Journal of Reproductive Immunology, 3 (198i) 15-27 Elsevier/North-Holland Biomedical Press 15 IMMUNOLOGICAL RESPONSIVENESS OF MATERNAL AND FOETAL LYMPHOCYTES DURING NORMAL PREGNANCY IN THE EWE M. MIYASAKA and P. McCULLAGH Department of Immunology, John Curtin School o f Medical Research, Australian National University, P.O. Box 334, Canberra City, A.C.T. 2601, Australia (Received 22 July 1980; revised 8 September 1980; accepted 10 October 1980) Peripheral blood lymphocytes collected from ewes before and during pregnancy manifested con- stant reactivity to concanavalin A and to paternal and third party peripheral blood lymphocytes. However, in some instances, the reactivity of these maternal cells against lipopolysaccharide and lymphatic lymphocytes from paternal, foetal and third-party donors increased markedly during preg- nancy. Apart from an indication that plasma from some pregnant ewes acquired the capacity to depress lymphocyte reactivity non-specifically, no evidence was obtained to suggest that maternal lymphocyte reactivity observed in vitro did not accurately reflect the capacity of these ceils in the donor ewe. In particular, there was no indication that populations of maternal peripheral blood lymphocytes returning from the gravid uterus had undergone any modification of reactivity against foetal determinants. INTRODUCTION The variety of conflicting observations on the influence of pregnancy on the immuno- logical responsiveness of different species (Solomon, 1971; Beer and BiUingham, 1976) militates against the formulation of any general description of the immunological features of pregnancy. It would in fact be surprising if interspecies differences in such matters as placental structure, duration of gestation and extent of maturation of the offspring at birth did not influence the immunological aspects of pregnancy. The choice of the sheep in the present experiments afforded the advantage that foetal specimens could be col- lected without interruption of pregnancy (Smeaton et al., 1969; Pearson et al., 1976), but introduced difficulties since characterization of inter-parental genetic differences is not at present feasible aiad cell donors identical with either parents or foetus are unobtainable. In the present experiments° assays have been selected for the sequential examination of maternal lymphocytes to monitor bQth specific inter-parental reactivity and other more general parameters of immunological responsiveness. In the absence of any general agreement as to the manner in which maternal immuno- logical responsiveness is modified as a result of pregnancy, the present experiments were intended primarily to demonstrate whether any immunological modifications were detec- table in the pregnant ewe and to determine the extent to which these modifications were reproducible. The mixed lymphocyte reactivity of maternal cells from a group of ewes against paternal, foetal and third-party cells was therefore examined throughout preg- 0165-0378/81/0000-0000/$02.50 © Elsevier/North-Holland Biomedical Press