The mechanism of carbohydrate-mediated complement activation by the serum mannan-binding protein

Serum mannan-binding protein (S-MBP), a lectin specific for mannose and N-acetylglucosamine, was documented to activate complement through the classical pathway. In this study, we examined the mechanism that initiates this activation. By a passive hemolysis test using sheep erythrocytes coated with...

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Bibliographic Details
Published in:The Journal of biological chemistry 1990-02, Vol.265 (4), p.1980-1984
Main Authors: OHTA, M, OKADA, M, YAMASHINA, I, KAWASAKI, T
Format: Article
Language:English
Subjects:
Analytical, structural and metabolic biochemistry
Animals
Binding and carrier proteins
Biological and medical sciences
Carrier Proteins - blood
Carrier Proteins - isolation & purification
Collectins
Complement Activation
Complement C1q - metabolism
Complement C1r - metabolism
Complement Pathway, Classical
Erythrocytes - drug effects
Fundamental and applied biological sciences. Psychology
Hemolysis
Humans
Kinetics
Mannans - blood
Mannans - pharmacology
Proteins
Sheep
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Summary:Serum mannan-binding protein (S-MBP), a lectin specific for mannose and N-acetylglucosamine, was documented to activate complement through the classical pathway. In this study, we examined the mechanism that initiates this activation. By a passive hemolysis test using sheep erythrocytes coated with yeast mannan, the activation of complement by human S-MBP was shown to proceed in the absence of C1q. The following binding studies using 125I-labeled C1r2s2 and C1s indicated that the activated form of C1r2s2 bound to S-MBP located on the surface of the cells with high affinity. The binding of C1s to the cell-bound S-MBP require the presence of C1r, suggesting that C1r2s2 binds to S-MBP through C1r. The activation of C1s from a proenzyme to a protease was mediated by cell-bound S-MBP in the presence of C1r and the activated protease remained associated with the cells and was not released into the medium. The activation of complement with S-MBP was a solid phase event and did not proceed in a fluid phase. On the basis of these results, it was concluded that S-MBP is responsible for the initiation of carbohydrate-mediated complement activation as C1q does in immune complex-mediated complement activation.
ISSN:0021-9258
1083-351X
DOI:10.1016/s0021-9258(19)39928-4