Expression analysis of K/k polymorphism. Flow cytometric analysis of 293T cells transiently transfected either with the wild-type Kell cDNA construct (pRc/CMV-wt) encoding the high incidence antigen k or with the Kell cDNA encoding the C698T mutation associated with K antigen (pRc/CMV-K). Antigen-positive RBCs were tested in parallel to control for antibody specificity. Alloimmune sera used were anti-k (GUE) and anti-K (6735416). The results are depicted as overlays of open histograms to represent negative control mock/RBCs and shaded histograms, representing positive control RBCs or transfected cells. Mean fluorescence intensity (as a measure of antibody binding) in log scale is on the x-axis and the relative number of cells is represented on the y-axis.