In Vivo and in Vitro Binding of IgA to the Plasma Membrane of Hepatocytes

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Abstract
IgA bound in vivo was shown by immunofluorescence on the plasma membrane of isolated hepatocytes from subjects with normal liver and patients with liver cirrhosis, chronic active hepatitis or fatty liver. IgA in sera with elevated IgA concentrations, especially from cases with alcoholic cirrhosis, was bound in vitro to isolated hepatocytes from rabbit and mouse. This was not due to the high IgA concentration per se. Moreover, polyclonal polymeric serum-type and secretory IgA, and three often polymeric monoclonal IgA preparations, showed similar binding properties. Conversely, purified polyclonal and monoclonal monomeric IgA did not show affinity for the hepatocytes. The binding of polymeric IgA did not seem to depend on the proportion of dimers and larger polymers, κ or λ-type light chains, heavy-chain subclasses, content of J chain or affinity for secretory component. The in vivo binding of IgA by hepatocytes is probably a physiological phenomenon which in part may explain the normal clearance of polymeric IgA from serum.