Inhibition of lactic acid production reverts the phenotypical changes induced by MelIm supernatants. Supernatants were generated in the presence or absence of oxamic acid, an inhibitor of lactate dehydrogenase. Monolayer cultures of the cell lines J82 and MelIm were grown in RPMI-1640 medium and oxamic acid was added on day 0. After 4 to 6 days, supernatants were harvested and stored at -20°C. Monocytes were cultured in the presence of 50% supernatant, and CD1a expression was determined after 7 days by flow cytometry (A). (B) Lactate in the tumor cell supernatants was determined with a routine procedure as described in “Materials and methods.” Error bars indicate SEM.