Lipopolysaccharide of Haemophilus influenzae induces interleukin-5 mRNA expression in human peripheral blood mononuclear cells.

Haemophilus influenzae is the bacterial species most often isolated from sputum of patients with chronic obstructive pulmonary disease (COPD). In this study, we examined the induction of interleukin-5 (IL-5) mRNA expression in human peripheral blood mononuclear cells (PBMC) stimulated with lipopolysaccharide (LPS) from H. influenzae to try to predict the effect of H. influenzae infection on the eosinophilic inflammation in COPD. Detection of IL-5 mRNA by RT-PCR showed that LPS from H. influenzae induced IL-5 mRNA expression in PBMC at a concentration of 1 microg/ml. Furthermore, the level of expression of IL-5 mRNA induced by LPS correlated with the amount of IL-5 protein in the culture supernatant. Inhibition of LPS-induced IL-5 mRNA expression by anti-CD14 antibody and diminution of this in a CD3(+) -cell-depleted fraction of PBMC, respectively, suggested that CD14 molecules were required for the increase in IL-5 mRNA and that T lymphocytes were the principal source of IL-5 mRNA expression in PBMC. Briefly, the IL-5 mRNA expression induced by LPS would be based on LPS-activated monocytes interacting with T lymphocytes to produce IL-5. These results may explain the role that colonization with H. influenzae plays in eosinophilic inflammation in patients with COPD.