ACTIVATED AND MEMORY PHENOTYPE OF CIRCULATING T-LYMPHOCYTES IN INTRAUTERINE LIFE

We examined the expression of T cell markers in the peripheral blood o f five immunologically normal human fetuses at 18-20 weeks of gestatio nal age. The distribution of T cells expressing CD1, CD3, CD4, CD8, CD 56, and the alpha/beta and gamma/delta receptors for antigen was compa rable to that of newborns and normal adults, except for the absence of gamma/delta cells expressing the delta TCS-1 epitope. The V beta repe rtoire, as evaluated by two-color now cytometry using mAbs to specific V beta families, was also comparable to that of adult samples. A sign ificant fraction (8.9 to 16.4%) of fetal CD3(+) T cells expressed the a chain of IL-2R (CD25) in the absence of HLA-DR; this suggests that a ntigenic stimuli trigger, during intrauterine life, an unusual pathway of T cell activation. Consistent with this, 7 to 27% of fetal T cells were found to express the CD45R0 marker of ''memory'' cells. (C) 1994 Academic Press, Inc.