Characterization of human erythrocyte alloantibodies by IgG subclass and monocyte interaction.

Human blood group antibodies of 11 specificities were examined for ability to mediate interaction with normal blood monocytes, IgG subclass composition, and titer score. Most antibodies were normally non-complement-binding (except anti-JKa) and clinically significant (except anti-Lub). A simple and relatively rapid in-vitro assay for the visualization of sensitized erythrocyte-monocyte interaction is described. Capillary procedures were adapted for IgG subclass composition determinations. Standard serologic tests were used to assess antibody titer score. A relationship appeared to exist between increased antibody titer score and increased interaction of sensitized erythrocytes (RBC) with normal blood monocytes (MNL), insofar as the mean titer score for antibodies that did mediate significant interaction was 52, whereas titer scores for antibodies that did not averaged 25. One or more examples within all antibody specificity, mediated significant RBC-MNL interaction. No relationship was observed between IgG subclass composition and mediation of RBC-MNL interaction except that all antibodies that did mediate interaction contained IgG1 or IgG3. Characteristic patterns of IgG subclass composition were observed for many antibody specificity groups, although too few examples were tested for valid statistical analysis. This study identifies two features of common blood group antibody populations that are instrumental in mediating erythrocyte destruction by monocytes in vitro. Similar information may be of value in predicting the result of erythrocytes transfused to patients with antibodies of unknown clinical significance.