High serum levels of secretory IgA in liver disease: possible liver origin of the circulating secretory component

Serological assays to measure dimeric IgA antibodies in SARS-CoV-2 infections

Current serological tests cannot differentiate between total immunoglobulin A (IgA) and dimeric IgA (dIgA) associated with mucosal immunity. Here, we describe two new assays, dIgA-ELISA and dIgA-multiplex bead assay (MBA), that utilize the preferential binding of dIgA to a chimeric form of secretory component, allowing the differentiation between dIgA and monomeric IgA. dIgA responses elicited through severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection were measured in (i) a longitudinal panel, consisting of 74 samples (n = 20 individuals) from hospitalized cases of coronavirus disease 2019 (COVID-19); (ii) a longitudinal panel, consisting of 96 samples (n = 10 individuals) from individuals with mild COVID-19; (iii) a cross-sectional panel with PCR-confirmed SARS-CoV-2 infection with mild COVID-19 (n = 199) and (iv) pre-COVID-19 samples (n = 200). The dIgA-ELISA and dIgA-MBA demonstrated a specificity for dIgA of 99% and 98.5%, respectively. Analysis of dIgA responses in the longitudinal panels revealed that 70% (ELISA) and 50% (MBA) of patients elicited a dIgA response by day 20 after PCR diagnosis with a SARS-CoV-2 infection. Individuals with mild COVID-19 displayed increased levels of dIgA within the first 3 weeks after diagnosis but responses appeared to be short lived, compared with sustained IgA levels. However, in samples from hospitalized patients with COVID-19 we observed high and sustained levels of dIgA, up to 245 days after PCR diagnosis. Our results suggest that severe COVID-19 infections are associated with sustained levels of plasma dIgA compared with mild cases.

A novel point-of-care test for cirrhosis based on dimeric to monomeric IgA ratio in blood: a pilot cohort study

BACKGROUND AND AIMS

Dimeric IgA to monomeric IgA ratio (dIgA ratio) is a biomarker of gut mucosal leakage in liver cirrhosis. We evaluated the diagnostic performance of a novel point-of-care (POC) dIgA ratio test for cirrhosis.

METHODS

Plasma samples from people with chronic liver disease were analyzed using the BioPoint POC dIgA ratio antigen immunoassay lateral flow test. Cirrhosis was defined by Fibroscan>12.5 kPa, clinical evidence of cirrhosis or liver histopathology. POC dIgA test diagnostic accuracy was determined in a test cohort using receiver operating characteristic curve analysis; optimal cutoffs for sensitivity and specificity were then applied to a validation cohort.

RESULTS

A total of 1478 plasma samples from 866 patients with chronic liver disease were included (test cohort n = 260, validation cohort n = 606). In all, 32% had cirrhosis; 44% Child-Pugh A, 26% Child-Pugh B, and 29% Child-Pugh C. Median POC dIgA ratio was higher in cirrhosis (0.9) compared with no cirrhosis (0.4, p < 0.001), and in Child-Pugh class B/C compared with A cirrhosis (1.4 Child-Pugh B/C vs. 0.6 Child-Pugh A, p < 0.001). POC dIgA ratio test had good diagnostic accuracy for liver cirrhosis in the test cohort (area under the receiver operating characteristic curve=0.80); a dIgA ratio cutoff of 0.6 had a sensitivity of 74% and specificity of 86%. POC dIgA test accuracy was moderate in the validation cohort (area under the receiver operating characteristic curve=0.75; positive predictive value 64%, negative predictive value 83%). Using a dual cutoff approach, 79% of cirrhosis cases were correctly diagnosed and further testing was avoided in 57%.

CONCLUSIONS

POC dIgA ratio test had moderate accuracy for cirrhosis. Further studies evaluating the accuracy of POC dIgA ratio testing for cirrhosis screening are warranted.

The relationship between maternal postpartum psychological state and breast milk secretory immunoglobulin A level

BACKGROUND

Maternal psychological state may influence the passive transfer of immune factors (e.g., immunoglobulin) via the mother's breast milk.

OBJECTIVE

The aim of this study was to determine whether a correlation exists between mothers' postpartum psychological state and their breast milk secretory immunoglobulin A (SIgA) levels.

STUDY DESIGN

Eighty-one mothers who delivered at an urban general hospital were included in our analysis. Two weeks after delivery, we measured their breast milk SIgA levels and simultaneously documented their psychological state using the Profile of Mood States (POMS), General Health Questionnaire (GHQ), and State-Trait Anxiety Inventory (STAI) scales.

RESULTS

Breast milk SIgA levels were negatively correlated with negative POMS states (tension-anxiety, depression-dejection, anger-hostility, fatigue, and confusion). A negative correlation was also observed between SIgA levels and GHQ mental health (r = -.625, P = .000), and a similar negative correlation was observed with STAI trait and state anxieties. However, no correlation existed between breast milk SIgA levels and the positive POMS state (vigor).

CONCLUSIONS

These results indicate that the maternal psychological state may affect the immune properties of breast milk.

Intestinal microbiota was assessed in cirrhotic patients with hepatitis B virus infection. Intestinal microbiota of HBV cirrhotic patients

To unravel the profile of intestinal microecological parameters in Chinese patients with asymptomatic carriage of hepatitis B virus (HBV), chronic hepatitis B, decompensated HBV cirrhosis, and health controls and to establish their correlation with liver disease progression, we performed quantitative PCR and immunological techniques to investigate fecal parameters, including population of fecal predominant bacteria and the abundance of some virulence genes derived from Escherichia coli, Bacteroides fragilis, Clostridium difficile, and Clostridium perfringens in fecal crude DNA and some immunological parameters in extracts of all fecal samples. Data analysis indicated that 16S rRNA gene copy numbers for Faecalibacterium prausnitzii, Enterococcus faecalis, Enterobacteriaceae, bifidobacteria, and lactic acid bacteria (Lactobacillus, Pediococcus, Leuconostoc, and Weissella) showed marked variation in the intestine of HBV cirrhotic patients. The Bifidobacteria/Enterobacteriaceae (B/E) ratio, which may indicate microbial colonization resistance of the bowel, was decreased significantly in turn from 1.15 ± 0.11 in healthy controls, 0.99 ± 0.09 in asymptomatic carriers, and 0.76 ± 0.08 in patients with chronic hepatitis B to 0.64 ± 0.09 in patients with decompensated HBV cirrhosis (for all, P < 0.01). This suggests that B/E ratio is useful for following the level of intestinal microecological disorder in the course of liver disease progression. The data for virulence gene abundance suggested increased diversity of virulence factors during liver disease progression. Fecal secretory IgA and tumor necrosis factor-α in decompensated HBV cirrhotic patients were present at higher levels than in other groups, which indicates that a complicated autoregulatory system tries to achieve a new intestinal microecological balance.

High plasma immunoglobulin (Ig) A and low IgG antibody titers to oxidized low-density lipoprotein are associated with markers of glucose metabolism

CONTEXT

Plasma oxidized low-density lipoprotein (OxLDL) is known to be associated with obesity, metabolic syndrome, and diabetes.

OBJECTIVE

The objective of the study was to investigate the association between plasma IgA, IgM, and IgG titers to OxLDL, phosphocholine (PC), and streptococcal cell wall polysaccharide (CWPS) and markers of glucose metabolism, type 2 diabetes, and liver adiposity.

SETTING AND PARTICIPANTS

A population-based cohort of middle-aged Finns (n = 1039) participated in the study.

DESIGN

Plasma IgM, IgG, and IgA to copper oxidized LDL (CuOx-LDL) and malondialdehyde-modified low-density lipoprotein (MDA-LDL), PC, and CWPS were determined with chemiluminescent ELISA and liver adiposity with ultrasonography.

RESULTS

IgA autoantibody titers to OxLDL and PC, but not CWPS, were positively associated with fasting blood glucose and plasma insulin levels and inversely with insulin sensitivity index. IgA to OxLDL was significantly higher (P = 0.013 for CuOx-LDL and P = 0.016 for MDA-LDL) and IgG to OxLDL significantly lower (P = 0.036 for CuOx-LDL and P = 0.001 for MDA-LDL) among the subjects with type 2 diabetes compared with subjects with normal or impaired glucose metabolism when adjusted for age, sex, body mass index, smoking, and alcohol consumption. Logistic regression analysis showed that high plasma IgA to OxLDL and low IgG to MDA-LDL were independent risk factors for type 2 diabetes. Plasma IgA titers to OxLDL demonstrated a significant association with liver adiposity (P = 0.012) and gamma-glutamyltransferase levels (P = 0.002).

CONCLUSIONS

Plasma IgA titers to OxLDL were positively and IgG titers negatively associated with markers of glucose metabolism. High plasma IgA and low IgG to OxLDL were independent risk factors for type 2 diabetes.

Biliary IgA secretion in obstructive jaundice: the effects of endoscopic drainage

BACKGROUND

Immunoglobulin A is the predominant immunoglobulin in the bile. Data on the effects of biliary obstruction on IgA secretion are few.

METHODS

The serum and bile IgA levels in patients with common duct stones (n = 27) or with malignant obstructive jaundice (n = 20) were collected by insertion of nasobiliary catheters. Single samples of common duct bile from patients with gallstones (n = 24) were collected as controls. Bile samples collected were measured for total IgA, secretory IgA, and free secretory component levels by sandwich enzyme-linked immunosorbent assays.

RESULTS

Bile total IgA, secretory IgA, and free secretory component in the common duct stones group (82.7 +/- 11.4 microgram/ml, 18.4 +/- 1.7 microgram/ml, 0.74 +/- 0.15 microgram/ml) and the malignant obstructive jaundice group (81.6 +/- 10.7 microgram/ml, 18.2 +/- 2.4 microgram/ml, 0.57 +2- 0.12 microgram/ml) were found to be significantly lower than those of the control gallstone patients (104.8 +/- 3.4 microgram/ml, 33.2 +/- 2.9 microgram/ml, 1.03 +/- 0.12 microgram/ml) (P < 0.05). Serum secretory IgA levels in the common duct stones (26.53 +/- 1.75 microgram/ml) and malignant obstructive jaundice groups (26.03 +/- 3.48 microgram/ml) were significantly higher than the gallstone group (18.45 +/- 4.56 microgram/ml). The bile-to-serum concentration ratio of total IgA, secretory IgA, and free secretory component levels rose significantly within 48 hours after relief of obstruction.

CONCLUSIONS

Biliary obstruction secondary to both calculus or malignancy of the hepatobiliary system causes suppression of bile IgA secretion and elevated serum level of secretory IgA. Bile secretory IgA secretion recovers with endoscopic drainage of the obstructed system.

Human eosinophils express a receptor for secretory component. Role in secretory IgA-dependent activation

The existence of a functional receptor for secretory component (SC) on the eosinophil membrane might explain the preferential degranulation induced by secretory IgA (sIgA) when compared to serum IgA. Indeed, flow cytometry analysis revealed that purified human SC could bind to a subpopulation (4-59%) of blood eosinophils purified from 19 patients with eosinophilia. Binding of radiolabeled human SC could be competitively inhibited using unlabeled SC or secretory IgA but not with serum IgA or IgG. Immunoprecipitation and immunosorbent chromatography using human SC revealed the presence of a major component at 15 kDa in eosinophil extracts as well as in culture supernatants but not in neutrophils. The 15-kDa protein eluted from the human SC immunosorbent was able to bind to SC or to sIgA but not to serum IgA. Eosinophils preincubated with human SC or sIgA released eosinophil cationic protein (ECP) and eosinophil peroxidase (EPO) after addition of anti-SC or anti-IgA monoclonal antibody as respective cross-linking reagents. These results indicated that binding of free or complexed SC to human eosinophils could induce eosinophil degranulation. Furthermore, the dose-dependent inhibition by SC of mediator release induced by sIgA but not by serum IgA, suggested that the receptor for SC could be involved in the preferential degranulation mediated by sIgA. These results indicate a novel pathway of eosinophil activation and its potential involvement in mucosal immunity, particularly in inflammatory diseases associated with infiltration of eosinophils and the enhanced production of sIgA.

Secretory immunoglobulins in serum from human immunodeficiency virus (HIV)-infected patients

Infection by the human immunodeficiency virus is associated with polyclonal B cell activation and increased levels of serum IgA. In order to characterize the molecular species of serum IgA, we have measured total IgA, IgA1, and IgA2 in sera from 60 HIV-1-infected patients and 40 healthy controls. In addition, secretory IgA (S-IgA), secretory IgM (S-IgM), free immunoreactive secretory component (SC), and the distribution of monomeric and polymeric IgA were determined. The data confirm the elevation of total serum IgA levels in HIV-1-infected patients, and both IgA1 and IgA2 concentrations are elevated. Furthermore, the data show a substantial increase in serum levels of both monomeric and polymeric IgA. Serum S-IgA levels were significantly increased in CDC group II patients versus controls and more frequently elevated in CDC group IV patients. The highest S-IgA levels were found among patients with the lowest blood CD4+ cell counts. Serum S-IgA levels were not correlated with serum levels of either total IgA or polymeric IgA. Serum S-IgM levels were also increased in HIV-1-infected patients and positively correlated with serum S-IgA levels. Conversely, serum levels of free SC were not altered. An increase in serum S-IgA was not related to human hepatitis B virus infection and/or to hepatic dysfunction or to diarrhea or overt intestinal infection. The data indicate that secretory Ig (S-IgM and S-IgA), which are likely to be produced at mucosal sites, increase in the serum of HIV-1-infected patients.

Polymeric Ig receptor expression in hepatocellular carcinoma

The cellular localisation of the polymeric Ig receptor (pIg-R) and carcinoembryonic antigen (CEA), hepatic and biliary cell markers, were investigated in patients with hepatocellular carcinoma (HCC) and high serum levels of secretory component. Serum SC were increased 6-20-fold in 8 HCC patients compared with normal subjects. Serum free SC was positively correlated bilirubin (r = 0.95, P less than 0.04). In normal liver tissue, cytokeratin (CK) 8 and 18 were localised in hepatocytes and biliary cells while pIg-R and CK 19 expression was restricted to biliary cells. In tumoral liver tissue, malignant cells expressed CK 8 and 18 weakly; pIg-R and CK 19 were not detected in tumoral cells. CEA was expressed by biliary cells in normal and proliferating ducts. In peritumoral fibrosis, proliferating biliary cells were strongly stained by anti-cytokeratins and anti-pIg-R antibodies. In one case, pIg-R was localised in isolated cells close to fibrosis without co-staining of anti-CK 19. Thus increased serum SC is not associated with pIg-R expression by tumoral cells, and pIg-R may be considered an additional marker of biliary cells. High SC might be explained either by reflux from bile to serum and/or release of unbound SC from the vascular pole of non-functional, proliferating biliary structures.

Jejunal immunoglobulin secretion in alcoholic patients with and without cirrhosis

Alcoholic liver diseases are associated with an elevation of serum immunoglobulin A (IgA). This could be the result of increased IgA production by the intestinal mucosa. Serum and jejunal immunoglobulin, albumin and orosomucoid were measured in 13 alcoholic patients with (n = 6) and without (n = 7) cirrhosis and compared to 11 controls. Jejunal secretions were obtained by segmental perfusion under an occluding balloon. High levels of serum monomeric and polymeric IgA were only found in patients with cirrhosis. Alcoholics with and without cirrhosis had normal monomeric and polymeric IgA jejunal secretion rates. jejunal clearances of albumin, orosomucoid and immunoglobulin G were significantly higher in both non-cirrhotic and cirrhotic patients than in controls. These findings indicate normal jejunal IgA secretion and increased permeability to plasma proteins, such as albumin and immunoglobulin G in alcoholics.

The occurrence and sources of natural antibody in human bile and serum against the O antigens of two Escherichia coli serotypes

Paired serum and bile samples from normal subjects as well as patients with biliary disease were tested for natural antibody to two individual Escherichia coli O antigens by ELISA. Serum antibody was most commonly of IgM and IgG class. Antibody was less frequently detected in bile and was more commonly IgM than IgA, with IgG activity detected infrequently. Little relation was apparent between antibody in paired samples; activity could be present in both serum and bile or in either fluid alone. Titres in paired samples also did not correspond when 'normalized' with respect to the concentrations of relevant isotypes; bile was frequently enriched for natural antibody as a proportion of total immunoglobulin compared with serum. Secretory component-bound antibody was detectable in some biles that contained IgA and/or IgM activity and in the serum of 33% of subjects with biliary disorders but not in normal sera. A series of paired samples taken from three individuals was also examined for antibody against each subject's own intestinal commensal E. coli. Serum IgM and IgG activity was present in all samples, but antibody in bile was less frequent and was of IgM or IgA class. These results suggest that natural antibody in human bile occurs independently of antibody in serum and that it is substantially derived from local sources.

The liver and IgA: immunological, cell biological and clinical implications

Secretory immunoglobulin A is the characteristic and predominant immunoglobulin of the mucosal immune system; it participates in immunological protection at the level of mucous membrane surfaces. During the past 10 to 15 years, a great deal of experimental and clinical evidence has shown that the liver is very much involved in the sIgA system. In certain animals (rats, mice, rabbits), polymeric forms of IgA are efficiently cleared by the liver and transported into bile by a receptor-mediated vesicular pathway across hepatocytes. Taking advantage of this easily accessible pathway, investigators have defined many of the events in the external secretion of pIgA, including details about the synthesis and secretion of its receptor, secretory component. In the rat hepatocyte, secretory component is synthesized as a transmembrane glycoprotein and is expressed preferentially on the sinusoidal plasma membrane; circulating pIgA that binds to secretory component is internalized into endocytic vesicles and transported across the hepatocyte to the bile canalicular membrane, where the pIgA is released into bile as a soluble complex with a portion of the secretory component, the complex being secretory IgA. In some other animals (dog, guinea pig, sheep) as well as man, biliary epithelial cells, not hepatocytes, express secretory component and perform the transcytosis and secretion of pIgA into bile. In those species, much of the pIgA that reaches bile is synthesized locally in plasma cells that populate the biliary tree; this design is analogous to the release of sIgA into various mucosae in the body. The major biological functions ascribed to the secretion of IgA into bile are enhancement of immunological defense of the biliary and upper intestinal tracts and the clearance of harmful antigens from the circulation as IgA-antigen complexes. However, the importance of biliary IgA antibodies is largely unclarified, and man lacks the capacity for effective clearance of IgA-antigen complexes via the secretory component-mediated transhepatocellular pathway; whether this deficit contributes to the propensity for man to develop IgA immune complex diseases should be clarified. Among liver diseases, alcoholic disease is most closely linked to alterations in IgA metabolism. This association is manifested principally by the deposition of IgA along the sinusoids in the livers of the majority of alcoholics and in the renal mesangium of many.(ABSTRACT TRUNCATED AT 400 WORDS)

An 'antigen capture' ELISA for secretory immunoglobulin A antibodies to hepatitis B surface antigen in human saliva

An enzyme-linked immunosorbent assay (ELISA) was developed which permits the assay of specific secretory immunoglobulin A (sIgA) antibodies against hepatitis B surface antigen (HBsAg) in saliva. The assay is based on the binding of sIgA antibodies present in saliva to microtitre plates coated with excess of F(ab')2 anti-secretory component antibodies, followed by the addition of specific antigen, HBsAg and finally peroxidase-labelled anti-HBsAg. The assay is fast, simple, reproducible and antigen specific as shown by total absence of inhibition of specific antigen by unrelated antigens but significant inhibition of labelled anti-HBsAg by unlabelled anti-HBsAg. The values obtained for hospital personnel exposed to hepatitis infections (0.068 +/- 0.083 U/ml) and for post-icteric hepatitis B patients (0.062 +/- 0.033 U/ml) were significantly higher than values in control subjects (0.013 +/- 0.006 U/ml).

Polymeric and monomeric IgA response in serum and milk after parenteral cholera and oral typhoid vaccination

The effect of vaccinating lactating Pakistani mothers with a combination of live oral typhoid vaccine and parenteral inactivated cholera vaccine on specific milk and serum IgA antibodies in both monomeric (m) and polymeric (p) forms was analysed. IgA antibody titres peaked for both antigenic specificities 2 weeks after the first dose of vaccine. 82 +/- 7% of anti-Vibrio cholerae and 72 +/- 17% of anti-Salmonella typhi IgA were in the polymeric form. These serum pIgA antibodies were mainly dimeric IgA, not complexed with the secretory component. They disappeared more rapidly from serum than mIgA antibodies. Anti-V. cholerae IgA responses were parallel in serum and milk samples, whereas anti-S. typhi responses were dissociated. In milk, IgA antibodies were secretory IgA for both antigenic specificities, being probably of local origin in the mammary gland. Our results indicate that both oral and parenteral vaccinations can induce pIgA antibodies in serum and secretions, confirming that the presence of pIgA in serum does not necessarily reflect an immune stimulation only at the mucosal level.

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.

Serum antibodies to mycobacterial antigens in active Crohn's disease

Infection with a species of Mycobacterium has been implicated in the pathogenesis of Crohn's disease. Therefore, we attempted to determine whether a specific serum antibody response to mycobacteria occurs in patients with the disease. We tested sera of patients with active Crohn's disease and several control groups in an enzyme-linked immunosorbent assay for reactivity with two mycobacterial antigens: (a) lipoarabinomannan, a highly immunogenic somatic lipopolysaccharide present in the cell walls of all species of the Mycobacterium genus, and (b) a protoplasmic antigenic preparation from M. sp strain linda, the mycobacterium that has been specifically implicated in Crohn's disease. We found no significant elevation in immunoglobulin A, immunoglobulin G, or immunoglobulin M antibody levels to these two antigen preparations in the Crohn's disease patients. Moreover, no subset of patients (sex, age, Crohn's disease activity index, location of disease, duration of disease, operations, or response to treatment) had elevated antibody levels. As virtually all known chronic infectious diseases have an associated serologic response to the etiologic agent, our findings greatly diminish the likelihood that Crohn's disease is caused by an infection with a mycobacterium.

Comparative studies on immunoglobulins, complement component (C3), albumin, and immunoglobulin A-containing circulating immune complexes in serum and bile of patients with biliary obstruction

We measured the concentrations of IgA, IgG, IgM, secretory IgA, albumin, complement component (C3), and IgA-containing circulating immune complex (IgA-CIC) in the serum and bile of patients with biliary obstruction. The bile-to-serum (BS) ratio of the concentrations of albumin and IgG increased with the increase in total serum bilirubin. This indicates that the permeability from blood to bile increases with the degree of biliary obstruction, and the blood-bile barrier function breaks down. The BS ratios of IgA and IgM, which are selectively secreted into bile, did not show a significant correlation with total serum bilirubin. The index of the BS ratio to the BS ratio of albumin (BS/BS-Alb index) of IgA and IgM was significantly larger than that of IgG. This indicates that the selective transport of IgA and IgM into bile is present even in patients with obstructive jaundice. Since the BS/BS-Alb index of C3 is larger than that of IgG, and the SGOT correlated directly with the BS ratio of C3, some of the C3 in bile may come from damaged hepatocytes.

Plasma levels of secretory IgA in patients with gastric cancer

The levels of plasma secretory IgA were measured in patients with gastric cancer and found to be slightly higher (9.6 +/- 6.2 micrograms/ml) than those in healthy controls (7.0 +/- 2.6 micrograms/ml, 0.05 less than P less than 0.1). Secretory IgA levels in those with hepatic metastases (19.7 +/- 12.2 micrograms/ml) were significantly higher than those in patients without hepatic metastases (P less than 0.001). In the latter, there was no significant relationship between plasma secretory IgA levels and the deepest layer of cancerous invasion or lymph node metastases. The secretory IgA levels in cases of well differentiated tubular adenocarcinoma were significantly higher than those with poorly differentiated adenocarcinoma (P less than 0.05). Although there is small diagnostic value in the detection of gastric cancer by measuring the levels of secretory IgA, high levels of secretory IgA in gastric cancer patients may be indicative of the presence of hepatic metastases.

Circulating secretory immunoglobulins of the A and M isotypes in chronic liver disease

Serum levels of secretory IgA (SIgA) and secretory IgM (SIgM) were quantified by an enzyme-linked immunosorbent assay in 97 patients with various chronic liver diseases and 17 patients with uncomplicated ulcerative colitis. The values obtained were compared with 89 matched controls and related to other serum variables. All types of liver disease had elevated median levels of serum SIg. Patients with primary biliary cirrhosis (PBC) had the highest SIg levels, particularly SIgM, but increased total serum IgM was slightly more specific for PBC. Thus, the SIg levels did not add more discriminative information than several other variables. Elevated levels of circulating SIgA correlated mainly with variables that indicate reduced liver function. The difference observed between patients with PBC and primary sclerosing cholangitis (PSC) in the alkaline phosphatase (ALP)-to-SIg ratio is discussed.

Advances in the application of biochemical tests to diseases of the liver and biliary tract: their role in diagnosis, prognosis, and the elucidation of pathogenetic mechanisms

Despite the biochemical complexity of the liver, few laboratory tests provide discriminatory diagnostic information in patients with hepatobiliary disease. Recent efforts have concentrated upon tests which assess the function of the liver, the severity of the disease state, and underlying pathological processes. Bile Acids: The emergence of facile technology and widespread application has brought the realization that these assays are not as sensitive in detecting liver disease as previously believed, although the cholate/chenate ratio may be useful in distinguishing cholestasis from chronic liver disease. The presence of unusual bile acids in serum or urine may be helpful in some cases. Drug Metabolism: A number of tests provide good evidence about liver function, hepatic blood flow and portal shunting, but the aminopyrine breath tests is the most useful, giving prognostic information in acetaminophen overdose and alcoholic liver disease. The antipyrine half-life identifies surgical cases at risk from poor hepatic function. Proteins and Immunochemical Tests: Interest has developed in plasma proteins such as prealbumin and retinol-binding protein to monitor hepatic protein synthetic function. Secretory IgA is more elevated in biliary tract disease, unlike the native protein which is increased principally in cirrhosis. Type III procollagen can be measured in serum, and correlates with the activity of collagen synthesis and the degree of fibrosis in biopsy samples. Reye's Syndrome: Biochemical tests play an essential role in diagnosis of this recently discovered disease. These will be presented and discussed.

Characteristics of serum IgA and liver IgA deposits in alcoholic liver disease

Patients with alcoholic liver disease frequently reveal an increase in IgA serum concentration and IgA deposits in a continuous pattern along hepatic sinusoids. We investigated whether the hepatic IgA deposits are a passive reflection of changes in concentration or composition of IgA in the circulation, or represent a distinct effect of alcohol on the liver. Forty-one patients with alcoholic liver disease (daily alcohol intake at least 50 gm for more than five consecutive years) were compared with 41 patients with nonalcoholic liver disease. Patients in both groups were matched for serum IgA and histopathological changes in the liver biopsy. IgA deposits in the liver were found in 78% of the alcoholic patients and in 12% of the nonalcoholic patients. The presence of deposits was not related to histopathological changes in the liver or to the serum IgA concentration. In serum IgA subclass distribution, alcoholic patients differed from nonalcoholic patients by a slight but significant shift to IgA2; in contrast, the hepatic IgA deposits in alcoholic patients were almost of the IgA1 subclass. Serum secretory component (which is an equivalent of serum secretory IgA) was elevated in both alcoholic and nonalcoholic patients; patients with a liver biopsy revealing hepatitis showed the highest level. In contrast, the hepatic deposits did not contain secretory component. We conclude that the continuous deposits of IgA along liver sinusoids are not a passive reflection of changes in concentration or composition of circulating IgA, but may represent a distinct effect of alcohol on the liver related to the role of this organ in IgA metabolism.

Relationship between secretory IgA, IgA-containing (C3-fixing) circulating immune complexes, and complement components (C3, C4) in patients with obstructive jaundice

Serum secretory IgA, IgA-containing circulating immune complexes (IgA-CIC), complement components, and major immunoglobulins were measured in patients with biliary tract stones and/or tumors of the biliary tract or pancreas. The levels of secretory IgA and total IgA were increased in patients with and without obstructive jaundice. The levels of both C3 and C4 were significantly higher in patients with or without obstructive jaundice than in healthy controls. In patients with obstructive jaundice the increased levels of secretory IgA, total IgA, and IgA-CIC were correlated with the increase of C3 but not with that of C4.

An enzyme-linked immunosorbent assay for differential quantitation of secretory immunoglobulins of the A and M isotypes in human serum

An enzyme-linked immunosorbent assay was developed for differential quantitation of secretory IgA (SIgA) and secretory IgM (SIgM) in human serum. The assay was based on non-competitive binding of SIgA and SIgM to microplates coated with an excess of antibodies to secretory component (SC). Appropriate standards were included to obtain absolute values. Mutual competition of SIgA and SIgM was avoided by testing the serum samples at sufficiently high dilutions. The assay is fast, simple, sensitive and reproducible. All of the 138 healthy individuals tested (1-91 years old) were found to have both SIgA and SIgM in their serum (medians, 10 mg/l and 14 mg/l, respectively). Lactating women, SIgA-deficient healthy individuals, and particularly patients with hepatitis had significantly increased serum SIgM levels compared with controls. Differential quantitation of SIgA and SIgM may turn out to be of diagnostic value and provide pathogenetic information.

Sources of proteins in human bile

The proteins of 46 human bile specimens, collected by several different routes have been studied by crossed immunoelectrophoresis, by rocket immunoelectrophoresis and by radioimmunoassay. The results were analysed by plotting the variation in the bile: plasma ratio of particular proteins against molecular weight and by examination of the correlation between the concentrations of different proteins in the biles of different patients. Our results show that the majority of human bile proteins derive from plasma although bile specific proteins are always present. The majority of plasma proteins appear to enter bile by a 'sieving' mechanism which results in an inverse relationship between the bile: plasma ratio and the molecular weight. In addition there was a very high degree of correlation between the biliary concentrations of alpha 2-macroglobulin, IgG, haptoglobin, haemopexin, albumin, prealbumin, and orosomucoid. A number of other proteins namely thyroxine binding globulin, GC globulin and alpha 2HS-glycoprotein appeared in bile at concentrations greater than those expected if entry is by the sieving mechanism. These three proteins, however, are of rather low molecular weight and the reason for the lack of correlation appears to be individual variation in the 'pore size', presumably reflecting variation in the porosity of tight junction between hepatocytes. Although the majority of human bile proteins would appear to enter bile by a molecular weight-dependent pathway, four proteins, namely secretory IgA, IgM, haemoglobin and caeruloplasmin, showed significant deviation from the predicted relationship and probably enter bile at least partly by transport across cells. The concentration of beta 2-glycoprotein I was also much greater than expected from its molecular weight. The reason for this is not yet clear but may well reflect a very efficient and specific transport mechanism.

The fate of polymeric and secretory immunoglobulin A after retrograde infusion into the common bile duct in rats

In the rat, plasma IgA is rapidly endocytosed by hepatocytes and translocated to the bile via a receptor-mediated vesicular transport system which appears to remain intact even during cholestasis. During the latter phenomenon, there is an accumulation of secretory IgA (sIgA) in plasma. These data suggest that biliary IgA can be regurgitated into the plasma compartment. The present study was designed to determine the location and mechanism(s) by which this might occur. 125I-labeled human polymeric IgA (pIgA) or sIgA was infused retrograde into the rat common bile duct at a flow rate of 20 microliter per min (5 to 10 micrograms per min pIgA; 7 micrograms per min sIgA) over 1 hr. Blood and liver samples were collected 10, 30 and 60 min, and radioactivity determined. Radioactive label appeared in the blood by 10 min and increased linearly with time. By 30 min, however, the liver had reached saturation. All of the label found in the blood was intact starting material, i.e., pIgA or sIgA. Electron microscopic autoradiography analysis clearly demonstrated the presence of grains in vesicles in hepatocyte pericanalicular cytoplasm, as well as in vesicles near the sinusoidal plasma membrane. No grains were observed associated with bile duct or ductule epithelium at any time period. Further, there was no grain accumulation near the parenchymal cell intercellular spaces indicating that paracellular flow plays little or no role in large protein regurgitation. In addition, by 60 min, there were grains associated with Kupffer cells. These data provide the first evidence that hepatocytes, during times of elevated biliary pressure can readily transport macromolecules from bile to plasma via nonreceptor-mediated membrane-limited vesicles.

Studies of the influence of immunological and serological factors from patients with cholestasis due to alcoholic or viral hepatitis on biliary function in the rat

Studies were undertaken to determine if cholestasis in alcoholic or viral hepatitis is related to immunologic hyperreactivity as suggested for cholestasis due to type-II drug-induced hepatitis, and evaluate possible mechanisms involved in lymphokine-induced cholestasis. Results indicate that a cholestatic factor exists in alcoholic and acute viral hepatitis. Supernatants of lymphocytes from patients with alcoholic hepatitis stimulated by an extract of alcoholic hyalin evoked a 28% +/- 7.3 SEM reduction in rat bile flow (P less than 0.03). Supernatants of lymphocytes from patients with acute viral hepatitis activated by liver-specific protein caused a reduction in rat bile flow of 24% +/- 5.9 SEM (P less than 0.03). A decrease in bile flow also occurred following injections of sera from patients with alcoholic or acute viral hepatitis. In contrast, injection of supernatants of non-stimulated lymphocytes or those from chronic active hepatitis or healthy subjects did not produce a significant change in bile flow. Supernatants of stimulated lymphocytes from tuberculin-sensitized guinea pigs caused a similar decrease in rat bile flow and reduced excretion of human secretory immunoglobulin A (IgA). Despite reductions in rat bile flow there were no alterations in liver morphology, liver plasma membrane Na-K-ATPase activity, microsomal cholesterol-7 alpha-hydroxylase activity or low-dose indocyanine green clearance during the period of observation.

[The gastrointestinal tract as an immunologic organ: the gut-associated immune system]

The gastrointestinal mucosa separates the intraluminal gastrointestinal fluid, which contains a high number of antigens from different sources, and prevents free access of antigens to the body. Simultaneously, it allows some vital host-environment interactions. A number of unspecific factors are important in preventing antigen invasion. The specific mucosal immunity is related to secretory IgA. IgA is derived from mucosal plasma cells after antigen-induced proliferation of its precursors in Peyer's patches. These IgA-positive B-lymphoblasts migrate through the systemic circulation and then "home" to the mucosa. IgA is translocated as a dimer to the gut lumen after attachment to the secretory component (SC). Part of it is excreted into the bile via small bile ducts after portal and possibly systemic circulation and binding to SC. T cells and mast cells are also considered to show migration and homing phenomena. In addition to the gut, some other mucosa-associated lymphoid tissues, (e.g. bronchus, mammary, salivary and lacrimal glands as well as the female genital tract), can participate in homing. Little is known about the local regulatory mechanisms, which allow an immunoglobulin class specifity of immune responses. Induction of local immunity and specific systemic tolerance seems to be a characteristic immune response of the gut-associated lymphoid tissue (GALT). The knowledge of the local immune system allows a better understanding of many aspects of gastrointestinal pathology, especially in immuno-inflammatory and immunoproliferative diseases as well as in gastrointestinal immunodeficiency syndromes.

The liver in the IgA secretory immune system. Dogs, but not rats and rabbits, are suitable models for human studies

The liver transport of polymeric IgA (pIgA) from plasma into bile and the immunohistochemical distribution of secretory component (SC) in the liver were studied in dogs, and compared to those in humans, rats, and rabbits. Results were as follows: (i) according to bile and serum protein concentrations and specific activities, plasma pIgA in dogs, like in humans, is transported into bile approximately 10 times more efficiently than albumin, as compared to 320 and 1060 times in rabbits and rats, respectively. (ii) Only approximately 1% of an i.v. dose of [125I]pIgA is transported into bile over 8 hr in dogs, like in humans, as compared to approximately 50% over 3 hr in rats and rabbits. These results agree with much smaller daily fractional catabolic rates of intravascular pIgA in dogs (0.28) and humans (0.48) than in rats (24.0). (iii) Total bile IgA contributes daily about 1.5 mg per kg to intestinal pIgA in dogs, a figure similar in humans (0.8 mg per kg) but much smaller than in rats (38 mg per kg) and rabbits (35 mg per kg). (iv) Biliary obstruction in dogs, like in humans, results only in minor and late increases in serum pIgA levels, contrasting with greater than 8-fold increases within 24 hr in rats and rabbits. (v) Unlike in rats and rabbits, SC in dog liver as well as in human liver cannot be detected in hepatocytes although clearly present in bile duct cells. To conclude: (i) major species differences in plasma-to-bile transport of pIgA exist, most probably related to species differences in the ability of hepatocytes to synthetize SC.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in size, subclass, and metabolic properties of serum immunoglobulin A in liver diseases and in other diseases with high serum immunoglobulin A

We have studied the relative contributions of monomeric (m-) and polymeric IgA (p-IgA) and of IgA1 and IgA2 to total serum IgA in healthy adults and patients with liver disease (LD) or with other diseases and high serum IgA. Serum concentration of total secretory component (SC) was also determined. In addition, fractional catabolic rates (FCR) and synthetic rates for both m- and p-IgA were measured in nine controls and nine cirrhotics. Our results support four main conclusions: (a) In healthy adults, intravascular p-IgA contributes to only 4-22% (mean 12%) of serum IgA, because its FCR and synthetic rate are approximately two times higher and four times smaller, respectively, than those of intravascular m-IgA. (b) in LD, biliary obstruction does not result in a significant increase in serum p-IgA unlike in rats and rabbits, indicating that in humans the SC-dependent biliary transport of p-IgA plays a much less significant role in selective removal of p-IgA from plasma than in rats and rabbits. (c) In contrast to biliary obstruction, parenchymal LD results in a significant and preferential increase in serum p-IgA, which in cirrhotics correlates with a selective reduction of the p-IgA-FCR. This supports a role for the human liver in selective removal of p-IgA from plasma, but another mechanism than the SC-dependent biliary transport should be considered. (d) Total SC, p-IgA, and IgA2 in serum are unlinked parameters, not necessarily reflecting mucosal events. A marked increase in serum SC occurs almost selectively in LD. Although a shift to IgA2 is suggested in Crohn's disease and alcoholic cirrhosis, a shift to IgA1 frequently associated to a shift to p-IgA occurs in chronic active LD, primary Sicca, and connective tissue diseases.

Intrahepatic synthesis of immunoglobulin in liver disease

Patterns of intrahepatic immunoglobulin production were investigated by an in vitro biosynthetic labelling technique which measured the rate of Ig production in liver biopsy fragments. This technique depends on the incorporation of 3H-leucine into proteins synthesized by cells in the biopsy fragment and subsequently released into the culture medium, and precipitation of Ig with monospecific antisera. Intrahepatic Ig production was expressed as counts of radioactivity precipitated/g of liver tissue/24 h. Mean values were high in various inflammatory diseases of the liver, including alcoholic hepatitis (AH) (17 cases), IgG, 87.8, IgA, 105.6 and IgM, 14.7, chronic active hepatitis (CAH) (19 cases), IgG, 86.0, IgA, 56.1 and IgM, 12.6, and acute viral hepatitis (3 cases), IgG, 116.0, IgA, 61.0 and IgM, 32.0, but low in histologically normal livers (6 cases), IgG, 4.5, IgA, 4.8 and IgM, 4.7, alcoholic fatty liver (11 cases), IgG, 9.4, IgA, 11.4 and IgM, 7.1, and miscellaneous non-inflammatory conditions (10 cases), IgG, 8.7, IgA, 11.1 and IgM, 5.0. Photomicrographs were used to measure the density of plasma cells, expressed as cells/mm2 of liver biopsy tissue: mean counts were for AH 5.1, CAH 16.2 and normal liver 0.0. Intrahepatic Ig production in vitro did not correlate with the density of plasma cells in biopsy samples from cases of AH or CAH, nor with serum Ig levels.

Selective transport of polymeric immunoglobulin A in bile. Quantitative relationships of monomeric and polymeric immunoglobulin A, immunoglobulin M, and other proteins in serum, bile, and saliva

In 17 adults, serum, hepatic bile, and saliva samples were analyzed for their sedimentation profile of IgA and secretory component (SC), and for their concentrations of albumin, orosomucoid, transferrin, IgG, IgA, alpha 2-macroglobulin (alpha 2M), IgM, and SC. Polymeric IgA(p-IgA) averaged 13% (50-700 micrograms/ml) of total IgA in serum, 70% (43-88%) in bile, and 93% (74-98%) in saliva. Most of the p-IgA in bile sedimented with SC, which also occurred free (8-44%), and with IgM. In bile, albumin (155-1,485 micrograms/ml) was the predominant protein, followed by IgG (32-480 micrograms/ml), and total IgA (37-209 micrograms/ml). In saliva, p-IgA (72-902 micrograms/ml) predominated, followed by albumin (16-385 micrograms/ml) and IgG (9-178 micrograms/ml). Secretion-to-serum albumin-relative concentration ratios (S/S-ARCR = 1 for albumin) in bile averaged 22 for p-IgA, 1.91 for IgM, 1.28 for monomeric IgA (m-IgA), 0.70 for IgG, and 0.57 for alpha 2M, indicating for p-IgA, IgM, and to a lesser extent for m-IgA, a selective excretion into bile. In saliva, a 16-fold greater selective excretion of p-IgA (mean S/S-ARCR = 354) was found. Labeled m- and p-IgA were injected intravenously into five patients. Specific activities indicated that for p-IgA 50% was serum derived in bile, as compared with 2% in saliva, and to 85% for m-IgA in bile. In the patient with the highest excretion of 125I-p-IgA in bile, only 2.8% of the injected dose was recovered in bile within 24 h after injection. Compared with rats and rabbits, the serum-to-bile transport of p-IgA in humans is much smaller.