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INDUCTION OF DELAYED-TYPE HYPERSENSITIVITY TO H-Y IN MICE OF ANY HAPLOTYPE-RESPONDER OR NON-RESPONDER. John Barrington-Leigh, and Thomas G. Wegmann, Department of Immunology, University of Alberta, Edmonton, Alberta, T6G 2H7

• An in vitro system for the induction of delayed-type hypersensitivity (DTH) to major and minor allo-antigens of the mouse, has been applied to the case of H-Y in both responder and classical non-responder haplotypes. In the latter case spleen cells sensitized by sub-cutaneous priming are boosted one week before re-stimulation in culture for six days. The harvested cells are injected directly into the footpads of normal male or female recipients (local transfer assay for DTH). A swelling reaction in male recipients only is easily and reliably measured between 24 and 48 hours after injection. Further appropriate controls demonstrate that the sensitiza- tion is specific for the H-Y product, and that the DTH is mediated by a Lyl + Ly2 + Thy-i + (T D cells) bearing population of cells. These data reject the current discrimination be- tween T D and cytotoxic effector (T c) cells in the mediation of graft rejection. To test this view, DTH-priming protocols have been performed on recipients of fetal heart grafts (iden- tified as male or female prior to grafting) and the rejection times followed by differential electrocardiography. Prelimi- nary results indicate that even classical non-rejector strains are induced by the DTH protocol to reject grafts bearing the H-Y. Further work will specify the cell type responsible for recognition of H-Y on the graft and the initiation of its re- jection (adoptive transfer experiments)•

IN VITRO AND IN VIVO STUDIES ON CELLULAR IMMUNITY DURING MURINE GESTATION AND LACTATION. Phillip Gambel and Frederick

G. Ferguson0 Department of Immunology, University of Alberta, Edmonton, Alberta T6G 2H7 and Laboratory Animal Resources, Pennsylvania State University, University Park, Pennsylvania 16802

This study clearly shows maternal spleen cell alloreactivity is intact but can be diminished when sensitized in situ, indicating the immunosuppressive potential of the maternal environment. Spleen cells from syngeneic (BALB/c x BALB/c) and aliogeneic (BALB/c x C57BI/6J) bred mice respond to in vitro sensitization in the MLR with proliferative and cytotoxic responses comparable to virgin controls. In contrast, cells from pregnant and lactating mice were depressed severely in their cytolytic responses to in vivo immunization with an allogeneic tumor (EL4 lymphoma). In addition, if the in vivo sensitized maternal spleen cells were adoptively immunized in

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irradiated allogeneic recipients, their responses were similar to virgin controls. Suppressor cells were not detected either in nonimmune of in immune maternal spleen cell populations. Decreased maternal immune responses occurred during lactation as well as gestation, suggesting modifying mechanisms are still evident after the fetoplacental unit is expelled. The significance of these regulatory mechanisms on maternal and neonatal resistance under the appropriate immunological stress is unknown.

NATURAL CYTOTOXICITY IN PREGNANT MICE. i. NATURAL KILLERS AT DIFFERENT STAGES OF PREGNANCY AND THEIR RESPONSE TO INTERFERON INDUCER V. Toder, M. Blank and L. Nebel, Department of Embryology and Teratology,Tel-Aviv University Medical School, Tel-Aviv

Like in tumor-host interrelations, pregnancy is characterized by non-rejection of an antigenically different transplant. Accordingly, it was of interest to study one of the factors of natural resistance against cancer, natural killers (NK) at dif- ferent stages of pregnancy. Splenocytes were obtained from vir- gin, as well as from pregnant Balb/c mice at first, second and third trimesters of gestation, and purified by Ficoll-Hypaque procedure. NK activity was measured by 4h-51CR release using YAC-I cells as targets. There was no difference between NK ac- tivity of normal and first-trimester pregnant Balb/c mice. Con- versely, the level of natural cytotoxicity on days 12-13 of pregnancy was significantly higher. At the end of gestation the number of NK cells decreased to a level even lower than that of virgin mice. The NK activity of lymphocytes from normal and pregnant mice was markedly enhanced by pretreatment with interferon inducer- poIy I:C (24 h, in vivo). However, when lymphocytes were taken from mice on 12-13 days of pregnancy, the extent of stimulation of NK activity by poly I:C was significantly lower than that ob- tained in virgin mice. One of the possible explanations of this observation could be that "immature" subpopulation of NK at this stage of gestation is already stimulated by one of the markers of pregnancy.

NATURAL CYTOTOXICITY IN PREGNANT MICE. 2. THE INFLUENCE OF PREGNANT SERUM AND ALPHA-FETOPROTEIN ON NATURAL KILLER ACTIVITY M. Blank, V. Toder and L. Nebel, Department of Embryology and Teratology, Tel-Aviv University Medical School, Tel-Aviv

We recently reported dataabout natural killer (NK) activity at different stages of gestation in mice. The level of natural cy-