Characterization of the role of TCR gammadelta in NK cell accumulation during viral liver inflammation

γδ T cells confer protection against murine cytomegalovirus (MCMV)

Cytomegalovirus (CMV) is a leading infectious cause of morbidity in immune-compromised patients. γδ T cells have been involved in the response to CMV but their role in protection has not been firmly established and their dependency on other lymphocytes has not been addressed. Using C57BL/6 αβ and/or γδ T cell-deficient mice, we here show that γδ T cells are as competent as αβ T cells to protect mice from CMV-induced death. γδ T cell-mediated protection involved control of viral load and prevented organ damage. γδ T cell recovery by bone marrow transplant or adoptive transfer experiments rescued CD3ε^−/− mice from CMV-induced death confirming the protective antiviral role of γδ T cells. As observed in humans, different γδ T cell subsets were induced upon CMV challenge, which differentiated into effector memory cells. This response was observed in the liver and lungs and implicated both CD27⁺ and CD27⁻ γδ T cells. NK cells were the largely preponderant producers of IFNγ and cytotoxic granules throughout the infection, suggesting that the protective role of γδ T cells did not principally rely on either of these two functions. Finally, γδ T cells were strikingly sufficient to fully protect Rag^−/−γc^−/− mice from death, demonstrating that they can act in the absence of B and NK cells. Altogether our results uncover an autonomous protective antiviral function of γδ T cells, and open new perspectives for the characterization of a non classical mode of action which should foster the design of new γδ T cell based therapies, especially useful in αβ T cell compromised patients.

γδ T cells are unconventional T lymphocytes that play a unique role in host protection against pathogens. Human Cytomegalovirus (HCMV) is a widespread virus that can cause severe organ disease such as hepatitis and pneumonitis in immune-compromised patients. Our decade-long study conveys compelling evidence for the implication of human γδ T cells in the immune response against HCMV, but their protective role could not be formally demonstrated in humans. In the present study we use the murine model of CMV infection which allows the spatial and temporal analysis of viral spread and anti-viral immune responses. We show that, in the absence of αβ T cells, γδ T cells control MCMV-induced hepatitis, pneumonitis and death by restricting viral load in the liver, lungs and spleen. γδ T cells expand in these organs and display memory features that could be further incorporated into vaccination strategies. In conclusion, γδ T cells represent an important arm in the immune response against CMV infection that could be particularly important in the context of αβ T cell immune-suppression.

Phenotypic and functional plasticity of gamma-delta (γδ) T cells in inflammation and tolerance

Gamma-delta T cells (γδ T cells) are an unique group of lymphocytes and play an important role in bridging the gap between innate and adaptive immune systems under homeostatic condition as well as during infection and inflammation. They are predominantly localized into the mucosal and epithelial sites, but also exist in other peripheral tissues and secondary lymphoid organs. γδ T cells can produce cytokines and chemokines to regulate the migration of other immune cells, can bring about lysis of infected or stressed cells by secreting granzymes, provide help to B cells and induce IgE production, can present antigen to conventional T cells, activate antigen presenting cells (APC) maturation, and are also known to produce growth factors that regulate the stromal cell function. γδ T cells spontaneously produce IFN-γ and IL-17 cytokines compared to delayed differentiation of Th1 and Th17 cells. In this review, we discussed the current knowledge about the mechanism of γδ T cell function including its mode of antigen recognition, and differentiation into various subsets of γδ T cells. We also explored how γδ T cells interact with different types of innate and adaptive immune cells, and how these interactions shape the immune response highlighting the plasticity and role of these cells-protective or pathogenic under inflammatory and tolerogenic conditions.

Involvement of NK 1.1-positive γδT cells in interleukin-18 plus interleukin-2-induced interstitial lung disease

Interstitial lung disease (ILD) is induced by various factors in humans. However, the exact mechanism of ILD remains elusive. This study sought to determine the role of natural killer (NK) 1.1(+) γδT cells in ILD. The injection of IL-18 plus IL-2 (IL-18/IL-2) into C57BL6 (B6) mice induced acute ILD that resembled early-stage human ILD. An accumulation of NK1.1(+) γδT cells similar to NK cells was evident in the lungs. The T Cell Receptor (TCR) Vγ and Vδ repertoires of NK1.1(+) γδT cells indicated polyclonal expansion. The expression of IL-2 receptor β (Rβ) and IL-18Rβ in NK1.1(+) γδT cells was higher than in NK1.1(-) γδT cells. IL-18/IL-2 stimulated the proliferation of NK1.1(+) γδT cells, but not NK1.1(-) γδT cells. The IL-18/IL-2-stimulated NK1.1(+) γδT cells produced higher concentrations of IFN-γ than did NK1.1(-) γδT cells. Moreover, NK1.1(+) γδT and NK1.1(-) γδT cells constituted completely different cell populations. The IL-18/IL-2-induced ILD was milder in TCRδ(-/-) and IFN-γ(-/-) mice, compared with B6 mice. Furthermore, cell-transfer experiments demonstrated that NK1.1(+) γδT cells could induce the expansion of NK cells and IFN-γ mRNA in the lung by IL-18/IL-2. Our results suggest that NK1.1(+) γδT cells function as inflammatory mediators in the early phase of IL-18/IL-2-induced ILD.

Toll-like receptor 3 ligand dampens liver inflammation by stimulating Valpha 14 invariant natural killer T cells to negatively regulate gammadeltaT cells

Valpha14 invariant natural killer T (Valpha14iNKT) cells are at the interface between the innate and adaptive immune responses and are thus critical for providing full engagement of host defense. We investigated the role of polyriboinosinic:polycytidylic acid (poly I:C), a replication-competent viral double-stranded RNA mimic and a specific agonist that recognizes the cellular sensor Toll-like receptor 3 (TLR3), in regulating Valpha14iNKT cell activation. We established for the first time that hepatic Valpha14iNKT cells up-regulate TLR3 extracellularly after poly I:C treatment. Notably, activation of TLR3-expressing hepatic Valpha14iNKT cells by a TLR3 ligand was suppressed by TLR3 deficiency. Our studies also revealed that Valpha14iNKT cell activation in response to poly I:C administration uniquely suppressed the accumulation and activation of intrahepatic gammadeltaT cells (but not natural killer cells) by inducing apoptosis. Furthermore, we established that activated hepatic Valpha14iNKT cells (via cytokines and possibly reactive oxygen species) influenced the frequency and absolute number of intrahepatic gammadeltaT cells, as evidenced by increased hepatic gammadeltaT cell accumulation in Valpha14iNKT cell-deficient mice after poly I:C treatment relative to wild-type mice. Thus, hepatic Valpha14iNKT cells and intrahepatic gammadeltaT cells are functionally linked on application of TLR3 agonist. Overall, our results demonstrate a novel and previously unrecognized anti-inflammatory role for activated hepatic Valpha14iNKT cells in negatively regulating intrahepatic gammadeltaT cell accumulation (probably through TLR3 signaling) and thereby preventing potentially harmful activation of intrahepatic gammadeltaT cells.