CD40 Ligand Potentiates Immunogenecity of Mycoplasma pneumoniae Subunit Vaccine Candidate in a Murine Model

Mycoplasma hyopneumoniae (Mhp) infection severely affects the daily weight gain and feed-to-meat ratio of pigs, while secondary infections with other pathogens can further lead to increased mortality, causing significant economic losses to the pig industry. CD40L is a molecular adjuvant that enhances the cellular and humoral immune responses to vaccines. In this study, the CD40L peptide was fused to the C-terminus of the chimeric P97R1P46P42 protein by genetic engineering using the pFastBac Dual vector. The recombinant chimeric protein P97R1P46P42 and its fusion P97R1P46P42-CD40L were expressed in Sf9 cells and purified. Mice were immunized with P97R1P46P42 or its fusion protein. Seppic ISA 201 emulsified protein, conventional Mhp vaccine and PBS control groups were included. Immunogenecity was assessed by specific IgG antibody response, splenic lymphocyte proliferation, and cytokine IL-4 and IFN-γ levels. We found that CD40L fusion significantly enhanced specific antibody response, lymphocyte proliferation and IL-4 level in the immunized mouse sera as compared to the P97R1P46P42 or conventional vaccine group. This study provides clear evidence that CD40L potentiates the humoral and cellular immune responses to the Mhp chimeric protein P97R1P46P42 in the mouse model. This CD40L-fused chimeric protein could be a MPS subunit vaccine candidate to be tested for its efficacy in pigs in response to challenges with pathogenic Mycoplasma hyopneumoniae strain(s).