Induction of the receptor for the Fc portion of IgA by secretory IgA on human T cell lines and T cell clones.

Human colostral secretory IgA (SIgA; predominantly present in dimeric of polymeric forms) induces receptors for the Fc portion of IgA (Fc alpha R) on cloned and noncloned human T cell lines. The binding of SIgA to its FcR was isotype specific, since it was not inhibited by IgG or IgM. Binding of SIgA was also not affected by ovalbumin asialoglycoprotein. In addition, SIgA blocked the binding of directly fluorescein isothiocyanate-labeled SIgA in a dose-dependent fashion, whereas IgG and IgM were ineffective, confirming the specificity of the binding. Expression of Fc alpha R was specifically induced by SIgA, whereas serum IgA (predominantly present in monomeric form) had no effect. In addition, IgG, IgM and IgE were ineffective. This induction of Fc alpha R by SIgA was dose dependent. Optimal induction was observed at concentrations of 500 micrograms/ml after incubation times of 48 h. Fc alpha R were predominantly induced on T cell lines and T cell clones derived from tonsils. T cell lines and T cell clones established from peripheral blood could only occasionally be induced to express Fc alpha R. Induction of Fc alpha R expression was obtained both with CD4+ and CD8+ T cell clones. Fc alpha R were readily induced on T cell clones tested up to 6 days after activation by alloantigen. T cell clones tested 10-12 days after alloantigen activation failed to respond to SIgA. These results indicate that the inducibility of Fc alpha R is related to the activation stage of the T cell clones.