A reappraisal of the macrophage electrophoretic mobility (MEM) test for the measurement of lymphokine activity.

Using a cell electrophoretic apparatus, which was sensitive in detecting small changes in electrophoretic mobility (EPM), the macrophage electrophoretic mobility (MEM) test was investigated as a routine method for detecting lymphokine activity. Electrophoretic analysis of guinea-pig macrophages revealed 2 main subpopulations, one with an EPM of 0.90 micron cm s-1 V-1 (fast) and the other, an EPM of 0.83 micron cm s-1 V-1 (slow). From 23 experiments the fast and slow populations were found to consist of 90% and 10% cells, respectively. When macrophages were incubated with standard guinea-pig lymphokine preparations there was a significant decrease in the fast population with a corresponding increase in the slow population. This lymphokine induced 'slowing' of the macrophages was shown to be very reproducible. Since only 50% of macrophages of high EPM were observed to respond to lymphokine activity, it is not surprising that the MEM test has failed in the past when investigators have accepted as significant a 10-15% reduction in EPM, estimated from measurements made on only 10 macrophages. Parallel bioassays indicated that there were appreciable potency differences for macrophage slowing factor (MSF) and macrophage migration inhibition factor (MIF) activities in the lymphokine preparations used which suggest that these activities may be due to different molecular entities.