Thioredoxin as a marker for inflammatory macrophages

Monocyte-derived macrophages are immune cells derived from hematopoietic progenitors.  They interact with a variety of environmental stimuli and carry out highly variable functions, from pathogen phagocytosis to wound healing.  Macrophages have traditionally been classified as M1 or M2 based on their mode of activation; this framework corresponds to proinflammatory and anti-inflammatory states, respectively. We hypothesized that these inflammatory states are associated with altered metabolic or redox environments within the cell. To test this hypothesis, human monocyte derived macrophages differentiated using granulocyte-monocyte colony stimulating factor (GMCSF) or monocyte colony stimulating factor (MCSF), which are known to respectively produce pro-inflammatory and anti-inflammatory macrophages, were analyzed by scRNAseq. This allowed an unbiased interrogation of cellular state while accounting for potential cell-to-cell heterogeneity.   Highly expressed genes distinguishing GMCSF-differentiated macrophages from MCSF-differentiated macrophages included thioredoxin 1, peroxidredoxin 1, and peroxiredoxin 3. We validated the increased expression of thioredoxin 1 on the protein level by western blot. MCSF-differentiated macrophages classically activated with IFNg and LPS also showed increased expression of thioredoxin, indicating that high thioredoxin expression is a conserved feature of an inflammatory macrophage state.