Persistence of immunological tolerance to HSA in chickens after cell transfer to immunosuppressed hosts

The nature of immunological tolerance to HSA in chickens was analyzed by means of spleen cell transfers to 3-day-old, cyclophosphamide-treated, syngeneic recipients. The cell donors were 2-week-old tolerant or control chickens. The primary challenge with HSA was done 26 days after cell transfer. Spleen cells from both control and tolerant donors restored the immunoglobulin levels and the ability to produce antibodies to SRBC to normal. While cells from normal donors also reconstituted the ability to form antibodies to HSA, the recipients of cells from tolerant donors either did not form detectable amounts or formed only low titres of these antibodies. The ability of cells from normal donors to respond by anti-HSA antibody formation, when transferred together with cells from tolerant donors, was neither suppressed nor decreased. Thus, tolerance to HSA in chickens was not reversible and the existence of an active immune process, causing its duration, could not be demonstrated.