Cell mediated and humoral immune response of chickens to live infectious bronchitis vaccines

A lymphocyte transformation microassay was used to study cell-mediated immune (CMI) responses in chickens following inoculation with live infectious bronchitis virus vaccines H 120 and H 52 and challenge with Massachusetts-41 (M-41). Humoral immunity was monitored for comparison, using haemagglutination inhibition (HI) microassay. Specific stimulation of infectious bronchitis virus sensitised lymphocytes was demonstrated by their lack of response to Mycoplasma synoviae and Newcastle disease virus antigens. Positive infectious bronchitis virus stimulation indices appeared before HI titres and ranged from 2.0 to 7.1 over a period of five to 33 days after primary vaccination with H 120. Revaccination with H 52 produced a strong secondary HI response and a relatively weak CMI response. Challenge of vaccinated and revaccinated birds also resulted in strong HI and weaker CMI secondary responses but the more pronounced CMI responses were in the revaccinated-challenged group. There was no correlation between CMI and HI antibody production but a negative correlation was demonstrated between peak CMI responses after vaccination and severity of clinical symptoms after subsequent challenge.