Steven K. Lundy

Th17 cells in human disease

Summary: Our understanding of the role of T cells in human disease is undergoing revision as a result of the discovery of T‐helper 17 (Th17) cells, a unique CD4+ T‐cell subset characterized by production of interleukin‐17 (IL‐17). IL‐17 is a highly inflammatory cytokine with robust effects on stromal cells in many tissues. Recent data in humans and mice suggest that Th17 cells play an important role in the pathogenesis of a diverse group of immune‐mediated diseases, including psoriasis, rheumatoid arthritis, multiple sclerosis, inflammatory bowel disease, and asthma. Initial reports also propose a role for Th17 cells in tumorigenesis and transplant rejection. Important differences, as well as many similarities, are emerging when the biology of Th17 cells in the mouse is compared with corresponding phenomena in humans. As our understanding of human Th17 biology grows, the mechanisms underlying many diseases are becoming more apparent, resulting in a new appreciation for both previously known and more recently discovered cytokines, chemokines, and feedback mechanisms. Given the strong association between excessive Th17 activity and human disease, new therapeutic approaches targeting Th17 cells are highly promising, but the potential safety of such treatments may be limited by the role of these cells in normal host defenses against infection.

Cells of the synovium in rheumatoid arthritis. T lymphocytes.

Recent findings have substantiated the importance of T lymphocytes to the pathogenesis of rheumatoid arthritis (RA). Here, we review emerging data regarding genetic predisposition, spontaneous animal models of arthritis, and cell-cell interactions that implicate T cells as driving synovial inflammation and joint destruction. Information regarding the proinflammatory role of interleukin-17-producing T cells and the functional state of regulatory T cells both in animal models and in patients with RA is also discussed. In light of the overwhelming evidence that disrupted T-cell homeostasis greatly contributes to joint pathology in RA, the therapeutic potential of targeting activators of pro-inflammatory T cells or their products is compelling.

Multiple Mechanisms of Immune Suppression by B Lymphocytes

Suppression of the immune system after the resolution of infection or inflammation is an important process that limits immune-mediated pathogenesis and autoimmunity. Several mechanisms of immune suppression have received a great deal of attention in the past three decades. These include mechanisms related to suppressive cytokines, interleukin (IL)-10 and transforming growth factor (TGF)-β, produced by regulatory cells, and mechanisms related to apoptosis mediated by death ligands, Fas ligand (FasL) and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), expressed by killer or cytotoxic cells. Despite many lines of evidence supporting an important role for B lymphocytes as both regulatory and killer cells in many inflammatory settings, relatively little attention has been given to understanding the biology of these cells, their relative importance or their usefulness as therapeutic targets. This review is intended to give an overview of the major mechanisms of immunosuppression used by B lymphocytes during both normal and inflammatory contexts. The more recent discoveries of expression of granzyme B, programmed death 1 ligand 2 (PD-L2) and regulatory antibody production by B cells as well as the interactions of regulatory and killer B cells with regulatory T cells, natural killer T (NKT) cells and other cell populations are discussed. In addition, new evidence on the basis of independent characterizations of regulatory and killer CD5+ B cells point toward the concept of a multipotent suppressor B cell with seemingly high therapeutic potential.

Soluble egg antigen-stimulated T helper lymphocyte apoptosis and evidence for cell death mediated by FasL(+) T and B cells during murine Schistosoma mansoni infection.

ABSTRACT Granuloma formation around schistosomal eggs is induced by soluble egg antigens (SEA) and mediated by the activity of CD4+ Th lymphocytes and their cytokines. Regulation of the inflammatory Th cell response during infection is still insufficiently understood. The hypothesis of this study was that activation-induced cell death (AICD) of CD4+ T cells is involved in the immune inflammatory response. This study investigated the dynamics of splenic and granuloma CD4+ Th cell apoptosis and Fas ligand (FasL) expression during the acute and chronic stages of murine schistosomal infection. Enhanced apoptosis of freshly isolated CD4+ Th lymphocytes commenced after egg deposition and persisted during the peak and modulated phases of granuloma formation. After oviposition, CD4+, CD8+, and CD19+ splenocytes and granuloma cells expressed elevated levels of FasL but FasL expression declined during the downmodulated stage of infection. In culture, SEA induced splenic and granuloma CD4+ T-cell apoptosis and stimulated expression of FasL on splenic but not granuloma CD4+ T cells, CD8+ T cells, and CD19+ B cells. SEA-stimulated splenocytes and granuloma cells preferentially lysed a Fas-transfected target cell line. Depletion of B cells from SEA-stimulated splenic cultures decreased CD4+ T cell apoptosis. Coculture of purified splenic B cells with CD4+ T cells and adoptive transfer of purified B cells indicated that antigen-stimulated B cells can kill CD4+ Th cells. However, CD4+ T cells were the dominant mediators of apoptosis in the granuloma. This study indicates that AICD is involved in the apoptosis of CD4+ T cells during schistosomal infection.

Fas Ligand-Expressing B-1a Lymphocytes Mediate CD4+-T-Cell Apoptosis during Schistosomal Infection: Induction by Interleukin 4 (IL-4) and IL-10

ABSTRACT A previous study of the murine model of Schistosoma mansoni infection has implicated splenic CD19+ B lymphocytes as Fas ligand (FasL)-bearing mediators of CD4+ T-lymphocyte apoptosis. The present study shows that B-cell deficiency leads to decreased CD4+ T-cell apoptosis during infection and compares FasL expression and killer function of B-1a- and CD5− B-lymphocyte subsets. B-1a cells from uninfected mice displayed constitutive expression of FasL compared with that of CD5− B cells. FasL expression was enhanced following worm egg deposition and antigenic stimulation on both subsets of B cells. Purified B-1a cells from uninfected mice were potent effectors of CD4+ T-cell apoptosis, and the killing effect was enhanced during schistosome infection. FasL expression by splenic B cells required CD4+-T-cell help that was replaced by addition of culture supernatants from antigen-stimulated splenocytes of infected mice. The culture-supernatant-stimulated FasL expression was inhibited by anti-interleukin 10 (IL-10) and anti-IL-4 antibodies. Culture of purified B cells with recombinant IL-4 (rIL-4), rIL-10, and soluble egg antigens (SEA) led to increased expression of FasL on B-1a cells. These results suggest that FasL-expressing, splenic B-1a cells are important mediators of SEA-stimulated CD4+-T-cell apoptosis and that maximal FasL expression on B-1a cells is dependent on antigenic stimulation and the presence of IL-4 and IL-10.

Killer B lymphocytes: the evidence and the potential

Immune regulation plays a critical role in controlling potentially dangerous inflammation and maintaining health. The Fas ligand/Fas receptor axis has been studied extensively as a mechanism of killing T cells and other cells during infections, autoimmunity, and cancer. FasL expression has been primarily attributed to activated T cells and NK cells. Evidence has emerged that B lymphocytes can express FasL and other death-inducing ligands, and can mediate cell death under many circumstances. Among B cell subsets, the expression of both Fas ligand and IL-10 is highest on the CD5+ B cell population, suggesting that CD5+ B cells may have a specialized regulatory function. The relevance of killer B cells to normal immune regulation, disease pathogenesis, and inflammation is discussed.

Soluble Egg Antigens from Schistosoma mansoni Induce Angiogenesis-Related Processes by Up-Regulating Vascular Endothelial Growth Factor in Human Endothelial Cells

Schistosomiasis mansoni is characterized by hepatic granuloma formation. Endothelial cell activation within these granulomas may contribute to their development and to increased vascularization in the granuloma periphery. The earliest event in granuloma formation is the lodging of schistosome eggs within presinusoidal capillaries. The eggs secrete factors that may activate endothelial cells. This study investigated the effects of Schistosoma mansoni soluble egg antigen (SEA) on angiogenic processes: proliferation, tube formation, and apoptosis of human umbilical vein endothelial cells (HUVECs). HUVECs require serum and growth factors to proliferate in vitro. Proliferation occurred when SEA or live eggs were substituted for growth factors, but not for serum. SEA increased HUVEC tube formation and decreased HUVEC apoptosis after serum and growth factor deprivation. Messenger RNA for vascular endothelial growth factor (VEGF) increased 2-fold in SEA-treated HUVECs. These findings suggest that products secreted by schistosome eggs may promote angiogenesis within hepatic granulomas by up-regulating endothelial cell VEGF.

Porphyromonas gingivalis oral infection exacerbates the development and severity of collagen-induced arthritis

IntroductionClinical studies suggest a direct influence of periodontal disease (PD) on serum inflammatory markers and disease assessment of patients with established rheumatoid arthritis (RA). However, the influence of PD on arthritis development remains unclear. This investigation was undertaken to determine the contribution of chronic PD to immune activation and development of joint inflammation using the collagen-induced arthritis (CIA) model.MethodsDBA1/J mice orally infected with Porphyromonas gingivalis were administered with collagen II (CII) emulsified in complete Freund’s adjuvant (CFA) or incomplete Freund’s adjuvant (IFA) to induce arthritis. Arthritis development was assessed by visual scoring of paw swelling, caliper measurement of the paws, mRNA expression, paw micro-computed tomography (micro-CT) analysis, histology, and tartrate resistant acid phosphatase for osteoclast detection (TRAP)-positive immunohistochemistry. Serum and reactivated splenocytes were evaluated for cytokine expression.ResultsMice induced for PD and/or arthritis developed periodontal disease, shown by decreased alveolar bone and alteration of mRNA expression in gingival tissues and submandibular lymph nodes compared to vehicle. P. gingivalis oral infection increased paw swelling and osteoclast numbers in mice immunized with CFA/CII. Arthritis incidence and severity were increased by P. gingivalis in mice that received IFA/CII immunizations. Increased synovitis, bone erosions, and osteoclast numbers in the paws were observed following IFA/CII immunizations in mice infected with P gingivalis. Furthermore, cytokine analysis showed a trend toward increased serum Th17/Th1 ratios when P. gingivalis infection was present in mice receiving either CFA/CII or IFA/CII immunizations. Significant cytokine increases induced by P. gingivalis oral infection were mostly associated to Th17-related cytokines of reactivated splenic cells, including IL-1β, IL-6, and IL-22 in the CFA/CII group and IL-1β, tumor necrosis factor-α, transforming growth factor-β, IL-6 and IL-23 in the IFA/CII group.ConclusionsChronic P. gingivalis oral infection prior to arthritis induction increases the immune system activation favoring Th17 cell responses, and ultimately accelerating arthritis development. These results suggest that chronic oral infection may influence RA development mainly through activation of Th17-related pathways.

Attenuation of Allergen-Induced Responses in CCR6−/− Mice Is Dependent upon Altered Pulmonary T Lymphocyte Activation

We have established a defect in CCR6−/− mice in response to a cockroach allergen airway challenge characterized by decreased IL-5 production, reduced CD4+ T and B cells as well as decreased eosinophil accumulation. To determine the nature of the defect in CCR6−/− mice T lymphocyte populations from allergen-sensitized wild-type mice were transferred into sensitized CCR6−/− mice. The reconstituted response was characterized by an increase in IL-5 levels, eosinophil accumulation, and serum IgE levels in recipient CCR6−/− mice. Analysis of lymphocytes from draining lymph nodes of CCR6+/+ and CCR6−/− sensitized or challenged mice demonstrated a significant decrease in IL-5 and IL-13 production in CCR6−/− mice. In contrast, the systemic response in allergen-rechallenged spleen cells demonstrated no significant alteration in allergen-induced cytokine production. Transfer of isolated splenic T lymphocytes from sensitized CCR6+/+ mice induced airway hyperresponsiveness in wild-type but not CCR6−/− naive mice, suggesting that T cells alone were not sufficient to induce airway hyperresponsiveness in CCR6−/− mice. Additional analysis demonstrated decreased CD11c+, CD11b+ and CD11c, and B220 subsets of dendritic cells in the lungs of CCR6−/− mice after allergen challenge. Using in vitro cell mixing studies with isolated pulmonary CD4+ T cells and CD11c+ cells from CCR6+/+ or CCR6−/− mice, we demonstrate alterations in both CCR6−/− T cells and CCR6−/− pulmonary APCs to elicit IL-5 responses. Altogether, the defect in CCR6−/− mice appears to be primarily due to an alteration in T cell activation, but also appears to include local pulmonary APC defects.

Deficiency of regulatory B cells increases allergic airway inflammation

Abstract.Objective: To investigate the effect of the X-linked immunodeficiency (Xid) B cell defect on the response to the cockroach allergen in mice. Methods: Two cockroach allergen immunization and challenge protocols were employed to sensitize CBA/J wild-type and CBA/CaHN-btk(-/-)xid/J (Xid) mice. Blood and tissue samples were collected 24 and 48 hrs after the last intratracheal antigen challenge and were analyzed for several parameters of allergic inflammation. Results: Nearly equivalent amounts of serum IgE were detected in Xid and CBA/J mice after short-term antigen challenge despite the B cell deficiency in Xid mice. A decreased concentration of IgE was detected in CBA/J mice after repeated allergen challenges but not in the Xid mice. Correlating with the discrepancy in serum IgE levels, higher levels of IL-13, IL-5, IL-10 and CCL5 were measured in whole lung homogenates from allergen-challenged Xid mice compared to CBA/J mice. In addition, draining lymph node cells from Xid mice expressed elevated levels of IL-4, IL-5, IL-10 and IFNγ mRNA compared to cells from CBA/J mice after in vitro culture with cockroach antigen. An increase in lung inflammation, interstitial eosinophilia and mucus production was also observed in allergen-challenged Xid mice. CD95L expression increased on B-1a cells following allergen challenge, which was accompanied by an increase in lung CD4+ Th cell apoptosis in wild-type CBA/J mice. In contrast, Xid mice did not have an increase in CD4+ T cell apoptosis following allergen challenge. Conclusions: These data suggest a regulatory role for B-1a cells in reducing cytokine production, pulmonary inflammation, and CD4+ T cell survival during cockroach allergen-induced airway inflammation.