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

Deposition of IgA is associated with macrophage influx in the kidney of rats

In the present study we treated rats with N-nitrosodimethylamine (DMN) or D-galactosamine (GALN) to achieve increased circulating IgA levels in rats. GALN-treated rats showed a six-fold increase in serum IgA levels after the first intraperitoneal (i.p.) injection, whereas a 10-fold increase after a second i.p. injection of GALN was seen. DMN-treated rats showed a three-fold increase in serum IgA levels. No differences were observed in IgG and IgM levels between treated and non-treated rats. Sequential renal biopsies analysed by immunofluroescence exhibited mesangial deposits of IgA with different intensities of C3 deposition. Rats treated with GALN showed more IgA deposition in the kidney than DMN-treated rats. The IgA deposition together with C3 was more prominent in rats treated with GALN than in rats treated with DMN. The deposition of C3 together with IgA was associated with an influx of monocytes as detected by ED-1, an antibody directed against a rat monocyte marker. These studies provide evidence that an increase in serum IgA levels is associated with deposition of IgA in the kidney and that IgA has an inflammatory potential.

Kupffer cell depletion in vivo results in clearance of large-sized IgA aggregates in rats by liver endothelial cells

We investigated the clearance kinetics and tissue distribution of different sized IgA in normal and macrophage-depleted rats. Rats were injected iv with liposomes containing dichloromethylene diphosphonate (DMDP). DMDP treatment resulted in complete depletion of liver macrophages 24-48 h after administration. Normal and macrophage depleted rats were injected intravenously with monomeric, dimeric, polymeric or aggregated polymeric IgA (AIgA) and assessed for blood clearance and tissue distribution. In normal rats, clearance of IgA was size dependent, i.e. a faster clearance with increasing size. No differences in clearance kinetics were observed of the different sized IgA between normal and DMDP-treated rats. TCA non-precipitable radioactivity, a measure for degradation of IgA, was found in the circulation of normal and DMDP-treated rats after AIgA administration. The liver was the main organ responsible for the clearance of IgA in normal and DMDP-treated rats. Immunofluorescence studies on liver biopsies indicated that AIgA was associated with Kupffer cells in normal rats. Electron microscopical studies revealed that the AIgA was internalized and located in vesicles in Kupffer cells. In DMDP-treated rats the AIgA was associated with endothelial cells and electron microscopy studies showed that this AIgA was taken up by endothelial cells. These data show that rat liver endothelial cells are able to bind, internalize and degrade AIgA in situations where Kupffer cells are absent, and that these cells may play an important role in the handling of AIgA and IgA-immune complexes.

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.

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.

Antibodies against acetaldehyde-modified epitopes: an elevated IgA response in alcoholics

Several recent reports have shown that antibodies reactive with acetaldehyde (AcH)-modified epitopes are present in alcoholics. However, similar antibodies have also been found in patients with non-alcoholic liver disease and control subjects. In each of these studies total immunoglobulin binding to the AcH-modified proteins was measured, with no attempt being made to identify the classes of immunoglobulin involved. In the present study we employed an enzyme-linked immunosorbent assay (ELISA) to assess the classes of immunoglobulin involved in this response, using plasma samples from 97 alcoholics with varying degrees of liver disease, 35 patients with non-alcoholic liver disease and 33 control subjects. All three groups exhibited a large IgM response and a negligible IgG response. However, the alcoholics exhibited a significantly higher IgA response than either of the other groups. This suggests that the measurement of the IgA response to AcH-modified epitopes may be a specific marker of ethanol abuse.