Major Histocompatibility Complex Class II-restricted CD4 Research Articles

Analyses of the TCR repertoire of MHC class II-restricted innate CD4⁺ T cells.

Analysis of the T-cell receptor (TCR) repertoire of innate CD4+ T cells selected by major histocompatibility complex (MHC) class II-dependent thymocyte–thymocyte (T-T) interaction (T-T CD4+ T cells) is essential for predicting the characteristics of the antigens that bind to these T cells and for distinguishing T-T CD4+ T cells from other types of innate T cells. Using the TCRmini Tg mouse model, we show that the repertoire of TCRα chains in T-T CD4+ T cells was extremely diverse, in contrast to the repertoires previously described for other types of innate T cells. The TCRα chain sequences significantly overlapped between T-T CD4+ T cells and conventional CD4+ T cells in the thymus and spleen. However, the diversity of the TCRα repertoire of T-T CD4+ T cells seemed to be restricted compared with that of conventional CD4+ T cells. Interestingly, the frequency of the parental OT-II TCRα chains was significantly reduced in the process of T-T interaction. This diverse and shifted repertoire in T-T CD4+ T cells has biological relevance in terms of defense against diverse pathogens and a possible regulatory role during peripheral T-T interaction.

Transcriptional reprogramming of mature CD4+ helper T cells generates distinct MHC class II–restricted cytotoxic T lymphocytes

TCRαβ thymocytes differentiate to either CD8αβ cytotoxic T lymphocytes or CD4+ T helper cells. This functional dichotomy is controlled by key transcription factors, including the T helper master regulator, ThPOK, which suppresses the cytolytic program in MHC class II-restricted CD4+ thymocytes. ThPOK continues to repress CD8-lineage genes in mature CD4+ T cells, even as they differentiate to T helper effector subsets. Here we show that the T helper-fate was not fixed and that mature antigen-stimulated CD4+ T cells could terminate Thpok expression and reactivate CD8-lineage genes. This unexpected plasticity resulted in the post-thymic termination of the T helper-program and the functional differentiation of distinct MHC class II-restricted CD4+ cytotoxic T lymphocytes.

Licensing of killer dendritic cells in mouse and humans: Functional similarities between IKDC and human blood γδ T-lymphocytes

Dendritic cells are characterized by the ability to induce primary antigen-specific immune responses in both major histocompatibility complex (MHC) Class I-restricted CD8 cells and MHC Class II-restricted CD4 cells. This professional antigen presentation function is associated with the up-regulation of co-stimulatory molecules and Class II MHC. While it has been recognized that several types of innate lymphocytes in mouse and humans can express co-stimulatory molecules and present antigen, the property of antigen presentation to elicit responses in naïve cells has been considered the exclusive domain of the dendritic cell. This concept has been challenged through the description of innate lymphocytes, capable of killing using NK receptors, but also up-regulating co-stimulatory molecules and driving the antigen-specific proliferation of naïve lymphocytes to the same extent as dendritic cells. Interferon (IFN)-γ secreting killer dendritic cells (IKDC) have been described in mice and share immunophenotypic properties of both dendritic cells and natural killer cells. Human blood γδ T-lymphocytes have innate tumor cell killing properties by both antibody-dependent and natural killer receptor-dependent mechanisms. This article reviews data from the authors’ own laboratory showing a particular feature in common between the mouse IKDC and human blood γδ T-lymphocytes; namely their requirement for interaction with a target cell for specific licensing for professional antigen presentation.

Molecular mechanism of barrel cortex development controlled by thalamocortical axon innervation

During thymic development, thymocytes expressing a T cell receptor consisting of an alpha and beta chain (TCRαβ), commit to either the cytotoxic- or T helper-lineage fate. This lineage dichotomy is controlled by key transcription factors, including the T helper (Th) lineage master regulator, the Th-inducing BTB/POZ domain-containing Kruppel-like zinc-finger transcription factor, ThPOK, (formally cKrox or Zfp67; encoded by Zbtb7b), which suppresses the cytolytic program in major histocompatibility complex (MHC) class II-restricted CD4+ thymocytes and the Runt related transcription factor 3 (Runx3), which counteracts ThPOK in MHC class I restricted precursor cells and promotes the lineage commitment of CD8αβ+ cytolytic T lymphocytes (CTL). ThPOK continues to repress the CTL gene program in mature CD4+ T cells, even as they differentiate into effector Th cell subsets. The Th cell fate however is not fixed and two recent studies showed that mature, antigen-stimulated CD4+ T cells have the flexibility to terminate the expression of ThPOK and functionally reprogram to cytotoxic effector cells. This unexpected plasticity of CD4+ T cells results in the post-thymic termination of the Th lineage fate and the functional differentiation of distinct MHC class II-restricted CD4+ CTL. The recognition of CD4 CTL as a defined separate subset of effector cells and the identification of the mechanisms and factors that drive their reprogramming finally create new opportunities to explore the physiological relevance of these effector cells in vivo and to determine their pivotal roles in both, protective immunity as well as in immune-related pathology.

Alternative Endogenous Protein Processing via an Autophagy-Dependent Pathway Compensates forYersinia-Mediated Inhibition of Endosomal Major Histocompatibility Complex Class II Antigen Presentation

Extracellular Yersinia pseudotuberculosis employs a type III secretion system (T3SS) for translocating virulence factors (Yersinia outer proteins [Yops]) directly into the cytosol of eukaryotic cells. Recently, we used YopE as a carrier molecule for T3SS-dependent secretion and translocation of listeriolysin O (LLO) from Listeria monocytogenes. We demonstrated that translocation of chimeric YopE/LLO into the cytosol of macrophages by Yersinia results in the induction of a codominant antigen-specific CD4 and CD8 T-cell response in orally immunized mice. In this study, we addressed the requirements for processing and major histocompatibility complex (MHC) class II presentation of chimeric YopE proteins translocated into the cytosol of macrophages by the Yersinia T3SS. Our data demonstrate the ability of Yersinia to counteract exogenous MHC class II antigen presentation of secreted hybrid YopE by the action of wild-type YopE and YopH. In the absence of exogenous MHC class II antigen presentation, an alternative pathway was identified for YopE fusion proteins originating in the cytosol. This endogenous antigen-processing pathway was sensitive to inhibitors of phagolysosomal acidification and macroautophagy, but it did not require the function either of the proteasome or of transporters associated with antigen processing. Thus, by an autophagy-dependent mechanism, macrophages are able to compensate for the YopE/YopH-mediated inhibition of the endosomal MHC class II antigen presentation pathway for exogenous antigens. This is the first report demonstrating that autophagy might enable the host to mount an MHC class II-restricted CD4 T-cell response against translocated bacterial virulence factors. We provide critical new insights into the interaction between the mammalian immune system and a human pathogen.

Patients with B cell chronic lymphocytic leukaemia have an expanded population of CD4+ perforin expressing T cells enriched for human cytomegalovirus specificity and an effector‐memory phenotype

We have previously shown an expansion of cytotoxic antigen-experienced CD4(+)T cells (CTLs) that express perforin (PF) in the peripheral blood of patients with B cell chronic lymphocytic leukaemia (B-CLL). Increased frequencies of CD4(+)CTLs have since been attributed to chronic viral infections, particularly, human cytomegalovirus (HCMV). The present study examined the involvement of CD4(+)CTLs in responses to HCMV in B-CLL, and characterized their differentiation. We studied 36 HCMV seropositive (SP) and seronegative B-CLL patients and 20 healthy age-matched individuals. The HCMV reactivity of CD4(+)PF(+) and CD4(+)PF(-) cells was determined by interferon-gamma expression, and expression of CD45RA and CCR7 was assessed by flow cytometry. Fluorescence in-situ hybridization was used to measure relative telomere lengths. CD4(+)PF(+)T cell expansion in B-CLL patients and controls was strongly associated with HCMV seropositivity. CD4(+)PF(+) compared to CD4(+)PF(-) cells from SP B-CLL patients elicited major histocompatibility complex (MHC) class II-restricted responses to HCMV. CD4(+)PF(+)T cells from patients and controls were enriched with highly differentiated T-effector/memory (CCR7(-)) and revertant (CCR7(-)CD45RA(+)) phenotype. CD4(+)PF(+)T cells from B-CLL patients had shorter telomeres than CD4(+)PF(-)T cells, indicating an extensive replicative history. We conclude that persistent exposure to HCMV antigens in SP B-CLL patients leads to an expansion of the circulating MHC class II-restricted CD4(+)PF(+)T cell population with effector/memory phenotype.

Autoreactive CD8‐specific T‐cell response in primary biliary cirrhosis

Primary biliary cirrhosis (PBC) is an autoimmune liver disease of unknown etiology. Autoimmune attack in PBC is predominantly organ-specific, despite the presence of mitochondrial autoantigens, the major targets of autoimmunity in PBC, in all nucleated cells. Cytotoxic T lymphocytes are thought to be directly involved in the tissue injury in PBC. The major histocompatibility complex (MHC) class I-restricted epitope for E2 components of pyruvate dehydrogenase complexes, namely amino acid 159-167, a region very close to the epitoperecognized by MHC class II-restricted CD4 cells and by antibody, has been characterized. In addition, there was a 10-fold increase in the frequency of autoreactive cytotoxic T lymphocytes in the liver as compared to the blood in PBC patients using tetramer technology.

Hierarchical immunogenicity of donor MHC class I peptides in allotransplantation

The recognition of major histocompatibility complex (MHC) allopeptides by recipient MHC class II-restricted CD4 + T cells via indirect pathway is a prerequisite for the generation of an immune response to the allograft. We tested 13-mer to 24-mer peptides from the MHC class I molecule for their possible immunogenicity in a fully MHC-mismatched rat strain combination. Our results confirm the hierarchical distribution of the immunogenicity of donor MHC class I peptides in the T cell alloactivation via indirect pathway. In addition, we show that allopeptide-induced immune response is critical for acute rejection of heart allografts. Among the seven allopeptides tested, peptide P1 was identified as immunodominant; it induced the greatest T cell proliferation and cytokine production in vitro as well as a significant reduction in allograft survival time. The TCR repertoire of T cells involved in the in vitro and in vivo responses induced by the dominant allopeptide P1 was found to be limited to the Vβ10 and Vβ 19 gene families. The identification of dominant allopeptides should greatly facilitate characterization of the specific T cell population responsible for allograft rejection and may be used to modulate the alloimmune response through antigen-specific therapy.

Peptide HER2(776-788) represents a naturally processed broad MHC class II-restricted T cell epitope.

HER2/neu-derived peptides inducing MHC class II-restricted CD4+ T helper lymphocyte (Th) responses, although critical for tumour rejection, are not thoroughly characterized. Here, we report the generation and characterization of CD4+ T cell clones specifically recognizing a HER-2/neu-derived peptide (776–788) [designated HER2(776–788)]. Such clones yielded specific proliferative and cytokine [gamma-interferon(IFN)-γ] responses when challenged with autologous dendritic cells (DCs) loaded with HER2(776–788). By performing blocking studies with monoclonal antibodies (MAbs) and by using DCs from allogeneic donors sharing certain HLA-DR alleles, we found that HER2(776–788) is a promiscuous peptide presented, at least, by DRB5*0101, DRB1*0701 and DRB1*0405 alleles. One TCRVbeta6.7+ clone recognized the HLA-DRB5*0101+ FM3 melanoma cell line transfected with a full length HER-2/neu cDNA. Moreover, this clone recognized the HER-2/neu+ SKBR3 breast cancer cell line induced to express HLA-DR, thus demonstrating that HER2(776–788) represents a naturally processed and presented epitope. Our data demonstrate that helper peptide HER2(776–788) represents a promiscuous epitope binding to at least three HLA-DR alleles, thus offering a broad population coverage. The use of antigenic peptides presented by major histocompatibility complex (MHC) class II in addition to those presented by class I may improve the therapeutic efficacy of active immunization.© 2001 Cancer Research Campaign http://www.bjcancer.com

Major histocompatibility complex class II-transfected tumor cells present endogenous antigen and are potent inducers of tumor-specific immunity.

We have developed an immunotherapy in which tumor cells transfected with syngeneic major histocompatibility complex (MHC) class II genes are cell-based vaccines for the treatment of established tumor and metastatic disease. If this strategy is to be used clinically, convenient methods for generating class II+ tumor cells are necessary. Interferon-gamma treatment or transduction of the class II transactivator (CIITA) gene induces class II expression but also up-regulates the class II-associated accessory molecules, invariant chain (Ii) and DM. To determine if interferon-gamma treatment and CIITA transduction are potential immunotherapies, we assessed the tumorigenicity of sarcoma cells expressing combinations of class II, Ii, and DM. Since we hypothesized that class II-transfected tumor cells not coexpressing Ii and DM present endogenously encoded tumor peptides, we have assessed the transfectants for antigen presentation activity to MHC class II-restricted antigen-specific CD4(+) T cells. Tumor challenge studies demonstrate that tumor cells expressing class II without coexpression of Ii or Ii plus DM are highly immunogenic and preferentially present endogenous antigens, while tumors coexpressing class II with Ii or Ii plus DM are not effective immunogens. Because tumor rejection correlates with expression of class II without coexpression of Ii and DM, the most efficacious vaccines will express MHC class II without coexpression of Ii and DM and will preferentially present endogenous antigen.

Expression of class II, but not class I, major histocompatibility complex molecules is required for granuloma formation in infection with Schistosoma mansoni.

Previous studies have suggested that granulomatous inflammation in schistosomiasis is mediated by CD4+ T helper lymphocytes sensitized to parasite egg antigens. However, CD8+ T cells have also frequently been associated with the immune response to schistosome eggs. To examine more precisely the role of CD4+ and CD8+ T cells in the pathology of the schistosomal infection, we used mice with targeted mutations in major histocompatibility complex (MHC) class II or class I molecules. These mutations lead, respectively, to the virtual absence of CD4+ and CD8+ T cells. The results clearly show that schistosome-infected MHC class II mutant mice failed to form granulomas around parasite eggs. In contrast, infected MHC class I mutant mice displayed characteristic granulomatous lesions that were comparable to those in wild-type control mice. Moreover, lymphoid cells from MHC class II mutant mice were unable to react to egg antigens with either proliferative or cytokine [interferon-gamma, interleukin (IL)-4, IL-10] responses; nor were they able to present egg antigens to specifically sensitized CD4+ T helper cells from infected syngeneic control mice. By comparison, cells from MHC class I mutant mice exercised all these functions in a manner comparable with those from wild-type controls. These observations clearly demonstrate that schistosomal egg granulomas are mediated by MHC class II-restricted CD4+ T helper cells. They also suggest that CD8+ T cells do not become sensitized to egg antigens and play little role, if any, in the pathogenesis of schistosomiasis.

Plasmid DNA vaccination: mechanism of antigen presentation.

Direct injection of naked plasmid DNA either intramuscularly or intradermally induces strong, long-lived immune responses to the antigen encoded by the gene vaccine. While the intradermal route of administration appears to be the most efficient, there is evidence that either route leads to production of antibody and the activation of major histocompatibility complex (MHC) class I-restricted, antigen-specific cytotoxic T lymphocytes (CTL) and MHC class II-restricted CD4+ T cells secreting Thl-type cytokines such as interferon-γ (IFN-γ) [1–9]. Plasmid DNA immunization has potential advantages compared to traditional protein vaccination due to the strong CTL and Thl responses induced, the prolonged antigen expression, and the resistance of the antigen source to antibody-mediated clearance. As a consequence, gene vaccination has potential applications in the fields of infectious diseases, allergy and cancer.

A role for CD4+ NK1.1+ T lymphocytes as major histocompatibility complex class II independent helper cells in the generation of CD8+ effector function against intracellular infection.

Major histocompatibility complex (MHC) class II (A beta) knockout mice were vaccinated with ts-4, an attenuated mutant strain of Toxoplasma gondii, which in normal animals induces strong T cell immunity mediated by interferon gamma (IFN-gamma). After challenge with the lethal parasite strain RH, the knockout mice displayed decreased resistance consistent with absence of CD4+ effectors. Nevertheless, these animals generated CD8+ lymphocyte effectors capable of mediating partial protection through IFN-gamma secretion. Moreover, in vivo neutralization experiments indicated that the development of resistance in knockout mice depends on CD4+ cells as well as interleukin 2 (IL-2). The identity of the IL-2-producing protective cell population was further characterized as CD4+, NK1.1+ by in vitro depletion studies and reverse transcriptase-PCR analysis of fluorescence-activated cell sorter (FACS)-purified CD4+ NK1.1+ T lymphocytes. These results demonstrate that in the absence of conventional MHC class II-restricted CD4+ T lymphocytes, CD8 priming persists and mediates partial protective immunity to T. gondii. Moreover, the data argue that CD4+, NK1.1+ cells, previously implicated in the initiation of T helper cell 2 (Th2) responses through their production of IL-4, can also play a role as alternative IL-2-secreting helper cells in Th1-mediated host resistance to infection.

Major histocompatibility complex class I-restricted CD8+ T cells and class II-restricted CD4+ T cells, respectively, mediate and regulate contact sensitivity to dinitrofluorobenzene.

Contact sensitivity (CS) is a form of delayed-type hypersensitivity to haptens applied epicutaneously and is thought to be mediated, like classical delayed-type hypersensitivity responses, by CD4+ T helper-1 cells. The aim of this study was to identify the effector T cells involved in CS. We studied CS to the strongly sensitizing hapten dinitrofluorobenzene (DNFB) in mice rendered deficient by homologous recombination in either major histocompatibility complex (MHC) class I, MHC class II, or both, and which exhibited deficiencies in, respectively, CD8+, CD4+, or both, T cells. MHC class I single-deficient and MHC class I/class II double-deficient mice, both of which have a drastic reduction in the number of CD8+ T cells, were unable to mount a CS response to DNFB. In contrast, both MHC class II-deficient mice and normal mice treated with an anti-CD4 monoclonal antibody (mAb) developed exaggerated and persistent responses relative to heterozygous control littermates. Furthermore, anti-CD8 mAb depletion of class II-deficient mice totally abolished their ability to mount an inflammatory response to DNFB. Removal of residual CD4+ T cells in class II-deficient mice by anti-CD4 mAb treatment did not diminish the intensity of CS. These data clearly demonstrate that class I-restricted CD8+ T cells are sufficient for the induction of CS to DNFB, and further support the idea that MHC class II-restricted CD4+ T cells down-regulate this inflammatory response.

The natural immune response to inhaled soluble protein antigens involves major histocompatibility complex (MHC) class I-restricted CD8+ T cell-mediated but MHC class II-restricted CD4+ T cell-dependent immune deviation resulting in selective suppression of immunoglobulin E production.

The immunological basis for atopy is currently ascribed to an inherent bias in the CD4+ T cell response to nonreplicating antigens presented at mucosal surfaces, resulting in dominance of the T helper 2 (Th2) interleukin 4 (IL-4)-producing phenotype, which favors IgE production. In contrast, the "normal" response to such antigens involves a predominance of interferon gamma (IFN-gamma)-producing Th1 clones. This difference has been suggested to be the result of active selection in atopics for Th2 (and hence against Th1) clones at the time of initial antigen presentation. In the study below, we demonstrate that the natural immune response to inhaled protein antigens, particularly in animals expressing the low immunoglobulin E (IgE) responder phenotype, includes a major histocompatibility complex (MHC) class I-restricted CD8+ T cell component, the appearance of which is associated with active suppression of IgE antibody production. Thus, continued exposure of rats to aerosolized ovalbumin (OVA) antigen elicits a transient IgE response, that is terminated by the onset of a state of apparent "tolerance" to further challenge, and this tolerant state is transferable to naive animals with CD8+ T cells. Kinetic studies on in vitro T cell reactivity in these aerosol-exposed rats demonstrated biphasic CD4+ Th2 responses which terminated, together with IgE antibody production, and coincident with the appearance of MHC class I-restricted OVA-specific IFN-gamma-producing CD8+ T cells. However, the latter were not autonomous in vitro and required a source of exogenous IL-2 for initial activation, which in CD(8+)-enriched splenocyte cultures could be provided by small numbers of contaminating OVA-specific CD4+ T cells. This represents the first formal evidence for the induction of an MHC class I-restricted T cell response to natural mucosal exposure to an inert protein antigen, and is consistent with a growing literature demonstrating sensitization of MHC class I-restricted CD8+ T cells by deliberate immunization with soluble proteins. We suggest that crossregulation of MHC class II-restricted CD4+ T cells via cytokine signals generated in parallel CD8+ T cell responses represents a covert and potentially important selection pressure that can shape the nature of host responses to nonreplicating antigens presented at mucosal surfaces.