Abstract 2113 Allergy, Immunology, and Rheumatology Poster Symposium, Sunday, 5/2

The presence of T cells within the inflamed synovium has led to uncontested conclusion that these cells are central to juvenile rheumatoid arthritis (JRA) disease pathogenesis. However, there are several lines of evidence that conflict with the hypothesis that the presence of such cells within inflamed synovium reflects a specific antigen-driven process or a loss of control of that process. The experiments described here provide an alternative explanation to the presence of T cells within the inflamed synovium. Since endothelial cells play a critical role in leukocyte homing to specific sites, we examined the potential role of C1q-bearing immune complexes (as are found in JRA synovial fluids) to activate endothelium and mediate leukocyte trafficking.

C1 was bound to model BSA-anti-BSA immune complexes, after which complexes were incubated with cultured human umbilical vein endothelial cells (HUVEC). Levels of interleukin-8, a chemokine that attracts both neutrophils and T cells, were measured in cell culture supernates after 36 hours. Cell adhesiveness was measured under flow conditions after specific time periods.

C1q-bearing immune complexes induced IL-8 secretion from HUVEC in a dose-dependent fashion These same results could be obtained using a cross-linking IgM antibody to the 127 kD C1q receptor (C1qR) expressed on HUVEC. Neither monomeric C1q nor C1q-bearing immune complexes pre-incubated with anti-C1q induced IL-8 from HUVEC. IL-8 secretion was inhibited by genestein, a nonspecific tyrosine kinase inhibitor, suggesting that the 127 kD C1qR is acts as a conventional tyrosine kinase-modulated receptor. Immunoprecipitated C1QR was shown to be phosphorylated on at least one tyrosine residue. Co-precipitating with the C1qR was another 72 kD phosphoprotein which we are in the process of identifying.

Adherence assays demonstrated a biphasic response of HUVEC to C1q-bearing immune complexes. Within 4 hours of stimulation, both neutrophils and T lymphocytes adhered to and rolled along stimulated (but not unstimulated) HUVEC. Adherence could be inhibited by antibody to E-selectin. Stimulated HUVEC maintained their capacity to mediate both T cell and neutrophil rolling for at least 48 hr. After 24hr, adherence and rolling could be inhibited by antibody to P-but not E-selectin.

These data demonstrate that C1q-bearing immune complexes stimulate the secretion of IL-8, an important neutrophil and T lymphocyte chemotactic factor, from HUVEC. These same complexes also mediate adherence of these cells to HUVEC. Thus, nonspecific inflammatory mechanisms, not an antigen-driven process, may account for the presence in rheumatoid synovial fluid and/or tissue.

Supported by grants from the National Institutes of Health and the Children's Medical Research Foundation of Oklahoma City.