9 weeks of age, 1 week after the commencement of CRIg-Fc or control Ig treatment, the skin looked similar in the two treatment groups (Fig. 1A). By 16 weeks of age, skin lesions developed as expected in the control-treated mice whereas they were absent in the CRIg-Fc-treated mice (Fig. 1B). Histopathologic evaluation of skin from 16 week old control-treated mice showed a trend for greater hyperkeratosis and infiltration with inflammatory cells and significantly more fibrosis (p = 0.04) as compared to the CRIg-Fc-treated mice (Figs. 1C/D).
A similar beneficial effect on skin disease in MRL/lpr mice has also been reported after the administration of the complement regulatory protein DAF [5]. Skin damage in MRL/lpr mice involves a number of mechanisms including the production of interferon (IFN) type I, tumor necrosis factor (TNF) and the presence of TNF receptor 1 [13]. Resident skin cells produce C3 and C5, and TNF enhances their production [14]. Therefore, inhibition of complement activation should benefit skin lesion in lupus and likely enhance therapeutic effects of IFN-blocking biologics. It should be though considered that absence of C5a receptors reduces TNF production in mice forced to develop arthritis after the injection of collagen [15] suggesting the existence of positive feedback pathways between the two effectors.