Antigenicity in mice of a recombinant <i>Neisseria gonorrhoeae</i> MafA 2/3 protein

There are no prophylactic vaccines for preventing the disease gonorrhea, caused by sexually transmitted infection with the Gram-negative pathogen <i>Neisseria gonorrhoeae</i>. In this study, we examined the antigenicity in mice of a recombinant rMafA 2/3 outer membrane protein (OMP). Mice were immunized with rMafA 2/3 with different adjuvants and delivery vehicles, which induced high levels of antibody that recognized the MafA 2/3 protein in i) antigen and OM-ELISA, ii) OM-western blots and iii) on whole bacteria examined with flow cytometry. Antisera to rMafA 2/3 in liposomes with monophosphoryl lipid A (MPLA) and with Zwittergent 3-14 ± MPLA, were bactericidal <i>in vitro</i> for homologous P9-17 (Allele 193) gonococcal strain (median 50% bactericidal titers of 256). Analysis of MafA 2/3 alleles among gonococcal isolates in the PubMLST database showed that ~50% and 26% of gonococci expressed Allele 90 and Allele 88-encoded protein respectively, and these proteins were identical bar one amino acid substitution. Murine antisera to Allele 193 rMafA 2/3 expressing strain P9-17 (~98% homology with Alleles 88/90 MafA 2/3 protein) showed bactericidal activity against heterologous strain FA1090 (Allele 88, 50% median titers from 4 to 64), but not to heterologous strain AR205 (Allele 90). By contrast, a rabbit anti-rMafA 2/3 serum was bactericidal for P9-17, FA1090, and AR205 (50% titers of 2048-4096), and inhibited significantly (<i>p</i> <0.05) the association of gonococci to human Chang conjunctival epithelial cells <i>in vitro</i>. These findings suggest that MafA 2/3 could be a promising OMP for further study as a component of future subunit gonococcal vaccines.