobulin A were determined by enzyme-linked immunosorbent assay in all women who were delivered preterm (n = 53) and in controls randomly selected from women delivered at > or =37 weeks' gestation (n = 178).

RESULTS

Serum concentrations of the secretory component of immunoglobulin A were similar in women delivered at term or preterm throughout pregnancy (n = 21 delivered at <34 weeks and n = 32 at 34 to 36.9 weeks, incidence 3.5%). Receiver-operator characteristic curves showed no discriminating ability of the secretory component of immunoglobulin A. Smokers had 50% higher concentrations than nonsmokers did (p < 0.0001 by analysis of variance).

CONCLUSION

The secretory component of immunoglobulin A in maternal serum does not predict preterm delivery in a low-risk population.

Serum concentrations of secretory IgA in pregnancies delivering at term or preterm

Secretory component (SC) is a phospholipase A2 inhibitor possibly associated with pregnancy maintenance and in serum is bound either to IgA (sIgA) or IgM (sIgM). To determine if serum secretory component levels a) increase during pregnancy, b) fall as term approaches, c) are low in women who will deliver prematurely, serum sIgA was measured at "booking in" and related to weeks of gestation and length of gestation at subsequent noninduced delivery. Levels of sIgA increased during pregnancy; sIgA increased from a non-pregnant value of 1.6 nM +/- 0.2 (mean +/- SEM) to 2.8 nM +/- 0.3 at the end of the second trimester, then fell significantly between 31-34 weeks. Delivery before 37 weeks was associated with significantly reduced serum sIgA levels, particularly in women who delivered before 32 weeks and in whom sIgA concentrations were similar to those of nonpregnant women.

Circulating secretory component in relation to early diagnosis and treatment of liver metastasis from colorectal carcinomas

AIMS

To evaluate serum secretory component in relation to early detection and clinical management of liver metastasis in patients with colorectal cancer.

METHODS

Secretory component and carcinoembryonic antigen (CEA) were analysed in serial serum samples from 23 patients who had liver metastases as the only apparent recurrence, and in sera from 54 matched controls. Results of surgical treatment of recurrences were classified peroperatively as radical when no residual tumour was apparent and resection margins were free of disease.

RESULTS

In total, 18 (78%) patients had increased secretory component during the whole follow up period (median 16 months); 12 (52%) had raised secretory component concentrations before clinical recurrence (median lead time 5.2 months). There was no difference before recurrence between circulating secretory component and CEA in sensitivity and lead times. Seventeen patients underwent surgery for hepatic metastasis; seven had radical hepatic resection of which only two (29%) showed increased secretory component concentrations before clinical recurrence; both had concurrent raised CEA values. By contrast, secretory component was raised in 83% of those cases considered inoperable.

CONCLUSIONS

Although serum secretory component clearly increases in most patients with liver metastases, its clinical value seems questionable because secretory component apparently indicates mainly inoperable hepatic metastases.

Secretory component is bound to the paraproteins in sera of IgA and IgM gammopathies

Secretory immunoglobulins A (SIgA) and M (SIgM) were investigated in 20 sera containing high levels of monoclonal polymeric IgM or IgA. In the sera of patients suffering from Waldenström's macroglobulinemia (WM), the level of SIgA was found to be low, whereas that of SIgM was extremely high. Reciprocally, in the multiple myeloma (MM) patients, SIgA were increased and SIgM were dramatically decreased. Electrophoretic analysis showed these SIgA and SIgM to have the same monoclonal pattern as the corresponding paraprotein. Hence these molecules must originate from the malignant clone. The most likely mechanism involved is an intravascular formation of the secretory-like immunoglobulins. Free secretory component (SC) could diffuse passively from the digestive lumen and bind the circulating myeloma polymeric immunoglobulins. Such a possibility of in vivo binding of free SC to IgM and IgA polymers leads to a reconsideration of the secretory origin of SIgM and SIgA in normal human serum.

Gravidin, an endogenous inhibitor of phospholipase A2 activity, is a secretory component of IgA

Gravidin, a phospholipase inhibitor characterised previously from amniotic fluid, was partially sequenced at the N-terminal and found to be identical to secretory component of human IgA. Inhibition of antiphospholipase activity was observed after incubation of gravidin with monoclonal antibody to human secretory component. Secretory component isolated from human saliva and breast milk was found to inhibit arachidonic acid release from human lymphocytes. It was concluded that gravidin is secretory component of IgA.

The presence and measurement of secretory component in human bile and blood

Five monoclonal antibodies which recognized three separate epitopes on the free secretory component molecule were produced using free secretory component obtained from human colostrum. Two-site immunoradiometric assays were developed to measure free secretory component and secretory IgA. Monoclonal antibody M9 was used on coated plates as the capture antibody. Monoclonal antibody M7 was used as the labelled signal antibody for the assay of free secretory component and a commercially available monoclonal anti-IgA antibody was used as the labelled signal antibody for the assay of secretory IgA. Free secretory component was found in human serum and bile. In serum, its concentration was raised in patients with high serum alkaline phosphatase due to liver disorders but not in patients with high serum alkaline phosphatase due to non-liver disorders. In bile from bile duct drains collected during the first week after liver transplantation, free secretory component was found in concentrations of up to 33 mg/l, in vast excess of that found in bile from gallstone patients (up to 0.3 mg/l). Bile from gallstone patients but not from liver transplant patients produced proteolytic degradation of free secretory component when incubated in vitro. The finding of large amounts of free secretory component, the free cleaved fragment of the polymeric IgA receptor in human bile, further supports the existence of the blood to bile transhepatocytic pathway in humans.

High serum levels of secretory component in hepatocellular carcinoma

PURPOSE

Elevated levels of secretory IgA (S-IgA) have been detected in serum samples from patients with liver diseases and neoplasia with liver metastasis. We undertook the current study in order to determine the concentrations of different forms of free secretory component (SC) in sera from patients with hepatocellular carcinoma.

MATERIALS AND METHODS

The concentrations of SC, S-IgA, and secretory IgM (S-IgM) were quantified in the sera of 100 patients with hepatocellular carcinoma, and in 77 matched healthy control subjects by using an enzyme-linked immunosorbent assay.

RESULTS

Free SC serum levels exceeded the upper limits of control values in 82 percent of patients with hepatocellular carcinoma, S-IgA levels in 88 percent of them, and S-IgM levels in 32 percent. Free SC levels were positively correlated with S-IgA and S-IgM levels. They were weakly correlated with gamma-glutamyl transpeptidase activity, but not with alpha-fetoprotein, beta 2-microglobulin, albumin, or IgA serum concentrations, nor with alkaline phosphatase activity.

CONCLUSION

The data clearly demonstrate the elevation of serum free SC concentrations as a novel biologic alteration in hepatocellular carcinoma since free SC levels appear to be correlated neither with tumor markers (alpha-fetoprotein, beta 2-microglobulin) nor with biliary obstruction.