The present invention relates to Neisserial Lipo-Oligo-Saccharides (LOS) that comprise a tri-saccharide outer core that shows increased binding to the DC-SIGN receptor on dendritic cells, as a result of which the Neisserial LOS's of the invention have increased immunostimulatory activity. The tri-saccharide outer core of the Neiserial LOS's combined with a Lipid A moiety with reduced toxicity is useful as an adjuvant in vaccine preparations.