Evidence for the Binding of Two Factors of the Third Component of Complement to Red Cells

Abstract

A NUMBER of recent investigations^1–4 have led to the view that there are two factors in serum which are responsible for the action of what has previously been called the third component of complement (C′3). This communication presents further evidence for this view, based on experiments with radioactive guinea pig complement prepared biosynthetically according to the method of Penn et al.⁵. This was used in preference to serum proteins labelled with iodine-131 with which Mayer et al.⁶ have demonstrated uptake of radioactivity by EAC′₁₄₂ in the reaction with C′3. It was felt that biosynthetically labelled complement would be less likely to be adsorbed non-specifically than complement labelled with iodine-131.