Induction of interteukin-10 and down-regulation of cytokine production by Klebsiella pneumoniae capsule in mice with pulmonary infection

The role of the capsule of Klebsiella pneumoniae in inducing cytokine produ ction was investigated by comparing the responses of mice with experimental ly induced pneumonia caused by capsulate (strain DT-S) or non-capsulate (mu tant strain DT-X) R pneumoniae. Anaesthetised PCR mice were inoculated intr anasally, Whereas all DT-S-infected mice died within 3 days, no deaths were observed in DT-X-infected mice by 14 days after infection. During the earl y stage of infection, interferon-gamma (IFN-gamma) levels in bronchoalveola r lavage fluid (BALF) of DT-X-infected mice were significantly higher than those in DT-S-infected mice. In contrast, in the late stage of infection, s erum levels of granulocyte macrophage-colony stimulating factor (GM-CSF) an d IFN-gamma in DT-S-infected mice were significantly higher than those in D T-X-infected mice. Levels of interleukin-10 (IL-10) in BALF and serum of DT -S-infected mice were significantly and persistently higher than those of D T-X-infected mice. The IL-10/TNF-alpha (tumour necrosis factor-alpha) ratio s in BALF and serum indicated that higher levels of IL-10 production were i nduced in mice infected with strain DT-S than in those infected with strain DT-X, The results suggest that the capsule of K., pneumoniae may induce IL -10 production at the site of infection and, thereafter, these high IL-10 l evels may serve to down-regulate the expression of pro-inflammatory cytokin es.