Differences in the characteristics of human monoclonal and polyclonal anti‐D as revealed by immunochemical investigations: human monoclonal antibodies share specificities with natural antibodies

To determine the basis of the tissue cross-reactions shown by some human monoclonal anti-Rh D antibodies, we have investigated the tissue reactivities of 48 further human monoclonal antibodies (mAb) against D and other Rh antigens, and compared them with those of normal and anti-D sera and immunoglobulin preparations, and affinity-purified polyclonal anti-D antibodies. Although we were unable to detect any tissue reactivities associated with the D-binding fraction of polyclonal antisera or prophylactic immunoglobulin, the non-erythroid cell types identified by the tissue-reactive human anti-Rh mAb of both IgM and IgG class were those recognized by antibodies present in both normal and anti-D sera. These results indicate: (a) that the tissue specificities of human anti-Rh mAb are similar to those of natural antibodies, and (b) that there are immunochemical differences between polyclonal and monoclonal anti-D antibodies, at least of IgG class, which may be relevant to the use of the latter in the prevention of haemolytic disease of the new-born by immune prophylaxis.