A TLR4-interacting surfactant protein-A-derived peptide improves host defense against Pseudomonas aeruginosa.

Abstract

Abstract Interaction between surfactant protein-A (SP-A) and toll-like receptor (TLR4) plays a critical role in host defense. We have identified SPA4 peptide (amino acids: GDFRYSDGTPVNYTNWYRGE) from a TLR4-interacting region of SP-A. The SPA4 peptide binds to TLR4 and suppresses the secreted levels of inflammatory cytokines against Gram-negative bacterial lipopolysaccharide. In this work, we studied the host defense function of SPA4 peptide against Pseudomonas aeruginosa. We examined the binding of SPA4 peptide to cellular TLR4 and bacteria, and direct antibacterial activity against P. aeruginosa. Pro-phagocytic and anti-inflammatory activities of SPA4 peptide were investigated in nontransfected and TLR4-transfected dendritic cells and primary mouse alveolar macrophages. The biological activity of SPA4 peptide was then studied in a mouse model of P. aeruginosa lung infection. Our results demonstrate that the SPA4 peptide binds to TLR4, but does not interact with live bacteria. Correspondingly, the SPA4 peptide does not directly affect bacterial growth. The SPA4 peptide treatment induces the uptake and localization of bacteria in the phagolysosomes of immune cells. At the same time, the secreted levels of inflammatory cytokines are significantly suppressed. Over-expression of TLR4 augments the pro-phagocytic and anti-inflammatory activity of SPA4 peptide. Furthermore, treatment with SPA4 peptide reduces the bacterial burden, inflammatory cytokines, phosphorylation of p38 MAPK, p54 SAPK/JNK and NF-κB-p65, and alleviates lung edema and pathology in a mouse model of P. aeruginosa infection. Together, our results suggest that the immunomodulatory activity of SPA4 peptide can potentially help control infection.