RESUMO
CTLA-4 is a crucial immune regulator that mediates both negative costimulation signals to T cells, and regulatory T (Treg)-cell extrinsic control of effector responses. Here we present evidence supporting a novel mechanism for this extrinsic suppression, executed by the alternatively spliced soluble CTLA-4 isoform (sCTLA-4). Analyses of human T cells in vitro show that sCTLA-4 secretion can be increased during responses, and has potent inhibitory properties, since isoform-specific blockade of its activity significantly increased Ag-driven proliferation and cytokine (IFN-γ, IL-17) secretion. Treg cells were demonstrated to be a prominent source of sCTLA-4, which contributed to suppression in vitro when their numbers were limiting. The soluble isoform was also produced by, and inhibited, murine T cells responding to Ag in vitro, and blockade of its activity in vivo protected against metastatic spread of melanoma in mice. We conclude that sCTLA-4 is an important immune regulator, responsible for at least some of the inhibitory effects previously ascribed to the membrane-bound isoform. These results suggest that the immune system exploits the different CTLA-4 isoforms for either intrinsic or extrinsic regulation of T-cell activity.
Assuntos
Anticorpos Neutralizantes/farmacologia , Antígeno CTLA-4/imunologia , Melanoma Experimental/tratamento farmacológico , Metástase Neoplásica/prevenção & controle , Linfócitos T Citotóxicos/imunologia , Linfócitos T Reguladores/imunologia , Animais , Antígeno CTLA-4/antagonistas & inibidores , Antígeno CTLA-4/genética , Células Cultivadas , Feminino , Humanos , Interferon gama/biossíntese , Interferon gama/imunologia , Interleucina-17/biossíntese , Interleucina-17/imunologia , Melanoma Experimental/genética , Melanoma Experimental/imunologia , Melanoma Experimental/patologia , Camundongos , Camundongos Endogâmicos BALB C , Isoformas de Proteínas/antagonistas & inibidores , Isoformas de Proteínas/genética , Isoformas de Proteínas/imunologia , Transdução de Sinais/efeitos dos fármacos , Transdução de Sinais/imunologia , Solubilidade , Linfócitos T Citotóxicos/citologia , Linfócitos T Citotóxicos/metabolismo , Linfócitos T Reguladores/citologia , Linfócitos T Reguladores/metabolismoRESUMO
The paroxysms of Plasmodium vivax malaria are antiparasite responses that, although distressing to the human host, almost never impart serious acute pathology. Using plasma and blood cells from P. vivax patients, the cellular and noncellular mediators of these events have been studied ex vivo. The host response during a P. vivax paroxysm was found to involve T cells, monocytes and neutrophils, and the activity, among others, of the pyrogenic cytokines tumor necrosis factor alpha and interleukin 2 in addition to granulocyte macrophage-colony stimulating factor. However, interferon gamma activity, associated with serious acute pathogenesis in other studies on malaria, was absent. Induction of the cytokines active during a P. vivax paroxysm depends upon the presence of parasite products, which are released into the plasma before the paroxysm. Chemical identification of these natural parasite products will be important for our understanding of pathogenesis and protection in malaria.