SIGN-R1, a novel C-type lectin expressed by marginal zone macrophages in spleen, mediates uptake of the polysaccharide dextran

Abstract

The marginal zone macrophages of the spleen are implicated in the clearance of polysaccharides, but underlying mechanisms need to be pinpointed. SIGN-R1 is one of five recently identified mouse genes that are homologous to human DC-SIGN and encode a single, external, C-terminal C-type lectin domain. We find that a polyclonal antibody to a specific SIGN-R1 peptide reacts primarily and strongly with a subset of macrophages in the marginal zone of spleen and lymph node medulla. In both sites, SIGN-R1 exists primarily in an aggregated form, resistant to dissociation into monomers upon boiling in SDS under reducing conditions. Upon transfection into three different cell lines, high-mol.-wt forms bearing SIGN-R1 are expressed, as well as reactivity with ER-TR9, a mAb previously described to react selectively with marginal zone macrophages. SIGN-R1-expressing macrophages preferentially sequester dextrans following i.v. injection. Likewise, when phagocytic cells are enriched from spleen and tested in culture, dextran is selectively endocytosed by a subset of very large SIGN-R1(+) cells representing approximately 5% of total released macrophages. Uptake of FITC-dextran by these macrophages in vivo and in vitro is blocked by ER-TR9 and polyclonal anti-SIGN-R1 antibodies. Following transfection with SIGN-R1, cell lines become competent to endocytose dextrans. The dextran localizes primarily to compartments lacking transferrin receptor and the LAMP-1 CD107a panlysosomal antigen. Therefore, SIGN-R1 mediates the uptake of dextran polysaccharides, and it is predominantly expressed in the macrophages of the splenic marginal zone and lymph node medulla.

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

“…Thermal treatment of sSIGNR1 with Strep-Tactin at 371C enhanced binding activity. This result may be due to the aggregation of SIGNR1 via its long neck domain (116 amino acids), which contains a heptad-repeat sequence, leading to increased ligand affinity and specificity, as previously reported [22,25].…”

“…Thermal treatment of sSIGNR1 with Strep-Tactin at 371C enhanced binding activity. This result may be due to the aggregation of SIGNR1 via its long neck domain (116 amino acids), which contains a heptad-repeat sequence, leading to increased ligand affinity and specificity, as previously reported [22,25].Our study and several other reports indicate that Dectin-1 and TLR2 recognize microbial components and induce inflammatory responses in either a cooperative [15,29,30] or independent manner [13,14]. In RAW-control cells, zymosan induced weak oxidative burst, but TLR ligand-depleted zymosan and PAM 3 CSK 4 did not.…”

“…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 various polysaccharides, such as dextran and mannan, but also lipopolysaccharides (LPS) from Gram-negative bacteria (E. coli and Salmonella typhimurium) [23].…”

New insights into SMA pathogenesis: immune dysfunction and neuroinflammation

“…In this manner, they trigger an innate immune response directly but also an adaptive immune response given their close proximity to the white pulp region, where T‐cells and B‐cells are located 16. Moreover, the spleen contains unique subsets of specialized macrophages that have better recognition for certain pathogens 17, 18, 19, 20. Indeed, this places the spleen as a major player in the clearance of encapsulated bacteria like Mycobacterium tuberculosis and Streptococcus pneumoniae , but also of Staphylococcus aureus , and potentially of viruses 16, 17, 18, 19, 20.…”

“…Moreover, the spleen contains unique subsets of specialized macrophages that have better recognition for certain pathogens 17, 18, 19, 20. Indeed, this places the spleen as a major player in the clearance of encapsulated bacteria like Mycobacterium tuberculosis and Streptococcus pneumoniae , but also of Staphylococcus aureus , and potentially of viruses 16, 17, 18, 19, 20. Moreover, asplenic patients are immunodeficient, are recommended to be on a more stringent immunization schedule, and more aggressive clinical management is initiated at an earlier stage when facing fever or infection 21, 22…”