Abstract 9603951 Adkins Newborn animals mount poor immune responses, a condition referred to as neonatal immunodeficiency. For decades it was widely believed that this conditions was at least partially due to the developmentally immature state of newborn T cells. The generally accepted hypothesis was that neonatal T cells were qualitatively different from adult T cells, resulting in deficient T cell mediated responses. However, several recent studies indicate that reduced T cell mediated responses may be caused solely by reduced numbers of T cells in the neonatal animal. This interpretation is difficult to reconcile with the wealth of data showing phenotypic and functional immaturity among the neonatal T cell population. Resolution of the relative importance of neonatal T cell numbers vs function is pivotal for our understanding of the developmental biology of the immune system. This investigator is proposing experiments to determine whether the deficient T cell mediated responses of neonates are due to qualitative or quantitative differences, or both, between newborn and adult T cells. First the relative capacities of newborn and adult T cells to provide help for B cell antibody responses in vivo will be measured. Then the types and amounts of cytokines produced by lymph node T cells in neonates and in adults in response to a primary stimulation will be compared. In neonates, these responses will also be measured when adult antigen presenting cells are provided. These studies will provide a definitive test of the functional capacities of newborn T cells in situ. Although it has been known for a long time that newborn animals have poor immune responses, the reason for this has not been determined. A number of recent experiments do not conform to the accepted hypothesis that this may due to reduced numbers of T cells, The experiments in this proposal will determine the functional capacities of newborn T cells in the immune response and provide a basis for understanding neonatal immunodeficiency. ***
