LAT and lymphoproliferative syndrome: A LAT-knockin (LAT-KI) strain of mice in which Tyr136 was mutated to phenylalanine (LATY136F) displays a severe but partial block in T cell maturation, but later develop a polyclonal lymphoproliferative disorder involving CD4+ T cells producing massive amounts of T helper type 2 (TH2) cytokines (7, 8).