Localization of lymphocytes producing macrophage migration inhibitory factor in albumin density gradients

Lymph node cells of guinea pigs immunized with complete Freund's adjuvant were fractionated by centrifugation on a discontinuous albumin gradient and the resulting cell layers tested for their ability to release macrophage migration inhibitory factor (MIF) upon in vitro exposure to tuberculin purified protein derivative. It was found that MIF production is limited to lymphocytes of lower density, representing only one fourth of all cells, while high density, small lymphocytes are inactive in this respect. Peak MIF production was usually associated with top layer (lowest density) cells, cultured at a concentration 5–10 times lower than that required for MIF formation by unfractionated cells.