Expression of soluble human signaling lymphocytic activation molecule in vivo

Background: Signaling lymphocytic activation molecule (SLAM) is a novel gly coprotein expressed on activated T and B cells. Ligation of cell surface SL AM, either by anti-SLAM mAbs or the recombinant soluble form of SLAM (sSLAM ), enhanced the proliferation of T and B cells in vitro. In addition, the e ngagement of SLAM on T cells preferentially induced IFN-gamma production ev en by allergen-specific T-H2 clones. Objective: In this study we investigated the expression of sSLAM in vivo in healthy individuals and in disease conditions that are associated with inc reased T-H1- or T-H2-cell responses. Methods: The expression of mRNA encoding sSLAM in peripheral blood and syno vial fluid (SF) lymphocytes was studied by using reverse transcriptase-PCR, and the presence of sSLAM protein in serum and SF samples was investigated by using a specific ELISA. Results: Lymphocytes from patients with rheumatoid arthritis (RA) and healt hy individuals consistently expressed mRNA encoding sSLAM. In addition, sSL AM protein mas present in 38% of serum and 54% of SF samples from patients with RA and in 47% of serum samples from healthy individuals. The revels of sSLAM in positive serum and SF samples from patients with Rd. and in posit ive serum samples from healthy individuals were not significantly different . In contrast, the levels of sSLAM were significantly lower in patients wit h reactive arthritis or in patients with elevated IgE levels than in patien ts with RA. Similarly, the frequency of positive SF samples mas significant ly lower in reactive arthritis (28%) than in RA (54%). Conclusion: These results indicate that sSLAM is present in serum and SF, f urther suggesting that sSLAM regulates T- and B-cell function in vivo. More over, these data suggest an association between low sSLAM production and th e occurrence of T-H2 responses in vivo.