Roles of CX3CR1 and probiotic lactobacilli on the development of autoimmunity in MRL/lpr mice

Systemic lupus erythematosus (SLE) is a multi-system autoimmune disease with no known cure. Gut microbiota and the immune system have a close relationship that controls inflammation. Alterations in the gut microbiota, known as dysbiosis, can trigger SLE in both human and mouse. We previously published differences between the gut microbiota in lupus-prone MRL/Mp-Faslpr (lpr) mice compared to healthy controls, with lower Lactobacillaceae abundance in lpr mice. Restoring the gut microbiota with a mix of 5 different strains of this family significantly attenuated lupus-liked disease in lpr mice. In this study, we sought to understand the potential benefit of this mix in lpr mice with Cx3cr1 deficiency (KO). KO mice on C57BL/6 background display increased translocation of commensal bacteria into the mesenteric lymph node (MLN) and increased susceptibility to intestinal inflammation. However, whether CX3CR1+ macrophages play a role in controlling systemic inflammation was unclear. After backcrossing the KO allele to lpr mice, we found that KO lpr mice exhibited exacerbated splenomegaly and lymphadenopathy, as well as increased proteinuria. Interestingly, treating the KO lpr mice with the 5 Lactobacillus strains attenuated the enlargement of MLN and abrogated the increase of proteinuria. Furthermore, the effects of the probiotic bacteria were accompanied by downregulation of serum endotoxin, suggesting the reversal of a leaky gut that may explain their benefits on KO lpr mice. Together, our results show an important role of CX3CR1+ macrophages in controlling systemic inflammation in lupus, and that probiotic Lactobacillus spp. may be an effective treatment against SLE through preventing bacterial translocation.