Mucosal immunity: The origin and migration patterns of cells in the secretory system (original) (raw)
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Demonstration of IgA and secretory component in human hepatocytes
Gut, 1980
By the immunoperoxidase technique, immunoglobulin A (IgA) was demonstrated in 50% ofhuman hepatocytes. The positively stained cells showed a tendency towards periportal clustering. Very few plasma cells were identified in the liver. The intrahepatocyte IgA is most probably derived from serum and on its way to the bile ducts. Secretory component (SC) had the same distribution as that of IgA.The presence of SC in the hepatocytes reflects either the synthesis of SC or the transport of pre-assembled SC-IgA by liver cells. The significance of transfer of IgA from serum into bile is as yet unknown. However, the transhepatic passage ofIgA may represent a reinforcement of local intestinal immunity, as part of the gut-originated IgA antibodies, which fail to go through the intestinal mucosa, may still gain access to the lumen of the gut.
The IgA system: a comparison of structure and function in different species
Veterinary Research, 2006
The predominant immunoglobulin isotype on most mucosal surfaces is secretory immunoglobulin A (SIgA), a polypeptide complex comprising two IgA monomers, the connecting J chain, and the secretory component. The molecular stability and strong anti-inflammatory properties make SIgA particularly well suited to provide protective immunity to the vulnerable mucosal surfaces by preventing invasion of inhaled and ingested pathogens. In contrast to SIgA, IgA in serum functions as an inflammatory antibody through interaction with FcαR on immune effector cells. Although IgA appears to share common features and protective functions in different species, significant variations exist within the IgA systems of different species. This review will give an overview of the basic concepts underlying mucosal IgA defence which will focus on the variations present among species in structure, antibody repertoire development, pIgR-mediated transport, colostral IgA content, hepatobiliary transport, and function with particular emphasis on the IgA system of the pig and dog. These interspecies variations emphasise the importance of elucidating and analysing the IgA system within the immune system of the species of interest rather than inferring roles from conclusions made in human and mouse studies. IgA / polymeric IgR / FcαR / mucosal antibodies / domestic animals Table of contents
Immunology, 2007
A detailed investigation of the binding of secretory component to immunoglobulin A (IgA) in human secretory IgA2 (S-IgA2) was made possible by the development of a new method of purifying S-IgA1, S-IgA2 and free secretory component from human colostrum using thiophilic gel chromatography and chromatography on Jacalin-agarose. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis of unreduced pure S-IgA2 revealed that, unlike in S-IgA1, a significant proportion of the secretory component was bound non-covalently in S-IgA2. When S-IgA1 was incubated with a protease purified from Proteus mirabilis the secretory component, but not the a-chain, was cleaved. This is in contrast to serum IgA1, in which the a-chain was cleaved under the same conditions -direct evidence that secretory component does protect the a-chain from proteolytic cleavage in S-IgA. Comparisons between the products of cleavage with P. mirabilis protease of free secretory component and bound secretory component in S-IgA1 and S-IgA2 also indicated that, contrary to the general assumption, the binding of secretory component to IgA is different in S-IgA2 from that in S-IgA1.
Hepatology, 2007
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 ~1 0 times more efficiently than albumin, as compared to 320 and 1060 times in rabbits and rats, respectively. (ii) Only ~1 % of an i.v. dose of ['261]pIgA is transported into bile over 8 hr in dogs, like in humans, as compared to -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 >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. (ii) Bile duct cells, despite their membranous SC, are much less efficient than hepatocytes to transport pIgA from plasma to bile. (iii) Dogs, but not rats and rabbits, provide a suitable experimental model for further studies on the relationships between the liver and the secretory IgA immune system in humans.