ADCC (K-cell) lysis of human erythrocytes sensitized with rhesus alloantibodies. III. Comparison of IgG anti-D agglutinating and lytic (ADCC) activity and the role of IgG subclasses.

Conventional manual (enzyme and antiglobulin titres) and AutoAnalyser quantitation of anti-D sera were compared with the ability of the same sera to mediate lysis of Rh(D) positive red cells in an ADCC assay. AutoAnalyser (AA) quantitation correlated significantly with manual titration methods, although there were wide discrepancies between individual sera. The ADCC activity of the anti-D sera did not correlate with any of the conventional assays (AA, enzyme, antiglobulin). There were significant differences between anti-D sera obtained from females immunized during pregnancy and male volunteers immunized by deliberate injection. The female sera contained significantly less anti-D when assessed by AA, yet were significantly more active in ADCC activity at equivalent concentrations. These functional differences in anti-D activity could not be attributed to the absence of IgG subclasses (IgG1 and IgG3) known to induce ADCC. However, there was a relationship between ADCC and IgG1/IgG3 titres in that high ADCC activity was seen where the IgG3 titre was higher than the IgG1 titre. In the male anti-D sera IgG1 titres were greater than or equal to IgG3 titres and ADCC activity was very low.