The induction and control of delayed type hypersensitivity reactions induced in chickens by infectious bronchitis...

Infectious bronchitis virus (IBV) was shown to induce delayed type hypersensitivity (DTH) reactions in the wattle, or to inhibit migration in a macrophage migration inhibition test (MIT) in sensitised birds. The magnitude of the reactions was related to the sensitising dose of the virus. The optimal dose for the cold attenuated A3-IBV was 10(3 .5) EID50, higher doses giving lower responses. Birds given a similar dose of T-IBV had negative DTH reactions, but the spleen non-adherent lymphocytes from these unreactive birds, and also birds sensitised with 10(6.5) EID50 of A3 virus, on transfer to allogeneic birds sensitised with the optimal dose of A3 virus (10(3.5) EID50) suppressed their DTH response. Treatment of birds with dexamethasone, 6-mercaptopurine, or cyclophosphamide, before vaccination with the dose of A3 virus which suppressed the DTH reaction (10(6.5)EID50), abrogated the DTH unresponsiveness. Drug treatment before optimal sensitisation (10(3 .5) EID50) did not increase the magnitude of the DTH response, but prolonged the time over which the DTH response could be elicited. MIT results mirrored the DTH responses. The antigens elicitating the response, or the transferred cells suppressing the response, derived from chickens immunised with any of the three strains of IBV studied had similar effects on DTH and MIT responses in A3 virus sensitised birds.