Induction of FcR alpha on murine lymphocytes by IgA in vitro.

The regulatory influence of IgA on the expression of Fc receptors specific for IgA (FcRα) on mouse spleen cells was studied. In normal BALB/c spleen cells, the proportion of FcRa-bearing (FcRα+) cells was less than 2%, determined by the rosette formation with IgA-coated sheep red blood cells (SRBC) or with trinitrophenylated (TNP) SRBC after incubation with soluble MOPC 315 IgA, which specifically binds with TNP. There was no marked increase of FcRα+ cells after 24-hr culture in IgA-free medium or treatment with acid pH (pH 5.0). When cultured with MOPC 315 IgA for 18 hr, there was a dose-dependent increase of the cells binding TEPC 15 IgA-coated SRBC as well as the cells forming rosettes with TNP-SRBC. Twenty to 30% of spleen cells expressed FcRα when cultured with 300 µg/ml IgA. The induced receptors bound both soluble IgA and IgA-coated SRBC, and proved to be specific for IgA by the inhibition with other isotypes. The induction of FcRα by IgA was inhibited by the inhibitors of RNA and protein synthesis (actinomycin, puromycin, cycloheximide), and required more than 8 hr of culture for the expression. Mytomycin (50 µg/ml) failed to inhibit the induction, indicating that proliferation of the cells is not required. FcRα was induced by dimer IgA but not by monomer IgA. Reduction of IgA with 0.02 M dithiothreitol resulted in the loss of inducing ability. However, reduced IgA competitively inhibited the induction of FcRα by nonreduced IgA and cytophilic binding of nonreduced IgA to the receptor. FcRα was induced by IgA on spleen cells depleted of adherent cells by Sephadex G-10 column passage. Both T and B lymphocytes were shown to express FcRα.