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On the Nature of the Presumed Receptor for IgE on Mast Cells

I. The Effect of Sialidase and Phospholipase C Treatment on the Capacity of Rat Peritoneal Cells to Participate in IgE-Mediated, Antigen-Induced Histamine Release in Vitro

From the Department of Hypersensitivity Disease Research, The Upjohn Company, Kalamazoo, Michigan 49001

Abstract

The ability of sialidase and phospholipase C to interfere with the capacity of rat peritoneal cells to release histamine in an antigen-induced, IgE antibody-mediated manner was examined in some detail. Both enzymes cause a loss of histamine from the cells which is dependent on the concentration of enzyme employed. Although the loss of histamine from cells treated with phospholipase C ceases when the enzyme is removed by washing, loss from cells treated with sialidase persists for several hours after the free enzyme has been removed. Superimposed on this loss of histamine from enzyme-treated cells is the ability of both enzymes, under certain circumstances, to inhibit the capacity of the cells to release histamine in an antigen-specific manner after their preparation with IgE antibody. Attempts were made to test the hypothesis that this inhibition is a consequence of the destruction of a mast cell "receptor" for IgE by treatment with the enzymes. Phospholipase C does not appear to act on such a receptor since it was equally inhibitory to nonimmunologic histamine release caused by compound 48/80. Furthermore, treatment with this enzyme inhibited immunologic histamine release equally well when enzyme treatment preceded or followed preparation of the cells with IgE. By contrast, treatment with sialidase only inhibited histamine release when treatment with the enzyme preceded preparation of the cells with IgE, suggesting that it may act on the "receptor." However, the enzyme failed to inhibit histamine release initiated with IgGa antibody and antigen, a reaction which had previously been presumed to involve the same cell "receptor" as the one involved in the IgE-mediated reaction. Possible explanations for these findings are offered.