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

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.