Study objectives: To investigate the expression of interleukin-18 receptor α chain (IL-18Rα) in BAL and peripheral blood (PB) T cells in patients with sarcoidosis compared with control subjects, to evaluate the relationship between the expression and clinical manifestations, and to clarify the mechanisms of altered expression.
Subjects and methods: The study subjects consisted of 21 patients with sarcoidosis and 8 normal control subjects. The expression of IL-18Rα was examined by flow cytometry.
Results: The proportions of BAL CD4+ and PB CD4+ T cells expressing IL-18Rα were significantly increased in patients with sarcoidosis compared to control subjects. BAL CD4+ T cells expressed IL-18Rα in a higher proportion than did paired CD8+ T cells in patients with sarcoidosis but not in control subjects. Greater proportions of BAL CD4+ T cells and BAL CD8+ T cells than of their PB counterparts expressed IL-18Rα in both patients and control subjects. CD4+ T cells were more sensitive to the induction of IL-18Rα by cytokines in vitro, such as interleukin (IL)-2, IL-12, and tumor necrosis factor-α than were CD8+ T cells. Increased expression of IL-18Rα by BAL T cells commonly observed in patients and control subjects was associated with the expansion of CD45RO+ cells in BAL T cells. However, there were no significant correlations between the expression of IL-18Rα by any cell populations and BAL findings, serum angiotensin-converting enzyme activities, radiograph stages, or clinical courses.
Conclusion: The overexpression of IL-18Rα predominantly by CD4+ T cells in sarcoidosis emphasizes crucial roles played by T-helper type 1 cells in the IL-18/IL-18Rα system in sarcoidosis.