Lupus-Prone Mice Have an Abnormal Response to Thioglycolate and an Impaired Clearance of Apoptotic Cells

Deficiency of complement in humans and mice is associated with the development of lupus and with abnormal repair of inflammatory and immune complex-mediated tissue injury. Here we ask whether similar defects in the resolution of inflammation are found in mice prone to spontaneous lupus. We compared the response to an i.p. injection of thioglycolate between two lupus-prone strains (MRL/Mp and NZB/W) and two non lupus-prone strains of mice (C57BL/6 and BALB/c). In all four strains the influx of polymorphonuclear neutrophils (PMN) was similar. However, by 96 h clearance of PMN in the control strains was complete, whereas in the autoimmune-prone strains PMN were still detectable. The number of mononuclear cells recruited was markedly reduced in the lupus-prone strains compared with the controls, and their phenotype was different. The lupus-prone strains had significantly fewer elicited macrophages that were CD11b-high and Ly6C-negative. In lupus-prone mice at 24 h there was a significantly increased number of apoptotic PMN free in the peritoneum, accompanied by a reduced percentage of macrophages containing apoptotic bodies, suggesting a defect in their uptake. An impaired ability of resident peritoneal macrophages from lupus-prone mice to engulf apoptotic cells was demonstrated by in vivo and in vitro cell clearance assays. These observations indicate that lupus-prone strains have an abnormal inflammatory response to thioglycolate and an intrinsic impairment in apoptotic cell uptake. These findings have implications for the initiation of autoimmunity, as lupus autoantigens are expressed on dying cells, and impaired disposal of these could enhance the development of autoimmunity.