The membrane expression of Neisseria meningitidis adhesin A (NadA) increases the proimmune effects of MenB OMVs on human macrophages, compared with NadA– OMVs, without further stimulating their proinflammatory activity on circulating monocytes

Anti‐Meningococcus B vaccine candidate stimulates macrophages. Hypervirulent MenB causing fatal human infections frequently display the oligomeric‐coiled coil adhesin NadA, a 45‐kDa intrinsic outer membrane protein implicated in binding to and invasion of respiratory epithelial cells. A recombinant soluble mutant lacking the 10‐kDa COOH terminal membrane domain (NadAΔ351–405) also activates human monocytes/macrophages/DCs. As NadA is physiologically released during sepsis as part of OMVs, in this study, we tested the hypothesis that NadA+ OMVs have an enhanced or modified proinflammatory/proimmune action compared with NadA– OMVs. To do this we investigated the activity of purified free NadAΔ351–405 and of OMVs from MenB and Escherichia coli strains, expressing or not full‐length NadA. NadAΔ351–405 stimulated monocytes and macrophages to secrete cytokines (IL‐1β, TNF‐α, IL‐6, IL‐12p40, IL‐12p70, IL‐10) and chemokines (IL‐8, MIP‐1α, MCP‐1, RANTES), and full‐length NadA improved MenB OMV activity, preferentially on macrophages, and only increased cytokine release. NadAΔ351–405 induced the lymphocyte costimulant CD80 in monocytes and macrophages, and NadA+ OMVs induced a wider set of molecules supporting antigen presentation (CD80, CD86, HLA‐DR, and ICAM‐1) more efficiently than NadA– OMVs only in macrophages. Moreover, membrane NadA effects, unlike NadAΔ351–405 ones, were much less IFN‐γ‐sensitive. The activity of NadA‐positive E. coli OMVs was similar to that of control OMVs. NadA in MenB OMVs acted at adhesin concentrations ∼106 times lower than those required to stimulate cells with free NadAΔ351–405.