Defective neutrophil function in the autoimmune mouse strain MRL/lpr. Potential role of transforming growth factor-beta.

Patients with systemic autoimmune diseases such as SLE and rheumatoid arthritis have increased rates of morbidity and mortality caused by infection. Although this increased risk of infection has been primarily attributed to therapeutic immuno-suppression, some reports exist of defective polymorphonuclear leukocytes (PMN) function in these patients. The purpose of the present work is to investigate the recruitment of PMN phagocytic function in a murine model of autoimmunity, the MRL/lpr mouse. PMN from MRL/lpr, but not from congenic MRL/n mice, exhibit a marked defect in the amplification of FcR-mediated phagocytosis stimulated by various inflammatory mediators. This defect is acquired and correlates with the onset of the autoimmune disease observed in this strain. In addition, MRL/lpr but not MRL/n PMN exhibit a defect in extravasation into the thioglycollate-inflamed peritoneum. Incubation of MRL/n PMN in MRL/lpr serum induces a defect in the amplification of PMN phagocytic function identical to that observed with MRL/lpr PMN. The activity in the serum that induces this defect is neutralized by an antibody to TGF-beta but not by control antibodies. Incubation of murine and human PMN with purified TGF-beta induces an identical defect in stimulated FcR-mediated ingestion. In addition, TGF-beta-treated MRL/n PMN fail to extravasate into the thioglycollate-inflamed peritoneum after injection into normal MRL/n recipient mice. In addition, direct injection of TGF-beta into MRL/n mice also reduces the percentage and number of PMN in the thioglycollate-stimulated peritoneal exudates of these mice. The defect in PMN extravasation and phagocytic function was not caused by failure of the defective PMN to modulate the expression of the adhesion molecules, Mac-1 and Mel-14. These data indicate that defects in PMN function can be observed in a murine model of autoimmunity and that spontaneous production of TGF-beta possibly may play a crucial role in the pathogenesis of the defective PMN function in this animal model.