The processing of T-lymphocytes by the but of the suckling neonate

The suggestion that intact effector lymphocytes can pass from maternal milk through the gut wall of the suckling neonate has been tested directly by labelling alloantigen-stimulated T cells in vitro with [125I]iododeoxyuridine and following their fate after intraoral administration to newborn mice by whole body gamma counting. The cells were rapidly lost from the animal when compared to cells injected intraperitoneally, and at a rate indistinguishable from cells deliberately killed and given intraorally. If the alloantigen used to stimulate the T cells in vitro was shared by the neonate, the T cells were lost even faster. It was also found that highly lethal labelled leukemia cells behaved in a similar fashion and did not cause excess mortality if given intraorally. These results suggest that few, if any, lymphocytes traverse the neonatal gut wall and indicate that subcellular fractions may be responsible for maternal to neonatal transfer of immunological effector functions.