The indirect leucocyte migration inhibition assay--an endotoxin-sensitive chemokinetic assay. Part II

Depletion of agarose for endotoxins resulted in a low spontaneous migration of polymorphnuclear cells (PMNC). Re-addition of endotoxin, in casu lipopolysaccharide from E. coli 026:B6 (LPS), enhanced the spontaneous PMNC migration in a two-phased dose-response pattern, reaching maximum migration with LPS 1 x 10(-7) g/ml. Thus, the migration of PMNC under agarose seems to be a chemokinesis. Leucocyte migration inhibition factor (LIF), induced by PPD 50 micrograms/ml at endotoxin-free conditions, significantly reduced the PMNC migration compared to supernatants from control cultures, however not compared to the conventional limit of significance, MI = 0.80. With increasing PMNC migration there was an insignificant decrease in the MI. Addition of LPS, 1 x 10(-9) g/ml, during LIF induction caused a significant increase in LIF production, an effect which overshadowed the effect of PPD. Thus, the application of the conventional limit of significance, MI = 0.80, may result in false-negative or false-positive conclusions, depending upon the endotoxin contamination. A standardization of the endotoxin content in both steps of the indirect leucocyte migration inhibition assay seems mandatory in order to obtain a reliable and reproducible bioassay.