Infection with Opportunistic Bacteria Triggers Severe Pulmonary Inflammation in Lupus-Prone Mice

Infection is a common cause of hospitalization and mortality in patients with systemic lupus erythematosus (SLE). How the underlying immune dysfunctions affect the antimicrobial immunity remains largely unknown. In the present study, employing the pulmonary infection model, we determined the antimicrobial defence of lupus-prone mice. After infecting with opportunistic bacterium Haemophilus influenzae (Hi), lupus-prone mice (B6/lpr) exhibited inefficient bacterial elimination and recovered slowly. They generated severer inflammation at the early stage of infection, as excessive accumulation of neutrophils and enhanced production of proinflammatory cytokines were observed in the lung. In addition, a large number of apoptotic cells were detected in the lungs of B6/lpr mice. For adaptive immune responses, B6/lpr mice were capable to generate enough protective Hi-specific Th17 cells. They evoked stronger Hi-specific γδ T17 response in both lungs and spleens. Unexpectedly, both CD4 and γδ T cells from lupus-prone mice showed deficiency in IFN-γ production. For humoral immune responses, compared with those of WT mice, the concentrations of Hi-specific IgA, IgM, and IgG, especially IgG, were significantly higher in the B6/lpr mice. Our findings suggest that lupus mice are capable to generate antibacterial immune responses; however, the overwhelming inflammation and overactivated immune responses increase the severity of infection.