Secretion of interleukin-6 by peripheral blood mononuclear cells from patients with pulmonary tuberculosis and their contacts.

The acute phase response, cell-mediated immunity and delayed type hypersensitivity in pulmonary tuberculosis (TB) may be mediated and regulated by the synthesis and release of interleukins 1 and 6 (IL-1, IL-6) and tumour necrosis factor (TNF) alpha. To examine this, peripheral blood mononuclear cells (PBMC) from TB patients, healthy controls and socially matched controls were cultured in the presence or absence of 5 micrograms/ml lipopolysaccharide-endotoxin (LPS) for 48 hours. IL-6 in the supernatant fluids (SNF) was measured using biological and immunoassays. Spontaneous release of functionally active IL-6 was significantly increased in PBMC SNF of TB patients when compared with both healthy controls and socially matched controls (median values of 4265, 356 and 1245 pg/10(6) cells respectively, p < 0.001). PBMC of social controls produced markedly more IL-6 than those of healthy controls (p < 0.001). LPS stimulated IL-6 production showed similar patterns for TB patients, healthy and social controls (median values of 6806, 1291 and 2667 pg/10(6) cells respectively, p < 0.001). In all three groups, LPS-stimulated cells produced significantly more IL-6 than non-stimulated cultures (p < 0.001). Constitutive production of IL-6 by PBMC from TB patients implies pre-activation of cells and suggests that IL-6 may be important in the regulation of the acute phase response in TB. Discrepant IL-6 release between the two control groups may be secondary to subclinical mycobacterial infection with non-specific immunological activation in the social controls.