Streptococcal preparation as an activator of host-mediated immune response: cellular immunity and alternate pathway of complement.

Streptococcal preparation, OK-432, was examined for its ability to initiate a host-mediated immune response. Aged individuals with negative skin response to phytohemagglutinin (PHA), as well as reduced in vitro blastoid transformation of lymphocytes, were treated with OK-432, and the response to PHA appeared in two out of three cases. The preparation was also demonstrated to convert C3 proactivator of complement when incubated with fresh human serum, as tested by immunoelectrophoresis, indicating the possibility that OK-432 might activate the alternate pathway of complement.