A low-density lipoprotein receptor (LDLR) class A domain-containing C-type lectin from Litopenaeus vannamei plays opposite roles in antibacterial and antiviral responses.

C-type lectins (CTLs) are a group of pattern recognition receptors (PRRs) that contain carbohydrate recognition domains and play important roles in innate immunity. CTLs that contain an additional low-density lipoprotein receptor (LDLR) class A domain (LdlrCTL) have been identified in many crustaceans, but their functions in immune responses are mostly unknown. In this study, a novel LdlrCTL was identified from pacific white shrimp Litopenaeus vannamei (LvLdlrCTL), which showed high homology with previously reported crustacean LdlrCTLs. LvLdlrCTL was highly expressed in hemocytes and its expression was up-regulated after immune stimulations. Silencing of LdlrCTL significantly promoted infection of shrimp by Vibrio parahaemolyticus but inhibited infection by white spot syndrome virus (WSSV), suggesting that LdlrCTL could play opposite roles in antibacterial and antiviral responses. LdlrCTL exhibited agglutination activity against bacteria and fungi and could potentiate the phagocytosis of hemocytes. Moreover, the expression of many immune effector genes and signalling pathway components was significantly changed in LdlrCTL-silenced shrimp, indicating that LdlrCTL could be involved in immune regulation.