Histological observations on thymic development in fetal and newborn mammals subject to intrauterine growth retardation.

Fetal growth retardation resulting from maternal dietary protein deprivation (rats) or Coxsackie virus B3 infection in mid-pregnancy (mice) was associated with delayed thymic development. Histological examination revealed that less darkly staining small lymphocytes were present and that the thymus was not well organised into cortex and medulla as seen in the normal-weight fetuses. In preterm or neonatal piglets, the histological pattern of the thymus did not vary appreciably according to the body weight of the fetus. Hassall's corpuscles were present and the tissues were well organised into cortex and medulla regions. Although fetal growth retardation in rats and mice leads to an apparent delay in the differentiation of the thymus, functional studies are necessary to understand the immunological significance of this finding.