Updated project metadata. Understanding the molecular mechanisms that initiate and control immunosuppression by myeloid cells is essential to overcoming the myeloid-induced disbalance of the immune system observed in patients. Myeloid cells are implicated in aggravated suppression of immunity as seen in cancer as well as in defective modulation of immune responses as observed in autoimmunity. Therefore, signaling pathways controlling immunomodulation by myeloid cells are an attractive target to potentially restore immune homeostasis and increase clinical benefit for a large number of patients. Here, we used label-free quantitative proteomics to identify proteins that are differentially expressed between different myeloid cells (myeloid-derived suppressor cells (MDSCs), tolerogenic dendritic cells (TolDCs), monocyte-derived dendritic cells (MoDCs) and precursor monocytes.