Characteristics of surfactant protein a and D binding to lipoteichoic acidand peptidoglycan, 2 major cell wall components of Gram-positive bacteria

Infection with gram-positive bacteria is a major cause of pneumonia. Surfac tant proteins A (SP-A) and D (SP-D) are thought to play an important role i n the innate immunity of the lung. Both proteins can bind to gram-positive bacteria. Until now, it was not known with which surface component(s) of gr am-positive bacteria SP-A and SP-D interact. Lipoteichoic acid (LTA) and pe ptidoglycan (PepG) are components of the cell wall of gram-positive bacteri a. By use of a solid phase-based binding assay, LTA of Bacillus subtilis wa s shown to be bound by SP-D but not by SP-A. Unmodified PepG of Staphylococ cus aureus was bound by SP-D. SP-D binding to both LTA and PepG was calcium dependent and carbohydrate inhibitable. These results indicate that SP-D i nteracts with gram-positive bacteria via binding to the cell wall component s LTA and PepG and that the carbohydrate recognition domain is responsible for this binding.