Its known that thymus plays a pivotal role in immune system, where T cell development occurs.Increasing evidence shows that RACK1 (official gene name Gnb2ll), receptor for activated C kinase 1, plays an important role in cell signaling.Specific inactivation of RACK1 in T cells was achieved by crossing mice homozygous for a Gnb211 conditional allele (Gnb2ll～) with mice expressing a transgene encoding Cre recombinase driven by the lymphocyte-specific protein tyrosine kinase (Lck) promoter.