Fetal and postnatal development of T-lymphocyte subpopulations

Changes in individual subpopulations of lymphocytes in primary and secondary lymphatic organs and circulating blood were observed in pig fetuses between days 51 and 112 of gestation, and in circulating blood in postnatal piglets. The technique of flow cytofluorimetry was used. CD4+ and CD8+ T lymphocytes were demonstrated in porcine thymus on day 51 of gestation. Their number continued to increase markedly. In the spleen only CD2+ cells were found on day 51 of gestation. Expression of lymphocytes with CD4+ and CD8+ receptors was shown on day 60. Their numbers increased with age. The percentage of T lymphocytes with CD4+ and CD8+ markers was higher in lymph nodes (observations made from day 90) than in the spleen. The CD4+/CD8+ ratio in spleen and thymus gradually decreased with advancing age to 1. In lymph nodes of pig fetuses CD8+ lymphocytes prevailed. In the blood of 28-day-old piglets the CD4+/CD8+ index was only 0.2. The numbers of B lymphocytes with IgM receptors in the blood increased gradually from day 90 of prenatal development until day 28 of postnatal life both in relative and actual terms.