Regulation of leukocyte binding to endothelial tissues by tumor‐derived GM‐CSF

The adherence of leukocytes to endothelial cells is the first step in the migration of these cells into tumor tissues. Specific binding to the endothelial cells by leukocytes is mediated by the development and maintenance of adhesion molecules on the endothelium; however, the mechanisms of leukocyte traffic into tumors and of their interactions with neoplastic tissue are not clearly understood. The infiltration of leukocytes occurs in most spontaneous and transplanted solid tumors and we have previously reported that not only are murine mammary tumors heavily infiltrated by leukocytes but tumor‐derived factors alter the development and function of leukocytes in tumor‐bearing mice. We now present evidence that a tumor‐derived cytokine, namely granulocyte‐macrophage‐colony‐stimulating factor, appears to be of importance in the regulation of leukocyte binding to endothelial cells. The data suggest that tumor‐derived factors may influence leukocyte trafficking within tumor tissue.