Semi-quantitative analysis of WBC contamination in purified PRBCs by PCR. WBC DNA was isolated from PRBC-enriched fractions and different dilutions of normal blood. PCR was performed to detect Y chromosome DNA as a marker of leukocytes from male mice. Normal blood with different dilutions was used as a marker to evaluate the quantity of contaminating WBCs. These data are representative of three independent experiments. PRBC-enriched fractions isolated by the magnetic (Lane 1), Nycodenz (Lane 2) and Percoll methods (Lane 3). Normal blood diluted 104-fold (Lane 4), 103-fold (Lane 5), 102-fold (Lane 6), 10-fold (Lane 7) and undiluted (Lane 8).