CORRELATION OF CIRCULATING ANTIBODY AND CELLULAR-IMMUNITY WITH RESISTANCE AGAINST CRYPTOSPORIDIUM-BAILEYI IN BROILER-CHICKENS

The correlation of circulating antibody and cell-mediated immunity (CM I) with resistance to Cryptosporidium baileyi was studied using hormon al and chemical bursectomy in the one experiment and cyclosporin A in a second experiment. In Expt. 1, there was no correlation between anti body (confirmed by enzyme-linked immunosorbent assay) and resistance t o infection as measured by body weight, gross lesions, morbidity,and m ortality. Bursectomy altered antibody production, but not CMI, as meas ured by the delayed-type hypersensitivity skin reaction. In Expt. 2, c yclosporin A reduced CMI, but not antibody production. Chicks treated with cyclosporin A were more susceptible to C baileyi (more severe res piratory disease) than untreated controls. Results suggested that CMI is more important in resistance to C baileyi than circulating antibody .