Abstract
The functional antigenic expressions of peripheral blood lymphocytes (PBL) in 39 premature and 28 mature infants were investigated using monoclonal antibodies and flow cytometry to evaluate the age-related phenotypic differentiation in their cellular immune system. Although the cells expressed mature T cell differentiation antigens (CD 3 Ag) detected on PBL in extremely low birth weight (ELBW), very low birth weight (VLBW) and mature infants increased in the order of their gestational age, the percentage of the CD 3+ T cells in PBL from the ELBW infants elevated to a level comparable to that in adults until 2 months of age. The expression of CD 3 Ag on PBL from the VLBW infants was at approximately the same frequencies with that on adult PBL. And the percentage of the CD 3+ T cells in PBL from mature infants was rather higher than that in adult PBL. The relative percentages of CD 4+ T cells in the CD 3+ T cells from premature and mature infants were significantly higher figure than that detected in adult CD 3+ T cells and decreased to a level comparable to that in adults until 6 months of age. In contrast, the relative proportions of CD 8+ T cells in both premature and mature infants were significantly lower than the adult level during the first 3 months. There was no significant difference in the percentage of CD 4+ T cells or CD 8+T cells between ELBW, VLBW and mature infants. These data observed in the postnatal phenotipic changes in the T cell subsets suggest that the differentiational expression of the CD 4 or CD 8 antigen on CD 3+ T cells might occur at least during the last trimester and the quantitative maturation of CD 3+ T cells might be near completion until 40 weeks of gestation. The predominance of Leu 8+ suppressor inducer T cells in the CD 4 subset during the first 6 months of age in premature and mature infants was also characteristic in neonatal T cell subsets. The Leu 8-CD 4+ subset was predominantly detecte in the CD 3+ T cells from the ELBW infants after birth who had higher risk for the exposure to foreign antigens than other 2 groups. Both VLBW and mature infants were lack in the percentage of Leu 8-CD 4+ T cells at birth, but the rapid increase in the percentage of the Leu 8-CD 4+ T cells nearly to adultlevel until 6 months of age was observed in the VLBW infants. These alterations in the percentage of distinct T cell subsets may be associated with the induction of suppression of immune responses rather than that of the up-regulation in neonates, however, our results indicate the possibility of early accomplishment of the phenotipic differentiation of the T cell subsets in premature and mature infants to provide adult levels of cellular immune system.
