Characterization of human lymphocytes separated from fetal liver and spleen at different stages of ontogeny.

Membrane markers on human lymphocytes separated from fetal liver and spleen were studied. Depending on the period of intrauterine development, a growing percentage of T- and B-lymphocytes (up to 16% and 45%, respectively) among spleen cells was seen, but in liver the number was low independent of the gestational age (T cells less than 10% and B cells less than 15%). The majority of early CD3+ spleen cells (21st-28th week) expressed TCR alpha beta but not TCR gamma delta, although a significant proportion of these cells was still lacking CD4, CD8, and CD5 differentiation antigens, suggesting their immaturity. Later spleen T cells (29th-36th week) expressed the phenotype as mature adult-type T cells (CD3+TCR alpha beta +CD4/8+CD5+). During ontogeny in fetal spleen, a growing number of B cells could be estimated without any changes in the proportion of subsets, expressing the different light and heavy chains. However, the proportion of CD5+ B cells decreased with gestational age. The results suggest that the functional immaturity of antenatal splenocytes could not be caused by dramatic phenotypical differences in comparison with adult-type splenic lymphocytes.