LAIR1 prevents excess inflammatory tissue damage in S. aureus skin infection and Cutaneous T-cell Lymphoma [BMDM]

Patients with cutaneous T cell lymphoma (CTCL) experience high morbidity and mortality due to S. aureus skin infections and sepsis, but the causative immune defect is unclear. We propose that high levels of LAIR2 in CTCL suppress LAIR1 inhibitory signaling, promoting inflammation and tissue damage, which increases S. aureus susceptibility. Mice do not have a LAIR2 homolog, so we used Lair1 KO mice to model LAIR2 overexpression. In a model of subcutaneous S. aureus skin infection, Lair1 KO mice had significantly larger abscesses and areas of dermonecrosis compared to WT. Lair1 KO exhibited a pattern of increased inflammatory responses in infection and sterile immune stimulation, including increased production of proinflammatory cytokines and myeloid chemokines, neutrophil ROS, and collagen/ECM remodeling pathways. Notably, compared to WT, Lair1 KO infected skin had a similar bacterial burden and neutrophils and monocytes had equivalent S. aureus phagocytosis. These findings support a model in which lack of LAIR1 signaling results in an excessive inflammatory response that does not improve infection control. CTCL tissues harbored similar patterns of increased cytokine and collagen production, suggesting that high levels of LAIR2 in CTCL recapitulates Lair1 KO, causing inflammatory tissue damage and compromising host defense against S. aureus infection. Overall design: To investigate the impact of LAIR1 loss on the macrophage immune response to S. aureus, we treated bone marrow-derived macrophages from 3 WT and 3 Lair1 KO mice with PBS or PAM3CSK4 for 6 hours. We then performed gene expression profiling analysis from RNA-seq of these cells.