The importance of the Fc receptors for IgA in the recognition of IgA by mouse liver cells: its comparison with carbohydrate and secretory component receptors.

The numbers of murine hepatocytes and Kupffer cells with receptors for human polymeric (pIgA) or monomeric IgA (mIgA) were determined by rosette formation with immunobeads coated with human pIgA or mIgA. About 63% of hepatocytes were found to express receptors for pIgA. Receptors for mIgA were also found in a significantly lower percentage of hepatocytes (50%). Only about 10% of Kupffer cells had this type of receptor. Blocking studies performed with purified human immunoglobulins suggested that both cells expressed a receptor that recognized the Fc portion of IgA (either pIgA or mIgA). In addition, murine multimeric MOPC-315 IgA strongly inhibited in a dose-dependent fashion the pIgA and mIgA rosette formation by both cells. When cells were incubated in the presence of a rabbit antiserum to secretory component (SC), only pIgA rosette-forming hepatocytes were partially inhibited. No such inhibition was seen when an antiserum to human IgG was used. Both galactose and mannose monosaccharides failed to inhibit the IgA rosette formation by either type of cell. These results show that murine hepatocytes, besides having SC receptors for polymeric IgA, also express receptors for the Fc portion of IgA. The carbohydrate receptors did not seem play any role in the recognition of IgA. The fact that Kupffer cells exclusively present Fc alpha R suggests that monomeric and polymeric IgA, either in form of immune complexes or not, are handled in a different manner by the liver cells.