This study aimed to characterize the type of immune response induced by an experimental vaccine based on a mutant
Haemophilus parasuis transferrin binding protein (Tbp) B (Y167A) defective in its ability to bind porcine transferrin.
Clinical and pathological signs, bacterial clearance, antibody response and the cytokine profile in alveolar macrophages
and spleen after the vaccination and challenge of twenty-two colostrum-deprived pigs with 108 CFU of H. parasuis were
analysed. Pigs vaccinated with Y167A were compared to those vaccinated with native TbpB (nTbpB), those treated with
a commercial bacterin (CB) against Glässer's disease, those unvaccinated challenged (CH) and those unvaccinated unchallenged
(UNCH) pigs. The rectal temperatures of Y167A pigs resembled those of UNCH pigs and were significantly
lower than those of the nTbpB, CB and CH animals. A major reduction in pathological changes of the challenged pigs
was observed in the Y167A group. H. parasuis was cleared from 88.9% of the samples from Y167A pigs versus 60.0%
and 55.6% from those of the CB and nTbpB groups, respectively. The antibody response elicited by Y167A by ELISA
was notably higher than that observed for nTbpB and CB pigs and was capable of preventing the expression and secretion
of IL-8. The expression of IL-4 and IL-5, which were associated with the specific antibody levels, suggests that the main
mechanism of protection conferred by Y167A vaccine is based on a strong T-helper 2 response
