Ontogeny of Lymphocyte Functions during Embryonic Life of the Rabbit

Abstract Various immunologic functions of rabbit lymphocytes were studied during ontogeny. Liver cells of 17-day-old fetuses responded to concanavalin A and only after 22 days responded to phytohemagglutinin. The thymus cells of 22-day-old fetuses and the spleen cells of 29-day-old fetuses were stimulated by concanavalin A but not by phytohemagglutinin. The response to phytohemagglutinin in thymus and spleen cells was obtianed only after the birth. These results suggest that, in the rabbit, there are different subsets of T lymphocytes that respond either to concanavalin A or phytohemagglutinin. An alternative hypothesis is that the receptor for concanavalin A and the receptor for phytohemagglutinin appear on the same cells at different stages of the development. No stimulation of fetal liver was obtained with B mitogens, i.e., Nocardia water soluble mitogen (NWSM) and antisera against allotypes of the b series whereas neonatal spleen cells were stimulated. These results indicate that the ability of lymphocytes to respond to a nonspecific rabbit B cell mitogen, namely NWSM, and to a specific rabbit B cell mitogen, namely anti-allotypic antibody, matured only in peripheral lymphoid organs, such as spleen, in spite of the fact that these two mitogens stimulate different subsets of B lymphocytes. Significant synthesis of immunoglobulins by liver cells was obtained in 22-day-old fetuses. The liver cells possessed Fc receptors after 17 days of gestation and a significant antibody dependent cell-mediated cytotoxicity after 22 days. Both functions decreased after birth in these cells. These results showed a sequential acquisition of immunologic functions of rabbit lymphocytes.