Mechanisms Of CD4 Research Articles

Aberrant differentiation and exhaustion of adenovirus vaccine-elicited CD8 T cells primed in the absence of CD4 T cells (VAC3P.940)

Abstract Replication-incompetent recombinant adenovirus (Ad) vectors have garnered considerable interest as candidate vaccine platforms for an array of diseases. However, the efficacy of such vaccines in settings of impaired CD4 T cell function remains poorly understood. We demonstrate that monoclonal antibody-mediated depletion of CD4 T cells prior to Ad immunization of C57BL/6 mice impaired expansion of responding CD8 T cells and led to aberrant differentiation and exhaustion. The absence of CD4 T cells resulted in a failure of antigen-specific CD8 T cells to differentiate into KLRG1hiCD127lo effector cells. This phenotypic defect corresponded to reduced ex vivo cytotoxicity and decreased expression of IFN-γ and TNF-α. Strikingly, CD8 T cells primed in the absence of CD4 T cells expressed elevated levels of the inhibitory molecules PD-1, LAG-3, and Tim-3. Consistent with this, these cells were identified as exhausted using gene expression profiling and gene set enrichment analysis. Blockade of PD-1 signaling by administration of anti-PDL-1 antibody at the time of immunization rescued expansion of antigen-specific CD8 T cells primed in the absence of CD4 T cells. This treatment also rescued differentiation into KLRG1hiCD127lo effector cells, and corrected defects in expression of IFN-γ and TNF-α. Collectively, these data suggest a novel mechanism of CD4 T cell help whereby CD4 T cells prevent the exhaustion of vaccine-elicited CD8 T cells by modulating PD-1 signaling during priming.

Mechanisms of CD4+ T Cell Exhaustion by persisting antigen (LYM3P.737)

Abstract When faced with chronic antigen presentation T cells are functionally impaired over time. Since detailed studies of antigen-exhausted CD4+ T cells are scarce, we followed AND TCR transgenic T cells transferred into antigen-transgenic recipients where they received chronic TCR signals of varying strength. In one of the recipient lines, transient antigen expression regulated by doxycycline treatment allowed for the efficient differentiation of memory T cells, with IL7R, Ly6C and swift cytokine production as their hallmarks, while chronic TCR signals exhausted the cells. We found two kinds of exhaustion: Strong stimulation was accompanied by reversible TCR downregulation, signaling impairment and an increase of PD-1 and the anergy markers CD73 and FR4. When stimulated with PMA/Ionomycin, which circumvent TCR-proximal signaling components, these cells produced effector cytokines almost like memory T cells. In contrast, T cells that experienced a weaker TCR stimulus chronically showed no cytokine production following PMA/Ionomycin restimulation. Since in such T cells TCR signaling via the AKT, MAPK and Ca2+ pathways was found only partially impaired, we conclude that strong signals impair TCR-proximal signaling components while weaker signals affect more distal elements. We suggest that the degree of T cell exhaustion correlates with antigen strength, leading either to a fast TCR and signaling downmodulation or to an irreversible functional impairment.

CD4+ T cells contain early extrapulmonary tuberculosis (TB) dissemination and rapid TB progression and sustain multieffector functions of CD8+ T and CD3- lymphocytes: mechanisms of CD4+ T cell immunity.

The possibility that CD4(+) T cells can act as "innate-like" cells to contain very early Mycobacterium tuberculosis dissemination and function as master helpers to sustain multiple effector functions of CD8(+) T cells and CD3(-) lymphocytes during development of adaptive immunity against primary tuberculosis (TB) has not been demonstrated. We showed that pulmonary M. tuberculosis infection of CD4-depleted macaques surprisingly led to very early extrapulmonary M. tuberculosis dissemination, whereas CD4 deficiency clearly resulted in rapid TB progression. CD4 depletion during M. tuberculosis infection revealed the ability of CD8(+) T cells to compensate and rapidly differentiate to Th17-like/Th1-like and cytotoxic-like effectors, but these effector functions were subsequently unsustainable due to CD4 deficiency. Whereas CD3(-) non-T lymphocytes in the presence of CD4(+) T cells developed predominant Th22-like and NK-like (perforin production) responses to M. tuberculosis infection, CD4 depletion abrogated these Th22-/NK-like effector functions and favored IL-17 production by CD3(-) lymphocytes. CD4-depleted macaques exhibited no or few pulmonary T effector cells constitutively producing IFN-γ, TNF-α, IL-17, IL-22, and perforin at the endpoint of more severe TB, but they presented pulmonary IL-4(+) T effectors. TB granulomas in CD4-depleted macaques contained fewer IL-22(+) and perforin(+) cells despite the presence of IL-17(+) and IL-4(+) cells. These results implicate a previously unknown innate-like ability of CD4(+) T cells to contain extrapulmonary M. tuberculosis dissemination at very early stage. Data also suggest that CD4(+) T cells are required to sustain multiple effector functions of CD8(+) T cells and CD3(-) lymphocytes and to prevent rapid TB progression during M. tuberculosis infection of nonhuman primates.

Correlation of Breg with CD4(+)T cells of peripheral blood in patients with CITP and its clinical significance

This study was aimed to detect the level of the peripheral blood Breg and CD4(+) T cell subgroups in patients with chronic idiopathic thrombocytopenic purpura (CITP) before and after therapy, and to analyse the charge of related cytokines and their correlation, to explore their roles in the pathogenesis of CITP. A total of 35 CITP cases were taken as the research group and 35 healthy persons were served as the control group. The peripheral blood mononuclear cells (PBMNC) were separated, the percentages of Th1, Th17, Th22 and Breg cells were detected by flow cytometry before and after treatment of glucocorticoid, and the IFN-γ, IL-17, IL-22 and IL-10 levels from PBMNC culture supernatant also were determined by ELISA. The results showed that there was significant difference as compared with the healthy controls, the proportion of peripheral blood Th1, Th17, Th22 cell subgroups all increased in CITP patients before treatment with glucocorticoid, the regulatory B cells (Breg) ratio was reduced, the differences had statistical significance (P < 0.05), but the differences were no statistically significant after treatment with glucocorticoid (P > 0.05). The levels of IFN-γ, IL-17, IL-22 from culture supernatant all increased in CITP patients before treatment, the level of IL-10 was lower than that of the healthy control, the difference was statistically significant (P < 0.05), but the there were no statistically significant differences after treatment (P > 0.05). There were positive correlation between the Breg cells and IL-10 expression in CITP patients (P < 0.05), the Breg cells and Th1, Th17, Th22 cells showed a negative correlation, IL-10 and IFN-γ, IL-17, IL-22 levels also showed a negative correlation. It is concluded that the down-regulation of regulatory B cells proportion and the IL-10 level may participate in the mechanism of CD4(+) T cell immunity disorder in CITP, which can provide new targets and ideas for the clinical immune regulation therapy.

Impaired selectin-dependent leukocyte trafficking induces T cell exhaustion and prevents chronic allograft vasculopathy and rejection (P2140)

Abstract Selectin-selectin ligand interactions mediate the initial steps in leukocyte emigration, an integral part of immune response. Fucosyltransferase-VII (FucT-VII) enzyme, encoded by Fut7 gene, is essential for post-translational modification and function of selectin ligands. In an established model of cardiac allograft vasculopathy and chronic rejection, Fut7-/- recipients, with impaired selectin-dependent leukocyte trafficking, enjoyed long-term graft survival with minimal vasculopathy. This was associated with T cell exhaustion in the periphery characterized by impaired effector cytokine production, proliferative defect, increased expression of inhibitory receptors PD-1 and Tim-3 and low levels of IL-7Ra on CD4 T cells and reduced trafficking of polyfunctional CD4 memory T cells to the allograft. Blocking PD-1, triggered rejection only in Fut7-/- recipients, whereas depleting regulatory T cells triggered rejection in WT recipients. Adoptive transfer experiments confirmed that the exhausted phenotype is seen primarily in CD4 T cells with impaired trafficking ability. In summary, these data suggest that impaired leukocyte trafficking is a novel mechanism of CD4 T cell exhaustion and our experimental system serves as an excellent model to study CD4 T cell exhaustion as a dominant mechanism of transplant tolerance. Further, targeting FucT-VII may serve as a promising strategy to prevent chronic allograft rejection and promote tolerance.

CD4+FoxP3+ regulatory T cell-mediated suppression of dendritic cells (P1049)

Abstract CD4+FoxP3+ regulatory T cells are a subset of T cells that play central role in regulating inflammatory responses during many different immunological diseases. However the mechanisms of CD4+FoxP3+ regulatory T cells-mediated suppression remain controversial and poorly understood. Several studies have shown that CD4+FoxP3+ regulatory T cells can interact with and suppress a large number of cell types including CD4+ T cells and antigen presenting cells. For instance in vitro studies have shown that CD4+FoxP3+ regulatory T cells can inhibit cytokine production especially IL-2 production on CD4+ T cells hence the inhibition of CD4+ T cell proliferation; CD4+FoxP3+ regulatory T cells can also confer infectious tolerance by converting conventional T cells into functional FoxP3+ T cells in a cell contact TGF-β-dependent manner.In addition, CD4+FoxP3+ regulatory T cells suppress dendritic cell maturation and function by down-regulating the expression of co-stimulatory molecules CD80/CD86 via the interaction with CTLA-4.In our study, we have observed that CD4+FoxP3+ regulatory T cells may also modulate dendritic cell function via the PD-1:PD-L pathway. Dendritic cells that have been previously cultured with CD4+FoxP3+ regulatory T cells have decreased ability to support CD4+CD25- T cell proliferation and they can also induce higher level of FoxP3 expression in CD4+CD25- T cells.

Langerin negative dendritic cells promote potent CD8 + T-cell priming by skin delivery of live adenovirus vaccine microneedle arrays

Stabilization of virus protein structure and nucleic acid integrity is challenging yet essential to preserve the transcriptional competence of live recombinant viral vaccine vectors in the absence of a cold chain. When coupled with needle-free skin delivery, such a platform would address an unmet need in global vaccine coverage against HIV and other global pathogens. Herein, we show that a simple dissolvable microneedle array (MA) delivery system preserves the immunogenicity of vaccines encoded by live recombinant human adenovirus type 5 (rAdHu5). Specifically, dried rAdHu5 MA immunization induced CD8(+) T-cell expansion and multifunctional cytokine responses equipotent with conventional injectable routes of immunization. Intravital imaging demonstrated MA cargo distributed both in the epidermis and dermis, with acquisition by CD11c(+) dendritic cells (DCs) in the dermis. The MA immunizing properties were attributable to CD11c(+) MHCII(hi) CD8α(neg) epithelial cell adhesion molecule (EpCAM(neg)) CD11b(+) langerin (Lang; CD207)(neg) DCs, but neither Langerhans cells nor Lang(+) DCs were required for CD8(+) T-cell priming. This study demonstrates an important technical advance for viral vaccine vectors progressing to the clinic and provides insights into the mechanism of CD8(+) T-cell priming by live rAdHu5 MAs.

E4BP4 overexpression: A protective mechanism in CD4+ T cells from SLE patients

Systemic lupus erythematosus (SLE) is a prototype autoimmune disease characterized by various immunological abnormalities, including dysregulated activation of T and B lymphocytes, which trigger autoantibody production and immune-complex deposition. E4BP4, also known as NFIL3, has emerged as a major transcription factor that regulates the development and function of immune cells in a number of lineages. E4BP4 has been shown to regulate cytokines expression, and its synthesis is in turn controlled by various cytokines. To date, the roles of E4BP4 in immune dysregulation and autoimmune disorders are unclear. In this study, we demonstrated that E4BP4 expression is increased in CD4+ T cells isolated from patients with active systemic lupus erythematosus (SLE), especially in patients treated with glucocorticoid (GC). Increased expression of E4BP4 inhibited the activation and self-reactivity of T cells stimulated by anti-CD3/CD28 antibodies. In contrast, the self-reactivity was enhanced in CD4+ T cells from SLE patients following E4BP4 gene silencing and the production of autoantibody was increased in autologous B cells. We further demonstrated that E4BP4 directly regulated CD40L expression by binding to the promoter region and altering histone acetylation and methylation of the CD40L loci. Taken together, our data provide evidence that E4BP4 can inhibit CD40L expression through epigenetic modifications in the promoter region of CD40L, thus negatively regulating self-reactivity of SLE CD4+ T cells. Furthermore, our data demonstrate that overexpression of E4BP4 initiates a protective mechanism in SLE CD4+ T cells, which may be a promising target in the therapy for SLE.

A20 Controls Macrophage to Elicit Potent Cytotoxic CD4+ T Cell Response

Emerging evidence indicates that CD4+ T cells possess cytotoxic potential for tumor eradication and perforin/granzyme-mediated cytotoxicity functions as one of the important mechanisms for CD4+ T cell-triggered cell killing. However, the critical issue is how the cytotoxic CD4+ T cells are developed. During the course of our work that aims at promoting immunostimulation of APCs by inhibition of negative regulators, we found that A20-silenced Mф drastically induced granzyme B expression in CD4+ T cells. As a consequence, the granzyme-highly expressing CD4+ T cells exhibited a strong cytotoxic activity that restricted tumor development. We found that A20-silenced Mф activated cytotoxic CD4+ T cells by MHC class-II restricted mechanism and the activation was largely dependent on enhanced production of IFN-γ.

Molecular Mechanisms Involved in the Aging of the T-cell Immune Response

T-lymphocytes play a central role in the effector and regulatory mechanisms of the adaptive immune response. Upon exiting the thymus they begin to undergo a series of phenotypic and functional changes that continue throughout the lifetime and being most pronounced in the elderly. The reason postulated for this is that the dynamic processes of repeated interaction with cognate antigens lead to multiple division cycles involving a high degree of cell differentiation, senescence, restriction of the T-cell receptor (TCR) repertoire, and cell cycle arrest. This cell cycle arrest is associated with the loss of telomere sequences from the ends of chromosomes. Telomere length is reduced at each cell cycle, and critically short telomeres recruit components of the DNA repair machinery and trigger replicative senescence or apoptosis. Repetitively stimulated T-cells become refractory to telomerase induction, suffer telomere erosion and enter replicative senescence. The latter is characterized by the accumulation of highly differentiated T-cells with new acquired functional capabilities, which can be caused by aberrant expression of genes normally suppressed by epigenetic mechanisms in CD4+ or CD8+ T-cells. Age-dependent demethylation and overexpression of genes normally suppressed by DNA methylation have been demonstrated in senescent subsets of T-lymphocytes. Thus, T-cells, principally CD4+CD28null T-cells, aberrantly express genes, including those of the KIR gene family and cytotoxic proteins such as perforin, and overexpress CD70, IFN-γ, LFA-1 and others. In summary, owing to a lifetime of exposure to and proliferation against a variety of pathogens, highly differentiated T-cells suffer molecular modifications that alter their cellular homeostasis mechanisms.

Th2 Skewing by Activation of Nrf2 in CD4+ T Cells

NF erythroid 2-related factor 2 (Nrf2) is a transcription factor that mediates the upregulation of a battery of cytoprotective genes in response to cell stress. Recent studies showed that Nrf2 also modulates immune responses and exhibits anti-inflammatory activity. In this article, we demonstrate that a common food preservative, tert-butylhydroquinone, can activate Nrf2 in T cells, as evidenced by Nrf2 binding to the antioxidant response element and the subsequent upregulation of Nrf2 target genes. The activation of Nrf2 suppresses IFN-γ production, while inducing the production of the Th2 cytokines IL-4, IL-5, and IL-13. Nrf2 activation also suppresses T-bet DNA binding and promotes GATA-binding protein 3 DNA binding. Collectively, the present studies suggested that Nrf2 activation skews CD4(+) T cells toward Th2 differentiation and, thus, represents a novel regulatory mechanism in CD4(+) T cells. Further studies are needed to determine whether the commercial use of Nrf2 activators as food preservatives promotes food allergies in humans.

Ex Vivo Expansion of Human CD8+ T Cells Using Autologous CD4+ T Cell Help

BackgroundUsing in vivo mouse models, the mechanisms of CD4+ T cell help have been intensively investigated. However, a mechanistic analysis of human CD4+ T cell help is largely lacking. Our goal was to elucidate the mechanisms of human CD4+ T cell help of CD8+ T cell proliferation using a novel in vitro model.Methods/Principal FindingsWe developed a genetically engineered novel human cell-based artificial APC, aAPC/mOKT3, which expresses a membranous form of the anti-CD3 monoclonal antibody OKT3 as well as other immune accessory molecules. Without requiring the addition of allogeneic feeder cells, aAPC/mOKT3 enabled the expansion of both peripheral and tumor-infiltrating T cells, regardless of HLA-restriction. Stimulation with aAPC/mOKT3 did not expand Foxp3+ regulatory T cells, and expanded tumor infiltrating lymphocytes predominantly secreted Th1-type cytokines, interferon-γ and IL-2. In this aAPC-based system, the presence of autologous CD4+ T cells was associated with significantly improved CD8+ T cell expansion in vitro. The CD4+ T cell derived cytokines IL-2 and IL-21 were necessary but not sufficient for this effect. However, CD4+ T cell help of CD8+ T cell proliferation was partially recapitulated by both adding IL-2/IL-21 and by upregulation of IL-21 receptor on CD8+ T cells.ConclusionsWe have developed an in vitro model that advances our understanding of the immunobiology of human CD4+ T cell help of CD8+ T cells. Our data suggests that human CD4+ T cell help can be leveraged to expand CD8+ T cells in vitro.

Quorum-Sensing in CD4+ T Cell Homeostasis: A Hypothesis and a Model

Homeostasis of lymphocyte numbers is believed to be due to competition between cellular populations for a common niche of restricted size, defined by the combination of interactions and trophic factors required for cell survival. Here we propose a new mechanism: homeostasis of lymphocyte numbers could also be achieved by the ability of lymphocytes to perceive the density of their own populations. Such a mechanism would be reminiscent of the primordial quorum-sensing systems used by bacteria, in which some bacteria sense the accumulation of bacterial metabolites secreted by other elements of the population, allowing them to “count” the number of cells present and adapt their growth accordingly. We propose that homeostasis of CD4+ T cell numbers may occur via a quorum-sensing-like mechanism, where IL-2 is produced by activated CD4+ T cells and sensed by a population of CD4+ Treg cells that expresses the high-affinity IL-2Rα-chain and can regulate the number of activated IL-2-producing CD4+ T cells and the total CD4+ T cell population. In other words, CD4+ T cell populations can restrain their growth by monitoring the number of activated cells, thus preventing uncontrolled lymphocyte proliferation during immune responses. We hypothesize that malfunction of this quorum-sensing mechanism may lead to uncontrolled T cell activation and autoimmunity. Finally, we present a mathematical model that describes the key role of IL-2 and quorum-sensing mechanisms in CD4+ T cell homeostasis during an immune response.

Induction of CD56 + T cells after prolonged activation of T cells in vitro: A possible mechanism for CD4 + T-cell depletion in acquired immune deficiency syndrome patients

The pathogenic mechanisms responsible for depletion of CD4 + T cells in aquired immune deficiency syndrome (AIDS) are not fully understood. Systemic immune activation mediated by persistent infection of human immunodeficiency virus (HIV) seems to be one of the predictors of disease progression. We predicted that certain lymphocytes responsible for CD4 + T-cell depletion could be induced in patients during prolonged activation of lymphocytes. Therefore, we have established an in vitro long-term culture system for peripheral blood mononuclear cells with PHA-P stimulation and Herpesvirus saimiri infection, and examined what types of cells having strong cytotoxic activity to be emerged under the activated conditions. We observed that percentage of CD56 + T cells was gradually increased in cultures from 30 days after stimulation and exhibited a cytotoxic activity against both autologous and allogeneic targets. Interestingly, HIV-1 infection enhanced the susceptibility of CD4 + T cells to their cytotoxic effectors, and CD4 + T cells from HIV-1–infected individuals showed decreased survival rate in the presence of autologous CD56 + T cells. These findings raised the possibility that induction of autoreactive CD56 + T cells in consequence of immune activation might be contributed to the depletion of CD4 + T cells in HIV-1–infected patients.

HIV disease progression despite suppression of viral replication is associated with exhaustion of lymphopoiesis

AbstractThe mechanisms of CD4+ T-cell count decline, the hallmark of HIV disease progression, and its relationship to elevated levels of immune activation are not fully understood. Massive depletion of CD4+ T cells occurs during the course of HIV-1 infection, so that maintenance of adequate CD4+ T-cell levels probably depends primarily on the capacity to renew depleted lymphocytes, that is, the lymphopoiesis. We performed here a comprehensive study of quantitative and qualitative attributes of CD34+ hematopoietic progenitor cells directly from the blood of a large set of HIV-infected persons compared with uninfected donors, in particular the elderly. Our analyses underline a marked impairment of primary immune resources with the failure to maintain adequate lymphocyte counts. Systemic immune activation emerges as a major correlate of altered lymphopoiesis, which can be partially reversed with prolonged antiretroviral therapy. Importantly, HIV disease progression despite elite control of HIV replication or virologic success on antiretroviral treatment is associated with persistent damage to the lymphopoietic system or exhaustion of lymphopoiesis. These findings highlight the importance of primary hematopoietic resources in HIV pathogenesis and the response to antiretroviral treatments.

CD4+ and CD8+ T cell- and IL-17-mediated protection against Entamoeba histolytica induced by a recombinant vaccine

Amebiasis in the murine model can be prevented by vaccination with the Gal/GalNAc lectin through a T cell-dependent mechanism. In this work we further decipher the mechanism of this protection. Mice vaccinated with the recombinant “LecA” fragment of the Gal/GalNAc lectin with alum were capable of transferring protection to naïve recipients by both CD4+ T cells and surprisingly CD8+ T cells. We then examined the cytokine profile of these cells. CD4+ T cells from PBMC of LecA-alum vaccinated mice were observed to be a major source of IFN-γ, known to be a protective cytokine with this vaccine. In contrast, CD8+ T cells produced relatively little IFN-γ but more IL-17 than the CD4 compartment. We thus examined the role of IL-17 in vaccine mediated protection and found through neutralization experiments that this cytokine contributed to LecA-alum vaccine protection. In addition we examined whether these cells exhibited direct amebicidal activity in vitro and found that both populations had amebicidal activity at high concentrations (1000:1) but CD8+ T cells appeared more potent, capable of cytotoxicity at a 100:1 ratio. In conclusion, both CD4 and CD8 T cells exert protection with this amebiasis vaccine. The mechanism of CD8 T cell-mediated protection may include direct amebicidal activity and/or IL-17 production. Both IL-17 and IFN-γ are useful surrogates for immune protection.

Elevated Caspase-3 Expression and T-Cell Activation in Elite Suppressors

Elevated Caspase-3 Expression and T-Cell Activation in Elite Suppressors

IL-21 is a central component of CD4 T cell help required to purge a persistent viral infection (44.27)

Abstract Therapies to cure persistent viral infections have largely been unsuccessful because it is unclear what is required of the immune system to purge virus once it proceeds past acute infection. T cell immunity is crucial to eliminate viral infection. However, CD4 and CD8 T cell functions are rapidly aborted during persistent infection, preventing viral clearance. To date the majority of work examining T cell function during viral persistence has focused on CD8 T cells. Yet, many aspects of immune exhaustion are associated with functions performed by CD4 T helper cells (which are also rapidly exhausted after persistent infection), suggesting that loss of CD4 T cell function is a key mechanism permitting viral persistence. CD4 T cell help is required throughout persistence to sustain CD8 T cell responses and resolve persistent viral infection, suggesting that CD4 T cells maintain some yet undefined, but essential, helper functions. We demonstrate that IL-21 as an essential component of CD4 T cell help during viral persistence. In the absence of IL-21 signaling, despite elevated CD4 T cell responses, help to CD8 T cells is not provided. CD4 T cells utilize IL-21 to prevent CD8 T cell deletion, sustain immunity and resolve persistent infection. Thus, we identify a novel mechanism of CD4 T cell help during viral persistence and propose that CD4 help is not lost during viral persistence, but instead is altered from promoting memory development toward the production of factors that ultimately sustain effector responses to control viral replication.

Differential Mechanisms for CD4+ and CD8+ Mediated Inflammation in the Development of Experimental Idiopathic Pneumonia Syndrome

Differential Mechanisms for CD4+ and CD8+ Mediated Inflammation in the Development of Experimental Idiopathic Pneumonia Syndrome

Acquired pMHC I Complexes Greatly Enhance CD4+ Th Cell's Stimulatory Effect on CD8+ T Cell-Mediated Diabetes in Transgenic RIP-mOVA Mice

CD4(+) helper T (Th) cells play pivotal roles in induction of CD8(+) CTL immunity. However, the mechanism of CD4(+) T cell help delivery to CD8(+) T cells in vivo is still elusive. In this study, we used ovalbumin (OVA)-pulsed dendritic cells (DC(OVA)) to activate OT-II mouse CD4(+) T cells, and then studied the help effect of these CD4(+) T cells on CD8(+) cytotoxic T lymphocyte (CTL) responses. We also examined CTL mediated islet beta cell destruction which led to diabetes in wild-type C57BL/6 mice and transgenic rat insulin promoter (RIP)-mOVA mice expressing beta cell antigen OVA with self OVA-specific tolerance, respectively. In adoptive transfer experiments, we demonstrated that help, in the form of peptide/major histocompatibility complex (pMHC) I acquired from DC(OVA) by DC(OVA) activation, was required for induction of OVA-specific CTL responses in C57BL/6 mice. However, in combination with TCR transgenic OT-I mouse CD8(+) T cells, the tolerogenic dosage of CD4(+) Th cells with acquired pMHC I, but not CD4(+) K(b-/-) Th cells without acquired pMHC I were able to cause diabetes in 8/10 (80%) RIP-mOVA mice. This study thus expands the current knowledge in T cell-mediated autoimmunity and provides insight into the nature of CD4(+) T cell-mediated help in CD8(+) CTL induction.