Additionally, when the thymus undergoes physiologic or pathologic involution during aging, infectious diseases, sepsis, malnutrition, physical or emotional stress, chemotherapeutics, glucocorticoids or radiation injury, cortical double positive cells, primarily, suffer apoptosis, while CD4+ or CD8+ cells are less affected [40–43], indicating that cortical double positive cells represent the most vulnerable cell population in the thymus. Here, CD4 is linked to infectious disease.