PSK, a polysaccharide from Coriolus vesicolor, enhances oxygen metabolism of murine peritoneal macrophages and the host resistance to listerial infection

PSK, a protein-bound polysaccharide isolated from the basidiomycete Coriolus vesicolor (Fr.) Quél. was examined with regard to its effects of macrophage (M phi) oxygen metabolism in mice, a function important for the expression of M phi antimicrobial activity. The O2(-)-producing ability and chemiluminescence (CL) of host peritoneal M phi s in response to phorbol myristate acetate were markedly elevated by preinjection of PSK (1 or 5 mg per mouse intraperitoneally) around 4-7d before M phi-harvest. The enhanced O2(-)-producing ability due to PSK injection persisted much longer than the enhanced CL, indicating a discrepancy in regulation of generation of active oxygen species such as O2-, H2O2, OH, and 1O2. Daily injections of PSK (1 mg per injection) from 10 to 4d before M phi harvest did not increase the efficacy of PSK over that given by a single 1 mg injection. When PSK (5 mg) was given intraperitoneally to mice in a single injection 10, 7 or 4d before the intravenous Listeria monocytogenes inoculation, a similar increase in the host resistance to the bacteria was noted regardless of the timing of the injection. Multiple PSK injections fron 10 to 4d before the infection also enhanced the host resistance, to the same degree. Therefore, PSK is thought to augment the host resistance to certain intracellular parasites including L. monocytogenes at least to some extent by enhancing oxygen metabolism of the host M phi.