Pneumonia recovery reprograms the alveolar macrophage pool

Community-acquired pneumonia is a widespread disease with significant morbidity and mortality. Alveolar macrophages are tissue-resident lung cells that play a crucial role in innate immunity against bacteria that cause pneumonia. We hypothesized that alveolar macrophages display adaptive characteristics after resolution of bacterial pneumonia. We studied mice 1 to 6 months after self-limiting lung infections with Streptococcus pneumoniae, the most common cause of bacterial pneumonia. Alveolar macrophages, but not other myeloid cells, recovered from the lung showed long-term modifications of their surface marker phenotype. The remodeling of alveolar macrophages was (a) long-lasting (still observed 6 months after infection), (b) regionally localized (observed only in the affected lobe after lobar pneumonia), and (c) associated with macrophage-dependent enhanced protection against another pneumococcal serotype. Metabolomic and transcriptomic profiling revealed that alveolar macrophages of mice that recovered from pneumonia had new baseline activities and altered responses to infection that better resembled those of adult humans. The enhanced lung protection after mild and self-limiting bacterial respiratory infections includes a profound remodeling of the alveolar macrophage pool that is long-lasting; compartmentalized; and manifest across surface receptors, metabolites, and both resting and stimulated transcriptomes.

Regulation of IL-10-producing T cells by polyunsaturated fatty acids

The modern day western diet has led to an increase of n-6 polyunsaturated fatty acid (n-6 PUFA) intake and is considered an environmental factor resulting in negative health outcomes in different disease settings. In relation to the immune system, it is not well understood how changes in dietary factors like n-6 PUFAs can influence immune responses, for example during autoimmune disease. PUFAs have a variety of roles within cells such as being used as an energy source, incorporation in cell membranes, and conversion into lipid mediators that influence cell signaling and gene expression. We initially sought to understand how n-6 PUFAs influence the phenotype and function of T cell subsets from the Type 1 Diabetes mouse model (NOD) and non-diabetic control mouse model (B6.NOD). By treating splenocytes from these mouse models in vitro with n-6 PUFA linoleic acid we discovered by flow cytometry a dose response inhibition of interleukin 10 (IL-10), an anti-inflammatory cytokine, in both CD4+ and CD8+ T cell subsets. To the contrary, interferon γ production was not diminished after linoleic acid treatment. While IL-10 inhibition was not strain-specific, further studies by gene expression analysis displayed a decrease of IL-10 mRNA expression and of transcription factors involved in regulation of IL-10 (c-maf, IRF4, and Bhlhe40) after linoleic acid treatment. These results demonstrate that dietary n-6 PUFAs regulate T cell cytokine production and can influence the balance of pro- and anti-inflammatory cytokines. Further studies will provide more insight into the regulation of T cell subsets by fatty acids present in the organismal environment, with potential implications for the development of new therapeutics to modulate autoimmune responses.