It is believed that memory CD8+ T cells are maintained in secondary lymphoid tissues, peripheral tissues, and BM by homeostatic proliferation. Their survival has been shown to be dependent on IL-7, but it is unclear where they acquire it. Here we show that in murine BM, memory CD8+ T cells individually colocalize with IL-7+ reticular stromal cells. The T cells are resting in terms of global transcription and do not express markers of activation, for example, 4-1BB (CD137), IL-2, or IFN-γ, despite the expression of CD69 on about 30% of the cells. Ninety-five percent of the memory CD8+ T cells in BM are in G0 phase of cell cycle and do not express Ki-67. Less than 1% is in S/M/G2 of cell cycle, according to propidium iodide staining. While previous publications have estimated the extent of proliferation of CD8+ memory T cells on the basis of BrdU incorporation, we show here that BrdU itself induces proliferation of CD8+ memory T cells. Taken together, the present results suggest that CD8+ memory T cells are maintained as resting cells in the BM in dedicated niches with their survival conditional on IL-7 receptor signaling.

Key Points A major part of CD8+ memory T cells expresses CD40L, the key molecule for T-cell–dependent help. CD40L-expressing CD8+ T cells resemble functional CD4+ helper T cells.

Induction of polyclonal B cell activation is a phenomenon observed in many types of infection, but its immunological relevance is unclear. In this study we show that staphylococcal protein A induces T cell–independent human B cell proliferation by enabling uptake of TLR-stimulating nucleic acids via the VH3+ BCR. We further demonstrate that Staphylococcus aureus strains with high surface protein A expression concomitantly trigger activation of human plasmacytoid dendritic cells (pDC). Sensitivity to chloroquine, cathepsin B inhibition, and a G-rich inhibitory oligodeoxynucleotide supports the involvement of TLR9 in this context. We then identify pDC as essential cellular mediators of B cell proliferation and Ig production in response to surface protein A–bearing S. aureus. The in vivo relevancy of these findings is confirmed in a human PBMC Nod/scidPrkdc/γc−/− mouse model. Finally, we demonstrate that co-operation of pDC and B cells enhances B cell–derived IL-10 production, a cytokine associated with immunosuppression and induction of IgG4, an isotype frequently dominating the IgG response to S. aureus. IL-10 release is partially dependent on TLR2-active lipoproteins, a hallmark of the Staphylococcus species. Collectively, our data suggest that S. aureus exploits pDC and TLR to establish B cell–mediated immune tolerance.

The prevailing ‘division of labor’ concept in cellular immunity is that CD8+ T cells primarily utilize cytotoxic functions to kill target cells, while CD4+ T cells exert helper/inducer functions. Multiple subsets of CD4+ memory T cells have been characterized by distinct chemokine receptor expression. Here, we demonstrate that analogous CD8+ memory T-cell subsets exist, characterized by identical chemokine receptor expression signatures and controlled by similar generic programs. Among them, Tc2, Tc17 and Tc22 cells, in contrast to Tc1 and Tc17 + 1 cells, express IL-6R but not SLAMF7, completely lack cytotoxicity and instead display helper functions including CD40L expression. CD8+ helper T cells exhibit a unique TCR repertoire, express genes related to skin resident memory T cells (TRM) and are altered in the inflammatory skin disease psoriasis. Our findings reveal that the conventional view of CD4+ and CD8+ T cell capabilities and functions in human health and disease needs to be revised.

More than 70% of colorectal, prostate, ovarian, pancreatic and breast cancer specimens show expression of CD276 (B7–H3), a potential immune checkpoint family member. Several studies have shown that high CD276 expression in cancer cells correlates with a poor clinical prognosis. This has been associated with the presence of lower tumor infiltrating leukocytes. Among those, tumor-associated macrophages can comprise up to 50% of the tumor mass and are thought to support tumor growth through various mechanisms. However, a lack of information on CD276 function and interaction partner(s) impedes rigorous evaluation of CD276 as a therapeutic target in oncology. Therefore, we aimed to understand the relevance of CD276 in tumor-macrophage interaction by employing a 3D spheroid coculture system with human cells. Our data show a role for tumor-expressed CD276 on the macrophage recruitment into the tumor spheroid, and also in regulation of the extracellular matrix modulator PAI-1. Furthermore, our experiments focusing on macrophage-expressed CD276 suggest that the antibody-dependent CD276 engagement triggers predominantly inhibitory signaling networks in human macrophages.

CD40-CD40 ligand (CD40L) signaling plays multiple indispensable roles in cellular and humoral immunity. Impaired memory T-cell responses in the absence of CD40L have been well documented, but the requirement of this interaction for efficient priming of CD8 T cells especially under inflammatory conditions has been under debate. In contrast to previous publications, we report here that virus-specific CD8 T-cell responses as well as viral clearance are affected not only in the memory but also in the effector phase in CD40L mice infected with lymphocytic choriomeningitis virus (LCMV) Armstrong strain. Interestingly, a considerable part of the LCMV-specific effector and memory T cells consists of CD40L CD8 T cells. However, deficiency of CD40L in CD8 T cells did influence neither the quantity nor the quality of primary T-cell responses in LCMV infection. Virus-specific CD8 T cells in conditional knockout mice, with a selective deletion of the CD40L in CD8 T cells, were fully functional regarding cytokine production and efficient pathogen clearance. Thus, our results unambiguously demonstrate that while CD40L is critical to generate effective primary CD8 T-cell responses also under inflammatory conditions, CD40L expression by CD8 T cells themselves is dispensable in acute LCMV infection.

Elevated counts of alveolar macrophages and attenuated phagocytic capacity are associated with COPD. Factors governing macrophage phagocytosis are poorly understood. In this study we aimed to compare the influence of airway epithelial cell secretions from COPD and nonCOPD subjects on macrophage phagocytic activity, and the role of antimicrobial peptides (AMPs).Supernatants from nonCOPD and COPD small airway epithelial cell (SAEC) cultures exposed to Haemophilus influenzae (NTHi), were applied to human monocyte-derived macrophages (MDM) for assessment of their influence on phagocytosis. SAECs were analysed for changes in AMP expression by qRT-PCR and the influence of select AMPs on macrophage phenotype and function was assessed by flow cytometry and metabolic activity assay.Secretions from the apical and basolateral surface of NTHi-exposed SAECs from nonCOPD donors elicited superior phagocytic capacity of MDMs. Moreover, NTHi exposure led to a rapid increase in expression of a range of AMPs by nonCOPD SAECs, but this response was delayed in COPD SAECs. We demonstrate that treatment with AMPs β-defensin 2 and S100A8/A9 improved the phagocytic capacity of MDMs. In depth analysis of S100A8/A9 influence of MDMs revealed a role of this AMP in macrophage phenotype and function. Furthermore, we show that the expression of S100A8 and S100A9 is directly regulated by WNT/β-catenin signalling activity, a known deregulated pathway in COPD.In conclusion, for the first time, we demonstrate that airway epithelium from COPD subjects has a reduced capacity to support the phagocytic function of macrophages in response to acute NTHi exposure, and we identify the WNT/β-catenin signalling-modulated and epithelium-derived S100A8/A9 as a potent regulator of macrophage phenotype and function.

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