Yield and immunomodulatory effects of pneumococcal membrane vesicles change with bacterial growth phase

We investigated whether isolation of MVs during either the stationary-phase (24 h) or death-phase (48 h) affected their yield, immunogenicity and cytotoxicity in primary human immune cells. Death-phase vesicles showed higher yield than stationary-phase vesicles. Both vesicle types displayed excellent compatibility with primary human macrophages, and several cell lines, without cytotoxic effect. However, stationary-phase MVs showed slightly higher uptake into primary macrophages. Both vesicle types enhanced the release of inflammatory cytokines tumor necrosis factor and interleukin-6 from primary human macrophages. Proteomic analysis revealed similarities in vesicular immunogenic proteins in both vesicle types, such as pneumolysin, pneumococcal surface protein A, IgA1 protease, but stationary-phase MVs showed significantly lower autolysin levels, than death-phase MVs.