An ultrastructural study of two different responses of mouse mast cells to transplantation antibodies directed against the same transplantation antigens.

The present paper describes an ultrastructural study of two different kinds of behavior of mouse mast cells during two immunological reactions induced by transplantation antibodies: the direct allogeneic anaphylactic degranulation and the serocytotoxicity. In both situations, the same alloantigens, born by the mast cells themselves, are the targets of the reaction, but the first one is mediated by anaphylactic alloantibodies whereas the second one is mediated by cytotoxic alloantibodies in the presence of complement. The comparison of the ultrastructural aspects of the cells in these two systems demonstrated that mast cells can behave in two different ways depending on the nature of the immunological agents utilized. First, a physiological degranulation process with active granule expulsion was observed. This process was shown to be identical to the one induced in classical in vitro anaphylaxis or by histamine releasers such as compound 48/80. A second type of behavior was a lethal, complement-dependent, cell lysis without active granule expulsion.