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Tuberculosis (TB) remains a worldwide public health threat. Development of a more effective vaccination strategy to prevent pulmonary TB, the most common and contagious form of the disease, is a research priority for international TB control. A key to reaching this goal is improved understanding of the mechanisms of local immunity to Mycobacterium tuberculosis, the causative organism of TB. In this study, we evaluated global M. tuberculosis–induced gene expression in airway immune cells obtained by bronchoalveolar lavage (BAL) of individuals with latent TB infection (LTBI) and M. tuberculosis–naive controls. In prior studies, we demonstrated that BAL cells from LTBI individuals display substantial enrichment for M. tuberculosis–responsive CD4+ T cells compared with matched peripheral blood samples. We therefore specifically assessed the impact of the depletion of CD4+ and CD8+ T cells on M. tuberculosis–induced BAL cell gene expression in LTBI. Our studies identified 12 canonical pathways and a 47-gene signature that was both sensitive and specific for the contribution of CD4+ T cells to local recall responses to M. tuberculosis. In contrast, depletion of CD8+ cells did not identify any genes that fit our strict criteria for inclusion in this signature. Although BAL CD4+ T cells in LTBI displayed polyfunctionality, the observed gene signature predominantly reflected the impact of IFN-γ production on a wide range of host immune responses. These findings provide a standard for comparison of the efficacy of standard bacillus Calmette–Guérin vaccination as well as novel TB vaccines now in development at impacting the initial response to re-exposure to M. tuberculosis in the human lung.

Vaccines are less effective in older adults, and efforts to improve vaccine efficacy generally show limited clinical improvement. However, the vaccine Shingrix, developed by GlaxoSmithKline, is FDA approved and recommended for adults over the age of 50 for the prevention of shingles. Shingrix contains the novel adjuvant AS01 and shows remarkably high (>90%) effectiveness at both preventing shingles and reducing the development of postherpetic neuralgia, even in adults over 80. We seek to examine AS01-induced activation of myeloid cells and determine their impacts on T cell memory differentiation and function in an effort to understand how this vaccine’s high clinical efficacy is produced. We use peripheral blood samples to examine AS01-induced innate immune cell activation, including interactions with T cells once activated. We find that AS01 induces costimulatory marker upregulation and cytokine production in myeloid dendritic cells and monocytes in a synergistic manner, with the most upregulation seen in monocytes. Naïve and memory CD4 T cells incubated with AS01-treated monocytes have increased frequencies of TH17 (CCR6+ CXCR3−) cells and decreased frequencies of TH1 cells compared to controls. Naïve CD4 T cells proliferate more when incubated with AS01-treated monocytes than with controls. AS01-treated monocytes additionally induce 2x less IFN-γ and IL-5 in response to mitogen (SEB) from CD4 T cells, suggesting a modulation of response. We propose that AS01 influences monocytes to diversify the existing memory T cell repertoire and skews naïve T cells towards more cytotoxic phenotypes such as TH17, contributing to greater clinical efficacy in preventing shingles in vivo. Supported by VA Merit grant (CX002060)

Although influenza vaccination is recommended for all adults annually, the incidence of vaccine failure, defined as weak or absent increase in neutralizing Ab titers, is increased in the elderly compared with young adults. The T follicular helper cell (Tfh) subset of CD4 T cells provides B cell help in germinal centers and is necessary for class-switched Ab responses. Previous studies suggested a role for circulating Tfh cells (cTfh) following influenza vaccination in adults, but cTfh have not been studied in elderly adults in whom weak vaccine responses are often observed. In this study, we studied cTfh expressing CXCR5 and programmed death-1 (PD-1). cTfh from elderly adults were present at reduced frequency, had decreased in vitro B cell help ability, and had greater expression of ICOS compared with young adults. At 7 d after inactivated influenza vaccination, cTfh correlated with influenza vaccine–specific IgM and IgG responses in young adults but not in elderly adults. In sum, we have identified aging-related changes in cTfh that correlated with reduced influenza vaccine responses. Future rational vaccine design efforts should incorporate Tfh measurement as an immune correlate of protection, particularly in the setting of aging.

Little is known about CD4 T cell function in Varicella Zoster Virus (VZV) infection. Here we sampled peripheral blood of individuals (n=31) with acute shingles as a result of reactivation of VZV and persons with a remote history of shingles (n=15). Mitogen and whole VZV were added to peripheral blood mononuclear cells (PBMC) for an in vitro stimulation assay. IFN-γ, IL-2, TNF-α, CD107a, T-bet, EOMES and KLRG1 were examined by flow cytometry. Mitogen- and whole VZV-stimulated total memory CD4 T cells showed significant differences in polyfunction (p Supported by NIH and VA.

Recently defined specialized subset of Treg expressing CXCR5+PD1+FoxP3+ termed as T follicular regulatory (Tfr) cells regulates T follicular helper (Tfh) mediated B cell high-affinity and isotype-switched antibody production. To date, much of our understanding of the suppression mechanism of Tfr cells has been obtained from animal studies. The mechanism of Tfr regulation of humoral immunity in humans is still understudied. Here, we used cells from human mesenteric lymph nodes to study how Tfr affect Tfh and B cells and what specific Tfr-induced changes occur on Tfh and B cells in vitro. We report that Tfr suppress both Tfh and B cell function and proliferation in a dose dependent manner. We find that Tfr downregulate CD40, CD80/CD86 and CD38 on B cells and CD28, OX40, ICOS and CD38 on Tfh cells. We also show that blocking immune checkpoint receptors inhibits Tfr suppression of Tfh and B cells and partially restores the Tfh mediated B cell antibody production. These findings reveal that Tfr regulate activation of Tfh and B cells by downregulating key costimulatory receptors and ligands that help induce activation in both Tfh and B cells. These changes ultimately lead to decreased proliferation of both B cells and Tfh and reduced production of immunoglobulin by B cells. This research was supported in part by NIH R01 and VA.

Dendritic cells (DCs) cross process exogenous Ags and present them by class I MHC (MHC-I) molecules to CD8+ T cells specific for Ags from viruses and bacteria such as Mycobacterium tuberculosis. Unmethylated CpG DNA signals through TLR9 to induce type I IFN (IFN-α/β), which enhances MHC-I Ag cross processing, but lipoproteins that signal through TLR2 do not induce IFN-α/β. In these studies we observed that M. tuberculosis, which expresses agonists of both TLR9 and TLR2, did not induce production of IFN-α/β or cross processing by murine DCs. Furthermore, M. tuberculosis and TLR2 agonists inhibited induction of IFN-α/β and DC cross processing by CpG DNA. Exogenous IFN-α/β effectively enhanced cross processing of M. bovis bacillus Calmette-Guérin expressing OVA, bypassing the inhibition of induction of endogenous IFN-α/β. In addition, inhibition of TLR9-induced cross processing of M. bovis bacillus Calmette-Guérin expressing OVA could be circumvented by pretreating cells with CpG DNA to induce IFN-α/β and MHC-I cross processing before inhibitory mycobacterial TLR2 agonists were present. Inhibition of the response to one TLR by another may affect the ultimate response to pathogens like M. tuberculosis that express agonists of multiple TLRs, including TLR2 and TLR9. This mechanism may contribute to immune evasion and explain why IFN-α/β provides little contribution to host immunity to M. tuberculosis. However, downregulation of certain TLR responses may benefit the host by preventing detrimental excessive inflammation that may occur in the presence of persistent infection.

Professional phagocytosis in mammals is considered to be performed exclusively by myeloid cell types. In this study, we demonstrate, for the first time, that a mammalian lymphocyte subset can operate as a professional phagocyte. By using confocal microscopy, transmission electron microscopy, and functional Ag presentation assays, we find that freshly isolated human peripheral blood γδ T cells can phagocytose Escherichia coli and 1 μm synthetic beads via Ab opsonization and CD16 (FcγRIII), leading to Ag processing and presentation on MHC class II. In contrast, other CD16+ lymphocytes, i.e., CD16+/CD56+ NK cells, were not capable of such functions. These findings of distinct myeloid characteristics in γδ T cells strongly support the suggestion that γδ T cells are evolutionarily ancient lymphocytes and have implications for our understanding of their role in transitional immunity and the control of infectious diseases and cancer.

IgG anti-polysaccharide (PS) responses to both intact Streptococcus pneumoniae (Pn) and PS conjugate vaccines are dependent on CD4+ T cells, B7-dependent costimulation, and CD40-CD40-ligand interactions. Nevertheless, the former response, in contrast to the latter, is mediated by an ICOS-independent, apoptosis-prone, extrafollicular pathway that fails to generate PS-specific memory. We show that pre-existing PS-specific Igs, the bacterial surface or particulation, selective recruitment of B cell subsets, or activation and recruitment of Pn protein-specific CD4+ T cells do not account for the failure of Pn to generate PS-specific IgG memory. Rather, the data suggest that the critical factor may be the lack of covalent attachment of PS to protein in intact Pn, highlighting the potential importance of the physicochemical relationship of PS capsule with the underlying bacterial structure for in vivo induction of PS-specific Igs.

In vivo studies suggest that vascular endothelial cells (ECs) can acquire and cross-present exogenous Ag on MHC-I but the cellular mechanisms underlying this observation remain unknown. We tested whether primary female mouse aortic ECs could cross-present exogenous male Ag to the T cell hybridoma, MHH, specific for HYUty plus Db. MHC-I-deficient male spleen cells provided a source of male Ag that could not directly stimulate the MHH cells. Addition of male but not female MHC-I-deficient spleen cells to wild-type syngeneic female EC induced MHH stimulation, demonstrating EC cross-presentation. Lactacystin treatment of the donor male MHC-I-deficient spleen cells, to inhibit proteasome function, markedly enhanced EC cross-presentation showing that the process is most efficient for intact proteins rather than degraded peptide fragments. Additional experiments revealed that this EC Ag-processing pathway is both proteasome and TAP1 dependent. These studies demonstrate that cultured murine aortic ECs can process and present MHC-I-restricted Ag derived from a separate, live cell, and they offer insight into the molecular requirements involved in this EC Ag presentation process. Through this pathway, ECs expressing cross-presented peptides can participate in the effector phase of T cell-mediated inflammatory responses such as autoimmunity, anti-tumor immunity, and transplant rejection.

APCs process heat shock protein (HSP):peptide complexes to present HSP-chaperoned peptides on class I MHC molecules, but the ability of HSPs to contribute chaperoned peptides for class II MHC (MHC-II) Ag processing and presentation is unclear. Our studies revealed that exogenous bacterial HSPs (Escherichia coli DnaK and Mycobacterium tuberculosis HSP70) delivered an extended OVA peptide for processing and MHC-II presentation, as detected by T hybridoma cells. Bacterial HSPs enhanced MHC-II presentation only if peptide was complexed to the HSP, suggesting that the key HSP function was enhanced delivery or processing of chaperoned peptide Ag rather than generalized enhancement of APC function. HSP-enhanced processing was intact in MyD88 knockout cells, which lack most TLR signaling, further suggesting the effect was not due to TLR-induced induction of accessory molecules. Bacterial HSPs enhanced uptake of peptide, which may contribute to increased MHC-II presentation. In addition, HSPs enhanced binding of peptide to MHC-II molecules at pH 5.0 (the pH of vacuolar compartments), but not at pH 7.4, indicating another mechanism for enhancement of MHC-II Ag processing. Bacterial HSPs are a potential source of microbial peptide Ags during phagocytic processing of bacteria during infection and could potentially be incorporated in vaccines to enhance presentation of peptides to CD4+ T cells.

APCs process mammalian heat shock protein (HSP):peptide complexes to present HSP-chaperoned peptides on class I MHC (MHC-I) molecules to CD8+ T cells. HSPs are also expressed in prokaryotes and chaperone microbial peptides, but the ability of prokaryotic HSPs to contribute chaperoned peptides for Ag presentation is unknown. Our studies revealed that exogenous bacterial HSPs (Escherichia coli DnaK and Mycobacterium tuberculosis HSP70) delivered an extended OVA peptide for processing and MHC-I presentation by both murine macrophages and dendritic cells. HSP-enhanced MHC-I peptide presentation occurred only if peptide was complexed to the prokaryotic HSP and was dependent on CD91, establishing CD91 as a receptor for prokaryotic as well as mammalian HSPs. Inhibition of cytosolic processing mechanisms (e.g., by transporter for Ag presentation deficiency or brefeldin A) blocked HSP-enhanced peptide presentation in dendritic cells but not macrophages. Thus, prokaryotic HSPs deliver chaperoned peptide for alternate MHC-I Ag processing and cross-presentation via cytosolic mechanisms in dendritic cells and vacuolar mechanisms in macrophages. Prokaryotic HSPs are a potential source of microbial peptide Ags during phagocytic processing of bacteria during infection and could potentially be incorporated in vaccines to enhance presentation of peptides to CD8+ T cells.

Background Inflammatory indices such as IL-6 and soluble CD14 are elevated in the elderly, and aging is also associated with immune senescence and exhaustion. Soluble indices of inflammation and immune senescence have independently been associated with mortality and morbidity in the elderly. Whether these pathways are mechanistically linked is not clear. Methods This pilot study examined the relationship of plasma levels of IL-6, IP10, and sCD14 to T cell expression of immune checkpoint markers PD-1, CD57, and KLRG1 inelderly (≥70 years old; n=10) and young (≤40 years old;n=10) participants. Results Elderly participants had elevated plasma levels of IL-6 (p= Conclusion The relationship between soluble indices of inflammation and immune check pointmarker expression varies between elderly and young and between CD4 and CD8 T cells. Further studies are warranted to understand the complex interactions of inflammation and immune senescence and how they contribute tomortality and morbidity in the elderly.

Human immune responses to M. tuberculosis are characterized by activation of multiple T cell subsets including CD4+, CD8+, and γδ T cells, and the role of CD8+ αβ TCR+ T cells in this response is poorly understood. Stimulation of T cells from healthy tuberculin skin test-positive persons with live M. tuberculosis-H37Ra or soluble M. tuberculosis Ags readily up-regulated IL-2Rα (CD25) expression on CD8+ T cells. Purified resting and activated CD8+ T cells produced IFN-γ and proliferated to both M. tuberculosis bacilli and soluble mycobacterial Ags with monocytes as APC. Precursor frequency of mycobacterial Ag-specific CD8+ T cells by IFN-γ enzyme-linked immunospot was 5–10-fold lower than the precursor frequency of CD4+ T cells, and IFN-γ secretion by CD8+ T cells was 50–100-fold lower. CD8+ T cells secreted ∼10-fold less IFN-γ per cell than CD4+ T cells in response to mycobacterial Ags. CD8+ T cell responses to M. tuberculosis bacilli were blocked by anti-MHC class I antibody and required Ag processing. Processing of M. tuberculosis bacilli by monocytes for presentation to MHC class I-restricted CD8+ T cells was insensitive to brefeldin A treatment, which blocks the conventional MHC class I Ag-processing pathway. These results represent the first demonstration that human cells can process pathogen Ags via an alternate Ag-processing pathway for MHC class I and suggest a mechanism for participation of IFN-γ-secreting CD8+ T cells in the human immune responses to M. tuberculosis.

Ninety percent of deaths attributed to influenza are in the elderly. While age-related decline in T cell function has been demonstrated, much less is known about the innate immune responses during natural infection and vaccination that shape humoral and cell mediated responses. We analyzed interferon alpha (IFN-alpha) production in peripheral blood mononuclear cells (PBMCs) isolated from younger adult and geriatric individuals that were stimulated with influenza or TLR ligands. A majority of geriatric PBMCs made significantly lower amounts of IFN-alpha, a signature anti-viral cytokine, in response to influenza. Surprisingly, geriatric PBMCs had normal production of IFN-alpha in response to the TLR9 ligand, CpG ODN, and the TLR7 ligand, guardiquimod. We determined that plasmacytoid dendritic cells (pDCs) are the main producers of IFN-alpha in response to influenza, CpG ODN and guardiquimod in PBMCs by cell depletion studies, and that influenza signals through TLR7. We are currently investigating the mechanism for this defect in IFN-alpha production in response to influenza by geriatric pDCs. A better understanding of the specific innate immune responses to influenza in geriatric individuals may allow a better understanding of the pathophysiology of the host-influenza interaction and therefore allow a more targeted approach to vaccine design. This work is supported by AI077056 and AI36219.