Effect of E-64, a thiol protease inhibitor, on antibody formation in mice.

E-64, L-trans-epoxysuccinyl-leucylamido (4-guanidino) butane, a specific inhibitor of thiol proteases originally isolated from a culture broth of fungi, and its synthetic analogues, were examined for immune responses to the splenocytes of BDF1 mice. In the cultures of 2-day-primed splenocytes of the mice, E-64 and its close analogues, increased the number of direct splenic hemolytic plaque forming cells (PFC). In addition, it was demonstrated that E-64 enhanced the PFC responses in the mice. These results suggested that some thiol proteases might be involved in the immune response process in mice.