Quantitative proteomics analyses of activation states of human THP-1 macrophages.

Macrophages display large functional and phenotypical plasticity. They can adopt a broad range of activation states depending on their microenvironment. Various surface markers are used to characterize these differentially polarized macrophages. However, this is not informative for the functions of the macrophage. In order to have a better understanding of the functional changes of macrophages upon differential polarization, we studied differences in LPS- and IL4-stimulated macrophages. The THP-1 human monocytic cell line, was used as a model system. Cells were labeled, differentiated and stimulated with either LPS or IL-4 in a quantitative SILAC proteomics set-up. The resulting sets of proteins were functionally clustered. LPS-stimulated macrophages show increased secretion of proinflammatory peptides, leading to increased pressure on protein biosynthesis and processing. IL4-stimulated macrophages show upregulation of cell adhesion and extracellular matrix remodeling. Our approach provides an integrated view of polarization-induced functional changes and proves useful for studying functional differences between subsets of macrophages. Moreover, the identified polarization specific proteins may contribute to a better characterization of different activation states in situ and their role in various inflammatory processes.