MOLECULES FROM STAPHYLOCOCCUS-AUREUS THAT BIND CD14 AND STIMULATE INNATE IMMUNE-RESPONSES

Mammals mount a rapid inflammatory response to gram-negative bacteria by recognizing lipopolysaccharide (LPS, endotoxin). LPS binds to CD14, and the resulting LPS-CD14 complex induces synthesis of cytokines and up-regulation of adhesion molecules in a variety of cell types. Gram- positive bacteria provoke a very similar inflammatory response, but th e molecules that provoke innate responses to these bacteria have not b een defined. Here we show that protein-ti-ee, phenol extracts of Staph ylococcus aureus contain a minor component that stimulates adhesion of neutrophils and cytokine production in monocytes and in the astrocyto ma cell Line, U373. Responses to this component do not absolutely requ ire CD14, but addition of soluble CD14 enhances sensitivity of U373 ce lls by up to 100-fold, and blocking CD14 on monocytes decreases sensit ivity nearly 1,000-fold. Deletion of residues 57-64 of CD14, which are required for responses to LPS, also eliminates CD14-dependent respons es to S. aureus molecules. The stimulatory component of S. aureus bind s CD14 and blocks binding of radioactive LPS. Unlike LPS, the activity of S. aureus molecules was neither enhanced by LPS binding protein no r inhibited by bactericidal/permeability increasing protein. The activ e factor in extracts of S. aureus is also structurally and functionall y distinct from the abundant species known as lipoteichoic acid (LTA). Cell-stimulating activity fractionates differently from LTA on a reve rse-phase column, pure LTA fails to stimulate cells, and LTA antagoniz es the action of LPS in assays of IL-6 production, These studies sugge st that mammals may use CD14 in innate responses to both gram-negative and gram-positive bacteria, and that gram-positive bacteria may conta in an apparently unique, CD14-binding species that initiates cellular responses.