A recombinant chimaeric
protein containing three Mycoplasma hyopneumoniae
antigens (C-terminal portion of P97,
heat shock protein P42, and NrdF) fused to an adjuvant, the B subunit of heat-labile
enterotoxin of Escherichia coli (LTB), was used to immunize pigs against enzootic
pneumonia. The systemic and local immune responses, as well as the efficacy of the chimaeric
protein in inducing protection against experimental M. hyopneumoniae
infection were evaluated. In total, 60 male piglets, purchased from a M. hyopneumoniae-free herd, at 4 weeks of age were randomly allocated to six different experimental groups of 10 animals each: recombinant chimaeric
protein by intramuscular (IM) (1) or intranasal (IN) (2) administration, commercial
bacterin by IM administration (3), and the adjuvant LTB by IM (4, control group A) or IN (5, control group B) administration. All groups were immunized at 24 and 38 days of age and challenged at 52 days of age. The sixth group that was not challenged was used as the negative control (IN [n=5] or IM [n=5] administration of the LTB adjuvant). Compared with the non-challenged group, administration of the chimaeric
protein induced significant (P<0.05)
IgG and
IgA responses against all individual
antigens present in the chimaera, but it could not confer a significant protection against M. hyopneumoniae
infection in pigs. This lack of effectiveness points towards the need for further studies to improve the efficacy of this subunit-based
vaccine approach.