Elizabeth M. Andrew

Delineation of the function of a major gamma delta T cell subset during infection.

γδ T cells play important but poorly defined roles in pathogen-induced immune responses and in preventing chronic inflammation and pathology. A major obstacle to defining their function is establishing the degree of functional redundancy and heterogeneity among γδ T cells. Using mice deficient in Vγ1+ T cells which are a major component of the γδ T cell response to microbial infection, a specific immunoregulatory role for Vγ1+ T cells in macrophage and γδ T cell homeostasis during infection has been established. By contrast, Vγ1+ T cells play no significant role in pathogen containment or eradication and cannot protect mice from immune-mediated pathology. Pathogen-elicited Vγ1+ T cells also display different functional characteristics at different stages of the host response to infection that involves unique and different populations of Vγ1+ T cells. These findings, therefore, identify distinct and nonoverlapping roles for γδ T cell subsets in infection and establish the complexity and adaptability of a single population of γδ T cells in the host response to infection that is not predetermined, but is, instead, shaped by environmental factors.

A subset of IL-10-producing gammadelta T cells protect the liver from Listeria-elicited, CD8(+) T cell-mediated injury

Although γδ T cells play a role in protecting tissues from pathogen‐elicited damage to bacterial, viral and parasitic pathogens, the mechanisms involved in the damage and in the protection have not been clearly elucidated. This has been addressed using a murine model of listeriosis, which in mice lacking γδ T cells (TCRδ–/–) is characterised by severe and extensive immune‐mediated hepatic necrosis. We show that these hepatic lesions are caused by Listeria‐elicited CD8+ T cells secreting high levels of TNF‐α that accumulate in the liver of Listeria‐infected TCRδ–/– mice. Using isolated populations of γδ T cells from wild‐type and cytokine‐deficient strains of mice to reconstitute TCRδ–/– mice, the TCR variable gene 4 (Vγ4)+ subset of γδ T cells was shown to protect against liver injury. Hepatoprotection was dependent upon their ability to produce IL‐10 after TCR‐mediated interactions with Listeria‐elicited macrophages and CD8+ T cells. IL‐10‐producing Vγ4+ T cells also contribute to controlling CD8+ T cell expansion and to regulating and reducing TNF‐α secretion by activated CD8+ T cells. This effect on TNF‐α production was directly attributed to IL‐10. These findings identify a novel mechanism by which pathogen‐elicited CD8+ T cells are regulated via interactions with, and activation of, IL‐10‐producing hepatoprotective γδ T cells.

A Requirement for the Vγ1+ Subset of Peripheral γδ T Cells in the Control of the Systemic Growth of Toxoplasma gondii and Infection-Induced Pathology

γδ T cells are a diverse population of T cells that are widely distributed and are a common feature of pathogen-induced immune responses. It is not clear, however, whether different populations of γδ T cells have specific functions, and what factors determine the functional properties of individual populations. A murine model of peroral Toxoplasma gondii infection was used to determine the contribution Vγ1+ intestinal intraepithelial lymphocytes (IELs) vs systemic Vγ1+ T cells make to the acute and chronic stages of the host immune response, and whether the macrophage cytocidal activity of Vγ1+ T cells described in bacterial infections is seen in other, unrelated infectious disease models. In response to oral infection with virulent type 1 or avirulent type II strains of T. gondii, TCR-δ−/− mice rapidly developed severe ileitis. In contrast, in mice deficient in Vγ1+ T cells and IELs and wild-type mice, inflammation was delayed in onset and less severe. The protective effect of (Vγ1−) IELs to Toxoplasma infection was unrelated to their cytolytic and cytokine (Th1)-producing capabilities. Systemic Vγ1+ T cells were shown to play an essential role in limiting parasite growth and inflammation in peripheral tissues and, in particular, in the CNS, that was associated with their ability to efficiently kill parasite-elicited and infected macrophages. These findings suggest that macrophage cytocidal activity of Vγ1+ T cells may be a universal feature of pathogen-induced immune responses and that microenvironmental factors influence the involvement and function of γδ T cells in the host response to infection.

Evidence for the opposing roles of different γδ T cell subsets in macrophage homeostasis

To ensure invading pathogens are eliminated with minimal damage to host tissues it is essential that macrophage activation be tightly regulated. Previously we demonstrated that a subset of γδ T cells (Vγ1+) contributes to resolving pathogen‐induced immune responses by killing activated macrophages. However, the exaggerated macrophage response seen in infected Vγ1+ T cell‐deficient mice suggests that γδ T cells play a broader role in macrophage homeostasis and other subsets might promote macrophage activation. Using a macrophage:γδ T cell co‐culture system we have shown that γδ T cells increase the activity of macrophages activated in vivo by Listeria monocytogenes infection. In a dose‐dependent manner, γδ T cells up‐regulated production of cytokines (TNF‐α, IL‐6, IL‐10) and chemokines (MIP‐1α, MIP‐1β) by Listeria‐elicited macrophages. The ability to increase macrophage cytokine production was prominent among Vγ4+ γδ T cells. Reciprocally, Vγ4+ γδ T cells were activated by Listeria‐elicited macrophages, resulting in production of the anti‐inflammatory cytokine, IL‐10. γδ T cell adoptive transfer experiments showed that Vγ4+ T cells protected TCRδ–/– mice against Listeria‐induced liver injury and necrosis. These findings identify distinct and non‐overlapping roles for γδ T cell subsets in regulating macrophage function during pathogen‐induced immune responses.

Intestinal Intraepithelial Lymphocyte-Enterocyte Crosstalk Regulates Production of Bactericidal Angiogenin 4 by Paneth cells upon Microbial Challenge

Antimicrobial proteins influence intestinal microbial ecology and limit proliferation of pathogens, yet the regulation of their expression has only been partially elucidated. Here, we have identified a putative pathway involving epithelial cells and intestinal intraepithelial lymphocytes (iIELs) that leads to antimicrobial protein (AMP) production by Paneth cells. Mice lacking γδ iIELs (TCRδ-/-) express significantly reduced levels of the AMP angiogenin 4 (Ang4). These mice were also unable to up-regulate Ang4 production following oral challenge by Salmonella, leading to higher levels of mucosal invasion compared to their wild type counterparts during the first 2 hours post-challenge. The transfer of γδ iIELs from wild type (WT) mice to TCRδ-/- mice restored Ang4 production and Salmonella invasion levels were reduced to those obtained in WT mice. The ability to restore Ang4 production in TCRδ-/- mice was shown to be restricted to γδ iIELs expressing Vγ7-encoded TCRs. Using a novel intestinal crypt co-culture system we identified a putative pathway of Ang4 production initiated by exposure to Salmonella, intestinal commensals or microbial antigens that induced intestinal epithelial cells to produce cytokines including IL‑23 in a TLR-mediated manner. Exposure of TCR-Vγ7+ γδ iIELs to IL-23 promoted IL‑22 production, which triggered Paneth cells to secrete Ang4. These findings identify a novel role for γδ iIELs in mucosal defence through sensing immediate epithelial cell cytokine responses and influencing AMP production. This in turn can contribute to the maintenance of intestinal microbial homeostasis and epithelial barrier function, and limit pathogen invasion.

Identification of novel gammadelta T-cell subsets following bacterial infection in the absence of Vgamma1+ T cells:homeostatic control of gammadelta T-cell responses to pathogen infection by Vgamma1+ T cells

ABSTRACT Although γδ T cells are a common feature of many pathogen-induced immune responses, the factors that influence, promote, or regulate the response of individual γδ T-cell subsets to infection is unknown. Here we show that in the absence of Vγ1+ T cells, novel subsets of γδ T cells, expressing T-cell receptor (TCR)-Vγ chains that normally define TCRγδ+ dendritic epidermal T cells (DETCs) (Vγ5+), intestinal intraepithelial lymphocytes (iIELs) (Vγ7+), and lymphocytes associated with the vaginal epithelia (Vγ6+), are recruited to the spleen in response to bacterial infection in TCR-Vγ1−/− mice. By comparison of phenotype and structure of TCR-Vγ chains and/or -Vδ chains expressed by these novel subsets with those of their epithelium-associated counterparts, the Vγ6+ T cells elicited in infected Vγ1−/− mice were shown to be identical to those found in the reproductive tract, from where they are presumably recruited in the absence of Vγ1+ T cells. By contrast, Vγ5+ and Vγ7+ T cells found in infected Vγ1−/− mice were distinct from Vγ5+ DETCs and Vγ7+ iIELs. Functional analyses of the novel γδ T-cell subsets identified for infected Vγ1−/− mice showed that whereas the Vγ5+ and Vγ7+ subsets may compensate for the absence of Vγ1+ T cells by producing similar cytokines, they do not possess cytocidal activity and they cannot replace the macrophage homeostasis function of Vγ1+ T cells. Collectively, these findings identify novel subsets of γδ T cells, the recruitment and activity of which is under the control of Vγ1+ T cells.

γδT cell‐mediated regulation of chemokine producing macrophages during Listeria monocytogenes infection‐induced inflammation

Infection of γδT cell‐deficient (TcRδ−/−) mice with the intracellular bacterium Listeria monocytogenes (Lm) results in an exacerbated inflammatory response characterized by the accumulation of activated macrophages and necrotic liver lesions. Here we investigated whether changes in chemokine production by Lm‐elicited macrophages contribute to this abnormal inflammatory response. In response to Lm infection, activated macrophages accumulate in the primary sites of infection in TcRδ−/− mice and express high amounts of mRNA encoding the chemokines CCL3 (MIP‐1α), CCL4 (MIP‐1β), CXCL2 (MIP‐2) and CXCL10 (IP‐10). In the infected tissues of TcRδ−/− the number of chemokine‐synthesizing macrophages was higher than in wild‐type (WT) mice, with the amount of MIP‐1α and MIP‐1β secreted by individual macrophages in the spleen of TcRδ−/− mice also being significantly higher than in WT mice. By contrast, protease activity and NO production in individual splenic macrophages of Lm‐infected TcRδ−/− and WT mice were comparable. Pathogen‐elicited macrophages in TcRδ−/− mice also expressed high levels of the CCL3 and CCL4 receptor, CCR5. In macrophage‐γδT cell co‐cultures, chemokine‐producing macrophages were killed by cytotoxic Vγ1+ T cells in a Fas–FasL‐dependent manner consistent with the high levels of chemokine‐producing macrophages seen in infected TcRδ−/− mice being due to the absence of Vγ1+ T cells. Together these findings highlight the importance of γδT cells in regulating macrophage anti‐microbial responses. Copyright