Evaluation of the surface lipoprotein assembly modifier (Slam) as a vaccine candidate against Neisseria gonorrhoeae infection.

The surface lipoprotein assembly modifier (Slam) plays an essential role in the biogenesis and assembly of outer membrane components in Gram-negative bacteria. This study evaluated the potential of recombinant NG Slam as a vaccine candidate. Bioinformatics confirmed its high conservation (including with its Neisseria meningitidis homolog) and outer membrane localization. Immunofluorescence demonstrated antibody accessibility to Slam in fixed bacterial cells. Antigenic epitope mapping revealed that dominant B- and T-cell epitopes are primarily within α-helical and random coil regions. Molecular docking suggested potential interactions with Toll-like receptors TLR2 and TLR4, which warrant experimental validation. The recombinant protein corresponding to the C-terminal surface-exposed domain of Slam was successfully expressed and used to immunize BALB/c mice. Immunization elicited high titers of specific antibodies with potent complement-dependent serum bactericidal activity and significant inhibition of bacterial adhesion to epithelial cells. Furthermore, splenocyte proliferation and enhanced secretion of IL-4, IL-17 A, and IFN-γ were observed, with IL-17 A production markedly exceeding that induced by whole-cell antigens. These findings demonstrate that Slam is immunogenic and elicits functional antibody alongside a Th17-skewed cellular response, the protective relevance of which requires further evaluation in challenge models.