HUMAN CAP18 - A NOVEL ANTIMICROBIAL LIPOPOLYSACCHARIDE-BINDING PROTEIN

CAP18 (18-kKa cationic antimicrobial protein) is a protein originally identified and purified from rabbit leukocytes on the basis of its cap acity to bind and inhibit various activities of lipopolysaccharide (LP S). Here we report the cloning of human CAP18 and characterize the ant i-LPS activity of the C-terminal fragment, Oligonucleotide probes desi gned from the rabbit CAP18 cDNA were used to identify human CAP18 from a bone marrow cDNA library. The cDNA encodes a protein composed of a 30-amino-acid signal peptide, a 103-amino-acid N-terminal domain of un known function, and a C-terminal domain of 37 amino acids homologous t o the LPS-binding antimicrobial domain of rabbit CAP18, designated CAP 18(104-140). A human CAP18-specific antiserum was generated by using C AP18 expressed as a fusion protein with the maltose-binding protein. W estern blots (immunoblots) with this antiserum showed specific express ion of human CAP18 in granulocytes. Synthetic human CAP18(104-140) and a more active truncated fragment, CAP18(104-135), were shown to (i) b ind to erythrocytes coated with diverse strains of LPS, (ii) inhibit L PS-induced release of nitric oxide from macrophages, (iii) inhibit LPS -induced generation of tissue factor, and (iv) protect mice from LPS l ethality. CAP18(104-140) may have therapeutic utility for conditions a ssociated with elevated concentrations of LPSl