Uptake of γ-Globulin and Complement by Red Cells exposed to Serum at Low Ionic Strength

Abstract

AT low ionic strength the rate of association of certain antibodies with their corresponding antigens is increased (for review see ref. 1) and the detection of human blood group antibodies may be facilitated^2,3. In the course of testing sera which had been ‘de-ionized’ either by passage through ‘Sephadex G-50’ columns or by dialysis against a sucrose–saline solution of ionic strength 0.025, it was observed that the sera were giving ‘false positive’ reactions; that is to say, if red cells were incubated with their own ‘de-ionized’ serum at I = 0.025, then washed and mixed with anti-human globulin serum, agglutination occurred. The red cells were only very weakly agglutinated by specific anti-7S γ-globulin sera but were strongly agglutinated by anti-β_1E-globulin serum and less strongly by anti-β_1C-globulin serum; thus the complement components C′₄ and C′_3a were both present on the red cells⁴. Positive results were also obtained with an immunoconglutinin serum (‘auto-stimulation’ type⁵). As expected, the addition of EDTA to the serum before incubation with red cells prevented the uptake of complement.