Figure 1.

Cell communication between tissue-resident macrophages and parenchymal cells in different tissues. The parenchymal cells can be deemed the “primary cells,” which are responsible for performing the primary function of the tissue. During functions, parenchymal cells can release signals to inform the demand for or the accumulation of metabolites. Tissue-resident macrophages can be deemed “supportive cells,” which sense signals from the environment and parenchymal cells. In turn, tissue-resident macrophages respond to cell demand or modify the microenvironment to maintain the normal physiological functions of primary cells. The crosstalk between tissue-resident macrophages and parenchymal cells maintains tissue homeostasis.