C3/C4-Depleted Serum is normal human serum in which C3 and C4 have been removed by immunoaffinity chromatography. The product is tested for the absence of C3 and C4 activity by testing classical and alternative pathway function. It is certified to exhibit less than 2% classical pathway activity and less than 5% alternative pathway activity. After reconstitution with C3 (1.3 mg C3/mL), C3/C4-Depleted Serum is certified to possess a functional alternative pathway for complement activation (Morgan, B.P. (2000); Dodds, A.W. and Sim, R.B. (1997)). Similarly, a functional classical pathway can be reconstituted by addition of purified C4 protein (400 ug/mL) and C3 protein (1.3 mg/mL) indicating that all other complement components necessary for classical and alternative pathway activation are present. Although a functional lectin pathway should also be reconstituted by the addition of similar concentrations of C3 and C4, the function of this pathway is not tested.
Note that if only C4 is added there is a weak C3 by-pass mechanism whereby the convertase C4b,C2a is able to activate C5 (Rawal, N. & Pangburn, M.K. 2003) and form C5b-9 complexes capable of causing low grade lysis. This system of C5 activation is functional in both the classical and the lectin pathways and is approximately 1000-fold less active than in the presence of C3 and C4.
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