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

Abstract

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.Key words: C. albicans . Dectin-1 . Macrophages . SIGNR1 . TLR2 IntroductionInnate immunity is a crucial host defense system that eliminates pathogens as they initiate an infection and leads to the subsequent initiation of the adaptive immune response [1]. The system consists of germline-encoded genes, i.e. toll-like receptors (TLRs) [2] [8][9][10][11][12]. Microbe-mediated stimulation of Dectin-1 results in cellular oxidative burst and cytokine production through its ITAM and the Syk kinase pathway [13,14]. In addition, Dectin-1 has been shown to function collaboratively with TLR2 to stimulate cytokine production [15] and Th17/Treg induction [16].hDC-SIGN recognizes mannose and fucose moieties in the surface of a variety of microbes and viruses, such as Mycobacteria, Leishmania, Salmonella, Candida species, HIV, HCV, dengue virus, CMV, Ebola virus and Sindbis virus (refer to [17]). However, pathogens, i.e. HIV and HCV, have also found ways to subvert and use hDC-SIGN to their advantage [18,19]. Mycobacterium tuberculosis and HIV also target hDC-SIGN in order to upregulate DC production of the immunosuppressive cytokine IL-10 through Raf-1 kinase activation, which induces acetylation of the NF-kB p65 subunit in the presence of co-signaling from TLR4 [20].Mice have eight hDC-SIGN homologues [21,22]. One of these homologues, SIGNR1, has been shown to be expressed on particular Mf subsets in the marginal zone of the spleen, medulla of the lymph nodes and the peritoneal cavity [23][24][25] and to possess mannosebinding activities like hDC-SIGN. SIGNR1 recognizes not only vari...

Lipopolysaccharide-mediated enhancement of zymosan phagocytosis by RAW 264.7 macrophages is independent of opsonins, laminarin, mannan, and complement receptor 3

“…We also confirmed that macrophage recognition of zymosan was laminarin sensitive in the absence of LPS but laminarin insensitive for LPS-primed cells [22]. Zymosan particles are composed primarily of betaglucan, and cell surface macrophage PRRs reported to bind to this carbohydrate include Dectin-1 [25], CR3 [26], SIGNR1 [27], scavenger receptors [28], and lactosylceramide [29]. The mannose receptor has also been implicated as a PRR for zymosan via recognition of mannan on these particles [30].…”

Commensal Propionibacterium strain UF1 mitigates intestinal inflammation via Th17 cell regulation

“…CLRs, particularly SIGNR1, expressed by phagocytes (e.g., DCs) are critical pattern-recognition receptors interacting with microbial carbohydrate recognition domains (CRDs) (87) to efficiently internalize and phagocytize microbes in concert with other molecules, including complement receptors (88), and to potentiate the oxidative responses to pathogens (e.g., Candida albicans) via dectin-1/SyK-dependent signaling (89). One can speculate that the signaling pathways of SIGNR1 involve regulated immune complexes (e.g., SOCS1) whose activation may be dependent on a mannosylated S-layer binding to SIGNR1 to control proinflammation in DCs that influence regulatory Th17 cells (90,91).…”

Difference in Fine Specificity to Polysaccharides of Candida albicans Mannoprotein between Mouse SIGNR1 and Human DC-SIGN

“…Soluble lectin (sLectin) tetramers, such as sSIGNR1 and shDC-SIGN, were prepared as described previously (26). Briefly, cDNA fragments encoding their extracellular domains were cloned into pEXPR-IBA44 (IBA, Göttingen, Germany) to add N-terminal BM40 secretion signal and Strep-Tag II sequences, followed by transfer into pEF6/V5-His (Invitrogen).…”