Modulation of membrane-bound enzyme activity by binding of antibodies to major histocompatibility complex antigens

The preparation of right side-out vesicles from mouse plasmocytoma plasma membranes can be used to study the early functionnal events of the plasma membrane upon binding of ligands. Activation of two membrane-bound enzymes, 5'-nucleotidase and Na+/K+ ATPase, induced specifically by several anti-H-2 antisera was investigated. A simultaneous stimulation of these two enzymes was reported at high dilutions of antisera directed against antigens of the MHC. Comparison between the enzyme activation test and the classical cytotoxicity test showed the former being more sensitive than the latter by at least one order of magnitude. A structural coordination between some histocompatibility antigens and/or other cell surface receptors and the membrane-bound enzymes could be envisionned for the initiation of lymphocyte activation.