RESUMO
BACKGROUND: Several factors inhibit cellular immune response by deactivating macrophages, but very few, such as those described here, prevent macrophage 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 from lymphoblasts. The supernatant (S1) was obtained from the homogenized and centrifuged lymphoblasts. Then, macrophage cultures containing 0.2 x 10(6) cells from lymphoma-bearing or healthy mice were added to 10 microL of CFAL or S1, plus 5 micrograms of lipopolysaccharides (LPS)/mL, 40 U interferon-gamma or a blend of both. Macrophages were incubated with CFAL or S1 prior to or after adding the activators to investigate whether any of the previously mentioned lymphoma fractions inhibited macrophage activation or whether they deactivated them. The effect of CFAL or S1 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 lymphoma fractions). RESULTS: LPS, IFN-gamma, and the LPS/gamma blend activated macrophages from both lymphoma-bearing and healthy mice. None of the lymphoma fractions deactivated macrophages. CFAL, but not S1, inhibited the macrophage activation, i.e., the percentage of inhibition of nitric oxide releasing 76.7% and 78.1% in macrophages from healthy and lymphoma-bearing mice, respectively. In addition, CFAL was unable to inhibit the macrophage-activation effect of IFN-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 not by IFN-gamma controls.