Relationship Between Antibody and Immunity in Chickens Vaccinated With Newcastle Disease Living Vaccine (B1 Strain)

Hemagglutination Inhibition (HI) and Virus Neutralization (VN) test are widely used as antibody detection methods in Newcastle disease. The evaluation of the tests as an index of immune status has not yet been established, particularly HI test. The present paper deals with the correlation between antibody and protection against challenge and the susceptibility of antibody against 2-mercaptoethanol (2-ME).The correlation was obtained between the VN titer and the protection rate in chicks at 4 days of age, vaccinated with B1 strain of the virus and challenged 2 or 5 weeks after vaccination. The similar relationship was observed between HI titer and the protection rate, when challenged 5 weeks, but not, when challenged 2 weeks.The ratios of HI titer to VN titer were different at the stage of immunization; the ratio was smaller in sera collected 2 weeks after vaccination than that of 5 week ones. This findings suggested that the qualitative change of antibody took place.Then the 2-mercaptoethanol susceptibility of antibody was tested. The antibody sensitive to 2-ME appeared in serum during the first to second week after vaccination and was replaced with the resistant one in the following weeks.The appearance of the 2-ME sensitive HI antibody seems to be a reason why the HI titer did not correlated to the protection rate in 2-week-challenge case.