RESUMO
Natural killer group 2, member D (NKG2D) is a stimulatory receptor expressed by NK cells and a subset of T cells. NKG2D is crucial in diverse aspects of innate and adaptive immune functions. In this study, we characterize a novel splice variant of human NKG2D that encodes a truncated receptor lacking the ligand-binding ectodomain. This truncated NKG2D (NKG2D(TR)) isoform was detected in primary human NK and CD8(+) T cells. Overexpression of NKG2D(TR) severely attenuated cell killing and IFN-γ release mediated by full-length NKG2D (NKG2D(FL)). In contrast, specific knockdown of endogenously expressed NKG2D(TR) enhanced NKG2D-mediated cytotoxicity, suggesting that NKG2D(TR) is a negative regulator of NKG2D(FL). Biochemical studies demonstrated that NKG2D(TR) was bound to DNAX-activated protein of 10 kDa (DAP10) and interfered with the interaction of DAP10 with NKG2D(FL). In addition, NKG2D(TR) associated with NKG2D(FL), which led to forced intracellular retention, resulting in decreased surface NKG2D expression. Taken together, these data suggest that competitive interference of NKG2D/DAP10 complexes by NKG2D(TR) constitutes a novel mechanism for regulation of NKG2D-mediated function in human CD8(+) T cells and NK cells.
Assuntos
Linfócitos T CD8-Positivos/imunologia , Células Matadoras Naturais/imunologia , Subfamília K de Receptores Semelhantes a Lectina de Células NK/imunologia , Isoformas de Proteínas/genética , Receptores Imunológicos/imunologia , Processamento Alternativo/genética , Animais , Sequência de Bases , Células COS , Células Cultivadas , Chlorocebus aethiops , Humanos , Interferon gama/metabolismo , Subfamília K de Receptores Semelhantes a Lectina de Células NK/biossíntese , Subfamília K de Receptores Semelhantes a Lectina de Células NK/genética , Isoformas de Proteínas/imunologia , Interferência de RNA , RNA Interferente Pequeno , Análise de Sequência de DNARESUMO
African trypanosomiasis is caused by Salivarian trypanosomes, tsetse fly-transmitted protozoa that inhabit the blood plasma, lymph and interstitial fluids, and, in the case of Trypanosoma brucei species, also the cerebrospinal fluid of mammal hosts. Trypanosomiasis in people and domestic animals manifests as recurring waves of parasites in the blood and is typically fatal. In contrast, trypanosomiasis in Cape buffaloes, which are naturally selected to resist the disease, is characterized by the development of only one or a few waves of parasitemia, after which the infection becomes cryptic, being maintained by the presence of 1-20 mammal-infective organisms/ml of blood. The control of the acute phase of parasitemia in Cape buffaloes correlates with a decline in blood catalase activity and the generation of trypanocidal H(2)O(2) in serum during the catabolism of endogenous purine by xanthine oxidase. Here we review features of this response, and of trypanosome metabolism, that facilitate H(2)O(2)-mediated killing of the parasites with minimal damage to the host. We also discuss the origin and regulation of serum xanthine oxidase and catalase, and show how recovery of serum catalase in infected Cape buffaloes precludes a role for H(2)O(2) in the long-term, stable suppression of trypanosome parasitemia.
Assuntos
Trypanosoma/fisiologia , Tripanossomíase/parasitologia , Xantina Oxidase/sangue , Sequência de Aminoácidos , Animais , Búfalos , Glucose/metabolismo , Peróxido de Hidrogênio/farmacologia , Concentração de Íons de Hidrogênio , Modelos Biológicos , Dados de Sequência Molecular , Oxigênio/metabolismo , Processamento de Proteína Pós-Traducional , Homologia de Sequência de AminoácidosRESUMO
WC1 molecules are implicated in augmenting cellular activation as well as inducing cell cycle arrest of gammadelta T cells. Since WC1 is a large multigene family differences in outcome could result from modulation of different WC1 molecules. To further investigate this family of molecules, peripheral blood WC1(+) gammadelta T cell subpopulations were evaluated by 2-D Western blotting and RT-PCR. We found 13 cDNA intracytoplasmic tail sequences with differences in signaling motifs among them and at least 20 biochemically distinguishable WC1 spots associated with cell membranes, with some in lipid rafts. An understanding of the diversity of 2-D spots could not be resolved by evaluating T cell clones, removing sialyated carbohydrates or blotting with anti-WC1.1 or anti-WC1.2-specific antibodies. Nevertheless, while the major gammadelta T cell subpopulations in blood (WC1.1(+)/WC1.2(-) and WC1.2(+)/WC1.1(-)) both had complex 2-D patterns, virtually all spots associated with WC1.2(+)/WC1.1(-) cells bore the WC1.2 epitope, distinguishing them from the WC1.1(+) cells.