• Gut Microbiota Contributes to Resistance Against Pneumococcal Pneumonia in Immunodeficient Rag(-/-) Mice

      Felix, Krysta M.; Jaimez, Ivan A.; Nguyen, Thuy-Vi V.; Ma, Heqing; Raslan, Walid A.; Klinger, Christina N.; Doyle, Kristian P.; Wu, Hsin-Jung J.; Univ Arizona, Dept Immunobiol, Tucson, AZ 85721 USA; Univ Arizona, Coll Med, Dept Neurol, Tucson, AZ USA; et al. (FRONTIERS MEDIA SA, 2018-04-18)
      Streptococcus pneumoniae causes infection-related mortality worldwide. lmmunocompromised individuals, including young children, the elderly, and those with immunodeficiency, are especially vulnerable, yet little is known regarding S. pneumoniae-related pathogenesis and protection in immunocompromised hosts. Recently, strong interest has emerged in the gut microbiota's impact on lung diseases, or the "gut-lung axis." However, the mechanisms of gut microbiota protection against gut-distal lung diseases like pneumonia remain unclear. We investigated the role of the gut commensal, segmented filamentous bacteria (SFB), against pneumococcal pneumonia in immunocompetent and immunocompromised mouse models. For the latter, we chose the Rag(-/-) model, with adaptive immune deficiency. lmmunocompetent adaptive protection against S. pneumoniae infection is based on antibodies against pneumococcal capsular polysaccharides, prototypical T cell independent-II (TI-II) antigens. Although SFB colonization enhanced TI-II antibodies in C57BL/6 mice, our data suggest that SFB did not further protect these immunocompetent animals. Indeed, basal B cell activity in hosts without SFB is sufficient for essential protection against S. pneumoniae. However, in immunocompromised Rag(-/-) mice, we demonstrate a gut-lung axis of communication, as SFB influenced lung protection by regulating innate immunity. Neutrophil resolution is crucial to recovery, since an unchecked neutrophil response causes severe tissue damage. We found no early neutrophil recruitment differences between hosts with or without SFB; however, we observed a significant drop in lung neutrophils in the resolution phase of S. pneumoniae infection, which corresponded with lower CD47 expression, a molecule that inhibits phagocytosis of apoptotic cells, in SFB-colonized Rag(-/-) mice. SFB promoted a shift in lung neutrophil phenotype from inflammatory neutrophils expressing high levels of CD18 and low levels of CD62L, to pro-resolution neutrophils with low CD18 and high CD62L. Blocking CD47 in SFB(-) mice increased pro-resolution neutrophils, suggesting CD47 down-regulation may be one neutrophil-modulating mechanism SFB utilizes. The SFB-induced lung neutrophil phenotype remained similar with heat-inactivated S. pneumoniae treatment, indicating these SFB-induced changes in neutrophil phenotype during the resolution phase are not simply secondary to better bacterial clearance in SFB(+) than SFB(-) mice. Together, these data demonstrate that the gut commensal SFB may provide much-needed protection in immunocompromised hosts in part by promoting neutrophil resolution post lung infection.
    • The impact of age and gut microbiota on Th17 and Tfh cells in K/BxN autoimmune arthritis

      Teng, Fei; Felix, Krysta M.; Bradley, C. Pierce; Naskar, Debdut; Ma, Heqing; Raslan, Walid A.; Wu, Hsin-Jung Joyce; Univ Arizona, Dept Immunobiol; Univ Arizona, Coll Med, Arizona Arthrit Ctr (BIOMED CENTRAL LTD, 2017-08-15)
      Background: Age is an important risk factor for rheumatoid arthritis (RA), which often develops in middle age. However, how age-associated changes in immunity impact RA is poorly understood. Gut microbiota are known to be involved in the pathogenesis of RA, but the effects of microbiota in older subjects remain mostly unknown. Methods: We used segmented filamentous bacteria (SFB), a gut commensal species with immunomodulatory effects, and K/BxN mice, a T cell receptor (TCR) transgenic model, to study the effect of age and microbiota on autoimmune arthritis. Comparing young and middle-aged K/BxN T cells of the same TCR specificity allows us to study T cells with an age focus eliminating a key variable: TCR repertoire alteration with age. In addition to joints, we also studied pathological changes in the lung, an important extra-articular RA manifestation. We used flow cytometry to evaluate T follicular helper (Tfh) and T helper 17 (Th17) cells, as they both contribute to autoantibody production, a key disease index in both RA and K/BxN arthritis. Results: Middle-aged K/BxN mice had aggravated arthritis and pathological changes in the lung compared to young mice. Middle-aged mice displayed a strong accumulation of Tfh but not Th17 cells, and had defective Th17 differentiation and low expression of interleukin-23, a critical cytokine for Th17 maintenance. Although a soaring Tfh cell population accompanied by robust germinal center B cell responses were found in middle-aged mice, there was decreased cycling of Tfh cells, and SFB only induced the non-Tfh cells to upregulate Bcl-6, the Tfh master transcription factor, in the young but not the middle-aged group. Finally, the accumulated Tfh cells in middle-aged mice had an effector phenotype (CD62LloCD44hi). Conclusion: Age-dependent Tfh cell accumulation may play a crucial role in the increased autoimmune disease phenotype in middle-age. SFB, a potent stimulus for inducing Tfh differentiation, fails to promote Tfh differentiation in middle-aged K/BxN mice, suggesting that most of the middle-aged Tfh cells with an effector phenotype are Tfh effector memory cells induced at an earlier age. Our results also indicate that exposure to immunomodulatory commensals may allow the young host to develop an overactive immune system reminiscent of that found in the middle-aged host.
    • P2RX7 Deletion in T Cells Promotes Autoimmune Arthritis by Unleashing the Tfh Cell Response

      Felix, Krysta M.; Teng, Fei; Bates, Nicholas A.; Ma, Heqing; Jaimez, Ivan A.; Sleiman, Kiah C.; Tran, Nhan L.; Wu, Hsin-Jung Joyce; Univ Arizona, Dept Immunobiol; Univ Arizona, Coll Med, Arizona Arthrit Ctr (FRONTIERS MEDIA SA, 2019-03-19)
      Rheumatoid arthritis (RA) is an autoimmune disease that affects similar to 1% of the world's population. B cells and autoantibodies play an important role in the pathogenesis of RA. The P2RX7 receptor is an ATP-gated cation channel and its activation results in the release of pro-inflammatory molecules. Thus, antagonists of P2RX7 have been considered to have potential as novel anti-inflammatory therapies. Although originally identified for its role in innate immunity, P2RX7 has recently been found to negatively control Peyer's patches (PP) T follicular helper cells (Tfh), which specialize in helping B cells, under homeostatic conditions. We have previously demonstrated that PP Tfh cells are required for the augmentation of autoimmune arthritis mediated by gut commensal segmented filamentous bacteria (SFB). Thus, we hypothesized that P2RX7 is required to control autoimmune disease by keeping the Tfh cell response in check. To test our hypothesis, we analyzed the impact of P2RX7 deficiency in vivo using both the original K/BxN autoimmune arthritis model and T cell transfers in the K/BxN system. We also examined the impact of P2RX7 ablation on autoimmune development in the presence of the gut microbiota SFB. Our data illustrate that contrary to exerting an anti-inflammatory effect, P2RX7 deficiency actually enhances autoimmune arthritis. Interestingly, SFB colonization can negate the difference in disease severity between WT and P2RX7-deficient mice. We further demonstrated that P2RX7 ablation in the absence of SFB caused reduced apoptotic Tfh cells and enhanced the Tfh response, leading to an increase in autoantibody production. It has been shown that activation of TIGIT, a well-known T cell exhaustion marker, up-regulates anti-apoptotic molecules and promotes T cell survival. We demonstrated that the reduced apoptotic phenotype of P2rx7(-/-) Tfh cells is associated with their increased expression of TIGIT. This suggested that while P2RX7 was regulating the Tfh population by promoting cell death, TIGIT may have been opposing P2RX7 by inhibiting cell death. Together, these results demonstrated that systemic administration of general P2RX7 antagonists may have detrimental effects in autoimmune therapies, especially in Tfh cell-dependent autoimmune diseases, and cell-specific targeting of P2RX7 should be considered in order to achieve efficacy for P2RX7-related therapy.