Nature 386, 506 - 510 (03 April 1997); doi:10.1038/386506a0

A second serine protease associated with mannan-binding lectin that activates complement

Steffen Thiel, Thomas Vorup-Jensen, Cordula M. Stover^*, Wilhelm Schwaeble^*, Steen B. Laursen, Knud Poulsen, Anthony C. Willis^†, Paul Eggleton^†, Søren Hansen, Uffe Holmskov^‡, Kenneth B. M. Reid^† & Jens C. Jensenius

Department of Medical Microbiology and Immunology, University of Aarhus, DK 8000, Aarhus, Denmark
^*Department of Microbiology and Immunology, University of Leicester, Leicester LE1 9HN, UK
^†MRC Immunochemistry Unit, University of Oxford, Oxford OX1 3QU, UK
^‡Department of Medical Microbiology, University of Odense, Odense DK 5000, Denmark

The complement system comprises a complex array of enzymes and non-enzymatic proteins that is essential for the operation of the innate as well as the adaptive immune defence¹. The complement system can be activated in three ways: by the classical pathway which is initiated by antibody–antigen complexes, by the alternative pathway initiated by certain structures on microbial surfaces, and by an antibody-independent pathway² that is initiated by the binding of mannan-binding lectin (MBL; first described as mannan-binding protein³) to carbohydrates. MBL is structurally related to the complement Cl subcomponent, Clq, and seems to activate the complement system through an associated serine protease known as MASP (ref. 4) or p100 (ref. 5), which is similar to Clr and Cls of the classical pathway. MBL binds to specific carbohydrate structures found on the surface of a range of microorganisms, including bacteria, yeasts, parasitic protozoa and viruses⁶, and exhibits antibacterial activity through killing mediated by the terminal, lytic complement components⁷ or by promoting phagocytosis⁸. The level of MBL in plasma is genetically determined^9–11, and deficiency is associated with frequent infections in childhood^12,13, and possibly also in adults^14,15 (for review, see ref. 6). We have now identified a new MBL-associated serine protease (MASP-2) which shows a striking homology with the previously reported MASP (MASP-1) and the two Clq-associated serine proteases Clr and Cls. Thus complement activation through MBL, like the classical pathway, involves two serine proteases and may antedate the development of the specific immune system of vertebrates.

1. Law, S. K. A. & Reid, K. B. M. Complement 2nd edn (ed. Male, D.) 1−88 (IRL, Oxford, 1996).
2. Ikeda, K., Sannoh, T., Kawasaki, N., Kawasaki, T. & Yamashina, I. Serum lectin with known structure activates complement through the classical pathway. J. Biol Chem. 262, 7451−7454 (1987). | PubMed | ISI | ChemPort |
3. Kawasaki, T., Etoh, R. & Yamashina, I. Isolation and characterisation of a mannan-binding protein from rabbit liver. Biochem. Biophys. Res. Commun. 81, 1018−1204 (1978). | PubMed | ISI | ChemPort |
4. Matsushita, M. & Fujita, T. Activation of the classical complement pathway by mannose-binding protein in association with a novel Cls-like serine protease. J. Exp. Med. 176, 1497−1502 (1992). | Article | PubMed | ISI | ChemPort |
5. Ji, Y.-H. et al. Activation of the C4 and C2 components of complement by a proteinase in serum bactericidal factor, Ra reactive factor. J. Immunol. 150, 571−578 (1993). | PubMed | ISI | ChemPort |
6. Turner, M. W. Mannose-binding lectin: the pluripotent molecule of the innate immune system. Immunol. Today. 17, 532−540 (1996). | Article | PubMed | ISI | ChemPort |
7. Kawasaki, N., Kawasaki, T. & Yamashina, I. A Serum lectin (mannan-binding protein) has complement-dependent bactericidal activity. J. Biochem. 106, 483−489 (1989). | PubMed | ChemPort |
8. Kuhlman, M., Joiner, K. & Ezekowitz, R. A. B. The human mannose-binding protein functions as an opsonin. J. Exp. Med. 169, 1733−1745 (1989). | Article | PubMed | ISI | ChemPort |
9. Sumiya, M. et al. Molecular basis of opsonic defect in immunodeficient children. Lancet 337, 1569−1570 (1991). | Article | PubMed | ISI | ChemPort |
10. Lipscombe, R. J. et al. High frequencies in African and non-African populations of independent mutations in the mannose binding protein gene. Hum. Mol. Genet. 1, 709−715 (1992). | PubMed | ChemPort |
11. Madsen, H. O. et al. A new frequent allele is the missing link in the structural polymorphism of the human mannan-binding protein. Immunogenetics 40, 37−44 (1994). | Article | PubMed | ISI | ChemPort |
12. Super, M., Thiel, S., Lu, J., Levinsky, R. J. & Turner, M. W. Association of low levels of mannan-binding protein with a common defect of opsonisation. Lancet ii, 1236−1239 (1989). | Article |
13. Garred, P., Madsen, H. O., Hofmann, B. & Svejgaard, A. Increased frequency of homozygosity of abnormal mannan-binding-protein alleles in patients with suspected immunodeficiency. Lancet 346, 941−943 (1995). | Article | PubMed | ChemPort |
14. Summerfield, J. A. et al. Mannose binding protein gene mutations associated with unusual and severe infections in adults. Lancet 345, 886−889 (1995). | Article | PubMed | ISI | ChemPort |
15. Nielsen, S. L., Andersen, P. L., Koch, C., Jensenius, J. C. & Thiel, S. The level of the serum opsonin, mannan-binding protein in HIV-1 antibody-positive patients. Clin. Exp. Immunol. 100, 219−222 (1995). | PubMed | ChemPort |
16. Baatrup, G., Thiel, S., Isager, H., Svehag, S. E. & Jensenius, J. C. Demonstration in human plasma of a lectin activity analogous to that of bovine conglutinin. Scand. J. Immunol. 26, 355−361 (1987). | PubMed | ChemPort |
17. Sato, T., Endo, Y., Matsushita, M. & Fujita, T. Molecular characterization of a novel serine protease involved in activation of the complement system by mannose-binding protein. Int. Immunol. 6, 665−669 (1994). | PubMed | ISI | ChemPort |
18. Endo, Y., Sato, T., Matsushita, M. & Fujita, T. Exon structure of the gene encoding the human mannose-binding protein-associated serine protease light chain: comparison with complement Clr and Cls genes. Int. Immunol. 9, 1355−1358 (1996).
19. Tan, S. M. et al. Improvements on the purification of mannan-binding lectin and demonstration of its Ca²⁺-independent association with a Cls-like serine protease. Biochem. J. 319, 329−332 (1996). | PubMed | ChemPort |
20. Jensenius, J. C., Andersen, L., Hau, J., Crone, M. & Koch, C. Eggs: conveniently packaged antibodies. Methods for purification of yolk IgG. J. Immunol. Meth. 46, 63−66 (1981). | Article | ChemPort |
21. Barton, G. J. Protein multiple sequence alignment and flexible pattern matching. Meth. Enzymol. 183, 403−428 (1990). | Article | PubMed | ISI | ChemPort |
22. Takada, E., Takayama, Y., Hatsuse, H. & Kawakami, M. A new member of the Cls family of complement proteins found in a bactericidal factor, Ra-reactive factor, in human serum. Biochem. Biophys. Res. Commun. 196, 1003−1009 (1993). | Article | PubMed | ISI | ChemPort |
23. Journat, A. & Tosi, M. Cloning and sequencing of full-length cDNA encoding the precursor of human complement component Clr. Biochem. J. 240, 783−787 (1986). | PubMed | ISI | ChemPort |
24. Lytus, S. P., Kurachi, K., Sakariassen, K. S. & Davie, E. W. Nucleotide sequence of cDNA coding for human complement Clr. Biochemistry 25, 4855−4863 (1986). | PubMed | ISI | ChemPort |
25. Mackinnon, C. M., Carter, P. E., Smyth, S. J., Dunbar, B. & Fothergill, J. E. Molecular cloning of cDNA for human complement component Cls. The complete amino acid sequence. Eur. J. Biochem. 169, 547−553 (1987). | Article | PubMed | ISI | ChemPort |
26. Tosi, M., Duponchel, C., Meo, T. & Julier, C. Complete cDNA sequence of human complement CIS and close physical linkage of the homologous genes Cls and Clr. Biochemistry 26, 8516−8524 (1987). | Article | PubMed | ISI | ChemPort |