Immune evasion versus recovery after acute hepatitis C virus infection from a shared source

Acute infection with hepatitis C virus (HCV) rarely is identified, and hence, the determinants of spontaneous resolution versus chronicity remain incompletely understood. In particular, because of the retrospective nature and unknown source of infection in most human studies, direct evidence for emergence of escape mutations in immunodominant major histocompatibility complex class I–restricted epitopes leading to immune evasion is extremely limited. In two patients infected accidentally with an identical HCV strain but who developed divergent outcomes, the total lack of HCV-specific CD4+ T cells in conjunction with vigorous CD8+ T cells that targeted a single epitope in one patient was associated with mutational escape and viral persistence. Statistical evidence for positive Darwinian selective pressure against an immunodominant epitope is presented. Wild-type cytotoxic T lymphocytes persisted even after the cognate antigen was no longer present

Human Innate Mycobacterium tuberculosis–Reactive αβTCR+ Thymocytes

The control of Mycobacterium tuberculosis (Mtb) infection is heavily dependent on the adaptive Th1 cellular immune response. Paradoxically, optimal priming of the Th1 response requires activation of priming dendritic cells with Th1 cytokine IFN-γ. At present, the innate cellular mechanisms required for the generation of an optimal Th1 T cell response remain poorly characterized. We hypothesized that innate Mtb-reactive T cells provide an early source of IFN-γ to fully activate Mtb-exposed dendritic cells. Here, we report the identification of a novel population of Mtb-reactive CD4− αβTCR+ innate thymocytes. These cells are present at high frequencies, respond to Mtb-infected cells by producing IFN-γ directly ex vivo, and display characteristics of effector memory T cells. This novel innate population of Mtb-reactive T cells will drive further investigation into the role of these cells in the containment of Mtb following infectious exposure. Furthermore, this is the first demonstration of a human innate pathogen-specific αβTCR+ T cell and is likely to inspire further investigation into innate T cells recognizing other important human pathogens

Human mucosal associated invariant T cells detect bacterially infected cells

Control of infection with Mycobacterium tuberculosis (Mtb) requires Th1-type immunity, of which CD8+ T cells play a unique role. High frequency Mtb-reactive CD8+ T cells are present in both Mtb-infected and uninfected humans. We show by limiting dilution analysis that nonclassically restricted CD8+ T cells are universally present, but predominate in Mtbuninfected individuals. Interestingly, these Mtb-reactive cells expressed the Va7.2 T-cell receptor (TCR), were restricted by the nonclassical MHC (HLA-Ib) molecule MR1, and were activated in a transporter associated with antigen processing and presentation (TAP) independent manner. These properties are all characteristics of mucosal associated invariant T cells (MAIT), an "innate" T-cell population of previously unknown function. These MAIT cells also detect cells infected with other bacteria. Direct ex vivo analysis demonstrates that Mtb-reactive MAIT cells are decreased in peripheral blood mononuclear cells (PBMCs) from individuals with active tuberculosis, are enriched in human lung, and respond to Mtb-infected MR1-expressing lung epithelial cells. Overall, these findings suggest a generalized role for MAIT cells in the detection of bacterially infected cells, and potentially in the control of bacterial infection. © 2010 Gold et al

Spontaneous Recovery in Acute Human Hepatitis C Virus Infection: Functional T-Cell Thresholds and Relative Importance of CD4 Help▿

The mechanisms mediating protective immunity to hepatitis C virus (HCV) infection are incompletely understood because early infection in humans is rarely identified, particularly in those individuals who subsequently demonstrate spontaneous virus eradication. We have established a large national network of patients with acute HCV infection. Here, we comprehensively examined total HCV-specific CD4+ and CD8+ T-cell responses and identified functional T-cell thresholds that predict recovery. Interestingly, we found that the presence of HCV-specific cytotoxic T lymphocytes (CTLs) that can proliferate, exhibit cytotoxicity, and produce gamma interferon does not ensure recovery, but whether these CTLs were primed in the presence or absence of CD4+ T-cell help (HCV-specific interleukin-2 production) is a critical determinant. These results have important implications for early prediction of the virologic outcome following acute HCV and for the development of novel immunotherapeutic approaches

MR1 presents a protein-containing antigen from the mycobacterial cell wall.

<p>(A) CFP or CW from the Mtb strain H37Rv were added (5 µg/ml) to DCs (25,000/well) for 1 h prior to the addition of one of 21 NC clones (5,000/well) followed by IFN-γ ELISPOT assay. (B) DCs (25,000) loaded with CW overnight were incubated with anti-MR1 blocking antibody (clone 26.5) or a mouse IgG2a isotype control (both at 5 µg/ml) for 1 h prior to the addition of T-cell clones (10,000/well). (C) dCW from Mtb was treated with proteases (subtilisin, trypsin, chymotrypsin, pronase, Glu-C) and added (5 µg/ml) to DCs (25,000/well) for 1 h before the addition of 21 NC clones (5,000/well) that were tested for their ability to produce IFN-γ in an ELISPOT assay. Reversed phase- high performance liquid chromatography (RP-HPLC) chromatogram analyses were used to confirm the inactivation of proteases. No responses were detected in the absence of DCs. (D) DCs were infected with <i>S. typhimurium</i>, <i>L. monocytogenes</i>, <i>and S. aureus</i> for 1 h with a calculated moi of 145, 6, and 15, respectively. DCs were washed, antibiotics added, and DCs (25,000) were incubated with three different Mtb-reactive MAIT-cell clones (10,000/well) that were tested for their ability to produce IFN-γ in an ELISPOT assay. Results shown are similar to a minimum of three independent experiments where <i>S. typhimurium</i>, <i>L. monocytogenes</i>, <i>and S. aureus</i> were tested at a variety of moi ranging from 5 to 150.</p

Mtb-reactive MAIT cells in the human lung.

<p>Single cell suspensions were prepared from the lung and adjacent LNs with minor modifications <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1000407#pbio.1000407-Lewinsohn5" target="_blank">[52]</a>. The intracellular cytokine staining assay was performed using magnetic-bead purified CD8⁺ T cells from the lung and LNs as described in <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1000407#pbio-1000407-g006" target="_blank">Figure 6</a> legend. Only in the case of donor B were anti-MR1 or IgG2a isotype control antibodies added (2.5 µg/ml).</p

Mtb-specific NC CD8⁺ T cells are restricted by MR1.

<p>(A–E) Results of ELISPOT assays shown as IFN-γ spot forming units (SFU)/10,000 T cells in response to DCs (25,000/well) treated as described. (A) TLR agonist stimulation of DCs does not stimulate Mtb-reactive NC-restricted clones. DCs were treated (24 h) with TLR agonists specific for TLR2 (lipoteichoic acid, 10 µg/ml) and TLR4 (LPS; 100 ng/ml) at concentrations known to induce activation and cytokine production by DCs <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1000407#pbio.1000407-Gold1" target="_blank">[14]</a>. (B) TLR2 (5 µg/ml) or TLR4 (10 µg/ml) blocking antibodies were added to DCs that were uninfected or infected 1 h prior to the addition of Mtb-reactive NC T-cell clones. (C) Mtb-infected DCs were incubated with blocking antibodies (5 µg/ml) to NKG2D, ULBP1, MICA, CD94 for 1 h prior to the addition of the T-cell clones. (D) The pan HLA–I (W632) and CD1a, b, c, and d blocking antibodies were added to Mtb-infected DCs prior to the addition of T cells. (E) DCs infected with Mtb overnight were incubated with anti-MR1 blocking antibody (clone 26.5) or a mouse IgG2a isotype control (both at 5 µg/ml) for 1 h prior to the addition of T cells. (F–H) Cell surface phenotypic analyses of MR1-restricted clones and control clones. For cell surface detection, cells were incubated with antibodies specific for Vα7.2 (clone 3C10) (F), or CD8α, CD8β (G), or CD161 (H), and analyzed by flow cytometry. For (F) and (H), filled histograms represent the isotype control, bold lines represent antibody-specific staining. Columns 1, 2, and 3 represent MR1-restricted clones from different TB exposure groups: D470B1 (uninfected), D426B1 (latent), D466F5 (active), respectively. Column 4 represents HLA-E restricted clone D160 1–23 <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1000407#pbio.1000407-Heinzel1" target="_blank">[16]</a>. Column 5 represents HLA-B08-restricted clone D480C6 specific for the Mtb antigen CFP-10_3–11. Column 6 represents CD4⁺ HLA-II–restricted clone D454E12 specific for the Mtb antigen CFP-10. Error bars represent the mean and standard error from duplicate wells. N.D., not done.</p