Pulmonary tuberculosis in BALB/c mice with non-functional IL-4 genes: changes in the inflammatory effects of TNF-alpha and in the regulation of fibrosis.

In BALB/c mice, as in man, progressive pulmonary tuberculosis is accompanied by increasing expression of IL-4. Therefore we have used BALB/c mice with disrupted IL-4 genes (IL-4(-/-)) to investigate the role of IL-4 in pulmonary tuberculosis, with particular emphasis on the toxicity of TNF-alpha and on fibrosis, both of which are neglected aspects of human tuberculosis. Delayed-type hypersensitivity (DTH) sites in IL-4(+/+) mice were sensitive to the toxicity of locally injected TNF-alpha, whereas DTH sites in IL-4(-/-) mice were not. However, intravenous administration of IL-4 to IL-4(-/-) mice restored the sensitivity of the DTH sites to pro-inflammatory effects of TNF-alpha. In late disease, the lungs of IL-4(+/+) mice expressed low IFN-gamma, but high TGF-beta and IL-4, correlating with fibrosis, detected as a high hydroxyproline content. In contrast, TGF-beta peaked 7 days after infection in the lungs of the IL-4(-/-) mice, and then fell to very low levels in the late disease, while IFN-gamma remained high. Accordingly, hydroxyproline content was reduced in infected IL-4(-/-) mice compared to IL-4(+/+) controls. In conclusion, the findings suggest that IL-4 has modestly detrimental effects on the antibacterial efficacy of the Th1 response, and larger effects on the toxicity of TNF-alpha, and on fibrosis.