In vivo compartmentalization of functionally distinct, rapidly responsive antigen-specific T-cell populations in DNA-immunized or Salmonella enterica serovar Typhimurium-infected mice

The location and functional properties of antigen-specific memory T-cell populations in lymphoid and nonlymphoid compartments following DNA immunization or infection with Salmonella were investigated. Epitope-specific CD8+-T-cell expansion and retention during the memory phase were analyzed for DNA-immunized mice by use of a 5-h peptide restimulation assay. These data revealed that epitope-specific gamma interferon (IFN-{gamma})-positive CD8+ T cells occur at higher frequencies in the spleen, liver, and blood than in draining or peripheral lymph nodes during the expansion phase. Moreover, this distribution is maintained into long-term memory. The location and function of both CD4+ and CD8+ Salmonella-specific memory T cells in mice who were given a single dose of Salmonella enterica serovar Typhimurium was also quantitated by an ex vivo restimulation with bacterial lysate to detect the total Salmonella-specific memory pool. Mice immunized up to 6 months previously with S. enterica serovar Typhimurium had bacterium-specific CD4+ T cells that were capable of producing IFN-{gamma} or tumor necrosis factor alpha (TNF-{alpha}) at each site analyzed. Similar findings were observed for CD8+ T cells that were capable of producing IFN-{gamma}, while a much lower frequency and more restricted distribution were associated with TNF-{alpha}-producing CD8+ T cells. This study is the first to assess the frequencies, locations, and functions of both CD4+ and CD8+ memory T-cell populations in the same Salmonella-infected individuals and demonstrates the organ-specific functional compartmentalization of memory T cells after Salmonella infection

Pneumolysin binds to the mannose receptor C type 1 (MRC-1) leading to anti-inflammatory responses and enhanced pneumococcal survival

Streptococcus pneumoniae (the pneumococcus) is a major cause of mortality and morbidity globally, and the leading cause of death in children under 5 years old. The pneumococcal cytolysin pneumolysin (PLY) is a major virulence determinant known to induce pore-dependent pro-inflammatory responses. These inflammatory responses are driven by PLY–host cell membrane cholesterol interactions, but binding to a host cell receptor has not been previously demonstrated. Here, we discovered a receptor for PLY, whereby pro-inflammatory cytokine responses and Toll-like receptor signalling are inhibited following PLY binding to the mannose receptor C type 1 (MRC-1) in human dendritic cells and mouse alveolar macrophages. The cytokine suppressor SOCS1 is also upregulated. Moreover, PLY–MRC-1 interactions mediate pneumococcal internalization into non-lysosomal compartments and polarize naive T cells into an interferon-γlow, interleukin-4high and FoxP3+ immunoregulatory phenotype. In mice, PLY-expressing pneumococci colocalize with MRC-1 in alveolar macrophages, induce lower pro-inflammatory cytokine responses and reduce neutrophil infiltration compared with a PLY mutant. In vivo, reduced bacterial loads occur in the airways of MRC-1-deficient mice and in mice in which MRC-1 is inhibited using blocking antibodies. In conclusion, we show that pneumococci use PLY–MRC-1 interactions to downregulate inflammation and enhance bacterial survival in the airways. These findings have important implications for future vaccine design

The Neurotrophic Receptor Ntrk2 Directs Lymphoid Tissue Neovascularization during Leishmania donovani Infection

The neurotrophic tyrosine kinase receptor type 2 (Ntrk2, also known as TrkB) and its ligands brain derived neurotrophic factor (Bdnf), neurotrophin-4 (NT-4/5), and neurotrophin-3 (NT-3) are known primarily for their multiple effects on neuronal differentiation and survival. Here, we provide evidence that Ntrk2 plays a role in the pathologic remodeling of the spleen that accompanies chronic infection. We show that in Leishmania donovani-infected mice, Ntrk2 is aberrantly expressed on splenic endothelial cells and that new maturing blood vessels within the white pulp are intimately associated with F4/80hiCD11bloCD11c+ macrophages that express Bdnf and NT-4/5 and have pro-angiogenic potential in vitro. Furthermore, administration of the small molecule Ntrk2 antagonist ANA-12 to infected mice significantly inhibited white pulp neovascularization but had no effect on red pulp vascular remodeling. We believe this to be the first evidence of the Ntrk2/neurotrophin pathway driving pathogen-induced vascular remodeling in lymphoid tissue. These studies highlight the therapeutic potential of modulating this pathway to inhibit pathological angiogenesis

The role played by tumor necrosis factor during localized and systemic infection with Streptococcus pneumoniae.

Tumor necrosis factor (TNF) has been proposed as a major mediator of host resistance in murine models of Streptococcus pneumoniae infection; in humans, anti-TNF therapies have been implicated in increased susceptibility to pneumococcal infection. Here, we use nonlethal (serotype 6B) and lethal (serotype 3) S. pneumoniae, neutralizing monoclonal antibodies to TNF, and TNF gene-deficient mice to reexamine the role played by TNF in antistreptococcal responses. After nonlethal challenge, primary resistance and all examined parameters of the cellular inflammatory response occurred independently of TNF activity. After lethal challenge, TNF deficiency resulted in more-rapid death but did not affect lung inflammation. However, the livers of the TNF gene-deficient mice, but not of the control mice, exhibited extensive signs of systemic disease. TNF, therefore, is dispensable for a complete cellular pulmonary inflammatory response to S. pneumoniae infection but enhances survival from disseminated lethal infection, at least in part by delaying systemic organ damage

CD11b regulates recruitment of alveolar macrophages but not pulmonary dendritic cells after pneumococcal challenge.

Despite their close physical and functional relationships, alveolar macrophages (AMs) and pulmonary dendritic cells (pulDCs) have rarely been examined together in the context of infection. Using a nonlethal, resolving model of pneumonia caused by intranasal injection of Streptococcus pneumoniae, we demonstrate that AMs and pulDCs exhibit distinct characteristics during pulmonary inflammation. Recruitment of AMs and pulDCs occurred with different kinetics, and increased numbers of AMs resulted mainly from the appearance of a distinct subset of CD11b(High) AMs. Increased numbers of CD11b(High) and CD11b(Low) AMs, but not pulDCs, were recoverable from bronchoalveolar lavage fluid. CD11b expression on AMs was significantly increased by granulocyte-macrophage colony-stimulating factor but not by interleukin-10 or pathogen-associated stimuli. Finally, antibody blockade demonstrated that CD11b was critical for the recruitment of AMs, but not pulDCs, into the lung after pneumococcal challenge. These data demonstrate that there are significant differences between AM and pulDC responses to inflammatory pathogenic stimuli in vivo

The function and regulation of LFA-3 in oral mucosal inflammation

The adhesion molecule lymphocyte function-associated antigen 3 (LFA-3), the major ligand of the T lymphocyte receptor CD2, is involved in cellular adhesion, activation and functional modulation. However, the role of LFA-3 and regulation of LFA-3 expression in oral mucosal and other diseases is poorly understood. The role of LFA-3 was investigated in the inflammatory disease oral lichen planus (OLP). Expression of LFA-3 was found to be up-regulated in OLP lesions compared with healithy oral tissues. Two distinct expression patterns were identified in OLP lesions - intracellular LFA-3 was localised within a population of infiltrating cells, and a 'soluble' form of LFA-3 (sLFA-3) was apparent within affected tissues. In contrast with the increased lesional expression of LFA-3, systemic sLFA-3 levels were not significantly altered in the sera of OLP patients compared with control subjects. RT-PCR of mRNA from OLP, other oral mucosal diseases and healthy oral mucosa revealed LFA-3 mRNA isoform expression to be neither tissue- nor disease-specific. However, a novel in vivo isoform of LFA-3 mRNA was detected. This mRNA isoform was cloned, sequenced and identified as LFA-3 AD2. Possible mechanisms for LFA-3 regulation and sLFA-3 generation in vivo were investigated in vitro. An intracellular pool of LFA-3 was demonstrated to be present within a range of cell lines. Although both surf ace and intracellular LFA-3 expression were relatively unaffected by inflammatory cytokines, the release of sLFA-3 from these cells was susceptible to cytokine-mediated modulation. Differential susceptibility to cleavage of surface LFA-3 by a phospholipase C (PLC) was demonstrated. PLC-mediated LFA-3 cleavage, a possible mechanism of sLFA-3 generation, was found to be associated with an increase in intracellular LFA-3 followed by replacement of LFA-3 at the cell surface. Finally, the in vivo role of LFA-3 in OLP was examined by adaptation of the Stamper-Woodruff adhesion assay. The results of these antibody blockade studies suggest that LFA-3 may be of equivalent importance to intercellular adhesion molecule 1 (ICAM-1) for lymphocyte adhesion within the OLP inflammatory infiltrate, and may be a potential therapeutic target for the control of OLP

The innate immune response differs in primary and secondary salmonella infection.

This study examines innate immunity to oral Salmonella during primary infection and after secondary challenge of immune mice. Splenic NK and NKT cells plummeted early after primary infection, while neutrophils and macrophages (M{phi}) increased 10- and 3-fold, respectively. In contrast, immune animals had only a modest reduction in NK cells, no loss of NKT cells, and a slight increase in phagocytes following secondary challenge. During primary infection, the dominant sources of IFN-{gamma} were, unexpectedly, neutrophils and M{phi}, the former having intracellular stores of IFN-{gamma} that were released during infection. IFN-{gamma}-producing phagocytes greatly outnumbered IFN-{gamma}-producing NK cells, NKT cells, and T cells during the primary response. TNF-{alpha} production was also dominated by neutrophils and M{phi}, which vastly outnumbered NKT cells producing this cytokine. Neither T cells nor NK cells produced TNF-{alpha} early during primary infection. The TNF-{alpha} response was reduced in a secondary response, but remained dominated by neutrophils and M{phi}. Moreover, no significant IFN-{gamma} production by M{phi} was associated with the secondary response. Indeed, only NK1.1+ cells and T cells produced IFN-{gamma} in these mice. These studies provide a coherent view of innate immunity to oral Salmonella infection, reveal novel sources of IFN-{gamma}, and demonstrate that immune status influences the nature of the innate response