IFN-gamma as an indicator of successful immunization of goats vaccinated with a killed Cowdria ruminantium vaccine.

Abstract

Cowdria ruminantium-induced production of IFN-gamma was measured by ELISA on a weekly basis during the course of vaccination with killed organisms emulsified in ISA50. Upon challenge, all (3/3) vaccinated animals that gave the lowest IFN-gamma response died of peracute cowdriosis. On the other hand, only one of three animals showing high IFN-gamma responses to vaccination died, but with a delay of 4 days in comparison with naïve controls. Thus, there seems to be a threshold level of IFN-gamma below which the probability for vaccinated animals to survive a lethal challenge is very low. During challenge, a much lower, but still physiologically meaningful production of IFN-gamma was detected using the 24-hour whole blood assay on day 5 after infection in animals controlling the infection. In contrast, IFN-gamma production was absent or negligible in naïve and vaccinated animals that died within 8-10 days after infection. Although these results need to be validated on a larger number of animals, they strongly suggest that IFN-gamma is a useful indicator of protective immunity in animals immunized with killed COWDRIA: