Detection of a factor released by L5178Y lymphoblasts that inhibits mouse macrophage-activation induced by lipopolysaccharides

Background. Several factors inhibit cellular immune response by deactivatin g macrophages, but very few, such as those described here, prevent macropha ge activation. Methods. Ascites liquid from 12-day-old BALB/c mice bearing 5178Y lymphoma tumors was collected, and cell-free ascites liquid (CFAL) was separated fro m lymphoblasts. The supernatant (S1) was obtained from the homogenized and centrifuged lymphoblasts Then, macrophage cultures containing 0.2 X 10(6) c ells from lymphoma-bearing or healthy mice were added to 10 mu L of CFAL or S1, plus 5 mu g of lipopolysaccharides (LPS)/mL, 40 U interferon-gamma or a blend of both, Macrophages were incubated with CFAL or SI prior to or aft er adding the activators to investigate whether any of the previously menti oned lymphoma fractions inhibited macrophage activation or whether they dea ctivated them. The effect of CFAL or SI was estimated as the diminution of the amount of nitric oxide released by the experimental macrophage cultures with respect to controls (activated macrophages treated with none of the l ymphoma fractions). Results. LPS, IFN-gamma, and the LPS/gamma blend activated macrophages from both lymphoma-bearing and healthy mice, None of the lymphoma fractions dea ctivated macrophages. CFAL, but not SI, inhibited the macrophage activation , i.e., the percentage of inhibition of nitric oxide releasing 76.7% and 78 .1% Ln macrophages from healthy and lymphoma-bearing mice, respectively. In addition, CFAL was unable to inhibit the macrophage-activation effect of I FN-gamma or the LPS/IFN-gamma blend. Conclusions. Mouse L5178Y lymphoma releases a factor that in vitro inhibits the macrophage activation induced by LPS, but nut by IFN-gamma controls. ( C) 1999 IMSS, Published by Elsevier Science Inc.