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Gene Review

CD93  -  CD93 molecule

Homo sapiens

Synonyms: C1QR1, C1q/MBL/SPA receptor, C1qR, C1qR(P), C1qR(p), ...
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Disease relevance of CD93

  • Human antibodies from Sjögren's syndrome patients did not recognize C1qR, but showed positive reaction with the purified 53,000 MW component from spleen [1].
  • We now investigated whether Escherichia coli possesses a C1qR-like protein that protects these bacteria from complement-mediated injury [2].
  • We have previously demonstrated that hepatitis C virus (HCV) core, the first protein to be expressed and circulating in the blood of infected individuals, inhibited human T cell proliferative response through interaction with the complement receptor, globular domain of C1q receptor (gC1qR) [3].
  • The HD-increased C1qR that binds C1q to the surface of HEK might be a contributing mechanism or a marker for the inflammation and vesication associated with HD exposure [4].

High impact information on CD93

  • Likewise, C1-Inh leads to C1q remaining on the immune complex to interact with the C1q receptor [5].
  • Thus, CR1 is a cellular C1q receptor that recognizes all three complement opsonins, namely, C1q, C3b, and C4b [6].
  • Mannose binding protein (MBP) enhances mononuclear phagocyte function via a receptor that contains the 126,000 M(r) component of the C1q receptor [7].
  • C1q receptors (C1qR) have been identified on a variety of somatic and cultured cells including peripheral blood platelets [8].
  • Platelet aggregation was inhibited by the collagenous domain of C1q (c-Clq) and a monoclonal antibody directed against C1q receptors, suggesting the direct involvement of the 67-kD platelet C1qR [8].

Biological context of CD93


Anatomical context of CD93


Associations of CD93 with chemical compounds

  • While the cDNA for C1qRP encodes a 631 amino acid membrane protein, Chinese hamster ovary cells transfected with the cDNA of the C1qRP coding region express a surface glycoprotein with the identical 126,000 Mr in SDS-PAGE as the native C1qRP [15].
  • Furthermore, no supporting evidence for a role of CD93 as an adhesion molecule was found using intravital microscopy or analyzing peritoneal cell recruitment in response to three different inflammatory stimuli (thioglycolate, zymosan A, and IL-1beta) [16].
  • Whereas recombinant tumor necrosis factor-alpha (rTNF-alpha) slightly up-regulated CD93 expression on the U937 cells, recombinant interleukin-1beta (rIL-1beta), recombinant interleukin-2 (rIL-2), recombinant interferon-gamma (rIFN-gamma) and lipopolysaccharide (LPS) had no effect [17].
  • CD93 expression was analyzed using flow cytometry and glutaraldehyde-fixed cellular enzyme-linked immunoassay (EIA) techniques utilizing a CD93 monoclonal antibody (mAb), mNI-11, that was originally established in our laboratory as a CD93 detection probe [17].
  • This interaction was Ca(2+) independent and was not blocked by our anti-C1qRp mAb BIIG-4, but was blocked by the proadhesive mAb mNI-11 [18].

Physical interactions of CD93


Regulatory relationships of CD93

  • Upon DL-1 signaling, Pax5-deficient pro-B cells down-regulate both surface CD93 expression and transcripts for B cell-specific genes and concomitantly up-regulate T lineage gene transcripts [20].
  • In addition, both Go6976 and Rottlerin inhibited the up-regulation of CD93 expression induced by PMA and IL-8 or IFN-gamma production in the respective cell-lines [17].
  • In addition, B cell CSPG blocked C1q receptor binding in a dose-dependent manner [21].

Other interactions of CD93

  • C1qR/CRT is located on the surface of many cell types [11].
  • Calreticulin, a candidate C1q receptor, was shown recently to be present on the surface of human neutrophils in association with glycosylphosphatidylinositol (GPI) anchored proteins, particularly CD59 [22].
  • Recently, a novel 33-kDa C1q receptor (gC1qR) that interacts with the globular head region of C1q was identified on Raji cells, as well as PBLs, neutrophils, and eosinophils [23].
  • The up-regulation of C1qR by inflammatory mediators and the ability of C1q itself to increase ICAM-1 expression suggest a potential role for these binding sites in vascular inflammation and immune injury [24].
  • Antibodies to HK receptors on leukocytes including Mac-1, LFA-1, uPAR, and C1qR inhibited IL-1beta secretion induced by tKa 98%, 89%, 85%, and 62%, respectively [25].

Analytical, diagnostic and therapeutic context of CD93


  1. Structure and homology of human C1q receptor (collectin receptor). Malhotra, R., Willis, A.C., Jensenius, J.C., Jackson, J., Sim, R.B. Immunology (1993) [Pubmed]
  2. Inhibition of the hemolytic activity of the first component of complement C1 by an Escherichia coli C1q binding protein. van den Berg, R.H., Faber-Krol, M.C., van de Klundert, J.A., van Es, L.A., Daha, M.R. J. Immunol. (1996) [Pubmed]
  3. Hepatitis C virus core protein inhibits human T lymphocyte responses by a complement-dependent regulatory pathway. Yao, Z.Q., Nguyen, D.T., Hiotellis, A.I., Hahn, Y.S. J. Immunol. (2001) [Pubmed]
  4. Exposure of human epidermal keratinocyte cell cultures to sulfur mustard promotes binding of complement C1q: implications for toxicity and medical countermeasures. Cowan, F.M., Broomfield, C.A., Smith, W.J. Journal of applied toxicology : JAT. (2000) [Pubmed]
  5. Control of the complement system. Liszewski, M.K., Farries, T.C., Lublin, D.M., Rooney, I.A., Atkinson, J.P. Adv. Immunol. (1996) [Pubmed]
  6. Complement receptor type 1 (CR1, CD35) is a receptor for C1q. Klickstein, L.B., Barbashov, S.F., Liu, T., Jack, R.M., Nicholson-Weller, A. Immunity (1997) [Pubmed]
  7. Mannose binding protein (MBP) enhances mononuclear phagocyte function via a receptor that contains the 126,000 M(r) component of the C1q receptor. Tenner, A.J., Robinson, S.L., Ezekowitz, R.A. Immunity (1995) [Pubmed]
  8. Platelet activation by C1q results in the induction of alpha IIb/beta 3 integrins (GPIIb-IIIa) and the expression of P-selectin and procoagulant activity. Peerschke, E.I., Reid, K.B., Ghebrehiwet, B. J. Exp. Med. (1993) [Pubmed]
  9. CD93 interacts with the PDZ domain-containing adaptor protein GIPC: implications in the modulation of phagocytosis. Bohlson, S.S., Zhang, M., Ortiz, C.E., Tenner, A.J. J. Leukoc. Biol. (2005) [Pubmed]
  10. Cell surface expression of C1qRP/CD93 is stabilized by O-glycosylation. Park, M., Tenner, A.J. J. Cell. Physiol. (2003) [Pubmed]
  11. The C1q and collectin binding site within C1q receptor (cell surface calreticulin). Stuart, G.R., Lynch, N.J., Day, A.J., Schwaeble, W.J., Sim, R.B. Immunopharmacology (1997) [Pubmed]
  12. Identification of human CD93 as the phagocytic C1q receptor (C1qRp) by expression cloning. Steinberger, P., Szekeres, A., Wille, S., Stöckl, J., Selenko, N., Prager, E., Staffler, G., Madic, O., Stockinger, H., Knapp, W. J. Leukoc. Biol. (2002) [Pubmed]
  13. C1q receptors: regulating specific functions of phagocytic cells. Tenner, A.J. Immunobiology (1998) [Pubmed]
  14. Calreticulin is released from activated neutrophils and binds to C1q and mannan-binding protein. Eggleton, P., Lieu, T.S., Zappi, E.G., Sastry, K., Coburn, J., Zaner, K.S., Sontheimer, R.D., Capra, J.D., Ghebrehiwet, B., Tauber, A.I. Clin. Immunol. Immunopathol. (1994) [Pubmed]
  15. C1qRP is a heavily O-glycosylated cell surface protein involved in the regulation of phagocytic activity. Nepomuceno, R.R., Ruiz, S., Park, M., Tenner, A.J. J. Immunol. (1999) [Pubmed]
  16. Murine CD93 (C1qRp) contributes to the removal of apoptotic cells in vivo but is not required for C1q-mediated enhancement of phagocytosis. Norsworthy, P.J., Fossati-Jimack, L., Cortes-Hernandez, J., Taylor, P.R., Bygrave, A.E., Thompson, R.D., Nourshargh, S., Walport, M.J., Botto, M. J. Immunol. (2004) [Pubmed]
  17. Regulation of CD93 cell surface expression by protein kinase C isoenzymes. Ikewaki, N., Kulski, J.K., Inoko, H. Microbiol. Immunol. (2006) [Pubmed]
  18. Human C1qRp is identical with CD93 and the mNI-11 antigen but does not bind C1q. McGreal, E.P., Ikewaki, N., Akatsu, H., Morgan, B.P., Gasque, P. J. Immunol. (2002) [Pubmed]
  19. Surfactant protein A down-regulates proinflammatory cytokine production evoked by Candida albicans in human alveolar macrophages and monocytes. Rosseau, S., Hammerl, P., Maus, U., Günther, A., Seeger, W., Grimminger, F., Lohmeyer, J. J. Immunol. (1999) [Pubmed]
  20. The potential involvement of Notch signaling in NK cell development. Rolink, A.G., Balciunaite, G., Demolière, C., Ceredig, R. Immunol. Lett. (2006) [Pubmed]
  21. Secreted chondroitin sulfate proteoglycan of human B cell lines binds to the complement protein C1q and inhibits complex formation of C1. Kirschfink, M., Blase, L., Engelmann, S., Schwartz-Albiez, R. J. Immunol. (1997) [Pubmed]
  22. A role for lipid rafts in C1q-triggered O2- generation by human neutrophils. Otabor, I., Tyagi, S., Beurskens, F.J., Ghiran, I., Schwab, P., Nicholson-Weller, A., Klickstein, L.B. Mol. Immunol. (2004) [Pubmed]
  23. Identification of a novel 33-kDa C1q-binding site on human blood platelets. Peerschke, E.I., Reid, K.B., Ghebrehiwet, B. J. Immunol. (1994) [Pubmed]
  24. Up-regulation of endothelial cell binding proteins/receptors for complement component C1q by inflammatory cytokines. Guo, W.X., Ghebrehiwet, B., Weksler, B., Schweitzer, K., Peerschke, E.I. J. Lab. Clin. Med. (1999) [Pubmed]
  25. High-Molecular-Weight Kininogen Fragments Stimulate the Secretion of Cytokines and Chemokines Through uPAR, Mac-1, and gC1qR in Monocytes. Khan, M.M., Bradford, H.N., Isordia-Salas, I., Liu, Y., Wu, Y., Espinola, R.G., Ghebrehiwet, B., Colman, R.W. Arterioscler. Thromb. Vasc. Biol. (2006) [Pubmed]
  26. C1qRP, the C1q receptor that enhances phagocytosis, is detected specifically in human cells of myeloid lineage, endothelial cells, and platelets. Nepomuceno, R.R., Tenner, A.J. J. Immunol. (1998) [Pubmed]
  27. Structural and functional evidence for microglial expression of C1qR(P), the C1q receptor that enhances phagocytosis. Webster, S.D., Park, M., Fonseca, M.I., Tenner, A.J. J. Leukoc. Biol. (2000) [Pubmed]
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