cd T cells are highly cytolytic lymphocytes that produce large amounts of pro-inflammatory cytokines during immune responses to multiple pathogens. Furthermore, their ability to kill tumor cells has fueled the development of cd-T-cell-based cancer therapies. Thus, the regulation of cd-T-cell activity is of great biological and clinical relevance. Here, we show that murine CD4 1 CD25 1 ab T cells, the vast majority of which express the Treg marker, Foxp3, abolish key effector functions of cd T cells, namely the production of the pro-inflammatory cytokines, IFN-c and IL-17, cytotoxicity, and lymphocyte proliferation in vitro and in vivo. We further show that suppression is dependent on cellular contact between Treg and cd T cells, results in the induction of an anergic state in cd lymphocytes, and can be partially reversed by manipulating glucocorticoid-induced TNF receptor-related protein (GITR) signals. Our data collectively dissect a novel mechanism by which the expansion and pro-inflammatory functions of cd T cells are regulated.
IntroductionThe integration of multiple effector and regulatory mechanisms dictates the course of immune responses to self and non-self antigens. gd T cells are innate-like lymphocytes known to mount robust responses to infectious pathogens [1] and tumors [2], while also regulating tissue homeostasis and repair [3]. Importantly, several of these functions are non-redundant, as demonstrated by the immunopathology phenotypes of TCR-d-deficient mice [4]. It is also well documented that upon pathogen challenge (for example, with Plasmodium falciparum, Mycobacterium tuberculosis, Haemophilus influenzae, or Streptococcus pneumoniae), gd T cells are one of the immune populations that expands most dramatically in human peripheral blood [1,5,6].In contrast with adaptive ab T cells, activated gd lymphocytes are capable of ''immediate'' cytotoxicity and cytokine secretion [5]. In fact, we have recently shown that murine gd T cells become functionally competent in the thymus, particularly regarding the production of pro-inflammatory cytokines . Furthermore, several reports have demonstrated the crucial contributions of gd T cells to the reservoirs of such cytokines in the context of anti-tumor immunity [8], immune responses to infection [9], and autoimmunity [9,10]. While these data highlight the importance of understanding how the [17], and monocytes/macrophages [18]. As a result, CD4 1 CD25 1 ab T cells, and particularly those that develop in the thymus through a Foxp3-dependent genetic program [19,20], so-called ''naturally occurring '' Treg (nTreg), are pivotal to maintaining immune homeostasis and preventing inflammatory and autoimmune diseases [21]. On the other hand, Treg-suppressive functions are also known to diminish immunity to pathogens and to tumors [22,23]. Provocatively, an inverse correlation between circulating human Treg frequencies and gd-T-cell numbers in cancer patients has been recently reported [24].Building on these foundations, we show here that Treg suppress gd-T-cell ...