It has been hypothesized that a CD3 + CD4 + CD25 + Foxp3 + regulatory T cell (Treg) dysfunction and its association with increased numbers of CD19 + CD38 low CD21 low immature activated B cells may be involved in impaired immune tolerance in CVID and contribute to the immunopathology of autoimmune phenomena and immune dysregulation [38]. Here, CD4 is linked to common variable immunodeficiency.