The indirect assay for leukocyte migration inhibitory factor (LIF)--standardization and the effect of pH.

In the indirect assay for leukocyte migration inhibitory factor (LIF), lymphokine-rich supernatants were obtained by culture of stimulated lymphocytes and then tested for LIF activity in agarose plates using purified granulocytes as target cells. Studies on the standardization of the conditions under which LIF acts on the target cells are described, with emphasis on the use of "standard" supernatants of known LIF activity and the influence of pH on the action of LIF and the sensitivity of the assay. The observation that LIF activity is reduced when the ambient pH falls below 7.2 is suggested as an explanation firstly for the "escape" phenomenon seen particularly in capillary tube assays for LIF, and secondly for the reduced sensitivity of the capillarly tube assay in comparison with the corresponding agarose plate assay.