The Journal of Immunology, Vol 146, Issue 4 1265-1270, Copyright © 1991 by American Association of Immunologists

ARTICLES

Two major serum components antigenically related to complement factor H are different glycosylation forms of a single protein with no factor H- like complement regulatory functions

C Timmann, M Leippe and RD Horstmann
Bernhard Nocht Institute for Tropical Medicine, Hamburg, F.R.G.

Factor H is a 150-kDa serum glycoprotein with key regulatory functions in the alternative pathway of complement activation. Two glycoproteins with a molecular mass of approximately 42 and 37 kDa that react with an antiserum against factor H were purified from human plasma. The two glycoproteins have identical N-terminal amino acid sequences but differ in glycosylation. Sequence comparisons indicated that they both correspond to a 1.4-kb mRNA recently cloned from human liver cDNA. The serum concentration of the two glycoproteins together was estimated to be approximately 40 mg/liter. They were found not to exert factor H- like regulatory functions in the alternative pathway. Thus, the 42-kDa glycoprotein described here appears to be distinct from the previously characterized factor H-related protein of similar size, suggesting that human serum contains two factor-H related molecules which both have a molecular mass of 41 to 43 kDa but which differ largely in structure.

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