RESUMEN
In thymocyte ontogeny, Tcr-a genes rearrange after Tcr-b genes. TCR alpha beta transgenic (Tg) mice have no such delay, consequently expressing rearranged TCR alpha beta proteins early in the ontogeny. Such mice exhibit reduced thymic cellularity and accumulate mature, nonprecursor TCR(+)CD8(-)4(-) thymocytes, believed to be caused by premature Tg TCR alpha beta expression via unknown mechanism(s). Here, we show that premature expression of TCR alpha beta on early thymocytes curtails thymocyte expansion and impairs the CD8(-)4(-) --> CD8(+)4(+) transition. This effect is accomplished by two distinct mechanisms. First, the early formation of TCR alpha beta appears to impair the formation and function of pre-TCR, consistent with recently published results. Second, the premature TCR alpha beta contact with intrathymic MHC molecules further pronounces the block in proliferation and differentiation. These results suggest that the benefit of asynchronous Tcr-a and Tcr-b rearrangement is not only to minimize waste during thymopoiesis, but also to simultaneously allow proper expression/function of the pre-TCR and to shield CD8(-)4(-) thymocytes from TCR alpha beta signals that impair thymocyte proliferation and CD8(-)4(-) --> CD8(+)4(+) transition.
Asunto(s)
Inhibidores de Crecimiento/fisiología , Receptores de Antígenos de Linfocitos T alfa-beta/biosíntesis , Receptores de Antígenos de Linfocitos T alfa-beta/fisiología , Transducción de Señal/inmunología , Subgrupos de Linfocitos T/inmunología , Subgrupos de Linfocitos T/metabolismo , Timo/inmunología , Timo/metabolismo , Animales , Ciclo Celular/genética , Ciclo Celular/inmunología , Diferenciación Celular/genética , Diferenciación Celular/inmunología , División Celular/genética , División Celular/inmunología , Reordenamiento Génico de la Cadena alfa de los Receptores de Antígenos de los Linfocitos T , Reordenamiento Génico de la Cadena beta de los Receptores de Antígenos de los Linfocitos T , Genes Codificadores de la Cadena alfa de los Receptores de Linfocito T/fisiología , Genes Codificadores de la Cadena beta de los Receptores de Linfocito T/fisiología , Inhibidores de Crecimiento/genética , Glicoproteínas de Membrana/biosíntesis , Glicoproteínas de Membrana/genética , Ratones , Ratones Endogámicos C57BL , Ratones Transgénicos , ARN Mensajero/biosíntesis , Receptores de Antígenos de Linfocitos T alfa-beta/genética , Receptores de Interleucina-2/biosíntesis , Proteínas Recombinantes de Fusión/fisiología , Transducción de Señal/genética , Células Madre/citología , Células Madre/inmunología , Células Madre/metabolismo , Subgrupos de Linfocitos T/citología , Timo/citología , Transgenes/inmunologíaRESUMEN
Cytotoxicity is a major effector function of CD8(+) T cells. Although mitogen-activated protein kinase (MAP kinase) / extracellular regulatory kinase (ERK) activity is indispensable for cytotoxic activity of most CD8(+) T cells a portion of CD8(+) T cells appears resistant to MEK inhibition as cytotoxicity of bulk cultures was partially preserved in the presence of a MEK inhibitor. We have also identified a long-term CD8(+) T cell line with unaltered cytolytic activity after prevention of ERK activation. Antigen-induced microtubule organizing center (MTOC) reorientation was not prevented in this CD8(+) cell line by MEK inhibition, in sharp contrast to the MTOC reorientation prevention in a CD8(+) T cell clone with MEK inhibition-sensitive cytolytic activity. These findings suggest that resistance of lysis to MEK inhibition may be due to a lack of ERK control over MTOC reorientation in some CD8(+) T cells. Thus, there appears to be a heterogeneity of ERK-regulated cytolytic activity in CD8(+) T cells, most likely resulting from a differential control of ERK over MTOC motility.