Figure 1: Scheme of the classical CDC-crossmatch as the current standard procedure for the detection of donor-specific antibodies. (A) Antibodies (monomeric IgG and pentameric IgM) are part of of a recipient’s serum and may be directed against HLA-molecules (blue and yellow) expressed on a given donor’s lymphocytes. (B) Activation of the complement cascade from added rabbit complement (C’) through the antibodies (blue) bound to the respective HLA molecules. (C) Positive reaction by ethidium bromide staining of the nuclei of lethal cells (red colour) after their lyses by the complement system (right side) in contrast to a negative reaction detectable by acridine orange staining (green colour) of vital cells to which no antibodies had bound and which have accordingly not been lysed by the complement added (left side). The red cylinders symbolize the membrane attack complexes (MACs/C5b-9) as final complement activation products. The intensity of the complement reaction is categorized by indicating the percentage of red (dead/lysed) cells with the score system of the National Institute of Health as shown in the legend of Table 1A.