Gut microbiota has been recognized as an important environmental factor in health, as well as in metabolic and immunological diseases, in which perturbation of the host gut microbiota is often observed in the diseased state. However, little is known on the role of gut microbiota in systemic lupus erythematosus. We investigated the effects of host genetics, sex, age, and dietary intervention on the gut microbiome in a murine lupus model. In young, female lupus-prone mice resembling women at childbearing age, a population with the highest risk for lupus, we found marked depletion of lactobacilli, and increases in Lachnospiraceae and overall diversity compared to age-matched healthy controls. The predicted metagenomic profile in lupus-prone mice showed a significant enrichment of bacterial motility-and sporulation-related pathways. Retinoic acid as a dietary intervention restored lactobacilli that were downregulated in lupus-prone mice, and this correlated with improved symptoms. The predicted metagenomes also showed that retinoic acid reversed many lupus-associated changes in microbial functions that deviated from the control. In addition, gut microbiota of lupus-prone mice were different between sexes, and an overrepresentation of Lachnospiraceae in females was associated with an earlier onset of and/or more severe lupus symptoms. Clostridiaceae and Lachnospiraceae, both harboring butyrate-producing genera, were more abundant in the gut of lupus-prone mice at specific time points during lupus progression. Together, our results demonstrate the dynamics of gut microbiota in murine lupus and provide evidence to suggest the use of probiotic lactobacilli and retinoic acid as dietary supplements to relieve inflammatory flares in lupus patients.

It has long been recognized that the mammalian gut microbiota has a role in the development and activation of the host immune system. Much less is known on how host immunity regulates the gut microbiota. Here we investigated the role of adaptive immunity on the mouse distal gut microbial composition by sequencing 16 S rRNA genes from microbiota of immunodeficient Rag1 À / À mice, versus wild-type mice, under the same housing environment. To detect possible interactions among immunological status, age and variability from anatomical sites, we analyzed samples from the cecum, colon, colonic mucus and feces before and after weaning. High-throughput sequencing showed that Firmicutes, Bacteroidetes and Verrucomicrobia dominated mouse gut bacterial communities. Rag1 À mice had a distinct microbiota that was phylogenetically different from wildtype mice. In particular, the bacterium Akkermansia muciniphila was highly enriched in Rag1 À / À mice compared with the wild type. This enrichment was suppressed when Rag1 À / À mice received bone marrows from wild-type mice. The microbial community diversity increased with age, albeit the magnitude depended on Rag1 status. In addition, Rag1 À / À mice had a higher gain in microbiota richness and evenness with increase in age compared with wild-type mice, possibly due to the lack of pressure from the adaptive immune system. Our results suggest that adaptive immunity has a pervasive role in regulating gut microbiota's composition and diversity.

Recently, we demonstrated that treatment with all- trans-retinoic acid (tRA) induced a paradoxical effect on immune activation during the development of autoimmune lupus. Here, we further describe its negative effects on mediating neuroinflammation and neurodegeneration. Female MRL/lpr mice were orally administered tRA or VARA (retinol mixed with 10% tRA) from 6 to 14 weeks of age. Both treatments had a significant effect on brain weight, which correlated with histopathological evidence of focal astrogliosis, meningitis, and ventriculitis. Infiltration of CD138- and Iba1-positve immune cells was observed in the third ventricle and meninges of treated mice that co-labeled with ICAM-1, indicating their inflammatory nature. Increased numbers of circulating plasma cells, autoantibodies, and total IgG were also apparent. IgG and C3 complement deposition in these brain regions were also prominent as was focal astrogliosis surrounding the ventricular lining and meninges. Using Fluoro-Jade staining, we further demonstrate that neuroinflammation was accompanied by neurodegeneration in the cortex of treated mice compared with vehicle controls. These findings indicate that vitamin A exposure exacerbates the immunogenic environment of the brain during the onset of systemic autoimmune disease. Vitamin A may therefore compromise the immuno-privileged nature of the central nervous system under a predisposed immunogenic environment.

The transfer of maternal autoantibody (autoAb) to the progeny can cause neonatal autoimmune diseases. An example is the fatal congenital heart block elicited by maternal SSA/SSB antibodies in Sjogren’s patients. Disease mechanism is unknown but can now be investigated in a nAOD model developed in our laboratory. Ovarian inflammation and atrophy occurs in C57BL/6 Rag ko pups after the exposure to maternal autoAb against ovarian zona pellucida 3 within 1-5 days of life. Resistance to nAOD induction in both NK cell-depleted Rag ko pups, and Rag/common gamma chain (Rag/γc) double ko pups demonstrates the critical role of NK cells. Notably, neonatal but not adult NK cells restore nAOD in Rag/γc ko pups. Compared to adult NK cells, neonatal NK cells have lower expression of Ly49 receptors and higher frequency of the CD27+ subset. We now show that the expression of CD27, CXCR3 and IFNγ by neonatal NK cells are crucial for nAOD. Furthermore, Ly49C/I-depleted adult NK cells acquire the ability to induce nAOD. This suggests that the low expression of Ly49 reduces the activation threshold and enhances the pathogenic capacity of neonatal NK cells. Lastly, FcgRIII expression on both neonatal NK cells and ovarian resident macrophages and dendritic cells (APC) is obligatory for nAOD induction. However, ovarian APC requirement is not ontogenetically regulated. We conclude that the unique properties of neonatal NK cell predispose newborns to autoimmune disease by maternal autoAb.