Mutation analysis has shown that Y338, Y392 and Y510 are involved in IL-2-induced STAT protein binding. Phospho-tyrosines 338, 392 and 510 can each promote STAT5 activation (Gaffen et al. 1996), though Y510 appears to be the primary site for STAT5 binding (Gesbert et al. 1998). STAT3 may also be recruited to phospho-tyrosines on IL2RB and studies have shown defective IL-2 responses in STAT3-/- T cells, thereby supporting a functional role for STAT3 downstream of IL-2 signaling (Akaishi et al. 1998).