Abstract
Interaction of circulating leukocytes with tumor microvasculature is a critical event in the recruitment of effector cells into the tumor stroma. We have examined the ability of lymphotoxin (TNF-beta), to stimulate rolling, adhesion, and transmigration of leukocytes in angiogenic blood vessels induced by tumor spheroids of Lewis lung carcinoma (LLC) implanted in dorsal skinfold chambers of nude mice. In the absence of cytokine stimulation, circulating leukocytes failed to appreciably interact with tumor microvessels (TMV), although significant rolling and adhesion was observed in normal vessels. However, stimulation with lymphotoxin (LT) resulted in a rapid increase in the number of fast and slow rolling leukocytes in TMV. Treatment with anti-P-selectin mAb 5H1 resulted in inhibition of fast rollers alone, while combination treatment with anti-P-selectin and anti-E-selectin (9A9) mAbs effectively blocked slow rolling of leukocytes. Superfusion of the lymphotoxin-stimulated neovasculature with leukotriene B4 (LTB4) resulted in stable cell adhesion followed by emigration of leukocytes into the tumor stroma. LTB4-mediated adhesion and transmigration was significantly inhibited by treatment with anti-beta2 mAb 2E6. These studies delineate a multistep cascade of leukocyte adhesion in TMV and demonstrate that stimulation of the neovasculature with cytokines and chemoattractants can result in P- and E-selectin-dependent rolling and beta2-dependent stable adhesion followed by transmigration into the tumor stroma.