Circulating cytokine concentrations in tuberculosis and other chronic bacterial infections

Cytokines are a group of hormone-like polypeptides that play a variety of regulatory roles in host defense against infection. Because of the possible different involvement of these mediators in bacterial infections and tuberculosis, enzyme immunoassay was used to measure comparatively the plasma levels of the proinflammatory cytokines interleukin-1 beta (IL-1beta), tumor necrosis factor alpha (TNF-alpha), interleukin-6 (IL-6) and interferon gamma (IFN-gamma) in 25 immunocompetent patients divided into two groups: in 12 patients clinical and microbiological diagnosis showed a chronic bacterial infection and 13 patients had pleuropulmonar tuberculosis. After resolution of the infectious disorders (> or = 3 months), these measurements were repeated for each patient. High levels of IL-1b, TNF-alpha and IL-6 were observed at study entry, but no significant difference was found between the groups. In contrast, plasma levels (mean +/- SEM) of IFN-gamma were significantly higher in patients with tuberculosis when compared with the bacterial group (0.753 +/- 0.201 vs 0.325 +/- 0.105 IU/ml; P = 0.020). This different pattern of plasma proinflammatory cytokines could be ascribed to a prevaling role of the mediators of so-called Th-1 immune response (IFN-gamma) in host defense against infection with Mycobacterium tuberculosis.