RESUMEN
The BCR relays extracellular signals and internalizes Ag for processing and presentation. We have previously demonstrated that ligation of the BCR destabilizes Ig-alpha/Ig-beta (Ig-alphabeta) from mu-H chain (mum). In this study we report that receptor destabilization represents a physical separation of mum from Ig-alphabeta. Sucrose gradient fractionation localized Ig-alphabeta to G(M1)-containing lipid microdomains in the absence of mum. Confocal and electron microscopy studies revealed the colocalization of unsheathed mum with clathrin-coated vesicles. Furthermore, mum failed to associate with clathrin-coated vesicles when receptor destabilization was inhibited, suggesting that unsheathing of mum is required for clathrin-mediated endocytosis. In summary, we found that Ag stimulation physically separates Ig-alphabeta from mum, facilitating concomitant signal transduction and Ag delivery to the endocytic compartment.
Asunto(s)
Cadenas Pesadas de Inmunoglobulina/metabolismo , Receptores de Antígenos de Linfocitos B/metabolismo , Animales , Presentación de Antígeno , Transporte Biológico Activo , Línea Celular , Vesículas Cubiertas por Clatrina/inmunología , Vesículas Cubiertas por Clatrina/metabolismo , Endocitosis , Gangliósido G(M1)/metabolismo , Cadenas alfa de Inmunoglobulina/metabolismo , Cadenas mu de Inmunoglobulina/metabolismo , Cinética , Microdominios de Membrana/inmunología , Microdominios de Membrana/metabolismo , Ratones , Microscopía Electrónica , Transducción de SeñalRESUMEN
CD8 engagement is believed to be a critical event in the activation of naive T cells. In this communication, we address the effects of peptide-MHC (pMHC)/TCR affinity on the necessity of CD8 engagement in T cell activation of primary naive cells. Using two peptides with different measured avidities for the same pMHC-TCR complex, we compared biochemical affinity of pMHC/TCR and the cell surface binding avidity of pMHC/TCR with and without CD8 engagement. We compared early signaling events and later functional activity of naive T cells in the same manner. Although early signaling events are altered, we find that high-affinity pMHC/TCR interactions can overcome the need for CD8 engagement for proliferation and CTL function. An integrated signal over time allows T cell activation with a high-affinity ligand in the absence of CD8 engagement.