CD44 expression positively correlates with Foxp3 expression and suppressive function of CD4+ Treg cells

<p>Abstract</p> <p>Background</p> <p>CD4⁺CD25⁺regulatory T (T_reg) cells develop in the thymus and can suppress T cell proliferation, modulated by Foxp3 and cytokines; however, the relevance of CD44 in T_regcell development is less clear. To address this issue, we analyzed Foxp3 expression in CD44⁺T_regcells by using multiple parameters, measured the levels of the immunoregulatory cytokine interleukin (IL)-10 in various thymocyte subsets, and determined the suppressor activity in different splenic T_regcell populations.</p> <p>Results</p> <p>Within mouse thymocytes, we detected T_regcells with two novel phenotypes, namely the CD4⁺CD8^-CD25⁺CD44⁺and CD4⁺CD8^-CD25⁺CD44^-staining features. Additional multi-parameter analyses at the single-cell and molecular levels suggested to us that CD44 expression positively correlated with Foxp3 expression in thymocytes, the production of IL-10, and T_regactivity in splenic CD4⁺CD25⁺T cells. This suppressive effect of T_regcells on T cell proliferation could be blocked by using anti-IL-10 neutralizing antibodies. In addition, CD4⁺CD25⁺CD44⁺T_regcells expressed higher levels of IL-10 and were more potent in suppressing effector T cell proliferation than were CD4⁺CD25⁺CD44^-cells.</p> <p>Conclusion</p> <p>This study indicates the presence of two novel phenotypes of T_regcells in the thymus, the functional relevance of CD44 in defining T_regcell subsets, and the role of both IL-10 and Foxp3 in modulating the function of T_regcells.</p> <p>Reviewers</p> <p>This article was reviewed by Dr. M. Lenardo, Dr. L. Klein & G. Wirnsberger (nominated by Dr. JC Zungia-Pfluker), and Dr. E.M. Shevach.</p

Super-Droplet Method for the Numerical Simulation of Clouds and Precipitation: a Particle-Based Microphysics Model Coupled with Non-hydrostatic Model

A novel simulation model of cloud microphysics is developed, which is named Super-Droplet Method (SDM). SDM enables accurate calculation of cloud microphysics with reasonable cost in computation. A simple SDM for warm rain, which incorporates sedimentation, condensation/evaporation, stochastic coalescence, is developed. The methodology to couple SDM and a non-hydrostatic model is also developed. It is confirmed that the result of our Monte Carlo scheme for the coalescence of super-droplets agrees fairly well with the solution of stochastic coalescence equation. A preliminary simulation of a shallow maritime cumulus formation initiated by a warm bubble is presented to demonstrate the practicality of SDM. Further discussions are devoted for the extension and the computational efficiency of SDM to incorporate various properties of clouds, such as, several types of ice crystals, several sorts of soluble/insoluble CCNs, their chemical reactions, electrification, and the breakup of droplets. It is suggested that the computational cost of SDM becomes lower than spectral (bin) method when the number of attributes $d$ becomes larger than some critical value, which may be $2\sim4$

Aedes aegypti Saliva Alters Leukocyte Recruitment and Cytokine Signaling by Antigen-Presenting Cells during West Nile Virus Infection

West Nile virus (WNV) is transmitted during mosquito bloodfeeding. Consequently, the first vertebrate cells to contact WNV are cells in the skin, followed by those in the draining lymph node. Macrophages and dendritic cells are critical early responders in host defense against WNV infection, not just because of their role in orchestrating the immune response, but also because of their importance as sites of early peripheral viral replication. Antigen-presenting cell (APC) signals have a profound effect on host antiviral responses and disease severity. During transmission, WNV is intimately associated with mosquito saliva. Due to the ability of mosquito saliva to affect inflammation and immune responses, and the importance of understanding early events in WNV infection, we investigated whether mosquito saliva alters APC signaling during arbovirus infection, and if alterations in cell recruitment occur when WNV infection is initiated with mosquito saliva. Accordingly, experiments were performed with cultured dendritic cells and macrophages, flow cytometry was used to characterize infiltrating cell types in the skin and lymph nodes during early infection, and real-time RT-PCR was employed to evaluate virus and cytokine levels. Our in vitro results suggest that mosquito saliva significantly decreases the expression of interferon-β and inducible nitric oxide synthase in macrophages (by as much as 50 and 70%, respectively), whilst transiently enhancing interleukin-10 (IL-10) expression. In vivo results indicate that the predominate effect of mosquito feeding is to significantly reduce the recruitment of T cells, leading the inoculation site of mice exposed to WNV alone to have up to 2.8 fold more t cells as mice infected in the presence of mosquito saliva. These shifts in cell population are associated with significantly elevated IL-10 and WNV (up to 4.0 and 10 fold, respectively) in the skin and draining lymph nodes. These results suggest that mosquito saliva dysregulates APC antiviral signaling, and reveal a possible mechanism for the observed enhancement of WNV disease mediated by mosquito saliva via a reduction of T lymphocyte and antiviral activity at the inoculation site, an elevated abundance of susceptible cell types, and a concomitant increase in immunoregulatory activity of IL-10

Protective Immunity and Immunopathology in Ehrlichiosis

Human monocytic ehrlichiosis, a tick transmitted infection, ranges in severity from apparently subclinical to fatal toxic shock-like disease. Models in immunocompetent mice range from abortive to uniformly lethal infection, depending on the Ehrlichia species, inoculum dose, and inoculation route. Effective immunity is mediated by CD4 + T lymphocytes and gamma interferon. Lethal infection occurs with early overproduction of proinflammatory cytokines and overproduction of TNF alpha and IL-10 by CD8 + T lymphocytes. Furthermore, fatal ehrlichiosis is associated with TLR 9/MyD88 signaling, upregulation of several inflammasome complexes, and secretion of IL-1 beta, IL-1 alpha, and IL-18 by hepatic mononuclear cells, thus suggesting activation of canonical and noncanonical inflammasome pathways, a deleterious role of IL-18, and a protective role of caspase 1. Autophagy promotes ehrlichial infection, whereas MyD88 signaling hinders ehrlichial infection by inhibiting autophagy induction and flux. During infection of hepatocytes by the lethal ehrlichial species, after interferon alpha receptor signaling, the activation of caspase 11 results in the production of inflammasome-dependent IL-1 beta, extracellular secretion of HMGB1, and pyroptosis. HMGB1 has high levels in lethal ehrlichiosis, thereby suggesting a role in toxic shock. Studies of primary bone marrow-derived macrophages infected by highly avirulent or mildly avirulent ehrlichiae have revealed divergent M1 and M2 macrophage polarization associated with the generation of pathogenic CD8 T cells and neutrophils, and excessive inflammation, or with strong expansion of protective Th1 and NKT cells, resolution of inflammation, and clearance of infection, respectively

Pattern Recognition Receptors in Innate Immunity to Obligate Intracellular Bacteria

Host pattern recognition receptors (PRRs) are crucial for sensing pathogenic microorganisms, initiating innate responses, and modulating pathogen-specific adaptive immunity during infection. Rickettsia spp. , Orientia tsutsugamushi , Anaplasma spp. , Ehrlichia spp. , and Coxiella burnetii are obligate intracellular bacteria that can replicate only within host cells and must evade immune detection to successfully propagate. These five bacterial species are zoonotic pathogens of clinical or agricultural importance, yet uncovering how immune recognition occurs has remained challenging. Recent evidence from in vitro studies and animal models has yielded new insights into the types and kinetics of PRR activation during infection with Rickettsia spp. , A. phagocytophilum , E. chaffeensis , and C. burnetii . However, much less was known about PRR activation in O. tsutsugamushi infection until the recent discovery of the role of the C-type lectin receptor Mincle during lethal infection in mice and in primary macrophage cultures. This review provides a brief summary of the clinical and epidemiologic features of these five bacterial infections, with a focus on the fundamental biologic facets of infection, and recent advances in host recognition. In addition, knowledge gaps regarding the innate recognition of these bacteria in the context of disease pathogenesis are discussed

Coxiella burnetii and Leishmania Mexicana Residing Within Similar Parasitophorous Vacuoles Elicit Disparate Host Responses

Coxiella burnetii is a bacterium that thrives in an acidic parasitophorous vacuole (PV) derived from lysosomes. Leishmania mexicana, a eukaryote, has also independently evolved to live in a morphologically similar PV. As Coxiella and Leishmania are highly divergent organisms that cause different diseases, we reasoned that their respective infections would likely elicit distinct host responses despite producing phenotypically similar parasite-containing vacuoles. The objective of this study was to investigate, at the molecular level, the macrophage response to each pathogen. Infection of THP-1 (human monocyte/macrophage) cells with Coxiella and Leishmania elicited disparate host responses. At 5 days post-infection, when compared to uninfected cells, 1057 genes were differentially expressed (746 genes up-regulated and 311 genes downregulated) in C. burnetii infected cells, whereas 698 genes (534 genes up-regulated and 164 genes down-regulated) were differentially expressed in L. mexicana infected cells. Interestingly, of the 1755 differentially expressed genes identified in this study, only 126 genes (∼7%) are common to both infections. We also discovered that 1090 genes produced mRNA isoforms at significantly different levels under the two infection conditions, suggesting that alternate proteins encoded by the same gene might have important roles in host response to each infection. Additionally, we detected 257 micro RNAs (miRNAs) that were expressed in THP-1 cells, and identified miRNAs that were specifically expressed during Coxiella or Leishmania infections. Collectively, this study identified host mRNAs and miRNAs that were influenced by Coxiella and/or Leishmania infections, and our data indicate that although their PVs are morphologically similar, Coxiella and Leishmania have evolved different strategies that perturb distinct host processes to create and thrive within their respective intracellular niches

Differential microbicidal effects of human histone proteins H2A and H2B on Leishmania promastigotes and amastigotes

Recent studies have shown that histone proteins can act as antimicrobial peptides in host defense against extracellular bacteria, fungi, and Leishmania promastigotes. In this study, we used human recombinant histone proteins to further study their leishmaniacidal effects and the underlying mechanisms. We found that the histones H2A and H2B (but not H1(0)) could directly and efficiently kill promastigotes of Leishmania amazonensis, L. major, L. braziliensis, and L. mexicana in a treatment dose-dependent manner. Scanning electron microscopy revealed surface disruption of histone-treated promastigotes. More importantly, the preexposure of promastigotes to histone proteins markedly decreased the infectivity of promastigotes to murine macrophages (Mφs) in vitro. However, axenic and lesion-derived amastigotes of L. amazonensis and L. mexicana were relatively resistant to histone treatment, which correlated with the low levels of intracellular H2A in treated amastigotes. To understand the mechanisms underlying these differential responses, we investigated the role of promastigote surface molecules in histone-mediated killing. Compared with the corresponding controls, transgenic L. amazonensis promastigotes expressing lower levels of surface gp63 proteins were more susceptible to histone H2A, while L. major and L. mexicana promastigotes with targeted deletion of the lipophosphoglycan 2 (lpg2) gene (but not the lpg1 gene) were more resistant to histone H2A. We discuss the influence of promastigote major surface molecules in the leishmaniacidal effect of histone proteins. This study provides new information on host innate immunity to different developmental stages of Leishmania parasites