Recognition of by the pattern recognition molecules langerin, mannan-binding lectin, and surfactant protein D: the influence of capsular polysaccharides and wall teichoic acid.

The innate immune system plays a critical role in the rapid recognition and elimination of pathogens through pattern recognition receptors (PRRs). Among these PRRs are the C-type lectins (CTLs) langerin, mannan-binding lectin (MBL), and surfactant protein D (SP-D), which recognize carbohydrate patterns on pathogens. Each represents proteins from different compartments of the body and employs separate effector mechanisms. We have investigated their interaction with the Gram-positive opportunistic pathogen , a bacterium whose cell wall contains two key glycopolymers: capsular polysaccharide (CP) and wall teichoic acid (WTA). Using a langerin-expressing cell line and recombinant langerin, MBL, and SP-D, we demonstrated that langerin, MBL, and SP-D all recognize nonencapsulated S. However, the bacterium may produce CP that effectively shields from recognition by all three CTLs. Experiments utilizing mutant strains confirmed that WTA is a ligand for MBL, but that langerin likely interacts with an additional unknown ligand. A competition assay revealed that MBL and SP-D inhibit langerin's interaction with , highlighting the intricate redundancy and cooperation within the innate immune system. This study highlights the dynamic interplay of langerin, MBL, and SP-D in recognizing specific surface structures on and provides insight into how this pathogen evades innate immune recognition.