IDENTIFICATION OF CD14 RESIDUES INVOLVED IN SPECIFIC LIPOPOLYSACCHARIDE RECOGNITION

CD14 is a key molecule responsible for the innate host inflammatory re sponse to microbial infection, It is able to bind a wide variety of mi crobial ligands and facilitate the activation of both myeloid and nonm yeloid cells, However, its specific contribution to the innate recogni tion of bacteria is not known, Presently there is no information on th e contribution of individual CD14 residues to Escherichia coli lipopol ysaccharide (LPS) binding or on the molecular basis of the interaction between CD14 and LPS from other bacteria, LPS obtained from Porphyrom onas gingivalis, a bacterium associated with chronic inflammatory dise ase, binds CD14 and activates myeloid cells but does not facilitate th e activation of nonmyeloid cells, The transfer and binding of these tw o LPS species to soluble CD14 recombinant globulin proteins with singl e point mutations was examined, Functional activity of the mutant prot eins was monitored by E-selectin expression on human umbilical cord en dothelial cells. The analysis identified a charge reversal mutation in a single residue, E47, that demonstrated selective binding to E. coli LPS but not to P. gingivalis LPS. E-selectin activation assays indica ted that proteins with mutations at position E47 maintained their stru ctural integrity. Other mutations, including a charge reversal mutatio n of residue E58, did not significantly reduce the binding of either L PS ligand or the ability of the molecule to facilitate E-selectin acti vation, These data demonstrate that CD14 can selectively recognize dif ferent LPS ligands.