T cells are responsible fortheenhancedsynovial cellular immune response totriggering antigen inreactive arthritis

SUMMARY Inreactive arthritis (ReA)there isspecific proliferation ofsynovial fluid (SF)mononuclear cells (MNC)tothetriggering bacterial antigen; comparatively little or no responseisseen inperipheral blood(PB). Toinvestigate themechanism ofthis elevated local immuneresponse,we examined patients withtypical ReAwhoshowed an enhanced antigen-specific synovial immuneresponsein bulkculture. Usingseparated fractions ofTcells andantigen-presenting cells (APC)fromPBandSF we showedthat thesynovial Tcells rather thanSFAPCareresponsible forthespecific proliferation. Bylimiting dilution analysis, thefrequency ofTcells responding tothespecific antigen was found to besignificantly increased comparedwiththefrequency ofirrelevant antigen-specific T cells. Furthermore, thefrequency ofTcells responding tothespecific antigen was higher inSF(between 1/619and1/4846, mean 1/2389) thaninPB (between 1/1286 and1/16279, mean 1/7350). We conclude thatthespecific synovial cellular immuneresponseinReAismainly duetoanexpansion of antigen-specific Tcells within thejoint. However, thenon-specific hyper-reactivity ofSFTcells and differences between SFandPBAPC may makea more minorcontribution.