Assessing lymphocyte functions in neonates for revealing abnormal prenataldevelopment of the immune system

Because it is difficult to assess prenatally induced functional deficits of the human immune system, we developed an ex vivo method for differentiatio n and maturation of peripheral lymphocytes of newborn, preferentially using umbilical cord blood. Many lymphocyte subsets of newborn infants are "imma ture" with respect to defined surface receptors. An example of such an imma turity is the almost complete lack of "memory"-type helper T cells (also de signated as helper-inducer cells), characterized by expressing the surface receptors: CD4(+)CD45R0(+)CD45RA(-)CD29(high). On the other hand, umbilical cord blood contains many "naive"-type helper T cells (often designated as suppressor-inducer cells), with the receptors: CD4(+)CD45R0(-)CD45RA(+)CD29 (low). In this report, we demonstrate that the immature helper lymphocyte p opulation of umbilical cord blood is capable of differentiating to mature c ells following stimulation with pokeweed mitogen (PWM) and other stimulants ex vivo. The obtained receptor pattern is virtually indistinguishable from the one observed on the mature cells of adults. Such an extensive differen tiation can only be achieved with cells of newborns. As intermediates durin g differentiation in culture, CD45R0(+)CD45RA(+) cells may be observed whic h are rather rare in vivo. Additionally, the appearance of several activati on (CD25, CD69, HLA-DR) and adhesion (CD11a, CD11b, CD11c, CD18, CD49b, CD4 9d, CD54) receptors on CD4 cells were analyzed. With this model system evid ence for the sequence of events during differentiation and maturation may b e obtained. This ex vivo-model is capable of studying the capacity of lymph ocytes for differentiation and activation processes barely accessible in vi vo. It may also be expected to represent an interesting tool for measuring the capacity for maturation and differentiation in the blood of children of different ages under normal and pathological conditions ex vivo. In additi on, substance-induced effects may be studied in vitro with this approach on immature cells from newborn, or infants during culturing. Teratogenesis Ca rcinog. Mutagen. 20.171-193, 2000. (C) 2000 Wiley-Liss, Inc.