Nielsen LK, Norderhaug L, Sandlie I, Dziegiel MH. In vitro functional test of two subclasses of an anti-RhD antibody produced by transient expression in COS cells. APMIS 2006;114:345–51. For over 35 years hemolytic disease of the fetus and newborn (HDFN) due to RhD has been effectively prevented by anti-RhD antibodies obtained from alloimmunized women or deliberately immunized men. However, due to the reduced number of immunized women and for ethical reasons it is foreseen that other sources of anti-RhD will be needed. One such source is recombinant human antibodies. Here we describe the construction of plasmids encoding two subclasses (IgG1 and IgG3) of an anti-RhD antibody, their transient expression in COS cells, and subsequent functional characterization of the antibodies with regard to specificity and ability to mediate a respiratory burst. The recombinant anti-RhD antibodies were specific for the RhD antigen and were able to mediate a respiratory burst. Thus these antibodies might be of use as future rhesus prophylaxis.