T cell Activation
2-signal activation
CD8+ T cell differentiates to become a cytotoxic cell.
— The cell surface of the CD8+ has the T-cell Receptor Complex (TCR complex), which consists of the following components:
The T-cell receptor, which is specific to the peptide antigen displayed by the MHC molecule; CD3 proteins; and, the CD8 protein, which recognizes and interacts with the MHC class I molecule of the nucleated cell.
— The representative nucleated cell displays the class I MHC - antigen complex.
— The interaction between the TCR complex and nucleated cell allows for the second signal, which involves co-stimulation between CD28 and B7-2.
— Activation triggers proliferation, aka, cloning, of the T cell and differentiation into the effector type – which, for CD8+ cells, is the Cytotoxic T cell.
2-signal activation
CD4+ T cell differentiates to become a Helper T cell.
— The dendritic cell surface displays the MHC II-antigen complex.
— The CD4+ cell has the TCR complex: the T-cell receptor, which is specific to the antigen; the CD3 molecules; and, the CD4 protein that interacts with the MHC II molecule on the antigen-presenting cell.
— The second signal comprises co-stimulation: interaction between CD28 on the surface of the T cell and B7-2 on the dendritic cell.
— Activation results in proliferation and differentiation to effector cells.