A vaccine based on a mutant transferrin binding protein B of Haemophilus parasuis induces a strong T-helper 2 response and bacterial clearance after experimental infection

Abstract

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 10(8) 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.

New insights about functional and cross-reactive properties of antibodies generated against recombinant TbpBs of Haemophilus parasuis

“…The importance of Tf receptors for survival on the mucosal surface 11 , 25 makes them potential targets to intercept H. parasuis at the colonization stage, particularly if antigens capable of inducing a broadly cross-protective response are developed. The experimental challenge model for H. parasuis infection 12 , 13 , 17 , 18 involves direct intratracheal administration of the bacteria and thus addresses the two subsequent phases of pathogenesis after colonization. As a consequence, it is not readily apparent whether the enhanced protection induced by a non-binding mutant of TbpB 17 and the lack of protection observed with the individual lobes (Fig.…”

“…parasuis 17 . Follow up experiments suggested that the primary mechanism for superior protection induced by the mutant TbpB was a stronger T helper 2 response 18 . Analysis of the sequence and structural diversity of TbpBs from H. parasuis, A. pleuropneumoniae and A. suis revealed that this diversity was not associated with geographic region or species and that immunization with intact TbpB generated a substantially greater cross-reactive antibody response compared to the N-lobe, correlating with relative sequence and structural diversity 19 .…”

The amino acid selected for generating mutant TbpB antigens defective in binding transferrin can compromise the in vivo protective capacity

“…One of the engineered mutant TbpBs, Y167A, had a 300-fold reduction in binding affinity relative to native TbpB, and induced a more protective immune response than native TbpB against infection by H. parasuis in colostrum-deprived pigs 18 . This vaccine provided complete protection against infection and was shown to induce a strong T helper 2 response 19 , a high percentage of B cells in the peripheral blood after immunization 18 and antibody with wide cross-reactivity against different virulent strains of H. parasuis 20 .…”

Mutagenesis of the Loop 3 α-Helix of Neisseria gonorrhoeae TdfJ Inhibits S100A7 Binding and Utilization

“…A few recent studies have focused on identifying mutated forms of bacterial structures that are unable to bind the host ligands that are recognized by their wild-type counterparts, acting on the hypothesis that a bound host factor may dampen the immune recognition of said bacterial target. Such studies by Frandoloso et al and Martínez-Martínez et al ( 55 , 56 ) mutagenized the TbpB protein found in the pig pathogen Haemophilus parasuis and demonstrated that a transferrin-binding-defective mutant, which retained a wild-type-like conformation, conferred superior protection against bacterial challenge compared to WT TbpB and also elicited more robust B- and T-cell responses. Beernink et al similarly generated nonbinding mutants of meningococcal factor H-binding protein (fHbp) and found that upon immunizing factor H transgenic mice, a nonbinding mutant elicited more bactericidal antibodies and more factor H-blocking antibodies than what was seen for WT fHbp ( 57 ).…”