Synovial fluid cells in Reiter's syndrome.

Synovial fluid cells in Reiter's syndrome were studied by cell subset specific monoclonal antibodies and avidin-biotin-peroxidase complex staining. Mean leucocyte count was 9842/mm3 (9.842 X 10(9)/l), and 71% of all cells were polymorphonuclear leucocytes. 26 +/- 11 (SEM)% and 47 +/- 5% of all mononuclear cells in synovial fluid were M1+ monocytes and Ia+ cells, respectively. T11+ T lymphocyte was the predominant synovial fluid mononuclear cell (61 +/- 8%) but, in contrast to the inflammatory joint effusions in rheumatoid arthritis, T4+ cells clearly outnumbered T8+ cells in Reiter's syndrome. Thus the synovial fluid in Reiter's syndrome contains the immunocompetent and accessory cells required for immune response, which in fact is activated as suggested by lymphocyte Ia expression. Furthermore, in contrast with rheumatoid arthritis inducer/helper cells with T4 phenotype seem to be involved preferentially in the local pathogenetic mechanisms in Reiter's syndrome.