Furthermore, the major target cell for viral infection, the activated effector-memory CD4+ T lymphocyte, has a short lifespan of days after differentiating from the long-lived central memory pool of CD4+ T lymphocytes [34], [35], and it is inconceivable that an infected effector-memory CD4+ T lymphocyte could survive the 10 to 20 days required to demonstrate cytolysis as predicted by the fixed production model. Here, CD4 is linked to viral infectious disease.