Predominance of T cells that express CD45R in the CD4+ helper/inducer lymphocyte subset of neonates.

Neonates have an increased risk of severe infections. For several in vitro and in vivo immune responses, neonates have been shown to have significant differences when compared to normal adults. To indirectly study immune cellular defects, we compared cell surface markers on cord blood lymphocytes (CBL) from 58 term infants to peripheral blood lymphocytes (PBL) from 17 healthy adults using flow cytometry with standard as well as newly defined monoclonal antibodies (Mab) that distinguish regulatory T cells. CBL had significantly smaller percentages of lymphocytes that express the CD2 and CD8 markers (total T cells, and suppressor/cytotoxic T cells, respectively), although absolute numbers of CD2+ and CD8+ cells were comparable in neonates and adults. CBL and PBL were similar in terms of the percentage of CD4+ cells (helper/inducer T cells), although the absolute numbers of CD4+ cells were higher in CBL than in PBL. The CD4+ population was subdivided into cells bearing the virgin and memory T cell phenotypes using anti-2H4 and anti-4B4 Mab and dual parameter analysis with anti-CD4. Neonates were deficient in the percentage of CD4+, 4B4+ (3.8 +/- 2.8 vs 13.4 +/- 7.5, P less than 0.001), but equivalent to adults in the percentage of CD4+, 2H4+ T cells (21.4 +/- 9.8 vs 18.8 +/- 12.8). In absolute numbers, neonates had fewer CD4+, 4B4+ cells (178 +/- 173 vs 344 +/- 152 cells/microliters, P less than 0.001), but more CD4+,2H4+ cells (978 +/- 572 vs 542 +/- 518 cells/microliters, P less than 0.01) than adults. The predominance of 2H4+ virgin T cells in the CD4 population whose function is associated with that of the induction of suppression rather than the up-regulation of immune responses may contribute to the observed susceptibility of neonates to infection.