C1r depleted serum (C1r-Dpl) is normal human serum depleted of C1r by immunoaffinity chromatography. The product is tested for the absence of C1r by functional assays for classical pathway activity and for C1r protein by double immunodiffusion. C1r-Dpl is certified to possess a functional alternative pathway for complement activation (Morgan, B.P. (2000); Dodds, A.W. and Sim, R.B. (1997)).
In serum C1r is present in its proenzyme form (Valet, G and Cooper N.R. (1974); Ziccardi, R.J. and Cooper N.R. (1976)). C1r enzyme is the activated form of C1r proenzyme. C1r is a subunit of the C1 complex which is the first component in the classical pathway of complement. C1r proenzyme is an inactive zymogen until C1 is activated. C1r is activated when C1 binds to and is activated by antibodies bound to antigens (immune complexes) yielding C1r enzyme, the first protease that initiates the cascade. A functional classical pathway can be reconstituted by addition of purified C1r enzyme or proenzyme (31 µg/mL) to the C1r-Dpl indicating that all other complement components necessary for classical pathway activation are present and active.
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