Intranasal Interleukin-12 Therapy Inhibits Mycoplasma pneumoniae Clearance and Sustains Airway Obstruction in Murine Pneumonia▿

Mycoplasma pneumoniaeis a leading cause of pneumonia and is associated with asthma. Evidence linksM. pneumoniaerespiratory disease severity with interleukin-12 (IL-12) concentrations in respiratory secretions. We evaluated the effects of IL-12 therapy on microbiologic, inflammatory, and pulmonary function indices ofM. pneumoniaepneumonia in mice. BALB/c mice were inoculated withM. pneumoniaeor SP4 broth. Mice were treated with intranasal IL-12 or placebo daily for 8 days, starting on day 1 after inoculation. Mice were evaluated at baseline and on days 1, 3, 6, and 8 after therapy. Outcome variables included quantitative bronchoalveolar lavage (BAL)M. pneumoniaeculture, lung histopathologic score (HPS), BAL cytokine concentrations determined by enzyme-linked immunosorbent assay (tumor necrosis factor alpha [TNF-α], gamma interferon [IFN-γ], IL-1b, IL-2, IL-4, IL-5, IL-6, IL-10, IL-12, and granulocyte-macrophage colony-stimulating factor), and plethysmography, both before and after methacholine treatment.M. pneumoniae-infected mice treated with IL-12 (MpIL12 mice) were found to have significantly higher BALM. pneumoniaeconcentrations than those ofM. pneumoniae-infected mice treated with placebo (MpP mice) (P< 0.001). MpIL12 mice had higher BAL concentrations of IL-12, IFN-γ, TNF-α, and IL-6, with differences in IL-12 and IFN-γ concentrations reaching statistical significance (P< 0.001). Airway obstruction was statistically elevated in MpIL12 mice compared to that in MpP mice (P= 0.048), while airway hyperreactivity was also elevated in MpIL12 mice but did not reach statistical significance (P= 0.081). Lung parenchymal pneumonia subscores were significantly higher in MpIL12 mice (P< 0.001), but no difference was found for overall HPS, even though a strong trend was noticed (P= 0.051). Treatment of experimentalM. pneumoniaepneumonia with intranasal IL-12 was associated with more severe pulmonary disease and less rapid microbiologic and histological resolution.