Local cellular host response induced by Nocardia-delipidated cell mitogen in Lewis lung carcinoma-bearing mice.

Various Nocardial fractions have been shown to exert inhibitory effects against several experimental tumors, via a host response mechanism. With the aim of obtaining further information on the mechanism of action of these immunomodulators, we examined in the present study the local cellular host response induced by intratumoral administration of one of these fractions, the Nocardia-delipidated cell mitogen (NDCM), at the site of the tumor (Lewis lung carcinoma-3LL). The tumor itself was found to provoke a scanty cellular infiltration surrounding the tumor mass, mainly composed of lymphocytes. The site of the tumor in NDCM-treated mice was surrounded by a very thick rim of inflammatory cells, consisting of macrophages and lymphocytes. Although recognized decades ago, the existence of tumor infiltrating leukocytes still constitutes a puzzle. The composition and significance of these host cells, in both non-treated and treated tumors has not yet been elucidated. Since lymphocytes were also found around non-treated tumors and they apparently did not prevent tumor development, it is possible that macrophages play a more important role in the NDCM-elicited host defense against the Lewis lung carcinoma.