Galactoside-binding lectin in Solen grandis as a pattern recognition receptor mediating opsonization.

Abstract Galactoside-binding lectin (galectin) is a type of pathogen recognition molecule that occupies an important position in the invertebrate innate immunity system. Our previous study has identified a galectin gene in mollusk Solen grandis (SgGal-1) and illustrated its potential roles in innate immunity. By the functional study using recombinant protein and specific antibody, here, we confirmed the pivotal roles of SgGal-1 in immune defense of S. grandis. SgGal-1 protein was expressed in many tested tissues including gill, mantle, hepatopancreas and gonad, except hemocytes and muscle. The recombinant SgGal-1 (rSgGal-1) bound PGN and β-glucan instead of LPS in vitro , and it further caused significant agglutination of five different microbes, suggesting SgGal-1 served as a pattern recognition receptor (PRR) involved in immune defense of mollusk. Furthermore, SgGal-1 recruited hemocytes to encapsulate, which was blocked by anti-rSgGal-1 serum. In the meantime, rSgGal-1 as well as promoted the phagocytosis of hemocytes against Escherichia coli in vitro. All these results suggested that SgGal-1 in S. grandis not only acted as a PRR recognizing microbes but also directly participated in the process of immune opsonization to protect the host from pathogenic infection. Highlights • Galactoside-binding lectin is a multifunctional protein in Solen grandis. • SgGal-1 is distributed in many different tissues. • SgGal-1 serves as a PRR to bind PGN and glucan. • SgGal-1 involves in the anti-microbial response through agglutination. • SgGal-1 acts as an opsonin mediating encapsulation and phagocytosis of hemocytes. [ABSTRACT FROM AUTHOR]