COLEC11

COLEC11 (CL-K1/CL-11) is a secreted collectin that functions as a soluble pattern recognition molecule in innate immunity, complement activation, embryonic development, and bone homeostasis. It forms disulfide-linked oligomers that circulate predominantly as heterocomplexes with CL-L1 (CL-10) in two alternatively spliced isoforms, associates with MASP-1 and MASP-3, and activates the lectin complement pathway via MASP-2-dependent C4b deposition upon binding L-fucose, D-mannose, DNA, or zymosan through both Ca²⁺-dependent and Ca²⁺-independent recognition sites (PMID:20956340, PMID:23954398, PMID:30323815, PMID:38466278). Loss-of-function mutations in COLEC11 cause 3MC syndrome, a developmental disorder with craniofacial abnormalities, reflecting CL-K1's role as a guidance cue for neural crest cell migration during embryogenesis (PMID:21258343). CL-11 additionally suppresses T cell proliferation through its collagen-like domain via an integrin-dependent mechanism involving CD28 downregulation, and cooperates with complement components to regulate osteoclastogenesis and vertebral bone maintenance [PMID:37443840, PMID:bio_10.1101_2025.05.08.652605].

1. 2006 Medium

   Identification of COLEC11 as a secreted collectin with Ca²⁺-dependent sugar-binding activity established it as a new member of the collectin family capable of recognizing L-fucose and D-mannose.

   Evidence Cloning, recombinant expression in CHO cells, sugar-binding ELISA, and detection in human blood

   PMID:17179669

   Open questions at the time

   • Single lab; ligand specificity not fully characterized
   • No in vivo functional data
   • Oligomeric state and serum partners unknown
2. 2010 High

   Demonstration that CL-11 forms disulfide-linked oligomers, associates with MASP-1/MASP-3, binds intact pathogens, reduces influenza infectivity, and complexes with DNA revealed it as a functional innate immune recognition molecule capable of engaging both microbial and self ligands.

   Evidence Co-purification, ELISA, gel permeation chromatography, mass spectrometry, in vitro pathogen-binding and viral infectivity assays

   PMID:20956340

   Open questions at the time

   • Complement activation downstream of MASP association not yet demonstrated
   • DNA-binding site relationship to CRD not resolved
   • In vivo relevance of antiviral activity not tested
3. 2011 High

   Discovery that COLEC11 mutations cause 3MC syndrome and that CL-K1 acts as a neural crest cell migration guidance cue resolved the gene's developmental role and established a direct genotype–phenotype link to craniofacial malformation.

   Evidence Human genetic studies identifying causative mutations, mouse embryo expression mapping, zebrafish morpholino knockdown with craniofacial and pigmentary phenotypes, neural crest migration assay

   PMID:21258343

   Open questions at the time

   • Receptor on neural crest cells mediating CL-K1 guidance not identified
   • Whether complement activation is required for developmental function is unknown
   • Molecular mechanism of migration guidance not dissected
4. 2013 High

   Showing that CL-11 binds DNA with nanomolar affinity via a Ca²⁺-independent site distinct from the CRD, engages apoptotic cells, and triggers MASP-2-dependent C4b deposition established CL-11 as a dual-site recognition molecule linking self-DNA sensing to lectin pathway complement activation.

   Evidence Surface plasmon resonance (KD 9–20 nM), ELISA competition, C4b deposition assay, flow cytometry on apoptotic cells

   PMID:23954398

   Open questions at the time

   • Physiological relevance of DNA-triggered complement activation in vivo not tested
   • Whether CL-11-DNA binding contributes to autoimmune pathology unknown
5. 2014 Medium

   Characterization of MAP-1/MASP-1/MASP-3 heterocomplexes with CL-11 in normal human plasma defined the native serine protease partners of the CL-11 recognition complex.

   Evidence Reciprocal ELISA, size-exclusion chromatography, immunoblotting with recombinant and serum-derived proteins

   PMID:24683193

   Open questions at the time

   • Single lab study
   • Functional consequence of MAP-1 inclusion in the complex not determined
   • Stoichiometry of native complexes not resolved
6. 2018 Medium

   Three studies collectively established that CL-11 circulates as CL-10/CL-11 heterocomplexes of ~400 and >600 kDa, is co-expressed with CL-L1 in epithelial and secretory tissues, binds zymosan via a calcium-independent site, and recognizes L-fucose on ischaemic renal tubular cells to trigger local complement activation.

   Evidence Immunohistochemistry across human tissues, size exclusion chromatography, ELISA with blocking antibodies, C4b deposition assay, binding assays on ischaemic renal epithelial cells

   PMID:30108587 PMID:30237800 PMID:30323815

   Open questions at the time

   • In vivo ischaemia-reperfusion studies with CL-11 knockout not yet performed at this stage
   • Structural basis of calcium-independent zymosan binding unknown
   • Relative contribution of CL-10/11 heterocomplexes versus CL-11 homotrimers to complement activation in vivo unclear
7. 2023 Medium

   Discovery that CL-11's collagen-like domain suppresses T cell proliferation by downregulating CD28, blocked by RGD peptide, revealed a complement-independent immunoregulatory function mediated through integrin engagement.

   Evidence RPE/T cell co-culture, proliferation assays, RGD peptide competition, flow cytometry for CD28

   PMID:37443840

   Open questions at the time

   • Specific integrin receptor on T cells not identified
   • In vivo immunosuppressive relevance not demonstrated
   • Whether this function operates outside the ocular microenvironment is unknown
8. 2024 High

   Resolution of two alternatively spliced CL-11 isoforms (A and D) differing in collagen-like domain length, with isoform D showing reduced CL-10 association and ligand binding, clarified the molecular heterogeneity of circulating CL-10/11 complexes.

   Evidence Recombinant isoform production, immunoprecipitation, mass spectrometry of native serum complexes, size exclusion chromatography, functional binding assays

   PMID:38466278

   Open questions at the time

   • Functional consequence of isoform ratio differences in disease not tested
   • Crystal structure of CL-10/11 heterocomplex not available
   • Whether isoform D has distinct developmental or immunoregulatory roles is unknown
9. 2025 Medium

   Genetic epistasis experiments showing that CL-11 deletion combined with complement deficiency causes vertebral bone loss, rescued by CL-11 supplementation, established CL-11 as a regulator of osteoclastogenesis acting in concert with the complement cascade.

   Evidence (preprint) Double-knockout mice (CL-11 with MASP-2, CFB, or C3), ex vivo osteoclast differentiation with rescue, immunolocalization of CL-11 and C5b-9 in bone

   PMID:bio_10.1101_2025.05.08.652605

   Open questions at the time

   • Preprint, not yet peer-reviewed
   • Direct molecular mechanism by which CL-11 promotes osteoclast differentiation not defined
   • Whether the bone phenotype relates to 3MC syndrome skeletal features unknown

• The receptor on neural crest cells that mediates CL-K1 guidance signaling, the structural basis of the CL-10/CL-11 heterocomplex, and the relative physiological contributions of the two splice isoforms and complement-dependent versus complement-independent functions of CL-11 remain unresolved.
• Neural crest receptor for CL-K1 unidentified
• No high-resolution structure of CL-10/11 complex
• In vivo functional partitioning between isoforms A and D not established