Normal human serum was depleted of factor I by immunoaffinity chromatography. The product is tested for the absence of factor I by double immunodiffusion. Factor I is a regulator of complement activation (Pangburn, M.K., et al. (1977)). Factor I-Dpl is still capable of activating all three pathways of complement if metal ions are added. Activation of the alternative pathway is spontaneous and occurs in normal blood, in factor I deficient individuals and in Factor I-Dpl serum. Our depleted serum is stored with 0.1 mM EDTA to inhibit spontaneous activation. Upon the addition of magnesium ions spontaneous activation produces fluid phase C3b due to alternative pathway tick-over (Pangburn, M.K., Müller-Eberhard, H.J. (1980)). In normal human blood or serum this C3b would be rapidly inactivated to iC3b, by factors H and I (Pangburn, M.K., et al. (1977); (Laursen, S.B. et al. (1994)), however, in the absence of factor I, C3b remains as C3b. This C3b binds factor B and factor B is activated by factor D forming the C3b,Bb complex and the free Ba fragment. Because factor H is present in Factor I-Dpl Bb is rapidly decayed off the C3b,Bb complex. The free C3b then binds another factor B and the process repeats itself until little or no factor B remains. In factor I-deficient individuals their factor B levels are very low and they exhibit low or very low C3 levels (Davis, A.E.III, et al. (1977); Nilsson, S.C., et al. (2009)). Individuals with factor I deficiencies are susceptible to recurrent bacterial infections and exhibit little or no alternative pathway activity (Abramson, N. et al. (1971); Nilsson, S.C., et al. (2009)).
Factor I-Dpl is certified to possess a functional alternative pathway for complement activation only if factor I or a controlling factor with a function similar to that of factor I is added prior to the addition of metal ions (specifically Mg++). Full reconstitution requires addition of 34 µg factor I/mL serum. It is also tested for and certified to contain functional classical pathway indicating that all other complement components necessary for classical and alternative pathway activation are present except for factor I (Morgan, B.P. (2000); Dodds, A.W. and Sim, R.B. (1997)).
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