A GREATER REQUIREMENT FOR L-SELECTIN THAN CD44 FOR EARLY NEUTROPHIL ACCUMULATION IN THE SYNOVIAL MICROVASCULATURE IN ANTIGEN-INDUCED ARTHRITIS (AIA)

Background: Leukocyte recruitment is critical for host defense, but excessive accumulation of inflammatory leukocytes might cause significant tissue damage. L-selectin and CD44 are two major adhesion receptors that support the sequence of adhesion events during inflammatory cell recruitment including the rolling of the cells on the endothelium under blood flow, followed by firm adhesion, and then migration across the vessel wall. However, the specific contribution of L-selectin or CD44 to the regulation of leukocyte traffic to joints in inflammatory arthritis has not been investigated.Objectives: To determine, whether L-selectin or CD44 are directly involved in the regulation of leukocyte traffic into synovial joints in arthritic conditions.Methods: CD44-deficient, L-selectin-deficient, and CD44/L-selectin double knockout mice have been used to study the requirement for both receptors for leukocyte recruitment during AIA. Mice were immunized with methylated BSA, and then challenged with the same antigen injected into the knee joints. The animals were monitored for joint swelling at defined time points, and the inflamed knees were removed for histopathology. Rolling and adhesion of in vivo rhodamine 6G-labeled leukocytes in the synovial microvessels were monitored using intravital fluorescence videomicroscopy. The cells from the joint cavity were analyzed by flow cytometry.Results: Interestingly, expression of L-selectin was reduced in CD44-deficient leukocytes. Intraperitoneal immunization resulted similar antigen-specific responses in wild type and gene targeted mice. However, joint swelling after the intra-articular antigen injection was greater in Wt and CD44 KO than in L-selectin KO or CD44/L-selectin double KO mice. Extravasation of neutrophil granulocytes, but not the emigration of T cells, into the knee joints after intra-articular antigen injection was significantly delayed in L-selectin- and double knockout mice. Intravital microscopy on the synovial microcirculation revealed enhanced rolling and diminished adherence of leukocytes in mice lacking either CD44 or L-selectin, but CD44 deficiency did not influence the recruitment of L-selectin-null cells.Conclusion: This study demonstrates a requirement for L-selectin for neutrophil recruitment in the early phase of AIA. As indicated by intravital microsopy on the synovial microcirculation and histopathological findings, L-selectin expression in neutrophils is critical for establishment of firm adherence and subsequent extravasation. CD44 deficiency has only moderate negative effect on granulocyte influx into arthritic joints, and this effect might be the consequence of reduced L-selectin expression in CD44-deficient leukocytes.Citation: , volume , supplement , year 2004, page Session: Advances in autoantibodies/cell-to cell interaction