Complement component factor H (H) is a 155-kDa plasma protein. It was first observed by NILSSON and MüLLER-EBERHARD (1965) as a minor component in C3 preparations, and its function was not known. They termed this protein β1 H globulin because of its β-electrophoretic mobility in agarose gels. The first function for this protein was recognized by WHALEY and RUDDY (1976a). They isolated a protein from human serum based on its ability to accelerate the activity of C3b inactivator (now termed factor I) and found that this protein was biochemically and immunologically identical to β1 H globulin. At the time, it was thought that I alone cleaved C3b into two fragments, C3c and C3d. Addition of H synergistically enhanced the activity of I-mediated cleavage of C3b. H not only enhanced the activity of I (termed its cofactor activity) but was also able to accelerate the decay of the C3 convertases of the alternative pathway of complement activation C3b, Bb or C3b, Bb, P (Fig. 1) and to inhibit the formation of these convertases (WHALEY and RUDDY 1976 a).
KeywordsHuman Complement Alternative Complement Pathway Membrane Cofactor Protein Human Complement Component Human Complement Factor
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