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.