Complement (C) activation is believed to play an adverse role in several chronic degenerative disease processes, including
atherosclerosis,
myocardial infarction and
Alzheimer's disease. We developed several in vitro quantitative assays to evaluate processes which activate C in human serum, and to assess candidates which might block that activation. Binding of
C-reactive protein (CRP) to immobilized cell surfaces was used as a tissue-based method of activation, while
immunoglobulin G in
solution was used as a surrogate antibody method. Activation was assessed by deposition of C fragments on fixed cell surfaces, or by capture of
C5b-9 from
solution. We observed that several cell lines, including SH-SY5Y, U-937, THP-1 and ECV304, bound CRP and activated C following attachment of cells to a
plastic surface by means of air drying. Treatment of human
neuroblastoma SH-SY5Y cells with the
reactive oxygen intermediates generated by
xanthine (Xa) -
xanthine oxidase (XaOx) prior to air drying or by
hydrogen peroxide solutions after air drying, enhanced C activation, possibly through oxidation of the cell
lipid membrane. Several C inhibitors were tested for their effectiveness in blocking these systems. Pentosan polysulphate (PPS), an orally active agent, blocked C activation in the same concentration range of 1-1000 microg/ml as
heparin,
dextran sulphate,
compstatin and
fucoidan. PPS may have practical application as a C inhibitor.