Partial suppression of antibody formation in neonatally induced tolerance to HSA as observed during immunization at 6 weeks of age or at a later time, is caused mainly by a rapid escape from tolerance. The following findings support this view: 1. After immunization at 4 weeks of age with a larger dose of HSA, which elicits detectable circulating antibody formation in all control birds, anti-HSA antibodies cannot be demonstrated in a large majority of tolerant chickens. 2. Surgical bursectomy performed in tolerant birds on the day of hatching or 7 or 11 days after hatching increases considerably the degree of suppression of anti-HSA antibody formation and slows down the return of reactivity to HSA. These findings suggest that new immunocompetent cells originating in the bursa are responsible for escape from tolerance in this experimental system. The existence of suppressor cells in birds tolerant to HSA was not demonstrated by the transfers of spleen cell mixtures from immune and tolerant donors to young, irradiated recipients.

Animals↗

PubMed1976

The role of bursa of Fabricius and thymus in antibody-mediated allograft rejection in ducks.

Duck immune sera that are capable of destroying the tolerated skin allografts require the presence of functional host's lymphoid cells for a successful course of the rejection reaction. The effective sera are not able to destroy the grafts in birds surgically bursectomized or thymectomized at hatching. This deficiency can be repaired by thymic, not bursal, implants in bursectomized or thymectomized graft hosts. Similarly, measurements of the radioactivity after application of 125I-labelled gamma globulin to allografted or autografted ducklings confirm a major role of the bursa of Fabricius and thymus in the destruction of the tolerated skin allografts by immune serum.

Animals↗

PubMed1975

Different effects of bacterial lipopolysaccharide on neonatal immunological tolerance to HSA in rabbits and chickens.

Addition of bacterial lipopolysaccharide to HSA during repeated immunization of rabbits neonatally rendered tolerant to HSA led to anti-HSA antibody formation in 4 out of 5 animals. In all 6 tolerant animals immunized with HSA alone tolerance persisted after cessation of the immunization series, as shown by non-immune elimination of 125I-HSA. On the other hand, immunization with HSA together with different doses of LPS did not increase anti-HSA antibody levels in tolerant and control chickens.

Animals↗

PubMed1974