Priming of naïve T cells requires dendritic cell antigen presentation. Priming of naive CD8 T cells generates cytotoxic T cells capable of directly killing pathogen-infected cells. CD4 cells develop into a diverse array of effector cell types depending on the nature of the signals they receive during priming. CD4 effector activity can include cytotoxicity, but more frequently it involves the secretion of a set of cytokines that directs the target cell to make a particular response. This activation of naive T cell is controlled by a variety of signals: recognition of antigen in the form of a peptide:MHC complex on the surface of a specialized antigen-presenting cell delivers signal 1; interaction of co-stimulatory molecules on antigen-presenting cells with receptors on T cells delivers signal 2 (one notable example includes a B7 ligand complex on antigen-presenting cells binding to the CD28 receptor on T cells); and cytokines that control differentiation into different types of effector cells deliver signal 3.
- Janeway's immunobiology, Kenneth Murphy
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