Assessing lymphocyte functions in neonates for revealing abnormal prenatal development 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 differentiation and maturation of peripheral lymphocytes of newborn, preferentially using umbilical cord blood. Many lymphocyte subsets of newborn infants are "immature" with respect to defined surface receptors. An example of such an immaturity is the almost complete lack of "memory"-type helper T cells (also designated 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 population of umbilical cord blood is capable of differentiating to mature cells 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 differentiation can only be achieved with cells of newborns. As intermediates during differentiation in culture, CD45R0(+)CD45RA(+) cells may be observed which are rather rare in vivo. Additionally, the appearance of several activation (CD25, CD69, HLA-DR) and adhesion (CD11a, CD11b, CD11c, CD18, CD49b, CD49d, CD54) receptors on CD4 cells were analyzed. With this model system evidence for the sequence of events during differentiation and maturation may be obtained. This ex vivo-model is capable of studying the capacity of lymphocytes for differentiation and activation processes barely accessible in vivo. 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 addition, substance-induced effects may be studied in vitro with this approach on immature cells from newborn, or infants during culturing. Teratogenesis Carcinog. Mutagen. 20:171-193, 2000.