Proteolysis of lymphocytic surface immunoglobulin.

Limited proteolysis of lymphocytic surface immunoglobulins in guinea-pig, rabbit and man was investigated by immunofluorescence using conjugated antisera specific for immunoglobulin fragments. The cell surface IgM of guinea pig L2C leukaemic lymphocytes and rabbit blood lymphocytes was cleaved in situ at its hinge region by papain. The Fcmicron fragment remained attached to the membrane and could be stained with the appropriate anti-Fc conjugate. The surface IgD and IgM of human chronic lymphocytic leukaemia cells was cleared from the cell surface by papain, as shown by reagents directed against both Fab and Fc region determinants. This could be due either to proteolytic degradation of membrane bound Fc or to initial cleavage of Ig from the membrane at some point other than the hinge region.