Reduced inflammation and cytokine production in NKLAM deficient mice during Streptococcus pneumoniae infection

Abstract

Streptococcus pneumoniae is a leading cause of pneumonia and a significant economic burden. Antibiotic-resistant S. pneumoniae has become more prevalent in recent years and many pneumonia cases are caused by S. pneumoniae that is resistant to at least one antibiotic. The ubiquitin ligase natural killer lytic-associated molecule (NKLAM/RNF19b) plays a role in innate immunity and studies using NKLAM-knockout (NKLAM-KO) macrophages have demonstrated that NKLAM positively affects the transcriptional activity of STAT1. Using an inhalation infection model, we found that NKLAM-KO mice had a significantly higher lung bacterial load than WT mice but had less lung inflammation. Coincidently, NKLAM-KO mice had fewer neutrophils and NK cells in their lungs. NKLAM-KO mice also expressed less iNOS in their lungs as well as less MCP-1, MIP1α, TNFα, IL-12, and IFNγ. Both neutrophils and macrophages from NKLAM-KO mice were defective in killing S. pneumoniae as compared to wild type cells (WT). The phosphorylation of STAT1 and STAT3 in NKLAM-KO lungs was lower than in WT lungs at 24 hours post-infection. NKLAM-KO mice were afforded some protection against a lethal dose of S. pneumoniae compared to WT mice. In summary, our novel data demonstrate a role for E3 ubiquitin ligase NKLAM in modulating innate immunity via the positive regulation of inflammatory cytokine expression and bactericidal activity.

Mice deficient in NKLAM have attenuated inflammatory cytokine production in a Sendai virus pneumonia model

“…Recent studies from our laboratory demonstrated that STAT1 tyrosine phosphorylation is lower in NKLAM -/- than in WT mice upon bacterial infection [7]. We found that infection with SeV induced the phosphorylation of tyrosine 701 in STAT1 in the lungs of both WT and NKLAM -/- mice beginning at day 3 post-infection.…”

“…NKLAM has been localized to NK cell cytolytic granules [6] and macrophage phagosomes [5]. Additionally, we demonstrated that bone-marrow-derived macrophages (BMDM) and neutrophils from NKLAM-deficient mice have a significantly defective bactericidal response [5, 7]. These studies strengthen the role of NKLAM as an important component of the innate immune response.…”

“…Our previous studies demonstrate that NKLAM is involved in regulating the expression of key inflammatory cytokines in a mouse model of S . pneumoniae -induced pneumonia [7]. In our next set of experiments, we examined cytokine levels in lung homogenates from WT and NKLAM -/- mice at key timepoints during SeV infection.…”

“…In contrast, evidence suggests RBR ligases may also play a positive role in inflammatory cytokine expression. In a recent study from our laboratory we showed that mice lacking NKLAM were defective in the expression of key inflammatory cytokines, such as MCP-1, TNFα, and IFNγ and this defect in cytokine production was associated with a significantly decreased ability to kill Streptococcus pneumoniae in vivo [7]. Likewise, the downregulation of RBR ligase Parkin, resulted in decreased IL-6 and MCP-1 expression in response to LPS.…”

A Dynamic Variation of Pulmonary ACE2 Is Required to Modulate Neutrophilic Inflammation in Response to Pseudomonas aeruginosa Lung Infection in Mice

“…As such, bacterial pneumonia remains a significant public health concern (6)(7)(8). Although bacterial infection alone can initiate lung injury, it is the host-defense response that results in exaggerated inflammation and results in further lung injury and delayed recovery (9)(10)(11). Therefore, an improved understanding of the mechanisms underlying the host/pathogen interactions in bacterial pneumonia is imperative to develop new therapeutic strategies that balance the need for an adequate host defense with an injurious inflammatory response.…”