Primary HIV infection of infants: The effects of somatic growth on lymphocyte and virus dynamics

Acute HIV infection is characterized by the appearance of high concentratio ns of virus in the peripheral blood. In adults, this high-level viremia spo ntaneously abates after several weeks. In contrast, after perinatal infecti on of infants, blood! virus levels remain high for many months, during whic h the concentration of circulating CD4(+) lymphocytes remains well above no rmal values for adults. Here we suggest an explanation for these difference s, based on developmental factors including somatic growth and immunologica l ontogeny. Flow cytometric analysis revealed that at birth the thymus cont ains elevated levels of mature T lymphocytes, compared to the thymus after 3 months of age. A mathematical model is proposed incorporating immunologic al and virological data from longitudinally evaluated infants who acquired infection at the time of birth. This model explains the pattern of high-lev el viremia in infants as resulting from the replication of HIV within the p rogressively expanding lymphoid cell mass, (C) 1999 Academic Press.