Enhancement of Ia antigen expression and nonproliferating cells correlates with metastatic capacity

Maintaining B16F10 tumor cells in stirring culture for 48 h leads to an increase in lung and liver colonizing capacity in comparison with cells in adherent culture. Parallel to the increased metastatic capacity, we have observed a decrease in the proliferative rate of tumor cells (as the percentage of proliferating cell nuclear antigen-positive cells) and an increase in the population of tumor cells expressing Ia antigen. These results are not exclusive to B16F10 cells, since the same results were obtained when we analyzed 3LL cells maintained in identical culture conditions. In all the tumor lines tested, we found an association between the nonproliferating and the Ia-positive cell populations. We induced Ia expression by treating B16F10 cells in adherent culture with the lectin concanavalin A and again, coincident with an increase in metastatic capacity, we found the same association between the two parameters analyzed--nonproliferating state and Ia antigen expression. In addition, it was found that B16F10 cells induce lymphocytic proliferation, and a direct relationship was established between the number of Ia+ cells and lymphocytic proliferation.