The specificity and properties of a novel IgA receptor expressed on the surface of a tissue culture-adapted B cell lymphoma, T560, that originated in murine gut-associated lymphoid tissue, have been explored. Like the IgA receptors of murine T and splenic B cells studied by others, the T560 IgA receptor is trypsin sensitive and neuraminidase resistant and is up-regulated on T560 cells by exposing them overnight to high concentrations of polymeric IgA. Unlike them, the T560 IgA receptor is inhibited by low concentrations of IgM and high concentrations of IgG2a and IgG2b, binds at pH 4.0 but not at pH 8.0, is down-regulated by activation of protein kinase C and is sensitive to phosphatidylinositol-specific phospholipase C, indicating that it is glycosyl phosphatidylinositol-linked to the cell membrane. It is not a cell-bound form of galactosyl transferase, does not appear to bind to Ig through carbohydrate residues and does not react specifically with antibody to secretory component. It may be a completely new, cross-reactive receptor, perhaps related in some way to the polymeric Ig receptor or to the receptor for IgA expressed on the apical surface of Peyer's patch M cells, which is known to cross-react with IgG. Alternatively, it may be homologous to the highly IgA-specific Fc alpha R of T cells but, perhaps because of its glycosyl phosphatidylinositol linker, may have an ability to move and interact with other Ig receptors on the cell surface such that Ig bound to them are cross-inhibitory.

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