The role of the thymus for maturation of transferred bursa cells into immunocompetent B cells in chickens treated with cyclophosphamide.

Chickens injected with cyclophosphamide and X-ray irradiated in the newly hatched period were immunized with a mixture of sheep red blood cells, Brucella abortus and Salmonella pullorum at 4, 5 and 6 weeks of age, and were examined for serum antibody titres, serum immunoglobulin concentration and bursal and splenic structures at 7 weeks of age. The neonatal treatments suppressed completely or almost completely antibody responses, immunoglobulin production and formation of bursal follicles and splenic germinal centres. The transplantation of bursa cells into the chickens immunologically impaired by the treatments restored these functions and structures. In contrast, the transfer of bursa cells into chickens thymectomized, cyclophosphamide-treated and X-ray irradiated did not result in efficient restoration of the bursa-dependent immune system; 10-day-old bursa cells hardly restore the system, although 4-week-old bursa cells did so slightly. The chickens thymectomized, cyclophosphamide-treated, X-ray irradiated and repopulated with 10-day-old bursa cells were examined for the existence of functional B cells with the use of a syngeneic cell transfer system. The experiments verified that immunocompetent B cells had not developed in the chickens thus treated.