MIXED LEUCOCYTE REACTION - STUDIES USING LEUCOCYTES FROM UNRELATED HUMAN SUBJECTS

Summary. The MLR has been studied in 87 culture combinations assessed by morphological techniques. The upper limit of negativity in these cultures was taken as the mean index of transformation found in all control cultures plus 2 standard deviations. Two sampling times (4 days and 6 days) were used. 6/87 cultures were within the negative range on both occasions. Of the positive cultures, 4 different patterns of response were observed and are described. The significance of these patterns is not yet clear. Similar results were found in those 69 cultures which were assessed by the degree of incorporation of I125 iododeoryuridine. This method is more sensitive than the morphological technique and fewer cultures could be regarded as within the negative range (mean of controls ± 2 standard deviations). The same patterns of response were observed. The result of the MLR is not very reproducible when assessed by height of response. Non‐technical factors affecting reproducibility are discussed. It was found that a period of cooling of cells prior to culture increased the index of transformation. © 1969 Blackwell Publishing Ltd