Cell-mediated immune response of chickens to Newcastle disease vaccines.

The leukocyte migration inhibition (LMI) test was used to demonstrate cell-mediated immunity (CMI) and its relationship to immunoglobulin production, as assessed by the haemagglutination inhibition (HI) test, in chickens vaccinated with various Newcastle disease (ND) vaccines. Highest CMI levels were demonstrated in 3 or 7-week-old birds which had been vaccinated with live vaccine followed by an oil adjuvant vaccine 6 weeks later. There was no close correlation between LMI values and HI titres, LMI appearing earlier after primary vaccination and failing to give the strong secondary response seen in HI titres after challenge with live virus. There was a secondary CMI response after revaccination with oil adjuvant vaccine but this was not as strong as the humoral response.