Comparison of the suppressive effect of thymus cells and the suppression by neonatal application of antigen

The suppressive effect of thymus cells on the agglutinating antibody response in chickens is shown to be antigen‐specific. Experiments reveal that this effect can be seen several weeks after thymus cell transfer, if the respective antigen (A) is given 3 times weekly after transfer. Repeatedly applied high doses of the antigen (A) result in a stronger effect than low antigen doses, and mercaptoethanol‐resistant antibody (IgG) is usually more affected than the total titer (of which IgM is the major contributor). Finally, several weeks after thymus cell transfer, when the response to antigen A is still lower than that of the normal controls, the antibody response to an unrelated antigen B is normal. By these three criteria, as well as by the degree of suppression, the suppressive effect of thymus cells strikingly resembles the phenomenon of antigen‐specific suppression that is seen after antigenic stimulus in the prenatal or early postnatal period. The suppressive effect is already given by thymus cells from 10‐day old donors. As in previous studies, the suppressive activity was significantly diminished in thymus cells from neonatally bursectomized donors. The data indicate that a specifically acting suppressor cell compartment exists which is different from B cells and cooperative or graft‐vs‐host‐active T cells. The results are discussed in light of current concepts of “self‐tolerance”.