Complement and Ig Uptake by Erythrocytes in Low Ionic Strength Solutions

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Abstract
The uptake of Ig and complement from plasma by [human] red blood cells (RBC) under low ionic strength (LIS) conditions using Rh-negative RBC and anti-Rh antibodies was studied. The ionic strength of plasma/RBC mixtures was lowered by dialysis against 5% mannitol, pH 6.0. Bromelin-modified RBC failed to bind Ig or complement in low ionic strength conditions; unmodified RBC bound the majority of anti-D. The bound anti-D (consisting of IgG1, IgG3, IgA and IgM molecules) could be eluted into 0.9% NaCl yielding a higher recovery of antibody than that obtained by specific absorption-elution techniques. Although uptake of Ig by RBC was independent of complement activation, the subsequent elution of bound Ig into normal ionic strength solutions was not. Small amounts of Ig remained on EC43 [erythrocyte, complement component 4, complement component 3] and EC4, but not on RBC that did not become complement sensitized during low ionic strength exposure. Ig probably remained attached to RBC via a complement-RBC bond.