Evaluation of serum and salivary IgA against pertussis toxin in volunters immunized with the genetically inactivated mutant PT-9K/129G pertussis toxin

Study Objective: To ascertain whether subjects immunized with an acellular pertussis vaccine develop specific IgA antibodies. Design: Prospective study of 29 persons receiving vaccine and placebo (18 and 11 subjects respectively) before and after the administrations. Subjects: Adult volunteers aged 25-58 years. Interventions: Subjects were immunized or received placebo. The vaccine was an acellular pertussis vaccine containing an inactivated pertussis toxin (PT-9K/129G), obtained from a mutant bacterial strain of Bordetella pertussis. Sixteen subjects out of the group of vaccinees and 9 of the placebo group received a further dose one month after the first one. Saliva and blood samples were collected just before and one month after the first administration and 42 days after the second dose. Measurements and Main Results: An ELISA method for the detection of specific IgA antibodies in saliva and sera was used. A statistically significant increase in the titres of specific serum IgA (IgA anti-PT) occurred in vaccinated subjects. The titres were not boosted by the second vaccine dose. No significant rise of secretory IgA anti-PT was observed in saliva after both vaccine and placebo administrations. Conclusions: Although our results need further confirmation and the bactericidal effect of serum IgA is controversial, the demonstration that the mutant PT-9K/129G toxin induces also an increase in specific IgA serum antibodies confirms that the inactivated pertussis toxin has a good immunogenic power.