Enhancement of host immune response to cell surface antigens by a preparation of Streptococcus hemolyticus

A preparation (OK-432) of a low virulence strain, Su, of Streptococcus hemolyticus (Group A) has been found to possess 2 different effects on tumor cells: a) A direct pharmacological effect like other antitumor drugs, and b) an indirect effect through the enhancement of the host immune response. In order to examine the second effect, 2 different antigen systems were used, Gross (G) cell surface antigens (GCSAs) and the cell surface differentiation antigen PCl. At certain ages, untreated C57BL/6 and BALB/c mice occasionally produce natural antibodies to GCSAs and PCl, respectively. When the mice were injected intraperitoneally (i.p.) with OK-432 at 2 months of age, they produced natural antibodies to GCSAs or to PCl antigen, unlike untreated mice of the same strains at the same ages (negative controls), which produced no antibodies. The specificity of the antibodies was carefully examined by cytotoxicity tests. In addition, the activity of the natural antibodies was not neutralized with OK-432 itself. We have proven that OK-432 enhances the production of natural antibodies to specific cell-surface antigens.