Leucocyte migration inhibition assay from clotted plasma droplets.

Two different techniques for performing leucocyte migration inhibition factor (LIF) assays were compared. A clotted plasma droplet LIF assay gives similar results as the conventional capillary tube method, but it is more sensitive and technically simpler to perform, and less blood is required for the assay. The plasma droplet method is suitable for particulate (BCG) as well as soluble (PPD) antigens, provided that the culture medium is supplemented with horse or human serum. If foetal calf serum is used no inhibition can be demonstrated with soluble antigen. Defibrinated blood gives the most clear-cut results and LIF activity can still be detected even after 24 hours storage of samples. EDTA anti-coagulated blood can alternatively be used, but it is less stable. The assay can still be performed after 3 hours storage of the blood, although the migration inhibition is decreasing. After 24 hours storage EDTA anticoagulated blood cannot be used for LIF assays.