We plan to investigate the time sequences involved in the structural as well as functional development of the secretory immune system. Rat fetuses and neonates will be used. Human fetal tissue, when available will also be used for comparison with the animal studies. The structures under study are Peyer's patches, M-cells, plasma cells, intestinal epithelial cells, and liver cells. Using immunocytochemistry and electron microscopic autoradiography, we will determine when the various components of the secretory immune system become operational. Considerable emphasis will be placed on not only antigen processing and antibody production, but on the development of subcellular organelle relationships which are needed to transport antibodies from the plasma into secretions. Plasma membrane, Immunoglobulin A (IgA) receptor, secretory component (SC), endocytic vesicles and microtubules are vital to immunoglobulin transport. Studies in adult liver demonstrate that dynamically functioning microtubules and not simply microtubule structure are necessary for IgA secretion. We will apply the same type of approach to study the development of tubulin dynamics and microtubule-vesicle interactions in fetuses and neonates. We discovered that in the adult rat, lymphocytes which """"""""home"""""""" to the liver following an intraduodenal priming injection of antigen are apparently the only cells which participate in the early secretory immune response. We have developed a technique for isolating these cells from the liver to study their structural and functional characteristics. These latter studies require the use of monoclonal antibodies and cell sorting. The surface characteristics of adult lymphocytes will be compared to cells which home to the liver from the yolk sac during fetal development. Following the accumulation of sufficient data on the developing secretory immune system under physiological conditions, we will embark on the second portion of this project, namely what factors influence its maturation. Previous work by ourselves and others have clearly demonstrated that several polypeptide hormones play a major role in maturation of the key cells under consideration in liver and intestine. These hormones, insulin, thyroxin and epidermal growth factor will be administered to intact fetuses, neonates or isolated cells (liver) to determine the role, if any, on maturation of the secretory immune system with and without antigen presentation via the amniotic fluid.
