3-COLOR FLOW-CYTOMETRIC EXAMINATION OF CD4 CD45 SUBSETS REVEALS NO DIFFERENCES IN PERIPHERAL-BLOOD AND SYNOVIAL-FLUID BETWEEN PATIENTS WITHREACTIVE ARTHRITIS AND RHEUMATOID-ARTHRITIS/

Reactive arthritis (ReA) and rheumatoid arthritis (RA) are inflammator y joint diseases which differ in several clinical and immunological as pects. In both diseases locally activated T cells are considered impor tant for pathogenesis. Subsets of T cells are demonstrated by staining with monoclonal antibodies recognizing isotypes of the common leukocy te antigen: CD45RA, which is considered to be a marker of naive T cell s, and CD45RO a marker of primed T cells; a third subset was also iden tified according to the staining intensity of CD45RB:CD45RB(bright) an d CD45RB(dim). The expression of these and the surface markers CD3, CD 4, CD8, CD14 and CD56 was studied in synovial fluid (SF) and periphera l blood (PB) of patients with ReA (n=11), RA (n=10) and normal control s (n=10) by three-colour immunocytometry. Significantly more CD45RB(br ight) were found in the PB of patients with ReA (64.1%) and RA (63.5%) than in the SF of ReA (36.8%) and RA (40.6%) patients. However, when analyzed in relation to CD45RO, the CD45RO/CD45RB(bright) population w as not significantly different between the SF and PB of patients with ReA (32.2% vs. 26.8%) and RA (30.6% vs. 28.1%), respectively. Among th e three cellular subtypes of CD4+ lymphocytes demonstrated in this stu dy (CD45RA/RB(bright), CD45RO/CD45RB(bright) and CD45RO/CD45RB(dim)) n one, in contrast to previous results of other groups, showed marked di fferences between ReA and RA in either of the compartments examined.