Adherence of recombinant pneumococcal surface adhesin A (rPsaA)-coated particles to human nasopharyngeal epithelial cells for the evaluation of anti-PsaA functional antibodies

Pneumococcal surface adhesin A (PsaA) is a pneumococcal vaccine candidate. In this study, we detect functional antibodies to PsaA by using carboxylate-modified fluospheres coated with either recombinant non-lipidated PsaA (rPsaA) or synthetic peptides with relevant epitopes of PsaA. Peptides P1–P3 were derived from phage display sequences; peptides P4–P7 were homologous to rPsaA. P1- and P4-coated fluospheres had similar adherence to Detroit 562 nasopharyngeal cells when compared to rPsaA-coated fluospheres. Homologous and heterologous competitive inhibitions with peptides in solution determined the specificity of the adherence. There was no significant difference (P = 0.25) between the inhibition of adherence of rPsaA- and P4-coated fluospheres. This study indicates that P1 and P4 contain a functional epitope(s) for the adherence of PsaA to nasopharyngeal cells making them suitable targets for the measurement of functional antibodies to PsaA.