In vitro reactions of anti-Rh antibodies depending on the pattern of IgG subclasses.

In 47 serum samples obtained from 31 women immunized with D antigen of the Rh system the level of anti-Rh D antibodies was measured by the papain and antiglobulin tests and the IgG subclasses of anti-Rh antibodies were determined. If the antibodies were of the IgG1 subclass or if this subclass prevailed in the IgG subclass pattern, the antibody level determined by the papain test of Löw was higher or equal to their level found in the antiglobulin test. In all cases, in which the antibodies titer was higher in the antiglobulin test, the antibodies were either of the IgG3 subclass exclusively, or this subclass prevailed quantitatively. This was due to partial inactivation of antibodies belonging to the IgG3 subclass by papain added to the serum in the Löw's test. In the test with papainized erythrocytes (called two-stage test) the IgG subclasses could not be differentiated, and the results obtained then were always higher than in the antiglobulin test. The differences in the reactions of antibodies performed routinely for diagnostic purposes can be explained by differences in immunoglobulin subclasses produced during immunization.