Activation of human complement by glutaraldehyde-treated red cells

Abstract

THERE is now much evidence that the classical complement pathway can be activated by substances other than immune complexes. Leonard and Thorne1 found that precipitate formed between the polyanion, polyglutamic acid, and lysozyme was anticomplementary, although the site of action was not determined. Since then, many polyionic substances and complexes have been found to activate the classical complement pathway, namely polyinosinic acid2, dextran sulphate2,3, cellulose sulphate4, heparin–protamine complexes5, lipid A6, lysozyme–DNA complexes7, doublestranded DNA8 and C-reactive protein–polycation complexes9. Although activation by heparin–protamine complexes was found to take place in agammaglobulinaemic serum10, it is possible that the polyions do not react directly with C1, but that they bring about aggregation of IgG, which then combines with and activates C1. On the other hand, C-reactive protein attached to the surface of red cells can activate complement without involvement of antibody or IgG (refs 11, 12), as can certain oncaviruses13 and mitochondrial membranes14. It has also been shown that the complement component C1q will combine with glutaraldehyde-treated red cells and that the binding sites involved on the C1q molecule are probably those also involved in binding to immune complexes15. It has now been found that glutaraldehyde-treated red cells not only bind to C1q, but can also activate the complement system through the classical pathway, with no evidence of involvement of immunoglobulin.