Bibliography: leaves 170-206.vi, 206 leaves : ill. (some col.) ; 30 cm.In T-dependent antibody responses, costimulator molecules provide contact-medited signals during interactions between T cells and B cells that regulate lymphocyte activation. This study investigated the hypothesis that costimulator molecules are differentially expressed on lymphocytes from neonates and young children compared with adults, contributing to limitations of T-dependent antibody responses in early life. Results suggest that lymphocytes from young children should be able to deliver and respond to costimulatory signals. The differences in lymphocyte expression of these costimulator molecules in young children are unlikely to fully account for limitations in humoral immunity in early life, and may even represent a specialised adaptation for this stage of immune development.Thesis (Ph.D.)--University of Adelaide, Dept. of Paediatrics, 200