Activation of TGF- beta by dendritic cells (DCs) expressing alpha v beta 8 integrin is essential for the generation of intestinal regulatory T cells (Tregs) that in turn promote tolerance to ...intestinal Ags. We have recently shown that alpha v beta 8 integrin is preferentially expressed by CD103+ DCs and confers their ability to activate TGF- beta and generate Tregs. However, how these DCs become specialized for this vital function is unknown. In this study, we show that beta 8 expression is controlled by a combination of factors that include DC lineage and signals derived from the tissue microenvironment and microbiota. Specifically, our data demonstrate that TGF- beta itself, along with retinoic acid and TLR signaling, drives expression of alpha v beta 8 in DCs. However, these signals only result in high levels of beta 8 expression in cells of the cDC1 lineage, CD8 alpha +, or CD103+CD11b- DCs, and this is associated with epigenetic changes in the Itgb8 locus. Together, these data provide a key illustrative example of how microenvironmental factors and cell lineage drive the generation of regulatory alpha v beta 8-expressing DCs specialized for activation of TGF- beta to facilitate Treg generation.
CD4+ follicular helper T cells (Tfh) are essential for germinal center (GC) reactions in the lymph node that generate high-affinity, long-lived plasma cells (LLPCs). Temporal GC analysis suggests B ...memory cells (Bmem) are generated early, while LLPCs are generated late in the GC reaction. Distinct roles for Tfh at these temporally different stages are not yet clear. Tfh entry into the GC is highly dynamic and the signals that maintain Tfh within the GC for support of late LLPC production are poorly understood. The GC is marked by inflammation-induced presentation of specific ECM components. To determine if T cell recognition of these ECM components played a role in Tfh support of the GC, we immunized mice with a T cell-restricted deletion of the ECM-binding integrin αV (αV-CD4 cKO). T cell integrin αV deletion led to a striking defect in the number and size of the GCs following immunization with OVA protein in complete Freund’s adjuvant. The GC defect was not due to integrin αV deficiency impeding Tfh generation or follicle entry or the ability of αV-CD4 cKO Tfh to contact and support B cell activation. Instead, integrin αV was essential for T cell-intrinsic accumulation within the GC. Altered Tfh positioning resulted in lower-affinity antibodies and a dramatic loss of LLPCs. Influenza A infection revealed that αV integrin was not required for Tfh support of Bmem but was essential for Tfh support of LLPCs. We highlight an αV integrin–ECM-guided mechanism of Tfh GC accumulation that selectively impacts GC output of LLPCs but not Bmem.
Autophagy plays an important role in maintaining cell homeostasis by providing nutrients during periods of starvation and removing damaged organelles from the cytoplasm. A marker in the autophagic ...process is the reversible conjugation of LC3, a membrane scaffolding protein, to double membrane autophagosomes. Recently, a role for LC3 in the elimination of pathogenic bacteria and fungi, including Candida albicans (C. albicans), was demonstrated, but these organisms reside in single membrane phagosomes. This process is distinct from autophagy and is termed LC3-associated phagocytosis (LAP). This review will detail the hallmarks of LAP that distinguish it from classical autophagy and review the role of autophagy proteins in host response to C. albicans and other pathogenic fungi.
Germinal centers (GCs) are major sites of clonal B cell expansion and generation of long-lived, high-affinity antibody responses to pathogens. Signaling through TLRs on B cells promotes many aspects ...of GC B cell responses, including affinity maturation, class switching, and differentiation into long-lived memory and plasma cells. A major challenge for effective vaccination is identifying strategies to specifically promote GC B cell responses. Here, we have identified a mechanism of regulation of GC B cell TLR signaling, mediated by αv integrins and noncanonical autophagy. Using B cell-specific αv-KO mice, we show that loss of αv-mediated TLR regulation increased GC B cell expansion, somatic hypermutation, class switching, and generation of long-lived plasma cells after immunization with virus-like particles (VLPs) or antigens associated with TLR ligand adjuvants. Furthermore, targeting αv-mediated regulation increased the magnitude and breadth of antibody responses to influenza virus vaccination. These data therefore identify a mechanism of regulation of GC B cells that can be targeted to enhance antibody responses to vaccination.
Systemic lupus erythematosus (SLE) is defined by loss of B cell tolerance, resulting in production of autoantibodies against nucleic acids and other cellular Ags. Aberrant activation of TLRs by ...self-derived RNA and DNA is strongly associated with SLE in patients and in mouse models, but the mechanism by which TLR signaling to self-ligands is regulated remains poorly understood. In this study, we show that αv integrin plays a critical role in regulating B cell TLR signaling to self-antigens in mice. We show that deletion of αv from B cells accelerates autoantibody production and autoimmune kidney disease in the Tlr7.1 transgenic mouse model of SLE. Increased autoimmunity was associated with specific expansion of transitional B cells, extrafollicular IgG2c-producing plasma cells, and activation of CD4 and CD8 T cells. Our data show that αv-mediated regulation of TLR signaling in B cells is critical for preventing autoimmunity and indicate that loss of αv promotes escape from tolerance. Thus, we identify a new regulatory pathway in autoimmunity and elucidate upstream signals that adjust B cell activation to prevent development of autoimmunity in a mouse model.
Mast cells (MCs) within the airway epithelium in asthma are closely related to airway dysfunction, but cross talk between airway epithelial cells (AECs) and MCs in asthma remains incompletely ...understood. Human rhinovirus (RV) infections are key triggers for asthma progression, and AECs from individuals with asthma may have dysregulated antiviral responses.
We utilized primary AECs in an ex vivo coculture model system to examine cross talk between AECs and MCs after epithelial rhinovirus infection.
Primary AECs were obtained from 11 children with asthma and 10 healthy children, differentiated at air–liquid interface, and cultured in the presence of laboratory of allergic diseases 2 (LAD2) MCs. AECs were infected with rhinovirus serogroup A 16 (RV16) for 48 hours. RNA isolated from both AECs and MCs underwent RNA sequencing. Direct effects of epithelial-derived interferons on LAD2 MCs were examined by real-time quantitative PCR.
MCs increased expression of proinflammatory and antiviral genes in AECs. AECs demonstrated a robust antiviral response after RV16 infection that resulted in significant changes in MC gene expression, including upregulation of genes involved in antiviral responses, leukocyte activation, and type 2 inflammation. Subsequent ex vivo modeling demonstrated that IFN-β induces MC type 2 gene expression. The effects of AEC donor phenotype were small relative to the effects of viral infection and the presence of MCs.
There is significant cross talk between AECs and MCs, which are present in the epithelium in asthma. Epithelial-derived interferons not only play a role in viral suppression but also further alter MC immune responses including specific type 2 genes.
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Activation of TGF-β by dendritic cells (DCs) expressing αvβ8 integrin is essential for the generation of intestinal regulatory T cells (Tregs) that in turn promote tolerance to intestinal Ags. We ...have recently shown that αvβ8 integrin is preferentially expressed by CD103(+) DCs and confers their ability to activate TGF-β and generate Tregs. However, how these DCs become specialized for this vital function is unknown. In this study, we show that β8 expression is controlled by a combination of factors that include DC lineage and signals derived from the tissue microenvironment and microbiota. Specifically, our data demonstrate that TGF-β itself, along with retinoic acid and TLR signaling, drives expression of αvβ8 in DCs. However, these signals only result in high levels of β8 expression in cells of the cDC1 lineage, CD8α(+), or CD103(+)CD11b(-) DCs, and this is associated with epigenetic changes in the Itgb8 locus. Together, these data provide a key illustrative example of how microenvironmental factors and cell lineage drive the generation of regulatory αvβ8-expressing DCs specialized for activation of TGF-β to facilitate Treg generation.
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