CD8+ T Cells Mediate CD40-independent Maturation of Dendritic Cells In Vivo

Induction of cytotoxic T lymphocyte (CTL) responses against minor histocompatibility antigens is dependent upon the presence of T cell help and requires the interaction of CD40 on dendritic cells (DCs) with CD40 ligand on activated T helper cells (Th). This study demonstrates that CD40 is neither involved in Th-dependent nor Th-independent antiviral CTL responses. Moreover, the data show that DC maturation occurs in vivo after viral infection in the absence of CD40 and Th. This maturation did not require viral infection of  DCs but was mediated by peptide-specific CD8+ T cells. Surprisingly, naive CD8+ T cells were able to trigger DC maturation within 24 h after activation in vivo and in vitro. Moreover, peptide-activated CD8+ T cells were able to induce maturation in trans, as DCs that failed to present the relevant antigen in vivo also underwent maturation. Upon isolation, the in vivo–stimulated DCs were able to convert a classically Th-dependent CTL response (anti-HY) into a Th-independent response in vitro. Thus, antiviral CD8+ T cells are sufficient for the maturation of DCs in the absence of CD40

Structure, activity and interactions of the cysteine deleted analog of tachyplesin-1 with lipopolysaccharide micelle: Mechanistic insights into outer-membrane permeabilization and endotoxin neutralization

AbstractTachyplesin-1, a disulfide stabilized β-hairpin antimicrobial peptide, can be found at the hemocytes of horse shoe crab Tachypleus tridentatus. A cysteine deleted linear analog of tachyplesin-1 or CDT (KWFRVYRGIYRRR-NH2) contains a broad spectrum of bactericidal activity with a reduced hemolytic property. The bactericidal activity of CDT stems from selective interactions with the negatively charged lipids including LPS. In this work, CDT–LPS interactions were investigated using NMR spectroscopy, optical spectroscopy and functional assays. We found that CDT neutralized LPS and disrupted permeability barrier of the outer membrane. Zeta potential and ITC studies demonstrated charge compensation and hydrophobic interactions of CDT with the LPS-outer membrane, respectively. Secondary structure of the peptide was probed by CD and FT-IR experiments indicating β-strands and/or β-turn conformations in the LPS micelle. An ensemble of structures, determined in LPS micelle by NMR, revealed a β-hairpin like topology of the CDT peptide that was typified by an extended cationic surface and a relatively shorter segment of hydrophobic region. Interestingly, at the non-polar face, residue R11 was found to be in a close proximity to the indole ring of W2, suggesting a cation–π type interactions. Further, saturation transfer difference (STD) NMR studies established intimate contacts among the aromatic and cationic residues of CDT with the LPS micelle. Fluorescence and dynamic light scattering experiments demonstrated that CDT imparted structural destabilization to the aggregated states of LPS. Collectively, atomic resolution structure and interactions of CDT with the outer membrane-LPS could be exploited for developing potent broad spectrum antimicrobial and anti-sepsis agents

Tissue-Resident CD169+ Macrophages Form a Crucial Front Line against Plasmodium Infection

SummaryTissue macrophages exhibit diverse functions, ranging from the maintenance of tissue homeostasis, including clearance of senescent erythrocytes and cell debris, to modulation of inflammation and immunity. Their contribution to the control of blood-stage malaria remains unclear. Here, we show that in the absence of tissue-resident CD169+ macrophages, Plasmodium berghei ANKA (PbA) infection results in significantly increased parasite sequestration, leading to vascular occlusion and leakage and augmented tissue deposition of the malarial pigment hemozoin. This leads to widespread tissue damage culminating in multiple organ inflammation. Thus, the capacity of CD169+ macrophages to contain the parasite burden and its sequestration into different tissues and to limit infection-induced inflammation is crucial to mitigating Plasmodium infection and pathogenesis

Toll-like receptor 4, but not neutrophil extracellular Traps, Promote IFN Type I expression to enhance Th2 responses to Nippostrongylus brasiliensis

The induction of Th2 responses is thought to be multifactorial, and emerge from specific pathways distinct from those associated with antagonistic antibacterial or antiviral Th1 responses. Here, we show that the recognition of non-viable Nippostrongylus brasiliensis (Nb) in the skin induces a strong recruitment of monocytes and neutrophils and the release of neutrophil extracellular traps (NETs). Nb also activates toll-like receptor 4 (TLR4) signaling with expression of Ifnb transcripts in the skin and the development of an IFN type I signature on helminth antigen-bearing dendritic cells in draining lymph nodes. Co-injection of Nb together with about 10,000 Gram-negative bacteria amplified this TLR4-dependent but NET-independent IFN type I response and enhanced the development of Th2 responses. Thus, a limited activation of antibacterial signaling pathways is able to boost antihelminthic responses, suggesting a role for bacterial sensing in the optimal induction of Th2 immunity

Murine CD4+ T Cell Responses Are Inhibited by Cytotoxic T Cell-Mediated Killing of Dendritic Cells and Are Restored by Antigen Transfer

Cytotoxic T lymphocytes (CTL) provide protection against pathogens and tumors. In addition, experiments in mouse models have shown that CTL can also kill antigen-presenting dendritic cells (DC), reducing their ability to activate primary and secondary CD8+ T cell responses. In contrast, the effects of CTL-mediated killing on CD4+ T cell responses have not been fully investigated. Here we use adoptive transfer of TCR transgenic T cells and DC immunization to show that specific CTL significantly inhibited CD4+ T cell proliferation induced by DC loaded with peptide or low concentrations of protein antigen. In contrast, CTL had little effect on CD4+ T cell proliferation induced by DC loaded with high protein concentrations or expressing antigen endogenously, even if these DC were efficiently killed and failed to accumulate in the lymph node (LN). Residual CD4+ T cell proliferation was due to the transfer of antigen from carrier DC to host APC, and predominantly involved skin DC populations. Importantly, the proliferating CD4+ T cells also developed into IFN-γ producing memory cells, a property normally requiring direct presentation by activated DC. Thus, CTL-mediated DC killing can inhibit CD4+ T cell proliferation, with the extent of inhibition being determined by the form and amount of antigen used to load DC. In the presence of high antigen concentrations, antigen transfer to host DC enables the generation of CD4+ T cell responses regardless of DC killing, and suggests mechanisms whereby CD4+ T cell responses can be amplified

GM-CSF Signalling Boosts Dramatically IL-1Production

GM-CSF is mostly known for its capacity to promote bone marrow progenitor differentiation, to mobilize and mature myeloid cells as well as to enhance host immune responses. However the molecular actions of GM-CSF are still poorly characterized. Here we describe a new surprising facet of this “old” growth factor as a key regulator involved in IL-1βsecretion. We found that IL-1β release, a pivotal component of the triggered innate system, is heavily dependent on the signaling induced by GM-CSF in such an extent that in its absence IL-1β is only weakly secreted. GM-CSF synergizes with LPS for IL-1β secretion mainly at the level of pro-IL-1β production via strengthening the NF-κB signaling. In addition, we show that expression of Rab39a, a GTPase required for caspase-1 dependent IL-1β secretion is greatly augmented by LPS and GM-CSF co-stimulation suggesting a potential GM-CSF contribution in enhancing IL-1β exocytosis. The role of GM-CSF in regulating IL-1β secretion is extended also in vivo, since GM-CSF R−/− mice are more resistant to LPS-mediated septic shock. These results identify GM-CSF as a key regulator of IL-1β production and indicate GM-CSF as a previously underestimated target for therapeutic intervention

Turnover kinetics of pancreatic macrophages in lean and obese diabetic mice

Pancreatic resident macrophages, a heterogeneous family of cells with distinct origins and phenotypes, are the main myeloid cells in exocrine and endocrine tissues. Adult exocrine F4/80hi macrophages consist of three different subsets based on the embryonic marker Tim-4 and MHC II expression. Their frequencies shift during aging and obesity with the Tim-4-MHCII+ fraction becoming the predominant subpopulation in the inter acinar stroma. Endocrine resident F4/80hi macrophages are more homogenous and represent the prevalent leukocyte fraction residing within the islets in both lean and obese mice. We used an adult fate mapping mouse model to characterize turnover kinetics within the pancreatic resident macrophages under normal homeostasis and obese diabetic conditions. We demonstrate that islet resident macrophages show unique replenishment kinetics, with embryonic macrophages being gradually replaced by bone marrow-derived monocytes with increasing age. Their replenishment was independent of the CCL2/CCR2 axis. Furthermore, we confirmed that both exocrine Tim-4+MHCIIlow and Tim-4+MHCII+ fractions are long-lived and primarily independent from bone marrow-derived monocytes. In contrast, exocrine Tim-4-MHCII+ macrophages are gradually replaced through a CCR2-dependent influx of bone marrow-derived monocytes in aging. Moreover, we show that obesity and type 2 diabetes do not affect the turnover kinetics of any macrophage subpopulation residing in the pancreas. Our study uncovers new insights on pancreatic macrophage biology in aging and obesity.Ministry of Education (MOE)Published versionFunding for this paper was provided by a Ministry of Education Tier2 grant (MOE2018-T2-2-016) awarded to CR

Obesity retunes turnover kinetics of tissue-resident macrophages in fat

Adipose tissue-resident F4/80hi macrophages (ATMs) are the main leukocyte population found in the visceral adipose tissue (VAT). These macrophages comprise several phenotypically distinct subpopulations that rapidly shift in abundance during obesity-induced tissue remodeling. Here we used a fate-mapping approach in mouse models to determine the developmental origins and the differential turnover kinetics of ATMs in lean and obese adipose tissue. We found that in lean, murine VAT the majority of ATMs express T cell immunoglobulin and mucin domain containing 4 receptor (Tim-4), lack the expression of CCR2 and can be further subdivided based on their expression of MHC class II and CD11c. We showed that both embryonic-derived Tim-4+ MHCIIlow and Tim-4+ MHCII+ ATM subsets are long-lived and only slowly replenished by monocytes over time. Only a minor Tim-4- MHCII+ CD11c+ ATM fraction expresses CCR2 and is short-lived. In response to high-fat induced VAT remodeling, the majority of Tim-4+ MHCIIlow ATMs maintain their fetal identity as they are moderately displaced by monocytes. Conversely, Tim-4+ MHCII+ ATMs are quickly replaced in a CCR2-dependent manner by bone marrow-derived Tim-4- MHCII+ ATMs that have significantly higher turnover rates than those in lean mice. In addition, during high-fat diet, the subpopulation of CD11c+ macrophages invade the VAT with the fastest turnover kinetics of all three ATM subpopulations. Our results suggest that ATM subpopulation frequency is controlled by the VAT microenvironment and that obesity-induced tissue remodeling renders some of the ATM niches accessible and available for rapid monocyte replenishment. Specialized monocyte-derived macrophages, which are rapidly recruited may be contributing to control the excess of adipocyte-released lipids produced during obesity.Ministry of Education (MOE)This work was supported by Ministry of Education Tier2 grants awarded to C.R. (grant numbers: MOE2016-T2-1-012 and MOE2018-T2-2-016