The macrophage electrophoretic mobility test (MEM) some technical considerations.

The following parameters of the cytopherometric test system have been studied. 1. Temperature is less important for the production of macrophage slowing factor (MSF) by lymphocyte-antigen interaction than it is for the activity of MSF on macrophages. 2. Lymphocyte number titration curves allow discrimination between 'weak' and 'strong' antigen responses. 3. Lymphocyte-antigen reaction reaches a plateau after 30 min incubation, whilst maximum MSF-macrophage reaction requires 60 min. 4. Interaction of MSF with macrophages is sensitive to cycloheximide. 5. Irradiation of peritoneal exudate cells (200 rad) is essential in order to obtain a maximal result in the MEM test. In the 'split MEM test, 200 rad to the indicator peritoneal exudate cells produces a greater result, i.e. it in some way amplifies the macrophage response to MSF. 6. Excess of peritoneal exudate cells, especially when non-irradiated, suppresses the test result. This is not due to consumption of MSF produced. Probably macrophages rather than lymphocytes are responsible for the suppression.