EFFECTS OF EMBRYONIC BURSECTOMY AND INOVO ADMINISTRATION OF HIGHLY DILUTED BURSIN ON ADRENOCORTICOTROPIC AND IMMUNE-RESPONSES OF CHICKENS

Chick embryos were surgically bursectomized (BX) at 80 h of incubation and then given saline (BX + S) or bursin (BX + B) in ovo. BX + S, BX + B, and sham-operated birds (group N) were repeatedly immunized with porcine thyroglobulin (Tg) at 21, 30 and 39 days of age. Plasma ACTH a nd corticosterone (CORT) levels and serum titres of specific antibodie s against Tg were measured on days 20, 29, 38 and 47. Initial (day 20) hormone levels were low in all groups. The immunized N group had high concentrations of ACTH and CORT but not the BX + S birds. These level s were not restored in the BX + B group treated with 100 mug of bursin , but were restored almost completely in BX + B birds given 100 pg or 100 fg or a 5 x 10(-27) g dilution of bursin. Specific antibodies to T g remained at very low background levels in the BX + S chickens in spi te of repeated stimulations, whereas the N group produced a strong spe cific antibody response. In ovo administration of low doses of bursin (100 fg, 100 pg, 5 x 10(-27) g) also led to high antibody production a fter repeated immunization. These results support the hypothesis that bursal influences the functional maturation of the adrenocorticotropic axis and that production of specific antibodies operates, at least pa rtly, through bursin-dependent mechanisms. They also demonstrate that a bursin-specific informing structure remains in the highest diluted s olutions of bursin.