Antigen Presenting B Cells Facilitate CD4 T Cell Cooperation Resulting in Enhanced Generation of Effector and Memory CD4 T Cells

We show that the in vivo generation of cytokine-producing CD4 T cells specific for a given major histocompatibility class-II (MHCII)-binding peptide of hen egg lysozyme (HEL) is facilitated when mice are immunized with splenic antigen presenting cells (APC) pulsed with this HEL peptide and another peptide that binds a different MHCII molecule. This enhanced generation of peptide-specific effector CD4 T cells requires that the same splenic APC be pulsed with both peptides. Pulsed B cells, but not pulsed dendritic cells (DCs), can mediate CD4 T cell cooperation, which can be blocked by disrupting OX40-OX40L (CD134-CD252) interactions. In addition, the generation of HEL peptide-specific CD4 T cell memory is greater when mice are primed with B cells pulsed with the two peptides than with B cells pulsed with the HEL- peptide alone. Based on our findings, we suggest CD4 T cell cooperation is important for vaccine design, underlies the phenomenon of “epitope-spreading” seen in autoimmunity, and that the efficacy of B cell-depletion in the treatment of human cell-mediated autoimmune disease is due to the abrogation of the interactions between autoimmune CD4 T cells that facilitates their activation.     

Invariant NKT Cells Regulate the CD8 T Cell Response during Theiler's Virus Infection

Invariant NKT cells are innate lymphocytes with a broad tissue distribution. Here we demonstrate that iNKT cells reside in the central nervous system (CNS) in the absence of inflammation. Their presence in the CNS dramatically augments following inoculation of C57Bl/6 mice with the neurotropic Theiler''s murine encephalomyelitis virus (TMEV). At the peak of inflammation the cellular infiltrate comprises 45 000 iNKT cells for 1 250 CD8 T cells specific for the immunodominant TMEV epitope. To study the interaction between these two T cell subsets, we infected both iNKT cell deficient Jα18^-/- mice and iNKT cell enriched Vα14 transgenic mice with TMEV. The CD8 T cell response readily cleared TMEV infection in the iNKT cell deficient mice. However, in the iNKT cell enriched mice TMEV infection persisted and was associated with significant mortality. This was caused by the inhibition of the CD8 T cell response in the cervical lymph nodes and spleen after T cell priming. Taken together we demonstrate that iNKT cells reside in the CNS in the absence of inflammation and that their enrichment is associated with the inhibition of the anti-viral CD8 T cell response and an augmented mortality during acute encephalomyelitis.     

MicroRNA miR-155 Affects Antiviral Effector and Effector Memory CD8 T Cell Differentiation

MicroRNAs are key regulators of the immune response, but their role in CD8 T cell differentiation in vivo is not known. We show that miR-155 is important in both effector and memory antiviral CD8 T cell responses. Without miR-155, there was a weaker effector response and a skewing toward memory precursor cells. At the memory stage, miR-155-deficient CD8 T cells preferentially differentiated into central memory cells and were capable of mounting a potent secondary response.     

TRAF3 Regulates Homeostasis of CD8+ Central Memory T Cells

Our laboratory reported previously that TNF receptor associated factor 3 (TRAF3) is a positive regulator of TCR signaling and T cell function. In the current study, we present new findings that reveal differential roles for TRAF3 in the regulation of CD4⁺ and CD8⁺ T cells. In response to TCR stimulation in vitro, TRAF3 has greater impact in CD4⁺ T cells than in CD8⁺ T cells. However, T cell-specific TRAF3 deficient mice (CD4^Cre TRAF3^fl°^x/fl°^x; T-TRAF3^−/−) have a greater number of CD4⁺CD44^hi effector/memory T cells than littermate control (LMC) mice, possibly due to an inefficient suppressive effect of TRAF3 deficient Foxp3⁺ regulatory T cells. In contrast, CD8⁺CD44^hiCD62L^hi central memory (Tcm) cells are markedly reduced in T-TRAF3^−/− mice in comparison to LMC mice, although CD8⁺CD44^hiCD62L^l°^w effector memory T (Tem) cells and naïve T cells (CD8⁺CD44^l°^wCD62L^hi) do not show significant differences in number. Importantly, TRAF3-deficient Tcm cells exhibit defective homeostasis due to impaired IL-15 signaling. These results indicate that the involvement of TRAF3 in IL-15 mediated signaling to T cells plays a previously unappreciated and critical role in CD8⁺ Tcm cell regulation and maintenance.     

Tolerogenic Vaccination Reduced Effector Memory CD4 T Cells and Induced Effector Memory Treg Cells for Type I Diabetes Treatment

Background

Vaccination could induce immune tolerance and protected NOD mice from the development of type I diabetes (T1D). We previously demonstrated that insulin peptide (B9-23) combined with dexamethasone (DEX) stimulated the expansion of antigen specific regulatory T (Treg) cells which in turn effectively prevented T1D in NOD mice. Here, we aimed to investigate the therapeutic effect of tolerogenic vaccination for T1D treatment.

Methodology/Principal Findings

The diabetic NOD mice (Blood glucose level ≧250 mg/dl) were treated with B9-23 and DEX twice. The tolerance was restored by blocking maturation of dendritic cells (DCs) and inducing Treg cells in treated NOD mice. Remarkably, the reduction of autoreactive effector memory CD4 T (Tm) cells and the induction of functional effector memory Treg (mTreg) cells contributed to the improvement of T1D in treated NOD mice.

Conclusions/Significance

Tolerogenic vaccination restored tolerance and ameliorated T1D by suppressing effector CD4 Tm cells and inducing effector mTreg cells. Our findings implicate the potential of tolerogenic vaccination for T1D treatment.     

Differential Expression of CD96 Surface Molecule Represents CD8+ T Cells with Dissimilar Effector Function during HIV-1 Infection

During HIV-1 infection, immune dysregulation and aberrant lymphocyte functions are well-established characteristics. Cell surface molecules are important for immunological functions and changes in expression can affect lymphocyte effector functions, thereby contributing to pathogenesis and disease progression. In this study we have focused on CD96, a member of the IgG superfamily receptors that have generated increasing recent interest due to their adhesive and co-stimulatory functions in addition to immunoregulatory capacity. CD96 is expressed by both T and NK cells. Although the function of CD96 is not completely elucidated, it has been shown to have adhesive functions and enhance cytotoxicity. Interestingly, CD96 may also have inhibitory functions due to its immunoreceptor tyrosine-based inhibitory motif (ITIM). The clinical significance of CD96 is still comparatively limited although it has been associated with chronic Hepatitis B infection and disease progression. CD96 has not previously been studied in the context of HIV-1 infection, but due to its potential importance in immune regulation and relevance to chronic disease, we examined CD96 expression in relation to HIV-1 pathogenesis. In a cross-sectional analysis, we investigated the CD8⁺ T cell expression of CD96 in cohorts of untreated HIV-1 infected adults with high viral loads (non-controllers) and low viral loads (“elite” controllers). We demonstrated that elite controllers have significantly higher CD96 mean fluorescence intensity on CD8⁺ T cells compared to HIV-1 non-controllers and CD96 expression was positively associated with CD4⁺ T cell counts. Functional assessment showed that CD8⁺ T cells lacking CD96 expression represented a population that produced both perforin and IFN-γ following stimulation. Furthermore, CD96 expression on CD8⁺ T cells was decreased in presence of lipopolysaccharide in vitro. Overall, these findings indicate that down-regulation of CD96 is an important aspect of HIV-1 pathogenesis and differential expression is related to cell effector functions and HIV-1 disease course.     

Vaccination Expands Antigen-Specific CD4+ Memory T Cells and Mobilizes Bystander Central Memory T Cells

CD4⁺ T helper memory (Th_mem) cells influence both natural and vaccine-boosted immunity, but mechanisms for their maintenance remain unclear. Pro-survival signals from the common gamma-chain cytokines, in particular IL-7, appear important. Previously we showed in healthy volunteers that a booster vaccination with tetanus toxoid (TT) expanded peripheral blood TT-specific Th_mem cells as expected, but was accompanied by parallel increase of Th_mem cells specific for two unrelated and non cross-reactive common recall antigens. Here, in a new cohort of healthy human subjects, we compare blood vaccine-specific and bystander Th_mem cells in terms of differentiation stage, function, activation and proliferative status. Both responses peaked 1 week post-vaccination. Vaccine-specific cytokine-producing Th_mem cells were predominantly effector memory, whereas bystander cells were mainly of central memory phenotype. Importantly, TT-specific Th_mem cells were activated (CD38^High HLA-DR⁺), cycling or recently divided (Ki-67⁺), and apparently vulnerable to death (IL-7Rα^Low and Bcl-2 ^Low). In contrast, bystander Th_mem cells were resting (CD38^Low HLA-DR^- Ki-67^-) with high expression of IL-7Rα and Bcl-2. These findings allow a clear distinction between vaccine-specific and bystander Th_mem cells, suggesting the latter do not derive from recent proliferation but from cells mobilized from as yet undefined reservoirs. Furthermore, they reveal the interdependent dynamics of specific and bystander T-cell responses which will inform assessments of responses to vaccines.     

Immunodomination during Peripheral Vaccinia Virus Infection

Immunodominance is a fundamental property of CD8⁺ T cell responses to viruses and vaccines. It had been observed that route of administration alters immunodominance after vaccinia virus (VACV) infection, but only a few epitopes were examined and no mechanism was provided. We re-visited this issue, examining a panel of 15 VACV epitopes and four routes, namely intradermal (i.d.), subcutaneous (s.c.), intraperitoneal (i.p.) and intravenous (i.v.) injection. We found that immunodominance is sharpened following peripheral routes of infection (i.d. and s.c.) compared with those that allow systemic virus dissemination (i.p. and i.v.). This increased immunodominance was demonstrated with native epitopes of VACV and with herpes simplex virus glycoprotein B when expressed from VACV. Responses to some subdominant epitopes were altered by as much as fourfold. Tracking of virus, examination of priming sites, and experiments restricting virus spread showed that priming of CD8⁺ T cells in the spleen was necessary, but not sufficient to broaden responses. Further, we directly demonstrated that immunodomination occurs more readily when priming is mainly in lymph nodes. Finally, we were able to reduce immunodominance after i.d., but not i.p. infection, using a VACV expressing the costimulators CD80 (B7-1) and CD86 (B7-2), which is notable because VACV-based vaccines incorporating these molecules are in clinical trials. Taken together, our data indicate that resources for CD8⁺ T cell priming are limiting in local draining lymph nodes, leading to greater immunodomination. Further, we provide evidence that costimulation can be a limiting factor that contributes to immunodomination. These results shed light on a possible mechanism of immunodomination and highlight the need to consider multiple epitopes across the spectrum of immunogenicities in studies aimed at understanding CD8⁺ T cell immunity to viruses.     

Selected MicroRNAs Define Cell Fate Determination of Murine Central Memory CD8 T Cells

During an immune response T cells enter memory fate determination, a program that divides them into two main populations: effector memory and central memory T cells. Since in many systems protection appears to be preferentially mediated by T cells of the central memory it is important to understand when and how fate determination takes place. To date, cell intrinsic molecular events that determine their differentiation remains unclear. MicroRNAs are a class of small, evolutionarily conserved RNA molecules that negatively regulate gene expression, causing translational repression and/or messenger RNA degradation. Here, using an in vitro system where activated CD8 T cells driven by IL-2 or IL-15 become either effector memory or central memory cells, we assessed the role of microRNAs in memory T cell fate determination. We found that fate determination to central memory T cells is under the balancing effects of a discrete number of microRNAs including miR-150, miR-155 and the let-7 family. Based on miR-150 a new target, KChIP.1 (K ⁺ channel interacting protein 1), was uncovered, which is specifically upregulated in developing central memory CD8 T cells. Our studies indicate that cell fate determination such as surface phenotype and self-renewal may be decided at the pre-effector stage on the basis of the balancing effects of a discrete number of microRNAs. These results may have implications for the development of T cell vaccines and T cell-based adoptive therapies.     

Vaccinia Virus Infection of Synchronized Pig Kidney Cells

Vaccinia virus replication was studied in pig kidney (PK-15) cells synchronized by excess thymidine treatment. It was found that virus replication with concomitant inhibition of mitosis can occur at any period in the life cycle of the cell except for the narrow span of time from late prophase through telophase. Cells infected at this time continue to divide, and vaccinia does not replicate until cell division is complete.     

Peroxiredoxin II Regulates Effector and Secondary Memory CD8+ T Cell Responses

Reactive oxygen intermediates (ROI) generated in response to receptor stimulation play an important role in cellular responses. However, the effect of increased H₂O₂ on an antigen-specific CD8⁺ T cell response was unknown. Following T cell receptor (TCR) stimulation, the expression and oxidation of peroxiredoxin II (PrdxII), a critical antioxidant enzyme, increased in CD8⁺ T cells. Deletion of PrdxII increased ROI, S phase entry, division, and death during in vitro division. During primary acute viral and bacterial infection, the number of effector CD8⁺ T cells in PrdxII-deficient mice was increased, while the number of memory cells were similar to those of the wild-type cells. Adoptive transfer of P14 TCR transgenic cells demonstrated that the increased expansion of effector cells was T cell autonomous. After rechallenge, effector CD8⁺ T cells in mutant animals were more skewed to memory phenotype than cells from wild-type mice, resulting in a larger secondary memory CD8⁺ T cell pool. During chronic viral infection, increased antigen-specific CD8⁺ T cells accumulated in the spleens of PrdxII mutant mice, causing mortality. These results demonstrate that PrdxII controls effector CD8⁺ T cell expansion, secondary memory generation, and immunopathology.     

Decreased Memory B Cells and Increased CD8 Memory T Cells in Blood of Breastfed Children: The Generation R Study

BackgroundBreastfeeding provides a protective effect against infectious diseases in infancy. Still, immunological evidence for enhanced adaptive immunity in breastfed children remains inconclusive.ObjectiveTo determine whether breastfeeding affects B- and T-cell memory in the first years of life.MethodsWe performed immunophenotypic analysis on blood samples within a population-based prospective cohort study. Participants included children at 6 months (n=258), 14 months (n=166), 25 months (n=112) and 6 years of age (n=332) with both data on breastfeeding and blood lymphocytes. Total B- and T-cell numbers and their memory subsets were determined with 6-color flow cytometry. Mothers completed questionnaires on breastfeeding when their children were aged 2, 6, and 12 months. Multiple linear regression models with adjustments for potential confounders were performed.ResultsPer month continuation of breastfeeding, a 3% (95% CI -6, -1) decrease in CD27+IgM+, a 2% (95 CI % -5, -1) decrease in CD27+IgA+ and a 2% (95% CI -4, -1) decrease in CD27-IgG+ memory B cell numbers were observed at 6 months of age. CD8 T-cell numbers at 6 months of age were 20% (95% CI 3, 37) higher in breastfed than in non-breastfed infants. This was mainly found for central memory CD8 T cells and associated with exposure to breast milk, rather than duration. The same trend was observed at 14 months, but associations disappeared at older ages.ConclusionsLonger breastfeeding is associated with increased CD8 T-cell memory, but not B-cell memory numbers in the first 6 months of life. This transient skewing towards T cell memory might contribute to the protective effect against infectious diseases in infancy.