Antigen-Specific B Cells Reactivate an Effective Cytotoxic T Cell Response against Phagocytosed Salmonella through Cross-Presentation

Background: The eradication of facultative intracellular bacterial pathogens, like Salmonella typhi, requires the concerted action of both the humoral immune response and the cytotoxic CD8 + T cell response. Dendritic cells (DCs) are considered to orchestrate the cytotoxic CD8 + T cell response via cross-presentation of bacterial antigens onto MHC class I molecules. Cross-presentation of Salmonella by DCs however, is accompanied by the induction of apoptosis in the DCs. Besides antibody production, B cells are required to clear Salmonella infection for other unknown reasons. Methodology/Principal Findings: Here we show that Salmonella-specific B cells that phagocytose Salmonella upon BCRligation reactivate human memory CD8 + T cells via cross-presentation yielding a Salmonella-specific cytotoxic T cell response. The reactivation of CD8 + T cells is dependent on CD4 + T cell help. Unlike the DCs, B cell-mediated crosspresentation of Salmonella does not coincide with apoptosis. Conclusions/Significance: B cells form a new player in the activation of the cytotoxic effector arm of the immune respons

Alternative Ii-independent antigen-processing pathway in leukemic blasts involves TAP-dependent peptide loading of HLA class II complexes

During HLA class II synthesis in antigen-presenting cells, the invariant chain (Ii) not only stabilizes HLA class II complexes in the endoplasmic reticulum, but also mediates their transport to specialized lysosomal antigen-loading compartments termed MIICs. This study explores an alternative HLA class II presentation pathway in leukemic blasts that involves proteasome and transporter associated with antigen processing (TAP)-dependent peptide loading. Although HLA-DR did associate with Ii, Ii silencing in the human class II-associated invariant chain peptide (CLIP)-negative KG-1 myeloid leukemic cell line did not affect total and plasma membrane expression levels of HLA-DR, as determined by western blotting and flow cytometry. Since HLA-DR expression does require peptide binding, we examined the role of endogenous antigen-processing machinery in HLA-DR presentation by CLIP− leukemic blasts. The suppression of proteasome and TAP function using various inhibitors resulted in decreased HLA-DR levels in both CLIP− KG-1 and ME-1 blasts. Simultaneous inhibition of TAP and Ii completely down-modulated the expression of HLA-DR, demonstrating that together these molecules form the key mediators of HLA class II antigen presentation in leukemic blasts. By the use of a proteasome- and TAP-dependent pathway for HLA class II antigen presentation, CLIP− leukemic blasts might be able to present a broad range of endogenous leukemia-associated peptides via HLA class II to activate leukemia-specific CD4+ T cells

IL-17 and IL-22 in atopic allergic disease

A long standing paradigm is that antigen-specific Th2 cells and their cytokines such as IL-4, IL-5, and IL-13 orchestrate the characteristic features of atopic allergy. The discovery of a role for IL-17-producing (Th17) and IL-22-producing (Th22) T helper cells in inflammatory diseases has added an additional layer of complexity to the understanding of the pathogenesis of allergic diseases. Here we re-evaluate the role of T helper cells, with special focus on the Th17 and Th22 subsets in allergic asthma and atopic dermatitis. Whereas sparse data point to a protective role of the increasing amounts of Th22 cells that are found in chronic stages of both allergies, the data on Th17 cells paint different pictures for the contribution of Th17 cells during subsequent stages of these two forms of allerg

B Cell Receptor-Mediated Internalization of Salmonella: A Novel Pathway for Autonomous B Cell Activation and Antibody Production

The present paradigm is that primary B cells are nonphagocytosing cells. In this study, we demonstrate that human primary B cells are able to internalize bacteria when the bacteria are recognized by the BCR. BCR-mediated internalization of Salmonella typhimurium results in B cell differentiation and secretion or anti-Salmonella Ab by the Salmonella-specific B cells. In addition, BCR-mediated internalization leads to efficient Ag delivery to the MHC class II Ag-loading compartments', even though Salmonella remains vital intracellularly in primary B cells. Consequently, BCR-mediated bacterial uptake induces efficient CD4(+) T cell help, which boosts Salmonella-specific Ab production. BCR-mediated internalization of Salmonella by B cells is superior over extracellular Ag extraction to induce rapid and specific Immoral immune responses and efficiently combat infection. The Journal of Immunology, 2009, 182: 7473-748

Class II-associated invariant chain peptide down-modulation enhances the immunogenicity of myeloid leukemic blasts resulting in increased CD4+ T-cell responses

Background: Disease recurrence in patients with acute myeloid leukemia may be partially explained by the escape of leukemic blasts from CD4(+) T-cell recognition. The current study investigates the role of aberrant HLA class II antigen presentation on leukemic blasts by determining both the clinical and functional impact of the class II-associated invariant chain peptide (CLIP). Design and Methods: The levels of expression of CLIP and HLA-DR on blood and bone marrow samples from 207 patients with acute myeloid leukemia were correlated with clinical outcome. Irradiated CLIP and CLIP leukemic blasts were compared for their ability to induce CD4(+) T cells during mixed leukocyte reactions. To discriminate between these blasts, we down-modulated CLIP expression on myeloid leukemic cell lines by RNA interference of the invariant chain, a chaperone protein critically involved in HLA-DR processing, and performed flow cytometric sorting for their isolation from primary acute myeloid leukemia samples. Results: We found that patients with leukemic blasts characterized by a high amount of HLA-DR occupied by CLIP (relative amount of CLIP) had a significantly shortened disease-free survival. The clear reductions in amount of HLA-DR occupied by CLIP on blasts of the THP-1 and Kasumi-1 myeloid leukemic cell lines after treatment with invariant chain short interfering RNA resulted in enhanced rates of allogeneic CD4(+) T-cell proliferation. Similar findings were obtained in an autologous setting, in which there were strong increases in proliferation of remission CD4(+) T cells stimulated with CLIP--sorted leukemic blasts from HLA-DR+ acute myeloid leukemia patients, in contrast to CLIP+-sorted leukemic blasts from the same patients. Conclusions: These data highlight the relevance of CLIP expression on leukemic blasts and the potential of CLIP as a target for immunomodulatory strategies to enhance HLA class II antigen presentation and CD4(+) T-cell reactivity in acute myeloid leukemi

Acetylcholine-producing T cells in the intestine regulate antimicrobial peptide expression and microbial diversity

The cholinergic anti-inflammatory pathway reduces systemic tumor necrosis factor (TNF) via acetylcholine-producing memory T cells in the spleen. These choline acetyltransferase (ChAT)-expressing T cells are also found in the intestine, where their function is unclear. We aimed to characterize these cells in mouse and human intestine and delineate their function. We made use of the ChAT-enhanced green fluorescent protein (eGFP) reporter mice. CD4(Cre) mice were crossed to ChAT(fl/fl) mice to achieve specific deletion of ChAT in CD4(+) T cells. We observed that the majority of ChAT-expressing T cells in the human and mouse intestine have characteristics of Th17 cells and coexpress IL17A, IL22, and RORC The generation of ChAT-expressing T cells was skewed by dendritic cells after activation of their adrenergic receptor β2 To evaluate ChAT T cell function, we generated CD4-specific ChAT-deficient mice. CD4ChAT(-/-) mice showed a reduced level of epithelial antimicrobial peptides lysozyme, defensin A, and ang4, which was associated with an enhanced bacterial diversity and richness in the small intestinal lumen in CD4ChAT(-/-) mice. We conclude that ChAT-expressing T cells in the gut are stimulated by adrenergic receptor activation on dendritic cells. ChAT-expressing T cells may function to mediate the host AMP secretion, microbial growth and expansio

<i>Salmonella</i>-specific B cells form a survival niche supporting in vivo <i>Salmonella</i> spreading to systemic sites.

<p>C57BL/6 mice were adoptively transferred with 0, 2*10⁵ or 10⁶ HEL-specific CD43- naïve B cells labeled with CFSE, as indicated. Mice were orally infected with surface HEL-expressing <i>Salmonella</i> one day after B cell transfer. (A) Distribution of CFSE-labeled HEL-specific B cells in the mesenteric lymph nodes (mLN) and spleen before infection (BI), and 24 or 72 hours post-infection, as indicated. One representative example from 3 experiments with 4 mice for each experimental setting is shown. (B) Recovery of viable bacteria 72 hours post-infection from mesenteric lymph nodes (mLN) spleen (SP) and blood (BL) in infected mice transferred with 0, 2*10⁵ or 10⁶ HEL-specific B cells. Depicted are colony-forming units (CFU)/10⁵ eukaryotic cells. One representative example from 3 experiments with 4 mice for each experimental setting is shown.</p

Quantification of the fate of the GFP-expressing <i>Salmonella</i> in infected B cells.

<p>(A) B cells were infected with anti-BCR coated GFP-expressing <i>Salmonella</i> (green).The plasma membrane of the B cells (red) was stained using an anti-CD20 mAb to discriminate between intracellular and extracellular <i>Salmonella</i>. (B) The relative amount of intracellular <i>Salmonella</i> were measured immediately after infection (0 h), or 4 h and 18 h post-infection. Error bars represent SD from two independent experiments. (C) The number of <i>Salmonella</i> per B cell was measured immediately after infection and 18h post-infection. A representative experiment of two individual experiments is shown.</p