ARHGAP45 and lymphopenia: It suggests that the T‐cell lymphopenia observed in Arhgap45−/− mice does not result from the presence of slightly diminished SP numbers but is rather due to the reduced ability of Arhgap45−/− T cells to enter into LNs and receive enough survival‐promoting signals on fibroblastic reticular cells (Link et al, 2007; Chang & Turley, 2015).