[Functional evaluation of erythrocytic antibodies by photometric detection of erythrophagocytosis in the monocyte monolayer assay].

In haemolytic disease of newborn (erythroblastosis fetalis) the in vivo behaviour of erythrocytic IgG antibodies is of particular significance. The monocyte monolayer assay (MMA), which determines by microscopy the number of erythrocytes phagocytosed by monocytes, is an important functional test for the qualitative assessment of erythrocytic IgG antibodies. We set up a photometric MMA and compared it with the microscopic MMA. In both tests we employed commercially available rhesus antibody sera and examined 8 sera of pregnant women with mild and severe courses of haemolytic disease of newborn by the photometric MMA. Good agreement was found between the microscopic and photometric MMA (r = 0.93). Over and above this the photometric MMA correlated with the course of haemolytic disease of newborn in 7 out of 8 cases (with one false-positive finding). The photometric technique permits rapid, sensitive and reproducible determination of erythrophagocytosis in microtitre plates. This method is based on the photometric detection of haemoglobin of phagocytosed erythrocytes via a peroxidase reaction. Standardised photometric MMA could in future be more widely applied especially in haemolytic disease of newborn for the functional characterisation of erythrocytic antibodies, the incidence of intra-assay and inter-assay errors being low.