Rapid active transport of immunoglobulin A from blood to bile

Establishment of isotype-switched, antigen-specific B cells in multiple mucosal tissues using non-mucosal immunization

Although most pathogens infect the human body via mucosal surfaces, very few injectable vaccines can specifically target immune cells to these tissues where their effector functions would be most desirable. We have previously shown that certain adjuvants can program vaccine-specific helper T cells to migrate to the gut, even when the vaccine is delivered non-mucosally. It is not known whether this is true for antigen-specific B cell responses. Here we show that a single intradermal vaccination with the adjuvant double mutant heat-labile toxin (dmLT) induces a robust endogenous, vaccine-specific, isotype-switched B cell response. When the vaccine was intradermally boosted, we detected non-circulating vaccine-specific B cell responses in the lamina propria of the large intestines, Peyer's patches, and lungs. When compared to the TLR9 ligand adjuvant CpG, only dmLT was able to drive the establishment of isotype-switched resident B cells in these mucosal tissues, even when the dmLT-adjuvanted vaccine was administered non-mucosally. Further, we found that the transcription factor Batf3 was important for the full germinal center reaction, isotype switching, and Peyer's patch migration of these B cells. Collectively, these data indicate that specific adjuvants can promote mucosal homing and the establishment of activated, antigen-specific B cells in mucosal tissues, even when these adjuvants are delivered by a non-mucosal route. These findings could fundamentally change the way future vaccines are formulated and delivered.

Radiolabelled polymeric IgA: from biodistribution to a new molecular imaging tool in colorectal cancer lung metastases

By radiolabelling monomeric (m) and polymeric (p) IgA with technetium 99m (99mTc), this study assessed IgA biodistribution and tumour-targeting potency. IgA directed against carcinoembryonic antigen (CEA), a colorectal cancer marker, was selected to involve IgA mucosal tropism. Ig was radiolabelled with 99mTc-tricarbonyl after derivatisation by 2-iminothiolane. 99mTc-IgA was evaluated by in vitro analysis. The biodistributions of radiolabelled anti-CEA mIgA, pIgA and IgG were compared in normal mice. Anti-CEA pIgA tumour uptake was studied in mice bearing the WiDr caecal orthotopic graft. IgA radiolabelling was obtained with a high yield, was stable in PBS and murine plasma, and did not alter IgA binding functionality (Kd ≈ 25 nM). Biodistribution studies in normal mice confirmed that radiolabelled pIgA - and to a lesser extent, mIgA - showed strong and fast mucosal tropism and a shorter serum half-life than IgG. In caecal tumour model mice, evaluation of the anti-CEA-pIgA biodistribution showed a high uptake in lung metastases, confirmed by histological analysis. However, no radioactivity uptake increase in the tumoural caecum was discerned from normal intestinal tissue, probably due to high IgA caecal natural tropism. In microSPECT/CT imaging, 99mTc-IgA confirmed its diagnostic potency of tumour in mucosal tissue, even if detection threshold by in vivo imaging was higher than post mortem studies. Contribution of the FcαRI receptor, studied with transgenic mouse model (Tsg SCID-CD89), did not appear to be determinant in 99mTc-IgA uptake. Pre-clinical experiments highlighted significant differences between 99mTc-IgA and 99mTc-IgG biodistributions. Furthermore, tumoural model studies suggested potential targeting potency of pIgA in mucosal tissues.

High-affinity von Willebrand factor binding does not affect the anatomical or hepatocellular distribution of factor VIII in rats

Essentials Von Willebrand factor (VWF) stabilizes factor VIII (FVIII) and prevents its premature clearance. Rat anatomical and hepatocellular distribution studies assessed the VWF effect on FVIII clearance. Hepatocytes and liver sinusoidal endothelial cells play a key role in FVIII clearance. Anatomical and hepatocellular distribution of FVIII is independent of high-affinity VWF binding.

ABSTRACT

Background Von Willebrand factor (VWF) stabilizes factor VIII in the circulation and prevents its premature clearance. Objective To study the effects of VWF on FVIII clearance in rats with endogenous VWF. Methods Anatomical and hepatocellular distribution studies were performed in rats following intravenous administration of glycoiodinated recombinant FVIII (rFVIII) and a FVIII variant, FVIII-Y1680F, lacking high-affinity VWF binding. Radioactivity was quantified in organs, and in distinct liver cell populations. The role of VWF binding was also studied by immunohistochemical staining of rat livers perfused ex vivo with rFVIII alone or with a FVIII-binding VWF fragment. Results The liver was the predominant organ of rFVIII distribution, and a radioactivity peak was also observed in the intestines, suggesting FVIII secretion to the bile by hepatocytes. In the liver, ~60% of recovered radioactivity was associated with hepatocytes, 32% with liver sinusoidal endothelial cells (LSECs), and 9% with Kupffer cells (KCs). When calculated per cell, 1.5-fold to 3-fold more radioactivity was associated with LSECs than with hepatocytes. The importance of hepatocytes and LSECs was confirmed by immunohistochemical staining; strong staining was seen in LSECs, and less intense, punctate staining in hepatocytes. Minor staining in KCs was observed. Comparable anatomical and hepatocellular distributions were observed with rFVIII and FVIII-Y1680F, and the presence of the VWF fragment, D'D3A1, did not change the FVIII staining pattern in intact livers. Conclusions The present data support FVIII clearance via the liver, with hepatocytes and LSECs playing a key role. High-affinity VWF binding did not alter the anatomical or hepatocellular distribution of FVIII.

Recent findings on the structure and function of teleost IgT

As key effector molecules of jawed vertebrate's adaptive immune system, immunoglobulins are produced by B lymphocytes, either as a secretory form (antibody) or as a membrane form (B cell receptor). Until recently, teleost fish B cells were thought to express only two classes of immunoglobulins, IgM and IgD. In addition, IgM in these species was thought to be the only immunoglobulin isotype responding to pathogens both in systemic or mucosal compartments. However, the unexpected discovery of IgT, a new teleost immunoglobulin unearthed in 2005, has provided for new opportunities to analyze further roles of teleost immunoglobulins in these two physiologically distinct compartments. The smoke about the potential function of IgT has cleared recently with the finding that this immunoglobulin appears to be specialized in gut mucosal immunity. Significantly, the new capability of measuring not only IgM but also IgT responses will greatly facilitate the evaluation and understanding of fish immune responses as well as the protective effects of fish vaccines. The purpose of this review is to summarize the molecular characterization of new IgT orthologs and subtypes in teleosts, as well as to describe the new findings concerning the protein structure of IgT, the B cells producing it, and its role in mucosal immunity.

Duck immunoglobulins: structure, functions and molecular genetics

Four types of immunoglobulin (Ig) have been identified in ducks: IgM, a secretory Ig resembling IgM, a 7.8S IgG, and a 5.7S IgG. Structurally and antigenically the 5.7S IgG resembles an F(ab')2 fragment of the 7.8S IgG. When ducks mount serum antibody responses, the sequence of Ig involvement is IgM --> 7.8S IgG --> 5.7S IgG. Although serum Ig levels increase, and antigen-binding Igs can be demonstrated, sera from repeatedly immunized ducks commonly lack secondary antibody activities such as agglutination, precipitation, complement fixation and tissue sensitization. These deficiencies are most likely attributable to the absence of functionally important components of the predominant Ig (5.7S IgG) and/or a possibly unusual steric structure of duck Igs. A related issue concerns production of the two antigenically related IgGs: what are the cellular and molecular events involved, and how are they controlled? Evidence from current molecular genetic studies has confirmed the similarity of the VH, CH1 and CH2 domains of the 7.8S and 5.7S IgGs and shown, by virtue of the existence of separate mature messages for the heavy (H) chains of these molecules, that they are biosynthesized independently. Models for the possibilities that the two H chains are products of one gene or of two genes are presented. Cloning and sequencing the duck H chain gene locus, which is in progress, is providing data supporting the one gene hypothesis. The results obtained from cDNA sequencing also confirm that the duck IgGs are unusual in terms of the anatomy of the hinge region and of the number and location of intra- and inter-chain disulphide bonds, observations which will be of importance for understanding structure/function relationships of these unusual and interesting molecules.

Differentiation and homing of IgA-secreting cells

Most antibody-secreting cells (ASCs) in mucosal tissues produce immunoglobulin A (IgA), the most abundant immunoglobulin in the body and the main class of antibody found in secretions. IgA-ASCs differentiate in the mucosal-associated lymphoid tissues and are usually considered as a homogeneous population of cells. However, IgA-ASCs that travel to the small intestine have unique characteristics in terms of their migratory requirements. These IgA-ASCs require the homing molecules alpha4beta7 and CCR9 to interact with their ligands, mucosal addressin cell adhesion molecule-1 and CCL25, which are constitutively expressed in the small intestine. Indeed, recent work has shown that IgA-ASCs specific for the small bowel are generated under different conditions as compared with IgA-ASCs in other mucosal compartments. Moreover, the mechanisms inducing IgA class switching may also vary according to the tissue where IgA-ASCs differentiate. Here we describe the mechanisms involved in the differentiation of IgA-ASCs in mucosal compartments, in particular those involved in the generation of gut-homing IgA-ASCs.

IgA responses in the intestinal mucosa against pathogenic and non-pathogenic microorganisms

IgA is the most abundant immunoglobulin produced in mammals; most is secreted as a dimer across mucous membranes. This review discusses the different mechanisms of induction of IgA, and its role in protecting mucosal surfaces against pathogenic and non-pathogenic microorganisms.

Protection against Fasciola hepatica in the intestine is highly correlated with eosinophil and immunoglobulin G1 responses against newly excysted juveniles

Rats were infected with Fasciola hepatica and challenged at regular intervals up to 38 weeks using an ex vivo gut loop, a technique developed in our laboratory. The kinetics of the observed immune responses against F. hepatica in gut tissue and serum were investigated and correlated to protection. Immunohistochemical methods were used to measure the frequency of eosinophils, immunoglobulin (Ig)E-positive cells, and mucosal mast cells in the gut loop, and to determine whether the newly excysted juveniles were coated with IgG antibodies or surrounded by eosinophils, or both. Enzyme-linked immunosorbent assays and a radioimmuno assay were used to measure serum antibody reactive with newly excysted juveniles. Results showed that protection was highly correlated with the frequency of eosinophils and IgE-positive cells in the gut, but was only moderately correlated with the frequency of mucosal mast cells. Newly excysted juveniles taken from rats exhibiting high levels of protection were always coated with IgG antibodies and surrounded by eosinophils. Protection was highly correlated with titers of serum IgG1 antibodies directed against newly excysted juveniles, but was only weakly correlated with titers of serum IgA and IgE antibodies. Because protection was highly correlated with IgG1 in gut tissue and serum, and with eosinophils in gut tissue, we suggest that IgG1 and eosinophils are important in protecting rats against F. hepatica.

Cytokine mRNA expression in lymphoid organs associated with the expression of IgA response in the rat

The T-helper dependency of the IgA antibody response has been investigated in rats injected intravenously with Schistosoma mansoni eggs. This method, allowing the trapping of parasite eggs in the lung tissue, led to a strong anti-egg IgA antibody response in the bronchoalveolar lavage but not in the serum. To characterize the cytokine pattern associated with the IgA response, kinetic analysis of the cytokine mRNA expression in the lungs, periaortic nodes (PN) and spleen was undertaken. Under such conditions, significant levels of mRNA encoding IL-5 and IL-10 were recorded in spleen during the early period following egg injection, as well as a more prolonged expression of TGF-beta and IL-6 mRNAs. However, neither IFN-gamma nor IL-4 mRNA could be detected in these samples. Finally, in lungs and in PN, RT-PCR analysis revealed delayed production of cytokine mRNA. Taken together our data suggest that the rat mucosal IgA antibody response is predominantly linked to a Th2 response.

Synthesis of secretory component by rat hepatocytes in culture

Normal rat hepatocytes were isolated and cultivated in vitro. Synthesis of secretory component was demonstrated by its accumulation in the culture medium, as measured by radioimmunoassay; by incorporation of 14C-leucine in the protein specifically precipitated with anti-secretory component antiserum; and by a positive precipitin reaction of concentrated culture medium with the same antiserum. The results explain the high levels of secretory component found in rat bile and render plausible a mechanism of hepatic IgA transfer involving secretory component as the hepatocyte membrane receptor for polymeric IgA.

Antibody against the human J chain inhibits polymeric Ig receptor-mediated biliary and epithelial transport of human polymeric IgA

To emphasize the requirement for a J chain in native polymeric immunoglobulins for their selective transport into exocrine secretions, IgG, purified from two different antisera specific for the human J chain, was shown to: (i) bind in vitro to human polymeric IgA (pIgA) by density gradient ultracentrifugation; (ii) inhibit binding in vitro of rat secretory component to human pIgA; (iii) inhibit hepatic transport of human pIgA into rat bile in vivo; and (iv) inhibit apical transcytosis of pIgA in vitro by polarized human polymeric immunoglobulin receptor (pIgR)-expressing Madin-Darby canine kidney cells. Inhibition of biliary transport increased with the molar ratio of anti-J chain antibodies against pIgA and their incubation time. Anti-J chain F(ab')2 and Fab fragments also inhibited biliary transport, excluding a role for phagocytic clearance or excessive size of the immune complexes. Anti-human-Fc alpha Fab, bound to human pIgA in complexes of larger size than those with anti-J chain Fab, did not inhibit biliary transport of human pIgA. Propionic acid-denatured human pIgA, although containing J chains, was very poorly transported into rat bile. Altogether, our data strongly support, now also by in vivo experiments, the crucial role of the J chain of native pIgA in its selective pIgR-mediated transport into secretions, as suggested long ago by in vitro data only. Recent data on J chain-knockout mice, with low IgA levels in bile and feces, cannot explain the role of the J chain in contributing to the secretory component/pIgR-binding site of normal pIgA, but otherwise agree with our study.

Influence of fatty acid absorption on bidirectional release of immunoglobulin A into intestinal lumen and intestinal lymph in rats

Effects of absorption of long and middle chain fatty acids on IgA secretion into the intestinal lumen and intestinal lymph and the factors which evoke changes in IgA secretion during the absorptive process were examined in rat small intestine. Bidirectional secretion of IgA from the intestinal mucosa into the intestinal lumen and intestinal lymph was continuously observed in the control condition. Perfusion of oleic acid (a long-chain fatty acid) micelle into the jejunal loop induced a significant increase in IgA output into the intestinal lymph. In contrast, lymphatic output of IgA was significantly decreased when oleic acid micelle was administered intraduodenally. Absorption of octanoic acid, a middle-chain fatty acid, did not produce any significant changes in IgA output into either direction. CR1505, a CCK-receptor antagonist, significantly attenuated the oleic acid-induced increase in IgA secretion into the intestinal lumen, but did not affect the oleic acid-induced decrease in lymphatic IgA secretion. Pluronic L-81, an inhibitor of chylomicron formation and secretion, significantly attenuated the decrease in IgA output into the intestinal lymph during oleic acid absorption without affecting the luminal IgA output. The rate of release of IgA into the intestinal lumen is stimulated by absorption of long-chain fatty acids possibly through the influence of locally released CCK, while the transport process of IgA into lymphatics is controlled by a different mechanism which is closely correlated with the intracellular formation and secretion of chylomicron.

Soluble glycoprotein D blocks herpes simplex virus type 1 infection of rat eyes

Herpes simplex virus type 1 (HSV-1) ocular infection in rats was blocked by treating the eyes with UV-inactivated virions containing glycoprotein D (gD) prior to ocular challenge. In contrast, rats treated with UV-inactivated virions lacking gD were not protected. A soluble, truncated form of HSV-2 gD (gD-2t) also protected against ocular infection. Treatment with gD-2t not only reduced mortality but also restricted progression of pathology and reduced the amount of viral antigen in the cornea. Host antibody or alpha/beta interferon responses to the gD-2t treatment were not detected. These results are similar to those observed in cell culture (D. C. Johnson, R. L. Burke, and T. Gregory, J. Virol. 64:2569-2576, 1990). The in vivo effect of exogenous gD is consistent with blocking of a cell surface gD receptor or with an inhibitory interaction of gD with virions.

Further evidence that hepatic sources confer biliary antibody in the rat

The notion that bile-dedicated antibody is made within the liver by migratory antibody-forming cells (AFC) was examined further in rats. Livers from immunized animals were removed to perfusion in isolation so that plasma influences on bile antibody would be obviated. Antibody was secreted for at least 5 hr by the livers of rats that had received intravenous (i.v.) or intra-Peyer's patch (IPP) immunization with horse erythrocytes. After initially declining, the titres stabilized at 5-8% of the starting value for IPP-immunized rats and at 0.8% for i.v.-immunized animals, levels that were then sustained. In other experiments, the biliary antibody output was measured in immunized rats in the period immediately following splenectomy, an expedient that would deny the liver any newly formed AFC. Splenectomy during spleen-based, IgM antibody responses led to bile titres falling, over about 12 hr, to 21% of initial values. This level was then maintained for at least another 12 hr. Serum titres over this period remained static. Lastly, the bile ducts of immunized rats were ligated to test whether locally made antibody that was destined for bile could be forced instead to reflux to blood. Biliary obstruction during IgM responses to horse erythrocytes and pneumococcal polysaccharide, type 3, was found to raise significantly serum antibody titres. For pneumococcal polysaccharide, the serum response was also noticeably prolonged. These findings are consistent with the biliary antibody of immunized rats being constituted, in part, from local sources and not from plasma alone.

Biliary immune response to orally presented food antigen, ovomucoid, and its potentiation by cholera toxin B subunit

To clarify the biliary immune response against food antigen, we studied biliary antibody response to intravenous and oral primary immunization with ovomucoid (OM) and the effects of cholera toxin B subunit (CTB) on the oral response in mice. Specific antibodies against OM were induced in biliary and serum immunoglobulin (Ig) A, IgG and IgM by intravenous (i.v.) administration of the antigen. However, the antibodies were induced only in biliary Igs, but not in serum Igs, by oral intubation of the antigen. The higher levels of anti-OM in bile than in serum observed in the oral group may favour the assumption that antigen-stimulated lymphoid cells migrate to the liver, gall bladder or bile duct where they produce antibody. Both serum and biliary anti-OM responses to oral immunization were potentiated remarkably by oral administration of CTB with the antigen, the IgM anti-OM response being potentiated to the largest extent. In the CTB-treated mice, the IgA anti-OM level was higher in bile than in serum. Serum level of IgG anti-OM was much lower in the CTB-treated mice than in the i.v.-immunized mice, but the biliary level of IgG anti-OM in the CTB-treated mice was comparable to that in the i.v.-immunized mice. The relationship between serum and biliary IgA and IgG antibodies suggests that CTB potentiates biliary anti-OM responses not solely through increasing systemic levels of the antibodies but through modulating the processes specific to mucosal presentation of antigen.

The fate of aggregated immunoglobulin A injected in IgA nephropathy patients and healthy controls

Organ uptake of IgA-containing immunologically active material was studied in humans by intravenous (IV) injection of 131I-labeled heat-aggregated human secretory IgA (HAS-IgA) in nine patients affected by primary IgA nephropathy and 10 normal volunteers. Aggregated secretory IgA was found to be removed almost exclusively by the liver. The peak activity in liver was reached at 21.1 minutes (range, 18 to 26 minutes) in patients and 19 minutes (range, 14 to 22 minutes) in controls. The rate of increase of liver radioactivity was found to be significantly slower in patients (with a mean slope of 5.0; range, 3.4 to 7.1 v 7.6, 5.6 to 11.4; P less than 0.02). The mean liver to precordium ratio at the peak time was significantly lower in patients (mean value, 2.3; range, 1.9 to 3.1) compared with controls (mean value, 3.3; range, 2.4 to 4.0) (P less than 0.02). These data confirm the pivotal role of the liver in the removal of aggregated IgA in humans and the defective clearance capacity of this test probe in IgA nephropathy patients.

In vivo adjuvant effect of interleukins 5 and 6 on rat tear IgA antibody responses

Interleukins 5 and 6 have previously been shown to exhibit IgA-enhancing activity in vitro. This study investigated the effect of IL-5 and IL-6 on antigen-specific tear IgA antibody responses in vivo. Rats were given primary and secondary immunizations by the ocular-topical (OT) route with either antigen (DNP-Pn) alone or antigen plus IL-5 and IL-6 (IL-5/6). Antigen was administered for the first 3 days of each stimulation cycle and lymphokines (50 units of each lymphokine/eye/day) or control media for the first 7 days of the primary and secondary immunizations. Co-administration of antigen with IL-5/6 markedly enhanced (approximately three-fold) the secondary tear IgA anti-DNP antibody response in the lymphokine-treated group. Enhanced tear IgA antibody responses were maintained in the lymphokine-treated group following a tertiary immunization in the absence of IL-5/6. There was no apparent effect on the total tear IgA levels in either group of animals. Ocular topical immunization also elicited secondary and tertiary serum IgG antibody responses which were not affected by the administration of IL-5/6. Neither secondary nor tertiary serum IgM antibody responses were detected in either group of animals. These data indicate that IL-5 and IL-6 are able to augment tear IgA antibody responses in vivo. That the enhancement was maintained following a subsequent antigenic challenge in the absence of the lymphokines suggests a potential therapeutic application for lymphokines in augmenting IgA responses at mucosal surfaces.

IgA antibodies in the bile of rats. V. Primacy of the GALT as a source of IgA

In each of a series of rats the common bile duct and the thoracic duct (cisterna chyli) were cannulated so that both bile and thoracic duct lymph could be collected quantitatively for several hours. The concentrations of IgA in samples of lymph and bile were measured by radioimmunoassay so that the output of IgA per unit time could be calculated. Although the output of IgA in the lymph did not decline significantly, the output in the bile fell so that by 2 hr it had been reduced to less than 20% of the peak value. Similar experiments in rats which had been immunized actively by injecting antigens into the GALT showed a corresponding rapid decline in titres of specific biliary antibodies after fistulation of the thoracic duct. The low levels of IgA in the bile of rats that had been drained of thoracic duct lymph were restored quickly to normal values by the intravenous infusion of a volume of thoracic duct lymph equal to that which had been lost; this restoration was transient, and the concentration of IgA in the bile soon declined again after the infusion ceased.

Carboxy-terminal peptides from the B subunit of Shiga toxin induce a local and parenteral protective effect

Two synthetic peptides corresponding to overlapping sequences from the C-terminus of the B chain of Shiga toxin were prepared and characterized. These peptides consisted of residues 54-67 and 57-67 in the protein sequence. This region coincides with the major peak of surface area residues, as predicted from a computer-derived plot. For the purpose of immunization, the peptides were either conjugated with a protein or a synthetic carrier, or were polymerized. Polyclonal antibodies against these peptides derivatives, induced in rabbits, recognized the homologous peptides and cross-reacted with the intact toxin. These antibodies were capable of neutralizing the various biological activities of the toxin, namely the cytotoxic, enterotoxic and neurotoxic activities. Active immunization of mice with the peptide derivatives protected them from the lethal effect of the toxin. Moreover, oral immunization of rats led to inhibition of fluid secretion in ligated ileal loops into which toxin was injected. This effect was paralleled by the induction of high levels of specific anti-peptide IgA antibodies in the serum after bile duct ligation.

Effect of thermal injury in the rat on transfer of IgA protein into bile

Severe thermal injury is associated with bacterial sepsis; the intestine is considered a likely source of invasive organisms. Because IgA antibody in bile accounts for much of the specific immune defense of the upper intestinal tract in the rat, the effect of thermal injury on the quantity of IgA protein in bile was examined. Sprague-Dawley rats received a 20% to 30% body surface area burn under anesthesia. Eighteen hours later the common bile duct was cannulated and bile was collected for three hours. Total IgA protein in bile decreased 90% after thermal injury. The bile volume, the concentration of bile protein, and free secretory component did not change significantly. Although blood flow to the liver 18 hours after thermal injury was not changed, there was a significant reduction in total IgA concentration in the circulation; both monomeric (m-IgA) and polymeric IgA (p-IgA) were decreased. This finding may explain, in part, the reduced concentration of IgA protein in bile. Although not examined in this study, decreased local hepatic synthesis and/or transport of p-IgA across the hepatocyte may also contribute to the reduced IgA levels in bile.

Defective hepatic handling of IgA immune aggregates by mice with experimental IgA nephropathy

In an experimental model of IgA nephropathy induced in mice by chronic immunization with dextran, we tested the hypothesis that a defect in the hepatic handling of IgA could be an important determinant in the deposition of IgA in the mesangium. In mice injected with 1-16 doses of 1 mg of dextran (after a preimmunization period of 21 days) the blood clearance of IgA immune aggregates was significantly delayed in relation to control animals, becoming normal at 24 injections. This alteration seems specific since the clearance of IgG aggregates was normal. The percentage of isolated hepatocytes with Fc receptors for IgA decreased significantly over the whole period of dextran immunization. The binding rate of 125I-IgA aggregates to hepatocytes of mice with 24 dextran injections was twice lower than that of control animals. By contrast, the percentage of Kupffer cells with IgA receptors increased over ensuing dextran injections. A progressive increase in the IgA blood levels and in the percentage of mice with mesangial IgA deposits was seen along the period of study. At 24 injections most animals presented moderate to intense mesangial proliferation and abundant electron-dense deposits. On the whole, these data suggest that the early impairment in the liver IgA clearance capacity observed in these animals could facilitate the presence of circulating immune complexes (IC) and their deposition in the mesangium. The increase in serum IgA, seen thereafter, together with the normalization of the IgA clearance capacity, suggest that other pathophysiological mechanism(s) (e.g. in situ IC formation or IgA polymers deposition) must also be involved in this model of experimental IgA nephropathy.

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)

Mucosal IgA elaboration

Secretory IgA is the main immunoglobulin present along mucosal surfaces. It is elicited best by oral rather than parenteral administration of specific antigens. The role of antigen form on the development of a secretory IgA response is still unclear. IgA protects by preventing attachment of microorganisms or their toxic products to the surface epithelium. A wide variety of regulatory T cells are now known to be of considerable importance in optimizing the secretory IgA response. This regulation is at least partly due to the elaboration of small polypeptide products (lymphokines). These lymphokines have been shown to be key signals during the maturation of IgA precursor B cells to IgA-secreting plasma cells. By studying models of the mucosal immune system which closely approximate the natural mucosal immune response, it should be possible to develop vaccines against many pathogenic microorganisms, their toxic products, and to toxicants and carcinogens within the environment.

The role of the liver in translocation of IgA into the gastrointestinal tract

The liver plays a key role in the translocation of IgA into the upper gastrointestinal tract. The amount of IgA transported and the mechanisms involved, however, vary widely among species. In some, best defined in the rat, large amounts of polymeric IgA (pIgA) are cleared from the plasma by hepatocytes, which synthesize the polymeric immunoglobulin receptor, secretory component (SC), and express it on their sinusoidal plasma membranes. Circulating pIgA binds to SC, is internalized into endocytic vesicles and transported across the hepatocyte to the bile canalicular membrane, where the pIgA is released into bile in complex with a portion of the SC, i.e., secretory sIgA (sIgA). In some other species, including man, there is much less hepatic transport of circulating IgA, at least in part because SC is present only in biliary epithelium, and there is relatively more local synthesis of IgA within hepatobiliary tissues. On the other hand, certain IgA1 myeloma proteins appear to bind to and enter human hepatocytes via an asialoglycoprotein receptor. These species differences have implications for the biological significance of the biliary secretion of IgA, including the disposal of circulating IgA-antigen complexes into bile.

Synthesis and biliary secretion of immunoglobulins by rat liver

In this manuscript, we have attempted to first present an overview of the fundamentals of IgA secretion into rat bile via a receptor mediated process which involves the formation of vesicles and their vectorial movement to the bile canaliculus by a microtubule network. This transcellular pathway is used by all IgA secreting cells. The process is unique in that the transport vesicles do not pass through the Golgi-lysosomal region of the cell and therefore the ligand is allowed to enter the secretions intact with a portion of its receptor providing protection against proteases in the external environment. We also have demonstrated that the liver provides an early response to intestinal luminal antigen presentation. Stimulated B cells that are produced in the Peyer's patches in rodents home first to the liver. Only after boosting and the establishment of long term immunity are specific antibody producing cells found in other organs such as the intestine. Data are presented which would suggest that non-receptor mediated Ig transport into bile is by passive transport across tight junctional complexes between liver cells and by fluid phase vesicles. This observation may account for the small but consistent amount of IgA and IgG unattached to receptors that are found in the bile in humans. Exciting new evidence would indicate that the tight junctions can be made leaky by modifications in the hormonal environment. These observations may have wide range implications for understanding of how a variety of compounds enter the external secretions.

Different origins of IgA antibodies with various antigen specificities appearing in rat bile

Eight lactating and seven non-lactating female rats were immunized in Peyer's patches (Pp) with Escherichia coli 06 carrying type 1 pili. Eight days later the thoracic duct was drained and bile was collected at the same time. During the lymph drainage in the lactating rats, the biliary IgA anti-pili antibodies decreased less than the anti-lipopolysaccharide (LPS) antibodies. The non-lactating rats showed only a very small difference in decrease between the anti-pili and the anti-LPS antibodies. Transfer of mesenteric lymph node cells from male donor rats immunized with the E. coli strain to syngeneic male recipients resulted in the appearance of both IgA anti-pili and anti-LPS antibodies in the bile. This is at variance with the results seen in lactating rats, where only biliary IgA anti-LPS is seen after similar cell transfer. In conclusion, the study shows that in lactating rats a larger proportion of biliary IgA anti-pili antibodies than anti-LPS antibodies is derived from extraintestinal sites, such as the mammary glands or the liver. Thus, this study confirms that the nature of the antigen influences the transfer of the secretory antibody response to different secretions.

Role of hepatocytes in the uptake of IgA and IgA-containing immune complexes in mice

The role of parenchymal and nonparenchymal mouse liver cells in the uptake of polymeric IgA (pIgA) and pIgA-containing immune complexes (IC) of low mol. wt (less than 1 x 10(6)) was studied. As detected by immunofluorescence and immunoelectron microscopy, pIgA were bound on the surface of isolated hepatocytes. Following the injection of radiolabeled pIgA or pIgA-IC into mice, the total radioactivity recovered from isolated liver cells was preferentially associated with parenchymal cells. The ability to inhibit the transport of pIgA and pIgA-IC by pIgA of an irrelevant specificity suggests that pIgA-IC and pIgA are bound and transported by the same mechanism. These results indicate that mouse hepatocytes are involved in the uptake and hepatobiliary transport of pIgA and pIgA-IC of low mol. wt.

Contribution of hepatic reticuloendothelial system to glomerular IgA deposition in rat liver injury

Liver damage was induced in rats by a single dose of dimethylnitrosamine or D-galactosamine. In the dimethylnitrosamine model, marked glomerular IgA deposition occurred between Days 4 and 28, with its peak at Day 14. Serum IgA levels were significantly increased at Days 2 and 4, then gradually decreased, and normalized at Day 14. In the D-galactosamine model, however, no such deposition was observed, though serum IgA levels similarly increased on Days 2 and 4. IgA content in high molecular weight fraction from serum increased at Day 3 in both models. This increment remained at Day 7 only in the dimethylnitrosamine model, in which carbon clearance from the circulation was significantly decreased at Day 3. These data suggest that dysfunction of the hepatic reticuloendothelial system is a factor contributing to glomerular IgA deposition occurring in liver injury.

Investigation of endosomal compartments involved in endocytosis and transcytosis of polymeric immunoglobulin A by subcellular fractionation of perfused isolated rat liver

1. A gamma camera was used to monitor continuously the uptake of radiolabelled polymeric immunoglobulin A (pIgA) into the rat body after intravenous injection. Uptake into liver was fast but, since the peak of liver labelling occurred only after 9-15 min, it was not sufficiently rapid to constitute a pulse dose. A perfused, isolated rat liver system was therefore established which could be given a single pass dose of pIgA; a variety of tests showed such livers remained viable for at least 3 h and could be subsequently fractionated on Ficoll and Nycodenz gradients with normal distributions of marker enzymes. 2. Subcellular fractionation at different times after a single pass dose of pIgA showed that whilst pIgA appeared sequentially in sinusoidal plasma membrane, light endosomes, dense endosomes, very dense endosomes and lysosomes as in vivo, the predominance of pIgA in the light endosome compartment disappeared much earlier than after injection in vivo of pIgA, presumably because this compartment was not being continuously loaded over the first 10-15 min. The time course of appearance of label in bile was unchanged. A large excess of unlabelled asialofetuin did not change these patterns, indicating that the asialoglycoprotein receptor was not involved. 3. Low doses of the microtubule agent colchicine reduced the proportion of pIgA reaching the bile, but subcellular fractionation of treated liver showed that distribution of label amongst liver fractions was little changed, although the overall liver pIgA content had increased. This would suggest that pIgA did not remain in the common compartment which could have supplied bile or lysosomes but rather flowed out of it as rapidly as in untreated liver but towards those compartments supplying the lysosomes. 4. Experiments with nocodazole, which reversibly disrupts microtubules, showed that very little of the pIgA taken into an inhibited liver appeared in the bile after nocodazole was removed 30 min later, even though a second dose of pIgA, given after nocodazole removal, appeared in bile with a normal time course. The first dose of pIgA must therefore have passed beyond the compartments competent to supply the bile before nocodazole was removed. Such compartments were undamaged since the second dose of pIgA appeared in bile normally. We therefore conclude that the bulk of pIgA must be supplied to the bile from light or dense endosomes rather than from very dense endosomes and lysosomes.

Antibody production in rats following ocular-topical or gastrointestinal immunization: kinetics of local and systemic antibody production

The kinetics of the anti-DNP antibody response to DNP-pneumococcus appearing in tears and bile (IgA) and serum (IgM and IgG) was examined in rats after the application of antigen either via the ocular-topical (OT) or gastrointestinal (GI) routes. It was found that IgA responses were obtained each time in tears after either OT or GI antigen doses given monthly for three months, but that the OT route gave rise to consistently higher tear antibody titres than the GI route of immunization. Comparable IgA responses were found in bile using either route. In serum a small primary IgM response was consistently obtained but the main antibody found was IgG, the timing and degree of response being about the same for both routes. When the adjuvants Avridine in liposomes or MTP-PE were added along with the antigen it was found that with either immunization route, the tear IgA response was much reduced compared to when no adjuvant was used; the serum IgG response was marginally increased when adjuvant was added. The effects of binding anti-DNP monoclonal IgA or IgG1 to antigen before immunizing via the OT route was also studied. It was found that the presence of immunoglobulin of either isotype in the complex caused an increase in the serum IgG response, but that the tear IgA response was diminished in rats receiving IgA/antigen complexes compared with those receiving IgG/antigen or antigen alone.

Biliary antibody response in rats infected with rodent Giardia duodenalis isolates

Using a sensitive ELISA, specific serum and bile anti-Giardia IgM and IgA responses were studied in rats infected with two strains of Giardia duodenalis: a rat isolate which produces a chronic infection and a mouse isolate which produces a self-limiting infection. Paired samples of serum and bile were collected from groups of DA (RT1avl) rats at various times during primary and secondary infections. Antibody responses to both organisms were similar. Only IgA anti-Giardia antibodies were detected in bile whereas both IgM and IgA antibodies were detected in serum. Biliary IgA antibody titres increased throughout the course of the primary infection and remained at high levels for at least 10 weeks. Biliary IgA titres increased 16-fold during the secondary infection with both isolates. Serum IgA anti-Giardia titres also increased but more slowly than the titres in bile. Serum IgM antibody responses were observed against both organisms during the primary and secondary infections. Trophozoites harvested from the intestinal lumen during primary infections were examined for surface-bound IgA by immunofluorescence microscopy. IgA was detected on 3% of trophozoites on day 7 after infection but on over 70% of trophozoites by the 10th day. The data demonstrate the occurrence of a secretory IgA immune response in rats infected with both G. duodenalis isolates, some of which is directed against surface antigens of the trophozoites.

Receptor-mediated binding and uptake of immunoglobulin A by human liver

We have studied the molecular mechanisms of the binding and uptake of secretory and serum immunoglobulin A (IgA) of both subclasses (1 and 2) and molecular forms (monomer and polymer) by the particulate fraction of human liver homogenate and by a human hepatoma cell line (HepG2). Inhibition by asialoorosomucoid and the requirement for the presence of calcium indicated that the binding of secretory IgA and polymeric IgA1 was mediated by the asialoglycoprotein receptor. Secretory component, which functions as a receptor for polymeric IgA in several animal species, was detected in the epithelial cells of bile ducts, but not in hepatocytes. Secretory IgA and all molecular forms and subclasses of serum IgA were bound by HepG2 cells, which do not express secretory component. The requirement for the presence of calcium, the presence of a terminal galactose residue in IgA, and the molecular weight of the major plasma membrane protein responsible for binding (41,700 daltons) indicated the involvement of asialoglycoprotein receptor. Immunoglobulin A proteins bound by HepG2 cells were endocytosed and catabolized.

Bile immunoglobulin of the duck (Anas platyrhynchos). II. Antibody response in influenza A virus infections

The capacity of the IgM-like bile immunoglobulin (IgX) of the duck (Anas platyrhynchos) to express antibody activity to H3N2 influenza A viruses, and the dependence of this activity on the co-existence of serum IgM antibodies were investigated. Ducklings infected orally and intranasally at 15-29 days of age with viruses isolated from different host species were examined for haemagglutination-inhibiting (HI) antibodies in biles and sera 16-29 days after infection (p.i.). All biles had antibodies associated with IgX; all sera had antibodies associated only with the 7.8S IgG. Following oral infection of birds 42-days-old with influenza A/duck/HK/7/75 virus, serum HI antibodies were an initial IgM response occurring from 5-12 days p.i., followed by the appearance of 7.8S IgG antibodies. Virus-neutralizing (VN) antibodies in serum were also biphasic; isotype classification was not attempted. Bile IgX developed HI and VN activity. HI antibodies reached peak titres 12 days p.i. and fell to low levels by 24 days p.i. VN antibodies also reached peak titres 12 days p.i., but thereafter persisted at quite high levels throughout the experiment. Development of high titres of antibody in bile coincided with the termination of virus excretion in faeces. These experiments confirm that bile IgX of the duck can function as antibody in response to influenza A viruses, and that its activity appears to be independent of serum IgM. Its possible relevance in determining survival of virus in the intestine is discussed.

Specific antibody synthesis and biliary secretion by the rat liver after intestinal immunization with cholera toxin

This study was designed to investigate the location, specificity, and significance of antibody-containing cells in the liver. After intestinal administration of cholera toxin, high numbers of specific antibody-containing cells appeared in the liver during the early priming period and after boosting. In contrast, a significant number of specific antibody-containing cells appeared in the lamina propria of the intestine only after boosting. In the liver, the specific antibody-containing cells were predominantly located in the sinusoidal region of zone 1 of the liver lobules. About 80% of the specific antibody-producing cells in the liver synthesized anticholera toxin antibody of the immunoglobulin A class. During the priming period, the concentration of immunoglobulin A anticholera toxin in bile paralleled the increase and decrease in the number of specific antibody-containing cells in the liver. Liver perfusion experiments indicated that during the priming period at least 70% of the biliary immunoglobulin A anticholera toxin antibody was synthesized within the liver, whereas 30% was synthesized in the liver after boosting. Thus, during the early immune response, the liver seems to be the major source for specific biliary antibody to intestinally administered cholera toxin.

Rapid subcellular fractionation of the rat liver endocytic compartments involved in transcytosis of polymeric immunoglobulin A and endocytosis of asialofetuin

The distributions of two endocytosed radiolabelled ligands (polymeric immunoglobulin A and asialofetuin) in rat liver endocytic compartments were investigated by using rapid subcellular fractionation of post-mitochondrial supernatants on vertical density gradients of Ficoll or Nycodenz. Two endocytic compartments were identified, both ligands being initially associated with a light endocytic-vesicle fraction on Ficoll gradients, asialofetuin then accumulating in denser endosomes before transfer to lysosomes for degradation.

Secretory component-dependent binding of immunoglobulin A in the rat, monkey and human: a comparison of intestine and liver

The source and significance of immunoglobulin A in bile remains controversial. In the rat, and several other species, immunoglobulin A is transported through hepatocytes by a specific receptor, secretory component. In humans, immunohistochemical methods have indicated a distinct lack of receptors for immunoglobulin A on hepatocytes. Binding assays with 125I-immunoglobulin A and membranes from hepatocytes and intestinal cells of the rat display secretory component-dependent binding. Primate intestinal cells also show secretory component-specific binding of immunoglobulin A. Primate liver, on the other hand, does not show immunoglobulin A binding mediated by the polymeric immunoglobulin receptor.

Effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on IgA serum and bile levels in rats

Serum IgA is actively transported from blood to bile against a concentration gradient in the liver by the binding of dimeric IgA to secretory component, endocytosis and transport to the bile canaliculus by vesicles. As 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) has been shown to elicit hepatotoxicity, the effects of TCDD on rat serum and bile IgA levels were investigated. Rats were orally administered 50 micrograms TCDD/kg body weight in 95% corn oil: 5% acetone. At days 5, 10, 15, 20 and 30 after treatment, rats were anesthetized and a cannula inserted into the bile duct for collection of bile. In addition, blood was drawn, and, after euthanasia, the liver and thymus weights were recorded. Enzyme-linked immunosorbent assay (ELISA) techniques were employed to determine IgA in serum and bile and IgG levels in serum. Rocket immunoelectrophoresis was carried out to support ELISA results. It was found that serum IgA increased with time while serum IgG remained unchanged. In addition, while serum IgA levels were increasing, there was a concomitant decrease in biliary IgA. Thymus and liver weight changes were also observed. The data indicate that TCDD affects hepatic clearance of serum dimeric IgA and suggests that liver damage may be reflected by increased serum levels of IgA.

IgA deposition in alcoholic liver disease

Immunoglobulin deposition in alcoholic and non-alcoholic liver disease was studied using an indirect immunoperoxidase technique. A continuous pattern of IgA deposition, with IgA outlining the sinusoids, was shown to be a specific and sensitive marker for liver disease caused by alcohol in both cirrhotic and non-cirrhotic livers. The sensitivity was lowest in cases of alcoholic disease showing fatty change alone. In one case it was possible to show the absence of IgA in liver disease caused by a drug, which was histologically indistinguishable from alcoholic hepatitis.

Dimeric mouse IgA is transported into rat bile five times more rapidly than into mouse bile

The kinetics of the biliary dimeric IgA transport in rats is well documented from studies on animals with cannulated bile ducts, while in mice such information rests on the analysis of samples periodically removed from the gall bladder and on serum disappearance rates. We have quantitatively compared the kinetics of IgA transport in these two rodents by using affinity-purified radiolabelled monomeric and dimeric M315 IgA which specifically binds dinitrophenyl (DNP). Bile collection procedures, sample analysis, and administration of the radiolabelled M315 were the same for both species, although in mice the cystic duct was ligated to prevent reflux of any bile or IgA from the gall bladder into the common bile duct. A pronounced selection for transport of dimeric M315 was seen in both species. When dimeric M315 was administered, it was recovered in the dimeric form from the bile of both species, and 60-80% could specifically bind to DNP-gelatin. When monomeric M315 was administered, very little was transported, and the IgA recovered in bile had a much lower capacity to bind DNP-gelatin and appeared to be of low molecular weight. Approximately 60% of the intravenously administered dimeric IgA was transported into bile of both species but biliary transport of the heterologous dimeric IgA into rat bile was five times more rapid than the transport of the dimeric M315 into its homologous species, the mouse. Hence, IgA transport in these species is similar in specificity, integrity of the transported IgA and in the percentage cleared, while differing significantly in the rate of transport. This cannot be ascribed to the species source of the IgA.

Antibodies to Escherichia coli and anti-adhesive activity in paired serum, hepatic and gall bladder bile samples

Human bile contains a mixture of immunoglobulins excreted through the liver and produced in the biliary tract. This study examines the specific antibody activity of the biliary immunoglobulins against Escherichia coli antigens. Paired samples of serum, hepatic bile, and gall bladder bile were obtained from 23 patients with gallstones and five patients with healthy gall bladders. Antibody activity against E. coli antigens was found in all the sera and most of the bile samples. The levels of IgA, IgM, IgG, and secretory component (SC)-combined antibodies were lower in bile than in serum. Selective treatment of IgA by the liver was suggested by the finding of a correlation between the serum and the bile IgA antibody activity. IgG antibodies were only found in inflamed gall bladders. The bile was shown to have antibacterial activity against E. coli, i.e. an ability to inhibit the attachment to epithelial cells, but the inhibitory activity was not restricted to the immunoglobulin fraction of the bile.