A suitable procedure for the production of human
monokines was defined as 'differentiation-induction' culture. Human monocytic
leukemia THP-1 cells were well-differentiated from nonfunctional promonocytes into macrophage-like cells by the induction with a combination of
mezerein,
retinoic acid, and aMycoplasma fermentans extract. The differentiated THP-1 cells secreted a high amount of macrophage
differentiation-inducing factor (DIF) activity and concomitantly produced other known
monokines, such as
tumor necrosis factor-α (TNF-α), interleukin-1α (IL-1α) and interleukin-1β (IL-1β), into the medium. These results suggest that other novel human
monokines may also be found in the
conditioned medium of THP-1 cells induced by the 'differentiation-induction' culture conditions defined in this study. Macrophage DIF was purified to homogeneity and NH(2)-terminal amino acid sequence analysis revealed that macrophage DIF is very similar or identical to human
leukemia inhibitory factor (LIF). The
cDNA encoding human LIF was isolated using the polymerase chain reaction, and a clone producing 3.7 μg/10(6) cells day recombinant LIF was selected from Chinese hamster ovary (CHO) cells which were transfected with the LIF
cDNA. The recombinant LIF production in CHO cells was quantified using MTT reduction assay with M1 cells.