SPECIFIC ABOLITION REVERSAL OF PITUITARY-ADRENAL ACTIVITY AND CONTROLOF THE HUMORAL IMMUNITY IN BURSECTOMIZED CHICKENS THROUGH HIGHLY DILUTE BURSIN

We replicated and ascertained our previous data demonstrating that ver y dilute bursin (Lys-His-Gly-NH2) effectively and specifically induces complete restoration of both pituitary-adrenal responsiveness and hum oral immunity in bursa-lacking chickens sensitized to porcine thyroglo bulin (Tg); furthermore, we demonstrated that very dilute bursin is al so a specific ontogenic organizer of the circadian rhythms of pituitar y-adrenal hormones. In chickens bursectomized as early as 4-day-old em bryos, pituitary (corticotrophin: ACTH), adrenal (corticosterone: CORT ) and specific antibody (IgG) responses to immunization against porcin e Tg were suppressed: in bursa-lacking chickens, the plasma levels of ACTH and CORT, as well as the serum titres of specific IgG remained st eadily low at baseline levels (38 +/- 5 pg/ml, 4 +/- 0.8 ng/ml and 30 +/-2 respectively), unlike their bursa-intact counterparts whose ACTH, CORT and IgG levels increased by 6, 3 and 3000 respectively. Furtherm ore the circadian rhythms of plasma ACTH and CORT were abolished: in b ursa-intact chickens, peak levels were observed during the scotophase (100 +/- 4 pg/ml and 9 +/- 0.6 ng/ml respectively), while trout values occurred during the photophase (27 +/- 2 pg/ml and 3 +/- 0.3 ng/ ml r espectively); in bursa-lacking chickens, the levels of the pituitary-a drenal hormones did not vary significantly between the day and night, Conversely, when administered in ovo at the age of 6 and 9 days to bur sa-lacking embryos, very dilute bursin (100 fg or 5 x 10(-27) g), but not a control tripeptide without known biological activity (Trp-Leu-Le u-NH2), specifically cancelled the aforementioned alterations. Evidenc e was also presented that the endocrine response of bursa-intact chick ens sensitized to porcine Tg is linked to the immunization phenomenon: bursa-intact chickens sensitized to either keyhole limpet hemocyanin (KLH) or porcine Tg exhibited similar profiles of CORT and IgG respons es. These findings confirm the existence of a regulatory loop between the bursa Fabricii, pituitary-adrenal axis and immune system, specific ally mediated by discrete amounts of the bursa-derived signal termed b ursin.