Study of the immune maternal and fetal relationship in humans
We approached the problem of the survival of the fetal semi-allograft in the maternal environment by studying in vitro reactivity of the respective leukocyte populations. Mixed lymphocyte culture (MLC) reactions between parental, related newborn, unrelated newborn, and control cells were performed. The bidirectional MLC revealed weak responses between maternal and related newborn lymphocytes when compared to all other MLC combinations. Similarly, this weak maternal/newborn reaction could be seen in the unidirectional mixed lymphocyte reaction. This hyporeactivity was not due to impaired responses of either the maternal or newborn populations, as they showed normal reactivity with all other populations tested. The removal of TG lymphocytes from the responding (maternal or newborn) population resulted in an increase of reactivity of this population. The magnitude of this increase was specific for the stimulating population in the maternal/newborn cultures. The presence of specific suppressor cells was also confirmed by the irradiation of the stimulating population: The responding population showed an increased reactivity towards the irradiated stimulators when compared to a stimulating population treated with mitomycin C. Maternal and cord plasma both significantly suppressed bi- and unidirectional MLC, without having specific suppressive factors for any of the populations used. The action of the plasmas may be useful in vivo for the diminution of immune processes at the placental level, and may be additive to the more- specific suppressor cell activities described above. Cord lymphocyte competency was evaluated through mitogen blastogenesis, the presence of short-lived suppressor cells, the inducibility of Con A-activated suppressor cells, and the production of, and response to, lymphokines. Cord cells respond adequately, although the specific response is lower than that of adult cells, to all mitogens used: Concanavalin A (Con A), Phytohemagglutinin (PHA), Pokeweed Mitogen (PWM), and Staphage Lysate (SL). Similarly, their capacity for suppression is comparable to, or even better than adults, as evaluated through the presence of short-lived suppressor cells in the cord cell population, and the possibility of induction of Con A-activated suppressor cells in this same population. The production of the lymphokine Blastogenic Factor (BF) was slightly impaired, when compared to adult production, and although adult lymphocytes were capable of responding to neonatal BF, newborn cells were not. Neonatal Lymphocyte Derived Cheraotactic Factor (LDCF) production equaled that of adult cells and neonatal polymorphonuclear leukocytes (PMN) responded to both the adult- and neonatal-derived (LCDF) equally. The results suggest that the cord lymphocyte is essentially immunocompetent, but there may be a delay in maturation of some lymphocyte subpopulations. We suggest that, as both maternal and neonatal lymphocyte populations are immunocompetent, the observed hyporeactivity of maternal/newborn mixed lymphocyte cultures is due to the modulation of the reaction by specific suppressor cells present in both populations.