Platelet inhibition of human lymphocyte PHA-induced blastoid transformation

The reduced PHA responsiveness of human lymphocytes obtained from heparinized as compared to defibrinated blood has been shown to be due to platelet contamination in the former. Inhibition of blastoid transformation and lymphocyte death is directly related to the number of platelets added to a culture. Divalent ions partially reduce this platelet inhibitor phenomenon but do not block if completely. The "toxic" platelet components appear to be localized in the membranes and particulate matter after homogenization and hard centrifugation. Comparative studies of PHA transformation must control platelet contamination of the cultures in order to avoid severe difficulties of interpretation.