C-type lectin SIGNR1 enhances cellular oxidative burst response against C. albicans in cooperation with Dectin-1

We investigated the role of SIGNR1 in the recognition of Candida albicans and the subsequent cellular oxidative burst response. Soluble SIGNR1 (sSIGNR1) tetramer bound equally to zymosan and both heat‐killed (HK) and live C. albicans in an EDTA‐sensitive manner, whereas sDectin‐1 tetramer predominantly bound to zymosan and HK‐microbes in an EDTA‐independent manner. In cellular response, enhanced oxidative burst was observed in RAW264.7 cells expressing SIGNR1 (RAW‐SIGNR1) compared with RAW‐control cells upon stimulation with HK‐C. albicans and zymosan. This response was independent of TLR2 and the cytosolic portion of SIGNR1 but dependent on the recognition by SIGNR1 via carbohydrate recognition domain. Antagonistic laminarin and anti‐Dectin‐1 mAb cooperatively reduced the response with mannan and anti‐SIGNR1 mAb, respectively, although they had no effect by themselves. Moreover, oxidative response and bactericidal activity largely relied on Syk‐mediated signaling. RAW‐SIGNR1 cells not only captured microbes more efficiently but also showed higher responses than RAW‐control cells. Similar enhanced responses were observed in SIGNR‐1‐expressing resident peritoneal M?. Interestingly, Dectin‐1 was recruited to the phagosomal membrane upon the stimulation and physically associated with SIGNR1. These results suggest that SIGNR1 plays a significant role in inducing oxidative response to C. albicans by Syk‐dependent signaling, possibly through Dectin‐1.