Description: MHC class II (MHCII)–influenced CD4 + T cell differentiation and function play critical roles in regulating the development of autoimmunity. The lack of hematopoietic MHCII causes autoimmune disease that leads to severe wasting in syngeneic recipients. Using murine models of bone marrow transplantation (BMT), we find that MHCII –/– -〉wild-type BMT developed disease, with defective development of innate memory phenotype (IMP, CD44 hi /CD62L lo ) CD4 + T cells. Whereas conventional regulatory T cells are unable to suppress pathogenesis, IMP CD4 + T cells, which include conventional regulatory T cells, can suppress pathogenesis in MHCII –/– -〉wild-type chimeras. The functional development of IMP CD4 + T cells requires hematopoietic but not thymic MHCII. B cells and hematopoietic CD80/86 regulate the population size, whereas MHCII expression by dendritic cells is sufficient for IMP CD4 + T cell functional development and prevention of pathogenesis. Furthermore, the absence of Tec kinase IL-2–inducible T cell kinase in MHCII –/– donors leads to preferential development of IMP CD4 + T cells and partially prevents pathogenesis. We conclude that dendritic cells-MHCII and IL-2–inducible T cell kinase regulate the functional development of IMP CD4 + T cells, which suppresses the development of autoimmune disorder in syngeneic BMTs.

Description: IL-17–producing Th17 cells have gradually become considered as key factors in the pathogenesis of many autoimmune diseases, including multiple sclerosis (MS). Although the involvement of certain microRNAs in the development of MS has been reported, their role in Th17-driven autoimmunity is still poorly understood. In this study, we identified microRNA (miR)-15b as an important factor in Th17-associated effects and determined that the expression of miR-15b is significantly downregulated in MS patients and in mice with experimental autoimmune encephalomyelitis. Overexpression of miR-15b alleviated experimental autoimmune encephalomyelitis, whereas knockdown of miR-15b aggravated it. We demonstrated that miR-15b suppressed Th17 differentiation both in vivo and in vitro. We also found that O -linked  N -acetylglucosamine transferase is a potential target of miR-15b, enabling it to affect the transcriptional regulation of retinoic acid–related orphan receptor T through O -linked  N -acetylglucosamine glycosylation of NF-B. These results contribute to the importance of miR-15b in Th17 differentiation and the pathogenesis of MS.

Description: We previously reported that NOD.c3c4 mice develop spontaneous autoimmune biliary disease (ABD) with anti-mitochondrial Abs, histopathological lesions, and autoimmune T lymphocytes similar to human primary biliary cholangitis. In this article, we demonstrate that ABD in NOD.c3c4 and related NOD ABD strains is caused by a chromosome 1 region that includes a novel mutation in polycystic kidney and hepatic disease 1 ( Pkhd1 ). We show that a long terminal repeat element inserted into intron 35 exposes an alternative polyadenylation site, resulting in a truncated Pkhd1 transcript. A novel NOD congenic mouse expressing aberrant Pkhd1 , but lacking the c3 and c4 chromosomal regions (NOD. Abd3 ), reproduces the immunopathological features of NOD ABD. RNA sequencing of NOD. Abd3 common bile duct early in disease demonstrates upregulation of genes involved in cholangiocyte injury/morphology and downregulation of immunoregulatory genes. Consistent with this, bone marrow chimera studies show that aberrant Pkhd1 must be expressed in the target tissue (cholangiocytes) and the immune system (bone marrow). Mutations of Pkhd1 produce biliary abnormalities in mice but have not been previously associated with autoimmunity. In this study, we eliminate clinical biliary disease by backcrossing this Pkhd1 mutation onto the C57BL/6 genetic background; thus, the NOD genetic background (which promotes autoimmunity) is essential for disease. We propose that loss of functional Pkhd1 on the NOD background produces early bile duct abnormalities, initiating a break in tolerance that leads to autoimmune cholangitis in NOD. Abd3 congenic mice. This model is important for understanding loss of tolerance to cholangiocytes and is relevant to the pathogenesis of several human cholangiopathies.

Description: Emergency (stress) granulopoiesis is an episodic process for the production of granulocytes in response to infectious challenge. We previously determined that Fanconi C, a component of the Fanconi DNA-repair pathway, is necessary for successful emergency granulopoiesis. Fanconi anemia results from mutation of any gene in this pathway and is characterized by bone marrow failure (BMF) in childhood and clonal progression in adolescence. Although murine Fanconi anemia models exhibit relatively normal steady-state hematopoiesis, FANCC –/– mice are unable to mount an emergency granulopoiesis response. Instead, these mice develop BMF and die during repeated unsuccessful emergency granulopoiesis attempts. In FANCC –/– mice, BMF is associated with extensive apoptosis of hematopoietic stem and progenitor cells through an undefined mechanism. In this study, we find that TP53 haploinsufficiency completely rescues emergency granulopoiesis in FANCC –/– mice and protects them from BMF during repeated emergency granulopoiesis episodes. Instead, such recurrent challenges accelerated clonal progression in FANCC –/– TP53 +/– mice. In FANCC –/– mice, BMF during multiple emergency granulopoiesis attempts was associated with increased ataxia telangiectasia and Rad3-related protein (Atr) and p53 activation with each attempt. In contrast, we found progressive attenuation of expression and activity of Atr, and consequent p53 activation and apoptosis, in the bone marrow of FANCC –/– TP53 +/– mice during this process. Therefore, activation of Atr—with consequent Fanconi-mediated DNA repair or p53-dependent apoptosis—is an essential component of emergency granulopoiesis and it protects the bone marrow from genotoxic stress during this process.

Description: NK cells, which are highly enriched in the liver, are potent regulators of antiviral T cells and immunopathology in persistent viral infection. We investigated the role of the NKG2D axis in T cell/NK cell interactions in hepatitis B. Activated and hepatitis B virus (HBV)–specific T cells, particularly the CD4 fraction, expressed NKG2D ligands (NKG2DL), which were not found on T cells from healthy controls ( p 〈 0.001). NKG2DL-expressing T cells were strikingly enriched within HBV-infected livers compared with the periphery or to healthy livers ( p 〈 0.001). NKG2D + NK cells were also increased and preferentially activated in the HBV-infected liver ( p 〈 0.001), in direct proportion to the percentage of MICA/B-expressing CD4 T cells colocated within freshly isolated liver tissue ( p 〈 0.001). This suggests that NKG2DL induced on T cells within a diseased organ can calibrate NKG2D-dependent activation of local NK cells; furthermore, NKG2D blockade could rescue HBV-specific and MICA/B-expressing T cells from HBV-infected livers. To our knowledge, this is the first ex vivo demonstration that non-virally infected human T cells can express NKG2DL, with implications for stress surveillance by the large number of NKG2D-expressing NK cells sequestered in the liver.

Description: Innate memory phenotype (IMP) CD8 + T cells are nonconventional αβ T cells exhibiting features of innate immune cells and are significantly increased in the absence of ITK. Their developmental path and function are not clear. In this study, we show hematopoietic MHC class I (MHCI)-dependent generation of Ag-specific IMP CD8 + T cells using bone marrow chimeras. Wild-type bone marrow gives rise to IMP CD8 + T cells in MHCI –/– recipients, resembling those in Itk –/– mice, but distinct from those derived via homeostatic proliferation, and independent of recipient thymus. In contrast, MHCI –/– bone marrow does not lead to IMP CD8 + T cells in wild-type recipients. OTI IMP CD8 + T cells generated via this method exhibited enhanced early response to Ag without prior primary stimulation. Our findings suggest a method to generate Ag-specific "naive" CD8 + IMP T cells, as well as demonstrate that they are not homeostatic proliferation cells and can respond promptly in an Ag-specific fashion.

Description: Male NZW/BXSB.Yaa (W/B) mice express two copies of TLR7 and develop pathogenic autoantibodies, whereas females with only one copy of TLR7 have attenuated disease. Our goal was to analyze the regulation of the autoantibody response in male and female W/B mice bearing the autoreactive site-directed H chain transgene 3H9. Serum anti-dsDNA Abs appeared in males at 12 wk, and most had high-titer IgG anti-dsDNA and anti-cardiolipin Abs and developed 〉300 mg/dl proteinuria by 8 mo. Females had only low-titer IgG anti-cardiolipin Abs, and none developed proteinuria by 1 y. Males had a smaller marginal zone than females with a repertoire that was distinct from the follicular repertoire, indicating that the loss of marginal zone B cells was not due to diversion to the follicular compartment. Vk5-43 and Vk5-48, which were rare in the naive repertoire, were markedly overrepresented in the germinal center repertoire of both males and females, but the VJ junctions differed between males and females with higher-affinity autoreactive B cells being selected into the germinal centers of males. Administration of IFN-α to females induced anti-cardiolipin and anti-DNA autoantibodies and proteinuria and was associated with a male pattern of junctional diversity in Vk5-43 and Vk5-48. Our studies are consistent with the hypothesis that presence of the Yaa locus, which includes an extra copy of Tlr7 , or administration of exogenous IFN-α relaxes the stringency for selection in the germinal centers resulting in increased autoreactivity of the Ag-driven B cell repertoire.

Description: IL-2–inducible T cell kinase (ITK) is a key signaling mediator downstream of TCR, mediating T cell positive selection, as well as innate T cell and CD4 + Th2/Th17 differentiation. In this article, we show that ITK also negatively tunes IL-2–induced expansion of conventional Foxp3-expressing regulatory T cells (Tregs). In vivo, Treg abundance is inversely correlated with ITK expression, and inducible Treg development is inversely dependent on ITK kinase activity. While Treg development normally requires both hematopoietic and thymic MHC class 2 (MHC2) expression, the absence of ITK allows Treg development with MHC2 expression in either compartment, with preference for selection by thymic MHC2, suggesting a gatekeeper role for ITK in ensuring that only Tregs selected by both thymic and hematopoietic MHC2 survive selection. Although ITK suppresses Treg development and is not required for maintenance of neuropilin-1–positive natural Tregs in the periphery, it is indispensable for Treg functional suppression of naive CD4 + T cell–induced colitis in Rag –/– recipients. ITK thus regulates the development and function of Tregs.

Description: Mast cells play critical roles in allergic responses. Calcium signaling controls the function of these cells, and a role for actin in regulating calcium influx into cells has been suggested. We have previously identified the actin reorganizing protein Drebrin as a target of the immunosuppressant 3,5-bistrifluoromethyl pyrazole, which inhibits calcium influx into cells. In this study, we show that Drebrin –/– mice exhibit reduced IgE-mediated histamine release and passive systemic anaphylaxis, and Drebrin –/– mast cells also exhibit defects in FcRI-mediated degranulation. Drebrin –/– mast cells exhibit defects in actin cytoskeleton organization and calcium responses downstream of the FcRI, and agents that relieve actin reorganization rescue mast cell FcRI-induced degranulation. Our results indicate that Drebrin regulates the actin cytoskeleton and calcium responses in mast cells, thus regulating mast cell function in vivo.

Description: The type I IFN (IFN-α) response is crucial for viral clearance during primary viral infections. Plasmacytoid dendritic cells (pDCs) are important early responders during systemic viral infections and, in some cases, are the sole producers of IFN-α. However, their role in IFN-α production during memory responses is unclear. We found that IFN-α production is absent during a murine viral memory response, despite colocalization of virus and pDCs to the splenic marginal zone. The absence of IFN was dependent on circulating Ab and was reversed by the transgenic expression of the activating human FcRIIA receptor on pDCs. Furthermore, FcRIIB was required for Sendai virus immune complex uptake by splenic pDCs in vitro, and internalization via FcRIIb prevented cargo from accessing TLR signaling endosomes. Thus, pDCs bind viral immune complexes via FcRIIB and prevent IFN-α production in vivo during viral memory responses. This Ab-dependent IFN-α regulation may be an important mechanism by which the potentially deleterious effects of IFN-α are prevented during a secondary infection.