A deficient leukocyte recruitment has been suggested in tumor vasculature, but little is known about the underlying molecular mechanism. To characterize leukocyte-endothelium interaction in experimental colon cancer, quantify the main endothelial cell adhesion molecules (CAMs), and evaluate the effect of tumor-derived products.

Leukocyte recruitment was assessed by intravital videomicroscopy in mice bearing HT29-derived tumors. Endothelial CAMs were measured using the dual-radiolabeled antibody technique. The role of molecules mediating leukocyte rolling (P-, E-, and L-selectin) or adhesion (intercellular adhesion molecule 1 [ICAM-1] and vascular cell adhesion molecule 1 [VCAM-1]) carcinoembryonic antigen (CEA), and transforming growth factor (TGF) 01 was assessed through immunoblockade, whereas participation of nitric oxide (NO) and cyclooxygenase (COX) metabolites were evaluated by means of nonselective and selective inhibition.

Basal and lipopolysaccharide-stimulated leukocyte rolling and adhesion were markedly reduced in tumor vasculature. ICAM-. immunoblockade prevented leukocyte adhesion in both tumor and nontumor microvessels. Neither baseline nor LPS-induced endothelial ICAM-1, P-, and E-selectin expression in tumors were reduced with respect to nontumor vasculature. Although VCAM-1 expression was reduced in tumor endothelium, immunoneutralization of VCAM-1 failed to reverse LPS-induced leukocyte recruitment in this setting. CEA immunoblockade and COX inhibition did not modify the deficient leukocyte rolling. Nonselective NO inhibition partially reversed the defective adhesion response in tumor microvessels. Finally, TGF-β1 immunoblockade partially and selectively restored impaired leukocyte rolling and adhesion in tumor microvessels.

Impaired leukocyte recruitment in tumor vasculature cannot be attributed to a depressed expression of the main CAMs. Selective restoration after NO inhibition and TGR-β1 immunoblockade suggests involvement of both molecules in this phenomenon.