Human Th17- and IgG3-associated autoimmunity induced by a translocating gut pathobiont.

Extraintestinal autoimmune diseases are multifactorial with translocating gut pathobionts implicated as instigators and perpetuators in mice. However, the microbial contributions to autoimmunity in humans remain largely unclear, including whether specific pathological human adaptive immune responses are triggered by such pathobionts. We show here that the translocating pathobiont Enterococcus gallinarum induces human IFNγ + Th17 differentiation and IgG3 subclass switch of anti- E. gallinarum RNA and correlating anti-human RNA autoantibody responses in patients with systemic lupus erythematosus and autoimmune hepatitis. Human Th17 induction by E. gallinarum is cell-contact dependent and involves TLR8-mediated human monocyte activation. In murine gnotobiotic lupus models, E. gallinarum translocation triggers IgG3 anti-RNA autoantibody titers that correlate with renal autoimmune pathophysiology and with disease activity in patients. Overall, we define cellular mechanisms of how a translocating pathobiont induces human T- and B-cell-dependent autoimmune responses, providing a framework for developing host- and microbiota-derived biomarkers and targeted therapies in extraintestinal autoimmune diseases. One Sentence Summary: Translocating pathobiont Enterococcus gallinarum promotes human Th17 and IgG3 autoantibody responses linked to disease activity in autoimmune patients.

Pathogenic Autoreactive T and B Cells Cross-React with Mimotopes Expressed by a Common Human Gut Commensal to Trigger Autoimmunity.

Given the immense antigenic load present in the microbiome, we hypothesized that microbiota mimotopes can be a persistent trigger in human autoimmunity via cross-reactivity. Using antiphospholipid syndrome (APS) as a model, we demonstrate cross-reactivity between non-orthologous mimotopes expressed by a common human gut commensal, Roseburia intestinalis (R. int), and T and B cell autoepitopes in the APS autoantigen ß2-glycoprotein I (ß2GPI). Autoantigen-reactive CD4+ memory T cell clones and an APS-derived, pathogenic monoclonal antibody cross-reacted with R. int mimotopes. Core-sequence-dependent anti-R. int mimotope IgG titers were significantly elevated in APS patients and correlated with anti-ß2GPI IgG autoantibodies. R. int immunization of mice induced ß2GPI-specific lymphocytes and autoantibodies. Oral gavage of susceptible mice with R. int induced anti-human ß2GPI autoantibodies and autoimmune pathologies. Together, these data support a role for non-orthologous commensal-host cross-reactivity in the development and persistence of autoimmunity in APS, which may apply more broadly to human autoimmune disease.

Gastro-protective effects of isobrucein B, a quassinoid isolated from Picrolemma sprucei.

Infusions of Picrolemma sprucei roots, stems and leaves are used in traditional medicine throughout the Amazon region from the Guianas to Brazil and Peru in the treatment of gastritis, intestinal helminths and malaria. As there are no studies describing its mode of action in providing a gastroprotective effect, we determined herein that one of the main constituents found in P. sprucei infusions, the quassinoid isobrucein B (IsoB), reduces some of the pathophysiological effects in a mouse model of non-steroidal anti-inflammatory drug (NSAID)-induced gastritis and provides mechanisms of action. Then, IsoB (1.17 g) was isolated from the roots and stems (6.5 kg) of P. sprucei. Its structure was confirmed by 1D and 2D (1)H and (13)C NMR, ESI-tof-MS, IR and UV. C57BL/6 strain mice were subcutaneously injected with IsoB (0.5-5 mg kg(-1)) or vehicle before oral administration of indomethacin and sacrificed later at different time points. Gastric damage was assessed by measuring lesion length. Leukocyte migration was evaluated based on leukocyte rolling and adhesion using intravital microscopy in the mesenteric microcirculation and tissue MPO activity. Stomach extract cytokine (TNFα, IL-1ß and KC/CXCL1) and prostaglandin E2 (PGE2) levels were measured by ELISA and RIA, respectively. IsoB pre-treatment (0.5-5.0 mg kg(-1)) significantly reduced the formation of indomethacin-induced stomach lesions in a dose-dependent manner. The decrease in stomach lesions was associated with less observed leukocyte rolling, decreased leukocyte adhesion and less neutrophil infiltration (MPO activity). IsoB (1 mg kg(-1)) pre-treatment did not prevent indomethacin-induced decreases in stomach PGE2 levels. However, IL-1ß and KC/CXCL1 levels were inhibited by this same IsoB dosage, whereas TNF-α was unchanged. IsoB may be a prototypic compound to provide protective effects against NSAID-induced gastritis and possibly other gastropathies. Moreover, IsoB gastroprotective action may be due to a reduction in IL-1ß and KC/CXCL1 production/release and leukocyte rolling, adhesion and migration.

Regulation of type 17 helper T-cell function by nitric oxide during inflammation.

Type 17 helper T (Th17) cells are implicated in the pathogenesis many of human autoimmune diseases. Development of Th17 can be enhanced by the activation of aryl hydrocarbon receptor (AHR) whose ligands include the environmental pollutant dioxin, potentially linking environmental factors to the increased prevalence of autoimmune disease. We report here that nitric oxide (NO) can suppress the proliferation and function of polarized murine and human Th17 cells. NO also inhibits AHR expression in Th17 cells and the downstream events of AHR activation, including IL-22, IL-23 receptor, and Cyp1a1. Conversely, NO did not affect the polarization of Th17 cells from mice deficient in AHR. Furthermore, mice lacking inducible nitric oxide synthase (Nos2(-/-)) developed more severe experimental autoimmune encephalomyelitis than WT mice, with elevated AHR expression, increased IL-17A, and IL-22 synthesis. NO may therefore represent an important endogenous regulator to prevent overexpansion of Th17 cells and control of autoimmune diseases caused by environmental pollutants.