Evaluation of in vivo and in vitro effectivity of immune defense against a spontaneously arising, nonlymphoid rat tumor. I. Analysis of natural immune defense.

Possible mechanisms of natural defense against a nonimmunogenic, nonlymphoid rat tumor were evaluated in vitro and examined for effectivity in vivo, using BSp6S, the subcutaneously grown transplantation line of a spontaneously arising fibrosarcoma in the BDX rat strain, which is highly susceptible to natural killer (NK) cells and macrophages (Mø). The role of nonspecific immune defense in vivo was demonstrated by eliminating NK cells by irradiation and Mø by silica treatment. Especially after depletion of NK cells a significant acceleration of tumor growth and a reduction in the number of cells required for tumor takes was observed. Activation of Mø by Corynebacterium parvum (CP) did lead to retardation of tumor growth; prevention of tumor growth was only achieved after inoculation of a marginal dose of tumor cells. Activation of NK cells was of minor influence. It is concluded that NK cells and Mø are the main influences on survival time, the effectiveness of NK cells being limited to early periods of tumor growth.