DCIR interacts with ligands from both endogenous and pathogenic origin.

C-type lectins on dendritic cells function as antigen uptake and signaling receptors, thereby influencing cellular immune responses. Dendritic cell-specific intercellular adhesion molecule-3-grabbing non-integrin (DC-SIGN) is one of the best-studied C-type lectin receptors expressed on DCs and its glycan specificity and functional requirements for ligand binding have been intensively investigated. The carbohydrate specificity of dendritic cell immunoreceptor (DCIR), another DC-expressed lectin, was still debated, but we have recently confirmed DCIR as mannose/fucose-binding lectin. Since DC-SIGN and DCIR may potentially share ligands, we set out to elucidate the interaction of DCIR with established DC-SIGN-binding ligands, by comparing the carbohydrate specificity of DCIR and DC-SIGN in more detail. Our results clearly demonstrate that DC-SIGN has a broader glycan specificity compared to DCIR, which interacts only with mannotriose, sulfo-Lewis(a), Lewis(b) and Lewis(a). While most of the tested DC-SIGN ligands bound DCIR as well, Candida albicans and some glycoproteins on some cancer cell lines were identified as DC-SIGN-specific ligands. Interestingly, DCIR strongly bound human immunodeficiency virus type 1 (HIV-1) gp140 glycoproteins, while its interaction with the well-studied DC-SIGN-binding HIV-1 ligand gp120 was much weaker. Furthermore, DCIR-specific ligands were detected on keratinocytes. Furthermore, the interaction of DCIR with its ligands was strongly influenced by the glycosylation of DCIR. In conclusion, we show that sulfo-Lewis(a) is a high affinity ligand for DCIR and that DCIR interacts with ligands from both pathogenic and endogenous origin of which most are shared by DC-SIGN.

Convergence of signaling pathways induced by systemin, oligosaccharide elicitors, and ultraviolet-B radiation at the level of mitogen-activated protein kinases in Lycopersicon peruvianum suspension-cultured cells.

We tested whether signaling pathways induced by systemin, oligosaccharide elicitors (OEs), and ultraviolet (UV)-B radiation share common components in Lycopersicon peruvianum suspension-cultured cells. These stress signals all induce mitogen-activated protein kinase (MAPK) activity. In desensitization assays, we found that pretreatment with systemin and OEs transiently reduced the MAPK response to a subsequent treatment with the same or a different elicitor. In contrast, MAPK activity in response to UV-B increased after pretreatment with systemin and OEs. These experiments demonstrate the presence of signaling components that are shared by systemin, OEs, and UV-B. Based on desensitization assays, it is not clear if the same or different MAPKs are activated by different stress signals. To identify specific stress-responsive MAPKs, we cloned three MAPKs from a tomato (Lycopersicon esculentum) leaf cDNA library, generated member-specific antibodies, and performed immunocomplex kinase assays with extracts from elicited L. peruvianum cells. Two highly homologous MAPKs, LeMPK1 and LeMPK2, were activated in response to systemin, four different OEs, and UV-B radiation. An additional MAPK, LeMPK3, was only activated by UV-B radiation. The common activation of LeMPK1 and LeMPK2 by many stress signals is consistent with the desensitization assays and may account for substantial overlaps among stress responses. On the other hand, MAPK activation kinetics in response to elicitors and UV-B differed substantially, and UV-B activated a different set of LeMPKs than the elicitors. These differences may account for UV-B-specific responses.

Sialyl Lewis(x) (sLe(x)) and an sLe(x) mimetic, CGP69669A, disrupt E-selectin-dependent leukocyte rolling in vivo.

Leukocyte rolling is the earliest observable even in their recruitment from the circulation to inflamed tissue. This rolling is mediated largely by interaction between the selectin family of adhesion molecules and their glycosylated ligands. Although the nature of these ligands and their interaction with the selectins is not fully understood, it is accepted that expression of fucosylated sialylated glycans such as sialyl Lewis(x) (sLe(x)) is required for function. Despite findings that sLe(x) inhibits binding of leukocytes to E-selectin in vitro, and has beneficial effects in inflammatory disease models, inhibition of E-selectin-dependent leukocyte rolling in vivo has not been described. Functional overlap between the selectins has been noted and reduction of rolling by E-selectin antibodies only occurs if P-selectin is absent or blocked. We demonstrate that leukocyte rolling velocity in tumor necrosis factor alpha (TNF alpha)-stimulated mouse cremaster is increased following treatment with either sLe(x) or the sLe(x)-mimetic CGP69669A and that rolling is dramatically reduced if CGP69669A is applied in the presence of anti-P-selectin antibody. These effects are characteristic of E-selectin antagonism. In contrast, surgically stimulated (L- or P-selectin-dependent) rolling is unaffected by either sLe(x) or CGP69669A. Our data demonstrate that CGP69669A is an effective and selective antagonist of E-selectin in vivo.