Plays a role in the innate immune response. Binds to the lipid A moiety of bacterial lipopolysaccharides (LPS), a glycolipid present in the outer membrane of all Gram-negative bacteria (PubMed:7517398, PubMed:24120359). Acts as an affinity enhancer for CD14, facilitating its association with LPS. Promotes the release of cytokines in response to bacterial lipopolysaccharide (PubMed:7517398, PubMed:24120359). When bound to LPS, interacts (via C-terminus) with soluble and membrane-bound CD14. Membrane-associated in polymorphonuclear Leukocytes (PMN) granules. Detected in blood serum (at protein level). Belongs to the BPI/LBP/Plunc superfamily. BPI/LBP family.