Structures in Bacillus subtilis are recognized by CD14 in a lipopolysaccharide binding protein-dependent reaction

The CD14 molecule expressed on monocytes and macrophages is a high-affinity receptor for bacterial lipopolysaccharide (LPS) and hence an important com ponent of the innate immune system. LPS binding protein (LBP) is required t o facilitate the binding of LPS to CD14 in vitro and is necessary for the i nduction of an inflammatory response to LPS in vivo. Here we show that CD14 and LBP can also bind to lipoteichoic acid from the gram-positive bacteriu m Bacillus subtilis. Although CD14 does not interact with intact B, subtili s organisms, a brief exposure of the bacteria to serum converts them into a form which can bind to CD14 in an LBP-dependent reaction. When serum-pretr eated B. subtilis organisms are incubated with the myelomonocytic cell line U937, which expresses CD14, the bacteria are rapidly phagocytosed, The pha gocytosis is strictly dependent both on LBP and on CD14. These in vitro res ults suggest that LBP plays a role in the innate response not only to gram- negative but also to gram-positive infections.