SPONTANEOUS AUTOIMMUNE SKIN-LESIONS OF MRL N MICE - AUTOIMMUNE DISEASE-PRONE GENETIC BACKGROUND IN RELATION TO FAS-DEFECT MRL/LPR MICE/

The autoimmune-prone MRL/Mp-1pr/1pr (MRL/1pr) mouse is characterized b y the 1pr mutation, which is a defect in the Fas antigen, Since Fas me diates apoptosis, this defect results in CD4(-)CD8(-) double negative T-cell proliferation, lupus nephritis, and macroscopic lupus erythemat osus-like skin lesions. The control counterpart of MRL/1pr mouse is th e MRL/Mp-+/+ (MRL/n) mouse, which lacks the 1pr mutation and is almost normal during the first 6 mo of life, The 1pr) mutation, however, acc elerates autoimmune phenomena in MRL/1pr mice, Thus, it is important t o investigate autoimmune diseases like systemic lupus erythematosis in relation to the autoimmune disease-prone genetic background of MRL/n mice. We found that skin lesions in aged MRL/n mice had unique charact eristics. The first characteristic is spontaneous occurrence, and the second is epidermal cell nuclear immunostaining with IgGs by direct im munofluorescence. The skin lesions in aged MRL/n mice showed milder in flammation than in MRL/1pr mice, A homogeneous pattern of epidermal ce ll nuclear staining was always associated with nuclear staining in kid ney cells and also correlated with the in vitro binding of sera to ker atinocytes cultured from newborn MRL/n mice, These results suggest tha t the skin lesions of aged MRL/n mice are a good model for certain typ es of cutaneous lupus erythematosus and also can provide new insights into the long-standing controversy whether epidermal cell nuclear stai ning occurs in vivo.