Changes of antitumor immunity of hosts with murine mammary tumors regressed by lentinan: potentiation of antitumor delayed hypersensitivity reaction.

From 2 weeks after sc inoculation of MM46 mammary carcinoma cells into C3H/He mice, lentinan caused tumor regression, irrespective of its administration schedule (i.e., various doses and times of treatment, before and after tumor inoculation). The humoral and cellular immune responses of tumor-bearing mice with or without lentinan treatment were studied kinetically. From 2 weeks after tumor inoculation, antitumor antibodies (detected by macrophage-mediated or complement-dependent cytotoxicity assay) and LB (a serum protein) increased in tumor-bearing mice but the delayed-type hypersensitivity reaction against tumor (T-DHR) decreased. Lentinan restored and potentiated the T-DHR. The conditions under which lentinan is effective and the antitumor reactions responsible for tumor regression are discussed on the basis of these results.