PRIMARY ANTIBODY RESPONSE IN ORGAN CULTURES

Specific antibody formation has been elicited in vitro following antigenic stimulation by either sheep (in a total of 472 of 875 cultures) or chick erythrocytes (in 65 of 135 cultures tested). The response was manifested by mouse spleen and lymph node explants whereas thymus cultures were inactive. The reaction has been characterized as a primary immune response in view of its kinetics as compared to defined primary and secondary responses, the effect of 2-mercaptoethanol on the antibodies formed, its subject to puromycin inhibition and its sensitivity to X-irradiation. Histological studies revealed preservation of the lymphoid cell populations throughout the entire experimental period

GRAFT-VS.-HOST REACTION IN TISSUE CULTURE

The primary purpose of this study has been to validate the in vitro graft-vs.-host reaction as an experimental system. Time-dose studies have been presented for cells obtained from spleen, thymus, cortisone-treated thymus, inguinal lymph node, mesenteric lymph node, thoracic duct, and bone marrow cells. Both the degree of splenomegaly and the onset of spleen enlargement were found to be dependent on the number and source of cells tested. The effect of several immunosuppressive agents was examined. Amantadine was found to suppress completely the graft-vs.-host reaction in vitro when present at a concentration of 75 µg/ml. Pretreatment of effector cells with mitomycin C prevented their subsequent ability to cause a graft-vs.-host reaction. The effect of X irradiation on immunocompetence of spleen cells in vitro paralleled the known effect of irradiation on in vivo immunocompetence. Preimmunization did not increase the number or effectiveness of immunocompetent cells when measured under standard in vitro conditions. Preimmunization did, however, permit persistence of immunocompetence after immunosuppressive doses of X irradiation. Studies using congenic lines, moreover, indicated that the preimmunization effect could be demonstrated in strain combinations differing only in factors determined by the H-2 complex of genes. A weak graft-vs.-host reaction could be detected in strain combinations not involving differences at the H-2 locus. The potential of the in vitro graft-vs.-host reaction as a highly reproducible, quantifiable, internally controlled, and experimentally accessible system for study of such critical problems as cell differentiation and cell interactions is discussed

Defects in Thymocyte Differentiation and Thymocyte- Stromal Interactions in the Trisomy 16 Mouse

We have examined fetal thymic development in the trisomy 16 (Ts16) mouse, which is considered to be a model for human trisomy 21, or Down Syndrome. The Ts16 thymus contains 10 to 20% of the number of lymphocytes found in a normal thymus at a comparable stage. Expression of thymocyte differentiation markers (Thy-1, CD5, CD8, CD4, CD3, and HSA) is severely affected in Ts16 fetuses aged 14–18 gestational days. When thymuses from 14-day Ts16 mice were cultured in vitro, these markers eventually reached levels of expression comparable to those seen in normal thymuses in culture. On the other hand, expression of CD44 appears to be unaffected in Ts16 thymuses in vivo, but declines in vitro relative to normal thymuses. Reconstitution of depleted thymic stroma with thymocytes showed evidence of defects in both developmental compartments

INDUCTION OF TOLERANCE TO SHEEP RED BLOOD CELLS

Adult mice injected with a sheep red blood cell hemolysate supernatant fraction were found to have a severely reduced responsiveness to subsequent immunization with sheep red blood cells. The induced unresponsiveness was found to be specific, as tested by reciprocal experiments involving horse and sheep erythrocyte preparations. The tolerogenic material did not appear to be immunogenic