Functional comparison of the mouse DC-SIGN, SIGNR1, SIGNR3 and Langerin, C-type lectins

The mouse (m) DC-SIGN family consists of several homologous type II transmembrane proteins located in close proximity on chromosome 8 and having a single carboxyl terminal carbohydrate recognition domain. We first used transfected non-macrophage cell lines to compare the polysaccharide and microbial uptake capacities of three of these lectins--DC-SIGN, SIGNR1 and SIGNR3--to another homologue mLangerin. Each molecule shares a potential mannose-recognition EPN-motif in its carbohydrate recognition domain. Using an anti-Tag antibody to follow Tag-labeled transfectants, we found that each molecule could be internalized, although the rates differed. However, mDC-SIGN was unable to take up FITC-dextran, FITC-ovalbumin, zymosan or heat-killed Candida albicans. The other three lectins showed distinct carbohydrate recognition properties, assessed by blocking FITC-dextran uptake at 37 degrees C and by mannan binding activity at 4 degrees C. Furthermore, only SIGNR1 was efficient in mediating the capture by transfected cells of Gram-negative bacteria, such as Escherichia coli and Salmonella typhimurium, while none of the lectins tested were competent to capture Gram-positive bacteria, Staphylococcus aureus. Interestingly, transfectants with SIGNR1 lacking the cytoplasmic domain were capable of binding FITC-zymosan in a manner that was abolished by EDTA or mannan, but not laminarin. In addition, resident peritoneal CD11b+ cells expressing SIGNR1 bound zymosan at 4 degrees C in concert with a laminarin-sensitive receptor. Therefore these homologous C-type lectins have distinct recognition patters for microbes despite similarities in the carbohydrate recognition domains.