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Macrophages are a diverse and widespread type of innate immune cell which play an important role in homeostasis and defense. In a process called phagocytosis, macrophages engulf dying cells, foreign substances, and pathogens. Importantly, macrophages can present antigens from phagocytosed cells allowing them to initiate an adaptive immune response against remaining cells of the same type. Despite the immunosuppressive nature of the tumor microenvironment, macrophages often infiltrate tumors where they can either promote or inhibit cancer development, though the specific conditions influencing their pro- vs anti-cancer activity remain enigmatic. Recently, macrophages have been brought into the spotlight of immunotherapy research due to the hope of harnessing their ability to migrate into tumors, phagocytose cancer cells, and mobilize an antitumor T-cell response. However, questions remain about how macrophages recognize, or fail to recognize, cancerous cells for clearance, and how they can promote vs inhibit tumor progression.
To identify modulators of macrophage activation, we have developed a model to visualize and quantify phagocytosis. In this model, bone marrow-derived macrophages are stained with CMFDA, a green cell tracker dye. Cancer cells are stained with pHrodo red, a pH sensitive fluorogenic probe which is designed to fluoresce brighter when inside the acidic phagosome, indicating phagocytosis has occurred. Macrophages are co-cultured with the cancerous target cells then imaged and analyzed. Phagocytosed cells can be visualized through fluorescence microscopy and the number of fluorescent engulfed cells quantified with flow cytometry. This in vitro model allows us to test how macrophages differentially engulf target cells based on various conditions such as macrophage polarization state or cancer cell phenotype. Data acquired from these experiments helps us delineate which characteristics of cancer cells are recognized by macrophages allowing us to better understand the role of phagocytosis in cancer. Future studies will test modified macrophage states in our tumor models and determine how polarization can be exploited to alter the spectrum of pro- and anti-cancer macrophage activities.
Leyda, Molly; Nemechek, Jacqelyn; Szarejko, John; Perry, John M.; and Myers, Douglas, "Macrophage Mediated Cancer Cell Targeting" (2023). Research at Children's Mercy Month 2023. 2.