RAB4A and Splenomegaly: While total body and heart weights were unaffected, splenomegaly was markedly increased in B6.TC/Rab4AQ72L mice over B6.TC controls at 40 weeks of age, which was completely reversed by the inactivation of Rab4A in T cells of B6.TC/Rab4AQ72L-KO mice (Fig. 3C).