A detailed study of the effects of in vitro interferon treatment on the growth of two variants of the B16 mouse melanoma in the lungs: evidence for non-specific effects.

Interferon treatment increases the ability of tumour cells to colonize the lungs. Although it has been suggested that this effect can be explained by increases in the expression of MHC molecules the precise mechanism is still uncertain. The growth in the lungs of a low (F1) and a high colonizing variant (BL6) of the B16 mouse melanoma have been studied after in vitro treatment with interferon. Interferon-gamma, but not interferon-alpha/beta, increased the number of lung colonies formed after intravenous injection, but not after subcutaneous administration. Treatment also increased the sizes of the lung colonies formed and the number of radiolabelled cells retained by the lungs. However, no clear relationship was observed between the number of colonies formed and the concentration of interferon used. The effect of interferon on F1 was greater than on BL6, but the overall number of colonies formed was very similar. These results suggest that interferon increases the adhesiveness of these cell lines in a fairly non-specific manner, that seems unlikely to involve MHC molecules. As a results of this and other studies the importance of interferon in the process of tumour spread seems very questionable.