Human Rh monoclonal antibodies: assessment of functional activity by chemiluminescence and RhD antibody quantitation

In vitro cellular assays have been described which are capable of evaluating the interactions between sensitised red cells and monocyte or K cells. The chemiluminescence assay (CL) has several advantages over other cellular assays used to assess functional activity. The CL assay unlike the ADCC assays does not require the use of radioisotopes and therefore can be easily integrated into the work of a Reference Serology laboratory. The CL assay is an objective test and not labour intensive which is the main criticism of the monocyte monolayer assay. Seventy-four monoclonal anti-Ds and 29 other Rh specificities have been evaluated by a CL assay. The use of the chemiluminescent response produced by erythrophagocytosis of sensitised red cells has been shown to correlate well with the in vivo response to red cells sensitized with polyclonal IgG antibodies. This study aimed at investigating whether the CL assay could identify and differentiate monoclonal antibodies that are capable of eliciting a response from human monocytes. Poor correlation was obtained between the CL assay results and anti-D quantitation (r = 0.236). The chemiluminescence assay discriminated between anti-D's with high quantitation levels but low predicted functional activity and anti-Ds of low quantitation levels which produced elevated CL responses. Only 3 of the 29 non-Rh D specificities tested produced a response in the CL assay emphasising the importance of specificity in the functional activity of monoclonal antibodies. The demonstration of significant differences in the functional capabilities of monoclonal antibodies has important implications for reviewing the possible use of monoclonal anti-D preparations for Rh immune prophylaxis and highlights the requirement for factors other than the antibody concentration to be examined.