CD4 and infection: Moreover, children undergoing thymectomy during the first six months of their life suffer from T cell lymphopenia (premature immune aging) that predominantly affects their naïve T cells as the thymus is the primary site for their development and they exhibit decreased T cell (CD4+ helper and CD8+ cytotoxic T cells) diversity 18 years after thymectomy and suffer more episodes of infections and allergies (Figure 1) [78,79].