MONOCYTE-ENDOTHELIAL ADHESION IN CHRONIC RHEUMATOID-ARTHRITIS - INSITU DETECTION OF SELECTIN AND INTEGRIN-DEPENDENT INTERACTIONS

Blood monocytes are the principal reservoir for tissue macrophages in rheumatoid synovitis. Receptor-mediated adhesive interactions between circulating cells and the synovial venules initiate recruitment. These interactions have been studied primarily in cultured endothelial cell s. Thus the functional activities of specific adhesion receptors, such as the endothelial selectins and the leukocytic integrins, have not b een evaluated directly in diseased tissues. We therefore examined mono cyte-microvascular interactions in rheumatoid synovitis by modifying t he Stamper-Woodruff frozen section binding assay initially developed t o study lymphocyte homing. Specific binding of monocytes to venules li ned by low or high endothelium occurred at concentrations as low as 5 X 10(5) cells/ml. mAbs specific for P-selectin (CD62, GMP-140 / PADGEM ) blocked adhesion by > 90% in all synovitis specimens examined. In co ntrast, P-selectin-mediated adhesion to the microvasculature was eithe r lower or absent in frozen sections of normal foreskin and placenta. mAbs specific for E-selectin (ELAM-1) blocked 20-50% of monocyte attac hment in several RA synovial specimens but had no effect in others. mA bs specific for LFA-1, Mo1/Mac 1, the integrin beta2-chain, and L-sele ctin individually inhibited 30-40% of adhesion. An mAb specific for th e integrin beta1-chain inhibited the attachment of elutriated monocyte s up to 20%. We conclude that P-selectin associated with the synovial microvasculature initiates shear-resistant adhesion of monocytes in th e Stamper-Woodruff assay and stabilizes bonds formed by other selectin s and the integrins. Thus the frozen section binding assay permits dir ect evaluation of leukocyte-microvascular adhesive interactions in inf lamed tissues and suggests a prominent role for P-selectin in monocyte recruitment in vivo.