CD4 and lymphopenia: Loss of RIPK1 in T cells leads to peripheral T cell lymphopenia with an increased proportion of CD4+ and CD8+ effector T cells (Huysentruyt et al, 2024; Dowling et al, 2016; Imanishi et al, 2023; Wang et al, 2023), which may impair immune surveillance and alter immune responses, particularly in tissues such as the intestines, where effector T cells play a critical role in regulating inflammation (Cheroutre et al, 2011).