ARTHRITIS & RHEUMATISM Vol. 43, No. 4, April 2000, pp 827–833 © 2000, American College of Rheumatology REGULATION OF MACROPHAGE MIGRATION INHIBITORY FACTOR BY ENDOGENOUS GLUCOCORTICOIDS IN RAT ADJUVANT-INDUCED ARTHRITIS MICHELLE LEECH, CHRISTINE METZ, RICHARD BUCALA, and ERIC F. MORAND Objective. To explore the regulation of macro- phage 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  (TNF) were measured by enzyme- linked immunosorbent assay (ELISA). Synovial MIF immunostaining was detected by 3-layer immunohisto- chemistry. 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 adrena- lectomized (ADX) animals throughout AIA develop- ment. Results. Compared with sham operation, adrenal- ectomy was associated with significant exacerbation of clinical disease parameters (P < 0.05). Adrenalectomy was associated with significantly reduced levels of syno- vial MIF, but not TNF. In contrast, adrenalectomy was associated with increased serum MIF levels. Concomi- tant increased pituitary MIF levels were observed in ADX rats, consistent with the pituitary being the prin- cipal 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. Activation of the hypothalamic–pituitary–adrenal (HPA) axis by stress or inflammation culminates in the release of glucocorticoids from the adrenal gland. En- dogenous glucocorticoids have the capacity to regulate inflammatory events including antigen presentation, T cell expansion, cytokine production, and natural killer cell activity, and can also regulate the production of mediators such as nitric oxide and prostaglandins (1–4). The release of endogenous glucocorticoids in the setting of inflammatory stress has been proposed to be a counterregulatory mechanism preventing potentially harmful overactivity of the immune response. Adjuvant- induced arthritis (AIA) is a T cell– and macrophage- dependent model of immune-mediated disease in rats that shares many features with human rheumatoid ar- thritis (RA) (5–8). Production of endogenous glucocor- ticoids is elevated in AIA (9,10), and many of the immune processes that glucocorticoids modulate take place during AIA development (5,8,11). We and others have shown that interruption of glucocorticoid supply during the development of AIA is associated with a significant exacerbation of clinical and histologic aspects of disease (10,12). Macrophage migration inhibitory factor (MIF) is a recently cloned proinflammatory cytokine. MIF was first described and named in the setting of delayed-type hypersensitivity (DTH) responses as a putative constit- uent of T cell supernatants that could prevent the random migration of macrophages in culture (13,14). It has been identified subsequently as a predominantly Supported by the Arthritis Foundation of Australia and the National Health and Medical Research Council of Australia. Michelle Leech, MBBS(Hons), Eric F. Morand, MBBS(Hons), FRACP, PhD: Monash University, Monash Medical Centre, Melbourne, Australia; Christine Metz, PhD, Richard Bucala, MD, PhD: Picower Institute for Medical Research, Manhasset, New York. Address reprint requests to Eric F. Morand, MBBS(Hons), FRACP, PhD, Centre for Inflammatory Diseases, Monash Medical Centre, Locked Bag No. 29, Clayton 3168 Melbourne, Australia. Submitted for publication September 7, 1999; accepted in revised form December 1, 1999. 827