RESUMEN
Extensive evidence has been accumulated to implicate the intracellular protein tyrosine phosphatase, Src homology region 2 domain-containing protein tyrosine phosphatase-1 (SHP-1), as a negative regulator of TCR-signaling thresholds. Specifically, T cells from the SHP-1-deficient mouse, motheaten, exhibit a hyperproliferative phenotype when activated by cognate peptide-pulsed APCs. However, the cellular basis for this phenotype has not been fully explained. Using the intracellular fluorescent dye, CFSE, we show that a greater proportion of motheaten vs control naive CD8(+) T cells undergo cell division when activated by peptide-pulsed APCs. Furthermore, there is a greater likelihood of TCRs on SHP-1-deficient vs control T cells binding to peptide/MHC ligands on APCs when using TCR down-regulation as an indirect measure of TCR engagement. In addition, T cell-APC conjugate assays provide direct evidence that a greater proportion of SHP-1-deficient T cells are capable of forming stable conjugates with APCs and this may explain, at least in part, their hyperproliferative response to TCR-triggered stimulation. The physiological relevance of the combined in vitro observations is demonstrated by the significantly enhanced in vivo expansion and CTL capacity generated in mice receiving adoptively transferred SHP-1-deficient naive CD8(+) T cells when compared with control T cells.
Asunto(s)
Células Presentadoras de Antígenos/inmunología , Activación de Linfocitos , Proteína Tirosina Fosfatasa no Receptora Tipo 6/fisiología , Linfocitos T Citotóxicos/inmunología , Dominios Homologos src , Animales , Anticuerpos/farmacología , Células Presentadoras de Antígenos/efectos de los fármacos , Linfocitos T CD8-positivos/citología , Linfocitos T CD8-positivos/enzimología , Linfocitos T CD8-positivos/inmunología , Adhesión Celular/genética , División Celular/genética , Técnicas de Cocultivo , Regulación hacia Abajo , Fibronectinas/inmunología , Molécula 1 de Adhesión Intercelular/efectos de los fármacos , Molécula 1 de Adhesión Intercelular/inmunología , Activación de Linfocitos/genética , Antígeno-1 Asociado a Función de Linfocito/efectos de los fármacos , Antígeno-1 Asociado a Función de Linfocito/inmunología , Ratones , Ratones Mutantes , Péptidos/farmacología , Proteína Fosfatasa 1 , Proteína Tirosina Fosfatasa no Receptora Tipo 6/genética , Receptores de Antígenos de Linfocitos T/agonistas , Receptores de Antígenos de Linfocitos T/análisis , Receptores de Antígenos de Linfocitos T/metabolismo , Linfocitos T Citotóxicos/citología , Linfocitos T Citotóxicos/enzimologíaRESUMEN
The intracellular Src homology 2 (SH2) domain-containing protein-tyrosine phosphatase (SHP-1) has been characterized as a negative regulator of T cell function, contributing to the definition of T cell receptor signaling thresholds in developing and peripheral mouse T lymphocytes. The activation of SHP-1 is achieved through the engagement of its tandem SH2 domains by tyrosine-phosphorylated proteins; however, the identity of the activating ligand(s) for SHP-1, within mouse primary T cells, is presently unresolved. The identification of SHP-1 ligand(s) in primary T cells would provide crucial insight into the molecular mechanisms by which SHP-1 contributes to in vivo thresholds for T cell activation. Here we present a combination of biochemical and yeast genetic analyses indicating CD22 to be a T cell ligand for the SHP-1 SH2 domains. Based on these observations we have confirmed that CD22 is indeed expressed on mouse primary T cells and capable of associating with SHP-1. Significantly, CD22-deficient T cells demonstrate enhanced proliferation in response to anti-CD3 or allogeneic stimulation. Furthermore, the co-engagement of CD3 and CD22 results in a raising of TCR signaling thresholds hence demonstrating a previously unsuspected functional role for CD22 in primary T cells.
