Fighting infection: the role of lipopolysaccharide binding proteins CD14 and LBP.

An invading pathogen must be held in check by the innate immune system until a specific immune response is mounted. Nonclonal pattern recognition receptors like CD14 or lipopolysaccharide (LPS) binding protein (LBP) recognize ubiquitous pathogen-associated molecular patterns, e.g. LPS. LBP mediates the binding of minute amounts of LPS to membrane-bound CD14 (mCD14) triggering a proinflammatory response of macrophages, which is crucial for keeping an infection under control. Moreover, in vitro mCD14 and LBP are involved in recognition and phagocytosis of heat-killed bacteria. Living Salmonella typhimurium or Escherichia coli depend on the presence of LBP to induce the generation of reactive oxygen species in human or murine macrophages. Using LBP-deficient mice it could be demonstrated that LBP is essential to control low dose (100 CFU S. typhimurium) infection. Therefore, LPS binding proteins play a pivotal role in physiology as well as pathophysiology of Gram-negative infection.