PD-L1 deletion or blockade intrinsically reduces macrophage CD80 levels

Introduction Macrophages in the tumor microenvironment are known to upregulate PD-L1 expression, thereby suppressing T cells through PD-1 ligation. However, the manner in which PD-L1 expression intrinsically impacts macrophages and their immunomodulatory phenotype is less clear. Clarifying this knowledge gap may provide further insight into macrophage function within the tumor microenvironment. Methods To characterize the macrophage intrinsic role of PD-L1, we used complementary genetic and pharmacological approaches by analyzing primary murine bone marrow-derived macrophages (BMDMs) with complete genetic PDL1 deletion and wildtype BMDMs treated with anti-PD-L1 blocking antibodies. Macrophages were evaluated in vitro across naïve, pro-inflammatory, and tumor conditioned polarization states. Results Unlike prior reports, neither genetic deletion nor antibody blockade dramatically altered the expression of macrophage polarization markers or in vitro phagocytic capacity. However, both conditions consistently and robustly reduced surface levels of a costimulatory molecule, CD80. Reduced CD80 levels prompted further analysis of T cell interacting and antigen presentation associated surface proteins, in which we revealed disparate effects of expression in response to PD-L1 genetic deletion and antibody blockade. Discussion Collectively, these findings suggest that loss of macrophage PD-L1 reduces CD80 expression and regulates immunoregulatory surface protein expression in vitro .