Strategy to create chimeric proteins derived from functional adhesin regions of Mycoplasma pneumoniae for vaccine...

The cell wall-less bacterium Mycoplasma pneumoniae is one of the most common agents of respiratory tract diseases in humans. Adhesin-mediated binding of the bacteria to host cells is a crucial step in colonization and subsequent pathogenesis. For the first time, we expressed 16 recombinant proteins covering almost the whole major adhesin P1 and the adherence-associated protein P30 to characterize these proteins immunologically and functionally. We describe a new in vitro assay using several human cell lines in combination with fluorescence-activated cell sorting analysis to screen antisera raised against the recombinant proteins quantitatively for adherence inhibition activity. The protein derived from the nearly C-terminal part of the P1 adhesin (amino acids [aa] 1288 to 1518) and the protein P30 (aa 17 to 274) especially showed prominent immunoreactivity with sera from M. pneumoniae-immunized guinea pigs as well as with M. pneumoniae-positive patient sera. We demonstrate that the same protein regions are involved in mediating cytadherence since antibodies against these adhesin regions decrease mycoplasma adhesion to human cells significantly. For further vaccine studies, we optimized the immunogenic and adherence-mediating properties of the antigen by combining both the P1 and the P30 regions in a novel chimeric protein. Antibodies against this protein show an increased reduction of M. pneumoniae adherence to human bronchial epithelial cells by 95%, which is comparable to results with polyspecific anti-M. pneumoniae animal serum. Our strategy results in a promising defined antigen candidate for reducing or even preventing M. pneumoniae colonization of the respiratory tract in future vaccination studies.