Macrophage and lymphocyte potentiation of syngeneic tumor cell and host fibroblast collagenolytic activity in rats

Abstract

The collagenolytic responses of normal rat skin fibroblasts (NRS-F) and rat mammary MTLn3 tumor-derived fibroblasts (Ln3-F) were examined following exposure to rat macrophage (M phi-CM)- and lymphocyte (LYM-CM)-conditioned culture medium and/or tumor cell-conditioned medium. Alveolar, intratumoral, and peritoneal macrophages were prepared from mammary adenocarcinoma-bearing rats, as were the peritoneal lymphocytes. Incubation of the two fibroblast populations with LYM-CM produced a 10- and 7-fold stimulation of collagenolytic activity by NRS-F and Ln3-F cells, respectively. Similarly, exposure of NRS-F and Ln3-F fibroblasts to peritoneal M phi-CM produced a 7- and 4-fold increase in the expression of collagenolytic activity, respectively. Conditioned medium from MTLn2 tumor cells also stimulated the collagenolytic expression of both fibroblast populations. Incubation of tumor-associated Ln3-F or NRS-F fibroblasts with MTLn2 tumor cell-conditioned medium enhanced fibroblast collagenolytic activity approximately 20 and 17 times, respectively. When M phi-CM and LYM-CM were further "conditioned" by a subsequent incubation with MTLn2 tumor cells, each stimulated the expression of collagenolytic activity by both fibroblast populations and this was especially pronounced (120-fold increase) in the response of Ln3-F to LYM-CM further conditioned by MTLn2 tumor cells. The conditioned media derived from M phi, LYM, and MTLn2 tumor cells with or without trypsin activation contained low levels of interstitial-type collagenolytic activity which made no significant contribution to the collagenolytic activity of the stimulated fibroblasts. Some collagenase inhibitory activity, however, was detected in the M phi-CM, suggesting that the actual stimulation of collagenolysis by host fibroblasts is underestimated. We conclude that macrophages, lymphocytes, and tumor cells all have the potential to produce stimulatory factor(s) which enhance the collagenolytic activity of normal fibroblast populations. This study provides further evidence of the multifactorial control of collagenase production and supports the concept that host cell-tumor cell interactions can enhance the expression of collagenolytic enzymes.