T cell co-stimulatory molecules other than CD28.

CD28 is the primary co-stimulatory receptor for inducing high-level IL-2 production and survival of naïve CD4(+) T cells. While no other cell surface receptor can be considered fully redundant with CD28, recent developments suggest that additional co-stimulatory pathways have preferential effects at different stages of T cell activation, on different subsets of T cells or contribute to the development of different effector functions.