Objective: To explore the regulation of macrophage migration inhibitory factor (MIF) by endogenous glucocorticoids in adjuvant-induced arthritis (AIA).
Methods: Adrenalectomy or sham operation was performed 2 days prior to adjuvant arthritis induction. Synovial explant supernatant levels of MIF and tumor necrosis factor alpha (TNFalpha) were measured by enzyme-linked immunosorbent assay (ELISA). Synovial MIF immunostaining was detected by 3-layer immunohistochemistry. Serum MIF levels were measured by Western blotting. Pituitary MIF release was measured by ELISA. Anti-MIF monoclonal antibody (mAb) or isotype-matched control antibody was administered to adrenalectomized (ADX) animals throughout AIA development.
Results: Compared with sham operation, adrenalectomy was associated with significant exacerbation of clinical disease parameters (P < 0.05). Adrenalectomy was associated with significantly reduced levels of synovial MIF, but not TNFalpha. In contrast, adrenalectomy was associated with increased serum MIF levels. Concomitant increased pituitary MIF levels were observed in ADX rats, consistent with the pituitary being the principal source of this increase. The administration of specific anti-MIF mAb conferred 100% protection from lethality during arthritis development and decreased arthritis disease expression.
Conclusion: These findings provide the first in vivo confirmation of the observation that endogenous glucocorticoids are involved in the regulation of MIF in a site of inflammation, and that local and systemic MIF production are differentially regulated in this setting. The reversal of disease in ADX rats by anti-MIF mAb suggests that balance between glucocorticoids and MIF may influence the expression of inflammatory disease.