Suppressing neutrophil itaconate production attenuates Mycoplasma pneumoniae pneumonia.

Mycoplasma pneumoniae is a common cause of community-acquired pneumonia in which neutrophils play a critical role. Immune-responsive gene 1 (IRG1), responsible for itaconate production, has emerged as an important regulator of inflammation and infection, but its role during M. pneumoniae infection remains unknown. Here, we reveal that itaconate is an endogenous pro-inflammatory metabolite during M. pneumoniae infection. Irg1 knockout (KO) mice had lower levels of bacterial burden, lactate dehydrogenase (LDH), and pro-inflammatory cytokines compared with wild-type (WT) controls after M. pneumoniae infection. Neutrophils were the major cells producing itaconate during M. pneumoniae infection in mice. Neutrophil counts were positively correlated with itaconate concentrations in bronchoalveolar lavage fluid (BALF) of patients with severe M. pneumoniae pneumonia. Adoptive transfer of Irg1 KO neutrophils, or administration of β-glucan (an inhibitor of Irg1 expression), significantly attenuated M. pneumoniae pneumonia in mice. Mechanistically, itaconate impaired neutrophil bacterial killing and suppressed neutrophil apoptosis via inhibiting mitochondrial ROS. Moreover, M. pneumoniae induced Irg1 expression by activating NF-κB and STAT1 pathways involving TLR2. Our data thus identify Irg1/itaconate pathway as a potential therapeutic target for the treatment of M. pneumoniae pneumonia.