Antibody response to pertussis toxin and filamentous haemagglutinin in NIH mice immunized with the International Standard for Pertussis Vaccine.

The antibody response to filamentous haemagglutinin and pertussis toxin was studied in N:NIH mice vaccinated according to the WHO recommendations for potency test with the International Standard for Pertussis Vaccine (ISPV). Some of the vaccinated animals were challenged intracerebrally on day 14. All animals, whether challenged or not, were bled on days 7, 14, 21, 28 and 35 after immunization. The relationship between anti-PT and anti-FHA antibodies measured by ELISA and protection from intracerebral challenge was examined. All those mice with anti-PT titres on day 14 higher than 43 EU/ml survived challenge. No relationship was found between anti-FHA antibodies and survival. Anti-PT titres on day 14 below 43 EU/ml were related to the days of survival after challenge; a linear regression curve of y = 13 + 2.4x, with a correlation coefficient r = 0.61 was found. Anti-PT antibodies seem to play an important role in protection when animals are challenged intracerebrally, as is the case in the standard potency test for pertussis vaccine.