Th17 cells are a distinct lineage of T helper cells that protect the body from bacterial and fungal infection. However, Th17 cells also contribute to inflammatory and autoimmune disorders such as ...multiple sclerosis. Th17 cell generation requires exposure of naive T cells to the cytokine TGF-β in combination with proinflammatory cytokines. Here we show that differentiation of Th17 cells is also critically dependent on αv integrins. In mice, lack of integrin αv in the immune system resulted in loss of Th17 cells in the intestine and lymphoid tissues. It also led to protection from experimental autoimmune encephalomyelitis (EAE). Further analysis indicated that αv integrins on DCs activated latent TGF-β during T cell stimulation and thereby promoted differentiation of Th17 cells. Furthermore, pharmacologic inhibition of αv integrins using cyclic RGD peptides blocked TGF-β activation and Th17 cell generation in vitro and protected mice from EAE. These data demonstrate that activation of TGF-β by αv-expressing myeloid cells may be a critical step in the generation of Th17 cells and suggest that αv integrins could be therapeutic targets in autoimmune disease.
Abstract
Signaling through Toll-like receptors (TLR) has been implicated in activation of immune cell populations such as B lymphocytes. TLR ligands associated with self-antigens can drive increased ...self-reactive B cell responses however TLR ligands present in pathogenic products or vaccines can also enhance protective antibody responses. Our recent work has identified a novel mechanism by which αv integrins, a family of adhesion molecules and the autophagy proteins limit excessive B cell TLR signaling.
Specifically, we have found that αvβ3 integrin regulates TLR signaling (NFKB and IRF7 activation) by directing maturation of TLR containing endosomes, through activation of components of the autophagy pathway (LC3 and Atg5). B cells lacking either αv integrins or autophagy components show enhanced TLR signaling and increased proliferative responses to TLR ligands. Mice with disruption in this pathway develop increased autoantibodies with age and develop accelerated autoimmunity in murine lupus models. Therefore, we propose that αv-mediated regulation of TLR signaling exists to limit excessive B cell responses to self-antigens.
In addition, we find that mice in which αv is specifically deleted from B cells mount stronger antibody responses when immunized with exogenous antigens containing TLR-ligand adjuvants. Immune responses to these antigens are characterized by increased expansion of germinal center cells, increased somatic hyper-mutation and higher levels of high-affinity class-switched antibodies. Therefore this αv mediated regulation of TLR signaling not only regulates B cell responses to self-antigens but it is also important for regulating germinal center B cell responses and production of high-affinity antibodies.
Tetraspanins are a family of proteins possessing four transmembrane domains that help in lateral organization of plasma membrane proteins. These proteins interact with each other as well as other ...receptors and signaling proteins, resulting in functional complexes called "tetraspanin microdomains." Tetraspanins, including CD82, play an essential role in the pathogenesis of fungal infections. Dectin-1, a receptor for the fungal cell wall carbohydrate β-1,3-glucan, is vital to host defense against fungal infections. The current study identifies a novel association between tetraspanin CD82 and Dectin-1 on the plasma membrane of
-containing phagosomes independent of phagocytic ability. Deletion of CD82 in mice resulted in diminished fungicidal activity, increased
viability within macrophages, and decreased cytokine production (TNF-α, IL-1β) at both mRNA and protein level in macrophages. Additionally, CD82 organized Dectin-1 clustering in the phagocytic cup. Deletion of CD82 modulates Dectin-1 signaling, resulting in a reduction of Src and Syk phosphorylation and reactive oxygen species production. CD82 knockout mice were more susceptible to
as compared with wild-type mice. Furthermore, patient
-induced cytokine production was influenced by two human CD82 single nucleotide polymorphisms, whereas an additional CD82 single nucleotide polymorphism increased the risk for candidemia independent of cytokine production. Together, these data demonstrate that CD82 organizes the proper assembly of Dectin-1 signaling machinery in response to
.
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.
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 alpha.sub.v integrins and noncanonical autophagy. Using B cell-specific alpha.sub.v-KO mice, we show that loss of alpha.sub.v-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 alpha.sub.v-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.
Defects in apoptotic cell clearance are thought to contribute to autoimmunity by failure to induce tolerance, coupled with accumulation of immunogenic material. However, little is known about the ...contribution of apoptosis to immune responses at mucosal sites, where regulatory T cells (Treg cells) and other immune cells play an essential active role in maintaining tolerance to self‐associated antigens. In recent studies, we have found that αv integrins have an important role in apoptotic cell phagocytosis and induction of Treg cells in the intestine, and deletion of αv from myeloid cells causes colitis associated with failed apoptotic cell removal and loss of Treg cells. Our data show that activation of transforming growth factor (TGF)‐β by αvβ8 on dendritic cells (DCs) is essential for generating Treg cells and inducing mucosal tolerance. These results provide a mechanism by which tolerance to apoptotic cell–derived and –associated antigens is maintained by DC “licensing” at sites of high TGF‐β expression.
Summary The human soluble CD23 (sCD23) protein displays highly pleiotropic cytokine-like activity. Monocytic cells express the sCD23-binding integrins alphaVbeta3, alphaVbeta5, alphaMbeta2 and ...alphaXbeta2, but it is unclear which of these four integrins most acutely regulates sCD23-driven cytokine release. The hypothesis that ligation of different sCD23-binding integrins promoted release of distinct subsets of cytokines was tested. Lipopolysaccharide (LPS) and sCD23 promoted release of distinct groups of cytokines from the THP-1 model cell line. The sCD23-driven cytokine release signature was characterized by elevated amounts of RANTES (CCL5) and a striking increase in interleukin-8 (IL-8; CXCL8) secretion, but little release of macrophage inflammatory protein 1beta (MIP-1beta; CCL4). Antibodies to alphaVbeta3 or alphaXbeta2 both promoted IL-8 release, consistent with the sCD23-driven pattern, but both also evoked strong MIP-1beta secretion; simultaneous ligation of these two integrins further increased cytokine secretion but did not alter the pattern of cytokine output. In both model cell lines and primary tissue, integrin-mediated cytokine release was more pronounced in immature monocyte cells than in mature cells. The capacity of anti-integrin monoclonal antibodies to elicit a cytokine release response is epitope-dependent and also reflects the differentiation state of the cell. Although a pattern of cytokine release identical to that provoked by sCD23 could not be elicited with any individual anti-integrin monoclonal antibody, alphaXbeta2 and alphaVbeta3 appear to regulate IL-8 release, a hallmark feature of sCD23-driven cytokine secretion, more acutely than alphaMbeta2 or alphaVbeta5. PUBLICATION ABSTRACT
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