Helper cell function of human fetal thymocytes

Immunology of pregnancy: towards a unifying hypothesis

The variable findings of hormonal-immunoregulation and the variable cellular and humoral immune responses in pregnancy have been considered in relationship to the physiological response. From such considerations it appears that the peripheral blood lymphocyte/leukocyte response in pregnancy is not important, but rather the local uterine immune response at implantation and throughout pregnancy. It is proposed, and evidence is presented, that a normal allogeneic immune response is initiated at the time of implantation of the blastocyst. This immune response regulates the invasive nature of the trophoblast and initiates the first stage of parturition. The initiation and maintenance of this immune response is based on an interplay between maternal and paternal HLA and trophoblast antigens. In the case of HLA-incompatible donor-recipient blastocyst transplants, a more pivotal role for immunoregulation by trophoblast antigens is proposed. This is because it is considered that the local uterine immune response suppresses the expression of allogeneic HLA. This concept is further developed in terms of haploid HLA suppression on maternal and fetal lymphocytes that cross the placenta. This is considered to allow the interaction of these lymphocytes with each other and explains maternal transfer of cell-mediated immunity.

Inhibition of human lymphocyte activation by wheat germ agglutinin: a model for saccharide-specific suppressor factors

The suppressive effect of wheat germ agglutinin (WGA) on lectin-stimulated blastogenesis and immunoglobulin production was studied. Addition of WGA at 10 micrograms/ml inhibited phytohemagglutinin (PHA)-, concanavalin-A (Con-A)-, and pokeweed mitogen (PWM)-induced mitogenic responses by 70-80%. PWM-driven immunoglobulin synthesis was suppressed by 45% with WGA. The inhibitory effects of WGA were not due to cell death or to interference with lectin binding at the cell surface. Inhibition was dependent on the presence of WGA in the cell culture during the first 24 hr of mitogen exposure and was observed in cultures of both monocyte-depleted peripheral blood mononuclear cells as well as T-cell-enriched populations. WGA-induced inhibition of blastogenesis was blocked by the addition of N-acetylglucosamine (GluNAc) which prevents WGA binding to the cell surface. WGA was found to mimic the suppressive effect of a soluble immune suppressor supernatant (SISS) derived from Con-A-activated mononuclear cell cultures. PHA responses were inhibited by 80 and 95% with SISS and WGA, respectively. The inhibition by both WGA and SISS was totally reversed with addition of GluNAc. Furthermore, WGA and SISS demonstrated competition for the same cell surface receptor site. WGA may therefore be useful as an in vitro model of a saccharide-specific, biologically relevant, soluble mediator for the investigation of mechanisms of immunologic suppression.

The ontogeny of immunological receptors in the thymus

Receptors for sheep erythrocytes, for the Fc part of IgG (Fc gamma R) and IgM (Fc mu R), and for components of activated human complement C3 (C3bR and C3dR) in thymus tissue from fetuses, infants and children were studied using haemadsorption to cryostat sections in a closed chamber. Sheep erythrocytes (SE) did not adhere to sections of thymus from fetuses at 10-11 weeks of gestation, adhered weakly between 14 and 20 weeks, while they adhered in a dense monolayer in older fetuses, in infants and in children, denser in the cortex than in the medulla. Ox erythrocytes (OE), sensitized with IgG to demonstrate Fc gamma R, adhered focally to both cortical and medullary areas. The adherence was more pronounced to the sections of fetal thymus than to the sections from infants and children. OE, sensitized with IgM to demonstrate Fc mu R, adhered focally to all thymus tissue sections, preferentially to the cortex. The adherence was most pronounced in fetal thymus. SE, sensitized with IgM and coated with complement, adhered to sections of fetal thymus, but the density decreased markedly during fetal life. Indicator cells demonstrating C3bR adhered focally also to sections from infants and children, while indicator cells demonstrating C3dR did not adhere to sections from individuals older than 38 weeks of gestation. Indicator cells demonstrating C3bR and C3dR adhered both to cortex and medulla.