Plasma levels and in vitro production of tumor necrosis factor-alpha and interleukin-6 in patients with amebic liver abscess

We studied the plasma levels of tumor necrosis factor-alpha (TNF-alpha) interleukin-6 (IL-6) as well as the in vitro production of these cytokines by peripheral blood mononuclear cells, in 10 patients with amebic liver abscess (ALA) and seven healthy controls. TNF-alpha was measured using a bioassay with L929 fibroblasts; IL-6 was quantitated by the B9 cell line assay. In both assays, the number of viable cells was estimated by the conversion of MTT to formazan. TNF-alpha plasma levels were nondetectable (20 pg/mL) in ALA patients, as well as in the majority of healthy controls. The in vitro production of TNF induced by lipopolysaccharide was significantly decreased in ALA patients. Most ALA patients (8/10) had increased plasma levels of IL-6. Furthermore, the spontaneous production of IL-6 in vitro was significantly increased in ALA patients compared to controls. In the acute stage of the ALA, a negative relationship was found between the raised plasma levels of IL-6 and the in vitro diminished production of TNF-alpha. After recovery, ALA patients showed both normal plasma levels and in vitro production of TNF and IL-6. Our data corroborate previous reports regarding plasma levels of TNF in ALA, and suggest that E. histolytica induces the in vivo production of IL-6 through a TNF-independent pathway. The raised levels of IL-6 might in turn down-regulate the production of TNF in ALA patients.