Objective: While analyzing the phenotype of the synovial fluid mononuclear cells (SFMC) clustered about dendritic cells in rheumatoid arthritis (RA) joint effusions, it was noted that most of the clustering cells were CD8+ and coexpressed Leu-7. Therefore, the present study was conducted to investigate the frequency of CD8+, Leu-7+ cells in RA SF:
Methods: SFMC from 13 patients with RA and from 12 patients with non-RA inflammatory arthritides were examined for CD8 and Leu-7 expression using 2-color immunofluorescence flow cytometry.
Results: RA SFMC had statistically significantly greater percentages of total CD8+ cells, total Leu-7+ cells, and CD8+, Leu-7+ cells, compared with SFMC from the non-RA patients. These RA CD8+, Leu-7+ SFMC had a distinctive electron microscopic appearance compared with CD8+, Leu-7- SFMC. When peripheral blood mononuclear cells (PBMC) from 31 RA patients (including 7 from the SFMC group) were compared with PBMC from 15 normal controls, the percentage of CD8+, Leu-7+ cells was not significantly greater in the RA patients. However, the combination of a modest increase in CD8+, Leu-7+ cells and a decrease in total CD8 cells in RA PBMC altered the composition of the RA CD8 population compared with normal PBMC, such that over 40% of RA peripheral blood CD8 cells coexpressed Leu-7.
Conclusion: The increased frequency of CD8+, Leu-7+ cells in RA SFMC may arise from the fact that a high percentage of the CD8+ PBMC in RA patients are also Leu-7+. This altered composition of CD8 cells in RA SF may have a role in the pathogenesis of the disease.