Both Fc alpha domains of human IgA are involved in in vitro interaction between secretory component and dimeric IgA.

The sites of interaction between 125I labelled human secretory component (SC) and dimeric IgA were located by studying the inhibitory effect of various antibodies to IgA. Several Fab' fragments were isolated from three sera of hyperimmunized rabbits. The specificity of these different antibody preparations, as determined by a RIA inhibition test or by ELISA, showed that two were directed against both domains of Fc alpha, two against C alpha 2, two against C alpha 3 and one against Fd alpha. A monoclonal antibody against C alpha 3 was also used. The results indicate that both the C alpha 2 and C alpha 3 domains are equally and independently involved in the interaction between SC and dimeric IgA.