Biological properties associated with the enhanced lung-colonizing potential in a B16 murine melanoma line grown in a medium conditioned by syngeneicCorynebacterium parvum-elicited macrophages

A previous study by our laboratory showed that the peritoneal murine Coryne bacterium parvum-elicited macrophages released into their growth medium an activity which enhanced the ability of B16-F10 melanoma cells to form exper imental metastases in the lung of syngeneic mice. In the present study, we used a clone of B16-F10 line (F10-M3 cells) to investigate whether the incr ease in lung-colonizing potential due to the pro-clonogenic activity releas ed by C. parvum-elicited macrophages was associated with biological propert ies characteristic of a metastatic phenotype. We have found that the pulmon ary retention, growth rate in lung parenchyma, invasiveness through Matrige l, adhesiveness to IL-1-activated endothelium and MHC class I expression we re increased in F10-M3 cells stimulated by the macrophage pro-clonogenic ac tivity. By using an in vitro experimental protocol, the enhancement of lung -colonizing potential in the stimulated melanoma cells turned out to be a t ransient phenomenon as was the increase of invasiveness through Matrigel an d the higher expression of MHC class I antigens. In conclusion, the melanom a cells stimulated by the pro-clonogenic activity released by C. parvum-eli cited macrophages showed changes in biological parameters which are relevan t to metastatic diffusion. These changes appeared as a temporary phenomenon which sustains the view that the metastatic phenotype represents a transie nt biological character influenced by host factors.