Endogenous Interleukin 4 Is Required for Development of Protective CD4+ T Helper Type 1 Cell Responses to Candida albicans

Interleukin (IL)-4–deficient mice were used to assess susceptibility to systemic or gastrointestinal Candida albicans infections, as well as parameters of innate and elicited T helper immunity. In the early stage of systemic infection with virulent C. albicans, an unopposed interferon (IFN)-γ response renders IL-4–deficient mice more resistant than wild-type mice to infection. Yet, IL-4–deficient mice failed to efficiently control infection in the late stage and succumbed to it. Defective IFN-γ and IL-12 production, but not IL-12 responsiveness, was observed in IL-4–deficient mice that failed to mount protective T helper type 1 cell (Th1)-mediated acquired immunity in response to a live vaccine strain of the yeast or upon mucosal immunization in vivo. In vitro, IL-4 primed neutrophils for cytokine release, including IL-12. However, late treatment with exogenous IL-4, while improving the outcome of infection, potentiated CD4⁺ Th1 responses even in the absence of neutrophils. These findings indicate that endogenous IL-4 is required for the induction of CD4⁺ Th1 protective antifungal responses, possibly through the combined activity on cells of the innate and adaptive immune systems.     

Atypical Disease after Bordetella pertussis Respiratory Infection of Mice with Targeted Disruptions of Interferon-γ Receptor or Immunoglobulin μ Chain Genes

Using a murine respiratory challenge model we have previously demonstrated a role for Th1 cells in natural immunity against Bordetella pertussis, but could not rule out a role for antibody. Here we have demonstrated that B. pertussis respiratory infection of mice with targeted disruptions of the genes for the IFN-γ receptor resulted in an atypical disseminated disease which was lethal in a proportion of animals, and was characterized by pyogranulomatous inflammation and postnecrotic scarring in the livers, mesenteric lymph nodes and kidneys. Viable virulent bacteria were detected in the blood and livers of diseased animals. An examination of the course of infection in the lung of IFN-γ receptor–deficient, IL-4–deficient and wild-type mice demonstrated that lack of functional IFN-γ or IL-4, cytokines that are considered to play major roles in regulating the development of Th1 and Th2 cells, respectively, did not affect the kinetics of bacterial elimination from the lung. In contrast, B cell–deficient mice developed a persistent infection and failed to clear the bacteria after aerosol inoculation. These findings demonstrate an absolute requirement for B cells or their products in the resolution of a primary infection with B. pertussis, but also define a critical role for IFN-γ in containing bacteria to the mucosal site of infection.     

IL-4–producing CD4+ T cells in reactive lymph nodes during helminth infection are T follicular helper cells

Interleukin (IL)-4 is the quintessential T helper type 2 (Th2) cytokine produced by CD4⁺ T cells in response to helminth infection. IL-4 not only promotes the differentiation of Th2 cells but is also critical for immunoglobulin (Ig) G1 and IgE isotype-switched antibody responses. Despite the IL-4–mediated link between Th2 cells and B lymphocytes, the location of IL-4–producing T cells in the lymph nodes is currently unclear. Using IL-4 dual reporter mice, we examined the Th2 response and IL-4 production in the draining mesenteric lymph nodes during infection with the enteric nematode Heligmosomoides polygyrus. We show that although IL-4–competent Th2 cells are found throughout the B and T cell areas, IL-4–producing Th2 cells are restricted to the B cell follicles and associate with germinal centers. Consistent with their localization, IL-4 producers express high levels of CXCR5, ICOS, PD-1, IL-21, and BCL-6, a phenotype characteristic of T follicular helper (Tfh) cells. Although IL-4 was dispensable for the generation of Th2 and Tfh cells, its deletion resulted in defective B cell expansion and maturation. Our report reveals the compartmentalization of Th2 priming and IL-4 production in the lymph nodes during infection, and identifies Tfh cells as the dominant source of IL-4 in vivo.IL-4 is widely recognized as the canonical marker for Th2-polarized CD4⁺ T cells (1). IL-4 was originally identified by its function as a B cell–stimulating factor (2, 3), and numerous in vivo models of infection concur that IL-4 is critical for the isotype switch of B cells to IgE and IgG1 (4–10). IL-4 also promotes the Th2 polarization of naive CD4⁺ T cells in vitro (11, 12). However, in vivo studies have found that Th2 cells can develop in mice deficient for IL-4, the IL-4Rα chain, or the IL-4R–associated Stat 6 (4–8). Collectively, these observations suggest that IL-4 production in sentinel lymph nodes draining a site of infection may be more important to support type 2 B cell responses rather than to establish the underlying Th2 response. Therefore, it stands to reason that the production of IL-4 by Th2 cells should preferentially occur in B cell follicles to optimize B cell help. However, the localization and characterization of IL-4–producing T cells in the lymph nodes has not been assessed.T follicular helper (Tfh) cells are a subset of CD4⁺ T cells that migrate to B cell follicles after activation and promote germinal center formation and B cell Ig isotype switching in mice and humans (13–16). Phenotypically, Tfh cells are characterized by expression of CXCR5 (an obligatory receptor for the follicle-homing chemokine CXCL13) (17), the inducible co-stimulatory receptor ICOS (18, 19), and the inhibitory receptors PD-1 (also known as CD279) (14) and B and T lymphocyte attenuator (BTLA) (13). A previous study (13) using model antigens in adjuvant have suggested that Tfh cells are a distinct lineage of T helper cells that arises independently of Th1, Th2, and Th17 effector subsets. To date, however, no studies have examined the Tfh response during infection with a Th2-polarizing pathogen. To unambiguously identify and localize Th2 cells and IL-4 production in the reactive lymph nodes in vivo, we infected IL-4 dual reporter mice (20), in which cells that express IL-4 are marked by GFP and IL-4–producing subsets additionally display surface huCD2, with the mouse gastrointestinal helminth parasite Heligmosomoides polygyrus. We find that IL-4–producing Th2 cells localize to the B cell follicles and exhibit a Tfh cell phenotype in the draining lymph nodes of infected animals. In addition, we find that although IL-4 is dispensable for the generation of Tfh cells, it is critical for a mature B cell response. To our knowledge, this is the first report to show the location of IL-4–producing T cells in the reactive lymph nodes after helminth infection. Furthermore, our results challenge the prevailing concept that Tfh cells are a distinct T helper lineage. Rather, we suggest that Tfh cells act to support the demands of the impending immune response.     

B cell intrinsic TLR signals amplify but are not required for humoral immunity

Although innate signals driven by Toll-like receptors (TLRs) play a crucial role in T-dependent immune responses and serological memory, the precise cellular and time-dependent requirements for such signals remain poorly defined. To directly address the role for B cell–intrinsic TLR signals in these events, we compared the TLR response profile of germinal center (GC) versus naive mature B cell subsets. TLR responsiveness was markedly up-regulated during the GC reaction, and this change correlated with altered expression of the key adaptors MyD88, Mal, and IRAK-M. To assess the role for B cell–intrinsic signals in vivo, we transferred MyD88 wild-type or knockout B cells into B cell–deficient μMT mice and immunized recipient animals with 4-hydroxy-3-nitrophenylacetyl (NP) chicken gamma globulin. All recipients exhibited similar increases in NP-specific antibody titers during primary, secondary, and long-term memory responses. The addition of lipopolysaccharide to the immunogen enhanced B cell-intrinsic, MyD88-dependent NP-specific immunoglobulin (Ig)M production, whereas NP-specific IgG increased independently of TLR signaling in B cells. Our data demonstrate that B cell–intrinsic TLR responses are up-regulated during the GC reaction, and that this change significantly promotes antigen-specific IgM production in association with TLR ligands. However, B cell–intrinsic TLR signals are not required for antibody production or maintenance.     

T Helper Subset Differentiation in the Absence of Invariant Chain

The outcome of murine infection with Leishmania major is regulated by major histocompatibility complex class II–restricted T helper cells. Invariant chain-deficient (Ii −/−) mice have impaired ability to present major histocompatibility complex class II–restricted antigens, and reduced numbers of CD4⁺ T cells. Despite these deficits, C57BL/6 Ii −/− mice controlled L. major infection comparably to wild-type mice. As assessed by mRNA analysis and in vitro antigen restimulation for IFN-γ, Ii −/− mice had normal induction of Th1 subset differentiation even though antigen-dependent proliferation of their lymph node cells was substantially compromised. In addition, BALB/c Ii −/− mice exhibited a progressive course of infection and Th2 effector cell development that were comparable to that seen in wild-type BALB/c mice. We wished to determine whether this unexpected efficiency of T helper subset induction despite inefficient T cell stimulation could be modeled in vitro. In the presence of rIL-12 or rIL-4 naive parasite-specific transgenic T cells could mature into IFN-γ–or IL-4–secreting T helper cells, respectively, even when antigen presentation was suboptimal or antigen dose was submitogenic. These experiments demonstrate that activation of T helper cells to a threshold required for IL-2 production or proliferation is not required to achieve induction of disease-regulating T helper cell effector functions, and that pathogen-associated secondary activation signals may facilitate the full differentiation of T helper subsets during limiting presentation of antigenic peptides.Experimental infection of inbred strains of mice with Leishmania major remains an exceptional model for analysis of CD4⁺ subset differentiation in vivo (1). Control of disease is dependent on class II–restricted Th type 1 (Th1) cells and their production of IFN-γ which is required to activate macrophages to restrain intracellular replication of the organism. Studies in T cell– (2–4) and IFN-γ–deficient (5) mice have confirmed the critical requirements for these elements in host immunity. MHC class II–deficient mice from a genetically resistant background are completely susceptible to infection (6, 7), while MHC class I–deficient mice from a genetically resistant background retain resistance to infection (8). In contrast to most strains of mice, BALB animals are unable to contain L. major due to the development of an aberrant Th type 2 (Th2) response during infection. The absence of class I does not impact Th2 development or susceptibility in BALB/c mice (9). Leishmania replicates productively only in host macrophages within an endolysosomal-like compartment that contains MHC class II molecules, some of which are devoid of invariant chain (10, 11). Infection of macrophages in vitro is associated with diminished MHC class II–dependent presentation of exogenous antigens (12, 13). Although it is unclear whether this is due to degradation or inappropriate trafficking of MHC class II/peptide complexes from the parasitophorous vacuole (14), competent MHC class II molecules reach the cell surface as demonstrated by immunofluorescent, functional, and biochemical studies (12, 13, 15). Since invariant chain is involved in both targeting newly synthesized MHC class II molecules to peptide-generating compartments, and in protecting the peptide cleft during transit from the endoplasmic reticulum (16), we expected significant impairment in host immune responses to L. major using invariant chain–deficient (Ii −/−) mice. Unexpectedly, both Th1 and Th2 responses were maintained in mice on genetically resistant or susceptible backgrounds, respectively, emphasizing the capacity of the immune system to sustain T cell effector development even under conditions of suboptimal stimulation.     

Interferon γ Derived from CD4+ T Cells Is Sufficient to Mediate T Helper Cell Type 1 Development

Interferon γ (IFN-γ) has been implicated in T helper type 1 (Th1) cell development through its ability to optimize interleukin 12 (IL-12) production from macrophages and IL-12 receptor expression on activated T cells. Various systems have suggested a role for IFN-γ derived from the innate immune system, particularly natural killer (NK) cells, in mediating Th1 differentiation in vivo. We tested this requirement by reconstituting T cell and IFN-γ doubly deficient mice with wild-type CD4⁺ T cells and challenging the mice with pathogens that elicited either minimal or robust IL-12 in vivo (Leishmania major or Listeria monocytogenes, respectively). Th1 cells developed under both conditions, and this was unaffected by the presence or absence of IFN-γ in non-T cells. Reconstitution with IFN-γ–deficient CD4⁺ T cells could not reestablish control over L. major, even in the presence of IFN-γ from the NK compartment. These data demonstrate that activated T cells can maintain responsiveness to IL-12 through elaboration of endogenous IFN-γ without requirement for an exogenous source of this cytokine.     

Selective Expression and Functions of Interleukin 18 Receptor on T Helper (Th) Type 1 but not Th2 Cells

Interleukin (IL)-18 induces interferon (IFN)-γ synthesis and synergizes with IL-12 in T helper type 1 (Th1) but not Th2 cell development. We report here that IL-18 receptor (IL-18R) is selectively expressed on murine Th1 but not Th2 cells. IL-18R mRNA was expressed constitutively and consistently in long-term cultured clones, as well as on newly polarized Th1 but not Th2 cells. IL-18 sustained the expression of IL-12Rβ2 mRNA, indicating that IL-18R transmits signals that maintain Th1 development through the IL-12R complex. In turn, IL-12 upregulated IL-18R mRNA. Antibody against an IL-18R–derived peptide bound Th1 but not Th2 clones. It also labeled polarized Th1 but not Th2 cells derived from naive ovalbumin–T cell antigen receptor-αβ transgenic mice (D011.10). Anti–IL-18R antibody inhibited IL-18– induced IFN-γ production by Th1 clones in vitro. In vivo, anti–IL-18R antibody reduced local inflammation and lipopolysaccharide-induced mortality in mice. This was accompanied by shifting the balance from Th1 to Th2 responses, manifest as decreased IFN-γ and proinflammatory cytokine production and increased IL-4 and IL-5 synthesis. Therefore, these data provide a direct mechanism for the selective effect of IL-18 on Th1 but not Th2 cells. They also show that the synergistic effect of IL-12 and IL-18 on Th1 development may be due to the reciprocal upregulation of their receptors. Furthermore, IL-18R is a cell surface marker distinguishing Th1 from Th2 cells and may be a therapeutic target.     

MHCII-independent CD4+ T cells protect injured CNS neurons via IL-4

A body of experimental evidence suggests that T cells mediate neuroprotection following CNS injury; however, the antigen specificity of these T cells and how they mediate neuroprotection are unknown. Here, we have provided evidence that T cell–mediated neuroprotection after CNS injury can occur independently of major histocompatibility class II (MHCII) signaling to T cell receptors (TCRs). Using two murine models of CNS injury, we determined that damage-associated molecular mediators that originate from injured CNS tissue induce a population of neuroprotective, IL-4–producing T cells in an antigen-independent fashion. Compared with wild-type mice, IL-4–deficient animals had decreased functional recovery following CNS injury; however, transfer of CD4⁺ T cells from wild-type mice, but not from IL-4–deficient mice, enhanced neuronal survival. Using a culture-based system, we determined that T cell–derived IL-4 protects and induces recovery of injured neurons by activation of neuronal IL-4 receptors, which potentiated neurotrophin signaling via the AKT and MAPK pathways. Together, these findings demonstrate that damage-associated molecules from the injured CNS induce a neuroprotective T cell response that is independent of MHCII/TCR interactions and is MyD88 dependent. Moreover, our results indicate that IL-4 mediates neuroprotection and recovery of the injured CNS and suggest that strategies to enhance IL-4–producing CD4⁺ T cells have potential to attenuate axonal damage in the course of CNS injury in trauma, inflammation, or neurodegeneration.     

Expression of Recombination Activating Genes in Germinal Center B Cells: Involvement of Interleukin 7 (IL-7) and the IL-7 Receptor

Mouse germinal center (GC) B cells have been shown to undergo secondary V(D)J (V, variable; D, diversity; J, joining) recombination (receptor editing) mediated by the reexpressed products of recombination activating gene (RAG)-1 and RAG-2. We show here that interleukin (IL)-7 as well as IL-4 was effective in inducing functional RAG products in mouse IgD⁺ B cells activated via CD40 in vitro. Blocking of the IL-7 receptor (IL-7R) by injecting an anti– IL-7R monoclonal antibody resulted in a marked suppression of the reexpression of RAG-2 and subsequent V(D)J recombination in the draining lymph node of immunized mice, whereas RAG-2 expression was not impaired in immunized IL-4–deficient mice. Further, these peripheral B cells activated in vitro or in vivo were found to express IL-7R. These findings indicate a novel role for IL-7 and IL-7R in inducing receptor editing in GC B cells.     

Interleukin-4 Protects against a Genetically Linked Lupus-like Autoimmune Syndrome

Interleukin-4 (IL-4) provides support for humoral immune responses through upregulation of T helper (Th) type 2 cell differentiation, but it is not known whether IL-4 promotes antibodymediated autoimmune diseases such as systemic lupus erythematosus (SLE). Here, we show that the constitutive expression of an IL-4 transgene by B cells completely prevents the development of lethal lupus-like glomerulonephritis in the (NZW × C57BL/6.Yaa)F1 murine model of SLE. This was associated with marked changes in the serum levels of IgG subclasses, rather than in the total levels of anti-DNA antibodies, with a lack of IgG3, a decrease of IgG2a, and an increase in IgG1 subclasses, and by a strong reduction in the serum levels of gp70-antigp70 immune complexes. This effect of the transgene appears to result from a modulation of the Th1 versus Th2 autoimmune response, since the protected mice displayed comparably modified IgG2a and IgG3 antibody response against exogenous T cell–dependent antigen, but not against T cell–independent antigens. Thus, IL-4 prevents the development of this lupuslike autoimmune disease, most likely by downregulating the appearance of Th1-mediated IgG subclasses of autoantibodies such as the IgG3 autoantibodies which have been shown to be especially nephritogenic.Mice of the (NZB × NZW)F1 hybrid, mice of the MRL strain homozygous for the lpr gene (lymphoproliferation), and of the BXSB/MpJ strain carrying an autoimmune acceleration gene present on the Y chromosome, Yaa (Y-linked autoimmune acceleration), spontaneously develop a severe immune complex–mediated glomerulonephritis resembling human SLE (1). The spontaneous production of pathogenic IgG autoantibodies in these lupusprone mice reflects the intrinsic abnormal hyperactivity of B cells and their interaction with CD4⁺ Th cells in which the pattern of cytokine expression may have important immunopathological consequences (2). Among cytokines produced by Th cells, IL-4 has been shown to have important regulatory properties on humoral immune responses. First described as a costimulator for the proliferation of resting B cells, IL-4 has been also shown to enhance the expression of Ia molecules on resting B cells, to induce IgG1 and IgE antibody production, and to play a predominant role in vitro in the differentiation of CD4⁺ T cells into the Th type 2 subset (3). Notably, Th2 cells play an essential role in some humoral responses through the action of their cytokines such as IL-5, -6, and -10 on B cells (4–6).In view of the B cell–stimulatory properties and Th2 promoting activity ascribed to IL-4, it can be speculated that IL-4 may be involved in the development of autoantibody-mediated autoimmune diseases such as SLE. In fact, IL-4 has been shown to be an important mediator in the pathogenesis of murine lupus-like diseases induced by graftversus-host and host-versus-graft reactions, or by chemicals (7). This notion is also supported by the findings that treatment of lupus-prone (NZB × NZW)F1 mice with mAbs specific for the Th2-related cytokines IL-6 or -10 markedly delays onset of autoimmune disease (8, 9), and that administration of IL-5 or -10 is able to induce autoimmune anemia in anti-RBC autoantibody transgenic mice (10). It is, however, not yet known whether IL-4 promotes disease development in spontaneous murine models of SLE.To address this question, we determined the effect of constitutive expression of an IL-4 transgene by B cells on the development and progression of lupus-like syndrome. For this purpose, we have used the (NZW × C57BL/ 6.Yaa)F1 murine model of SLE (11), in which the development of an autoimmune syndrome in male mice is dependent on the abnormal autosomal NZW genome, and the presence of an unidentified mutant gene Yaa located on the Y chromosome derived from the lupus-prone BXSB strain (12). The IL-4 transgene was introduced into this lupusprone background by crossing C57BL/6.Yaa (B6.Yaa) males with females of the 129/Sv–IL-4 transgenic strain, which contains a single copy of murine IL-4–encoding cDNA under the control of IgH enhancer/promoter (13), and then crossing the F1 male progeny with NZW females. Our analysis of the development of SLE in these lupusprone mice indicates that the constitutive expression of the IL-4 transgene in B cells does not promote, but prevents, the development of lupus-like autoimmune syndrome, and provides a possible explanation for the capacity of IL-4 to control SLE by downregulating Th1-mediated IgG subclasses of autoantibodies.     

Induction of Airway Mucus Production By T Helper 2 (Th2) Cells: A Critical Role For Interleukin 4 In Cell Recruitment But Not Mucus Production

Airway inflammation is believed to stimulate mucus production in asthmatic patients. Increased mucus secretion is an important clinical symptom and contributes to airway obstruction in asthma. Activated CD4 Th1 and Th2 cells have both been identified in airway biopsies of asthmatics but their role in mucus production is not clear. Using CD4 T cells from mice transgenic for the OVA-specific TCR, we studied the role of Th1 and Th2 cells in airway inflammation and mucus production. Airway inflammation induced by Th2 cells was comprised of eosinophils and lymphocytes; features found in asthmatic patients. Additionally, there was a marked increase in mucus production in mice that received Th2 cells and inhaled OVA, but not in mice that received Th1 cells. However, OVA-specific Th2 cells from IL-4–deficient mice were not recruited to the lung and did not induce mucus production. When this defect in homing was overcome by administration of TNF-α, IL-4 −/− Th2 cells induced mucus as effectively as IL-4 +/+ Th2 cells. These studies establish a role for Th2 cells in mucus production and dissect the effector functions of IL-4 in these processes. These data suggest that IL-4 is crucial for Th2 cell recruitment to the lung and for induction of inflammation, but has no direct role in mucus production.     

Mechanisms of immunotherapeutic intervention by anti-CD40L (CD154) antibody in an animal model of multiple sclerosis

Relapsing experimental autoimmune encephalomyelitis (R-EAE) in the SJL mouse is a Th1-mediated autoimmune demyelinating disease model for human multiple sclerosis and is characterized by infiltration of the central nervous system (CNS) by Th1 cells and macrophages. Disease relapses are mediated by T cells specific for endogenous myelin epitopes released during acute disease, reflecting a critical role for epitope spreading in the perpetuation of chronic central CNS pathology. We asked whether blockade of the CD40–CD154 (CD40L) costimulatory pathway could suppress relapses in mice with established R-EAE. Anti-CD154 antibody treatment at either the peak of acute disease or during remission effectively blocked clinical disease progression and CNS inflammation. This treatment blocked Th1 differentiation and effector function rather than expansion of myelin-specific T cells. Although T-cell proliferation and production of interleukin (IL)-2, IL-4, IL-5, and IL-10 were normal, antibody treatment severely inhibited interferon-γ production, myelin peptide–specific delayed-type hypersensitivity responses, and induction of encephalitogenic effector cells. Anti-CD154 antibody treatment also impaired the expression of clinical disease in adoptive recipients of encephalitogenic T cells, suggesting that CD40–CD154 interactions may be involved in directing the CNS migration of these cells and/or in their effector ability to activate CNS macrophages/microglia. Thus, blockade of CD154–CD40 interactions is a promising immunotherapeutic strategy for treatment of ongoing T cell–mediated autoimmune diseases.     

MicroRNA-21 promotes Th17 differentiation and mediates experimental autoimmune encephalomyelitis

Accumulation of IL-17–producing Th17 cells is associated with the development of multiple autoimmune diseases; however, the contribution of microRNA (miRNA) pathways to the intrinsic control of Th17 development remains unclear. Here, we demonstrated that miR-21 expression is elevated in Th17 cells and that mice lacking miR-21 have a defect in Th17 differentiation and are resistant to experimental autoimmune encephalomyelitis (EAE). Furthermore, we determined that miR-21 promotes Th17 differentiation by targeting and depleting SMAD-7, a negative regulator of TGF-β signaling. Moreover, the decreases in Th17 differentiation in miR-21–deficient T cells were associated with defects in SMAD-2/3 activation and IL-2 suppression. Finally, we found that treatment of WT mice with an anti–miR-21 oligonucleotide reduced the clinical severity of EAE, which was associated with a decrease in Th17 cells. Thus, we have characterized a T cell–intrinsic miRNA pathway that enhances TGF-β signaling, limits the autocrine inhibitory effects of IL-2, and thereby promotes Th17 differentiation and autoimmunity.     

Engagement of Cytotoxic T Lymphocyte–associated Antigen 4 (CTLA-4) Induces Transforming Growth Factor β (TGF-β) Production by Murine CD4+ T Cells

Evidence indicates that cytotoxic T lymphocyte–associated antigen 4 (CTLA-4) may negatively regulate T cell activation, but the basis for the inhibitory effect remains unknown. We report here that cross-linking of CTLA-4 induces transforming growth factor β (TGF-β) production by murine CD4⁺ T cells. CD4⁺ T helper type 1 (Th1), Th2, and Th0 clones all secrete TGF-β after antibody cross-linking of CTLA-4, indicating that induction of TGF-β by CTLA-4 signaling represents a ubiquitous feature of murine CD4⁺ T cells. Stimulation of the CD3–T cell antigen receptor complex does not independently induce TGF-β, but is required for optimal CTLA-4–mediated TGF-β production. The consequences of cross-linking of CTLA-4, together with CD3 and CD28, include inhibition of T cell proliferation and interleukin (IL)-2 secretion, as well as suppression of both interferon γ (Th1) and IL-4 (Th2). Moreover, addition of anti–TGF-β partially reverses this T cell suppression. When CTLA-4 was cross-linked in T cell populations from TGF-β1 gene–deleted (TGF-β1^−/−) mice, the T cell responses were only suppressed 38% compared with 95% in wild-type mice. Our data demonstrate that engagement of CTLA-4 leads to CD4⁺ T cell production of TGF-β, which, in part, contributes to the downregulation of T cell activation. CTLA-4, through TGF-β, may serve as a counterbalance for CD28 costimulation of IL-2 and CD4⁺ T cell activation.     

Costimulation through B7-2 (CD86) Is Required for the Induction of a Lung Mucosal T Helper Cell 2 (TH2) Immune Response and Altered Airway Responsiveness

The recruitment of eosinophils into the airways after allergen exposure is dependent on interleukin (IL) 5 secreted from antigen-specific CD4⁺ T cells of the T helper cell (Th) 2 subset. However, while it is established that costimulation through CD28 is required for TCR-mediated activation and IL-2 production, the importance of this mechanism for the induction of a Th2 immune response is less clear. In the present study, we administered the fusion protein CTLA-4 immunoglobulin (Ig) into the lungs before allergen provocation to determine whether CD28/CTLA-4 ligands are required for allergen-induced eosinophil accumulation and the production of Th2 cytokines. Administration of CTLA-4 Ig inhibited the recruitment of eosinophils into the lungs by 75% and suppressed IgE in the bronchoalveolar lavage fluid. CTLA-4 Ig also inhibited the production of IL-4, IL-5, and IL-10 by 70–80% and enhanced interferon-γ production from CD3–T cell receptor–activated lung Thy1.2+ cells. Allergen exposure upregulated expression of B7-2, but not B7-1, on B cells from the lung within 24 h. Moreover, airway administration of an anti-B7-2 monoclonal antibody (mAb) inhibited eosinophil infiltration, IgE production, and Th2 cytokine secretion comparable in magnitude to that observed with CTLA-4 Ig. Treatment with an anti-B7-1 mAb had a small, but significant effect on eosinophil accumulation, although was less effective in inhibiting Th2 cytokine production. The anti-B7-2, but not anti-B7-1, mAb also inhibited antigen-induced airway hyperresponsiveness in vivo. In all of the parameters assessed, the combination of both the anti-B7-1 and anti-B7-2 mAb was no more effective than anti-B7-2 mAb treatment alone. We propose that strategies aimed at inhibition of CD28 interactions with B7-2 molecules may represent a novel therapeutic target for the treatment of lung mucosal allergic inflammation.     

SLAM family receptors control pro-survival effectors in germinal center B cells to promote humoral immunity

Expression of the signaling lymphocytic activation molecule (SLAM)–associated protein (SAP) is critical for the germinal center (GC) reaction and T cell–dependent antibody production. However, when SAP is expressed normally, the role of the associated SLAM family receptors (SFRs) in these processes is nebulous. Herein, we established that in the presence of SAP, SFRs suppressed the expansion of the GC reaction but facilitated the generation of antigen-specific B cells and antibodies. SFRs favored the generation of antigen-reactive B cells and antibodies by boosting expression of pro-survival effectors, such as the B cell antigen receptor (BCR) and Bcl-2, in activated GC B cells. The effects of SFRs on the GC reaction and T cell–dependent antibody production necessitated expression of multiple SFRs, both in T cells and in B cells. Hence, while in the presence of SAP, SFRs inhibit the GC reaction, they are critical for the induction of T cell–mediated humoral immunity by enhancing expression of pro-survival effectors in GC B cells.