Increased Memory Conversion of Naïve CD8 T Cells Activated during Late Phases of Acute Virus Infection Due to Decreased Cumulative Antigen Exposure

Background: Memory CD8 T cells form an essential part of protective immunity against viral infections. Antigenic load, costimulation, CD4-help, cytokines and chemokines fluctuate during the course of an antiviral immune response thus affecting CD8 T cell activation and memory conversion. Methodology/Principal Findings: In the present study, naïve TCR transgenic LCMV-specific P14 CD8 T cells engaged at a late stage during the acute antiviral LCMV response showed reduced expansion kinetics but greater memory conversion in the spleen. Such late activated cells displayed a memory precursor effector phenotype already at the peak of the systemic antiviral response, suggesting that the environment determined their fate during antigen encounter. In the spleen, the majority of late transferred cells exhibited a central memory phenotype compared to the effector memory displayed by the early transferred cells. Increasing the inflammatory response by exogenous administration of IFNc, PolyI:C or CpG did not affect memory conversion in the late transferred group, suggesting that the diverging antigen load early versus later during acute infection had determined their fate. In agreement, reduction in the LCMV antigenic load after ribavirin treatment enhanced the contribution of early transferred cells to the long lasting memory pool. Conclusions/Significance: Our results show that naïve CD8 cells, exposed to reduced duration or concentration of antigen during viral infection convert into memory more efficiently, an observation that could have significant implications fo

Helicobacter-Induced Chronic Active Lymphoid Aggregates Have Characteristics of Tertiary Lymphoid Tissue

Susceptible strains of mice that are naturally or experimentally infected with murine intestinal helicobacter species develop hepatic inflammatory lesions that have previously been described as chronic active hepatitis. The inflammatory infiltrates in some models of chronic autoimmunity or inflammation resemble tertiary lymphoid organs hypothesized to arise by a process termed lymphoid organ neogenesis. To determine whether hepatic inflammation caused by infection with helicobacter could give rise to tertiary lymphoid organs, we used fluorescence-activated cell sorting, immunohistochemistry, and in situ hybridization techniques to identify specific components characteristic of lymphoid organs in liver tissue sections and liver cell suspensions from helicobacter-infected mice. Small venules (high endothelial venules [HEVs]) in inflammatory lesions in Helicobacter species-infected livers were positive for peripheral node addressin. Mucosal addressin cell adhesion molecule also stained HEVs and cells with a staining pattern consistent with scattered stromal cells. The chemokines SLC (CCL 21) and BLC (CXCL13) were present, as were B220-positive B cells and T cells. The latter included a naïve (CD45lo-CD62Lhi) population. These findings suggest that helicobacter-induced chronic active hepatitis arises through the process of lymphoid organ neogenesis

No significant CTL cross-priming by dendritic cell-derived exosomes during murine lymphocytic choriomeningitis virus infection

Exosomes are small membrane vesicles of endocytic origin that are secreted by most cells in culture, but are also present in serum. They contain a wide array of protein ligands on their surface, which has led to the hypothesis that they might mediate intercellular communication. Indeed, data support that exosomes can transfer Ags to dendritic cells (DC), and, interestingly, that these DC can subsequently induce T cell priming or tolerance. We have investigated whether this concept can be expanded to antiviral immunity. We isolated exosomes from supernatant of cultured bone marrow-derived DC (BMDC) that were infected with lymphocytic choriomeningitis virus (LCMV) or loaded with an immunodominant LCMV peptide, and characterized them by flow cytometry upon binding to beads. We then incubated the exosome preparations with BMDC and looked at their potential to activate LCMV gp33-specific naive and memory CD8 T cells. We found that exosomes do not significantly contribute to CD8 T cell cross-priming in vitro. Additionally, exosomes derived from in vitro-infected BMDC did not exhibit significant in vivo priming activity, as evidenced by the lack of protection following exosome vaccination. Thus, DC-derived exosomes do not appear to contribute significantly to CTL priming during acute LCMV infection

Immunomodulatory dendritic cells require autologous serum to circumvent nonspecific immunosuppressive activity in vivo

In immunotherapy, dendritic cells (DCs) can be used as powerful antigen-presenting cells to enhance or suppress antigen-specific immunity upon in vivo transfer in mice or humans. However, to generate sufficient numbers of DCs, most protocols include an ex vivo culture step, wherein the cells are exposed to heterologous serum and/or antigenic stimuli. In mouse models of virus infection and virus-induced autoimmunity, we tested how heterologous serum affects the immunomodulatory capacity of immature DCs generated in the presence of IL-10 by comparing fetal bovine serum (FBS)- or normal mouse serum (NMS)-supplemented DC cultures. We show that FBS-exposed DCs induce a systemic immune deviation characterized by reduction of virus-specific T cells, delayed viral clearance, and enhanced systemic production of interleukin 4 (IL-4), IL-5, and IL-10 to FBS-derived antigens, including bovine serum albumin (BSA). By contrast, DCs generated in NMS-supplemented cultures modulated immunity and autoimmunity in an antigen-specific fashion. These cells did not induce systemic IL-4, IL-5, or IL-10 production and inhibited generation of virus-specific T cells or autoimmunity only if pulsed with a viral antigen. These data underscore the importance of using autologous serum-derived immature DCs in preclinical animal studies to accurately assess their immunomodulatory potential in future human therapeutic settings, where application of FBS is not feasible