Cathelicidin family of antibacterial peptides CAP18 and CAP11 inhibit the expression of TNF-alpha by blocking the binding of LPS to CD14(+) cells

Mammalian myeloid and epithelial cells express several kinds of antibacteri al peptides (alpha-/beta -defensins and cathelicidins) that contribute to t he innate host defense by killing invading micro-organisms. In this study w e evaluated the LPS-neutralizing activities of cathelicidin peptides human CAP18 (cationic antibacterial proteins of 18 kDa) and guinea pig CAP11 usin g the CD14(+) marine macrophage cell line RAW264.7 and the murine endotoxin shock model. Flow cytometric analysis revealed that CAP18 and CAP11 inhibi ted the binding of FITC-conjugated LPS to RAW264.7 cells. Likewise, Norther n and Western blot analyses indicated that CAP18 and CAP11 suppressed LPS-i nduced TNF-alpha mRNA and protein expression by RAW264.7 cells. Interesting ly, CAP18 and CAP11 possessed LPS-binding activities, and they strongly sup pressed the interaction of LPS with LPS binding protein that mediates the t ransport of LPS to CD14 to facilitate the activation of CD14(+) cells by LP S. Moreover, when CAP18 and CAP11 were preincubated with RAW264.7 cells, th ey bound to the cell surface CD14 and inhibited the binding of FITC-LPS to the cells. Furthermore, in the murine endotoxin shock model, CAP18 or CAP11 administration inhibited the binding of LPS to CD14(+) cells (peritoneal m acrophages) and suppressed LPS-induced TNF-alpha expression by these cells. Together these observations indicate that cathelicidin peptides CAP 18 and CAP11 probably exert protective actions against endotoxin shock by blockin g the binding of LPS to CD14(+) cells, thereby suppressing the production o f cytokines by these cells via their potent binding activities for LPS and CD14.