Abstract Body: During atherosclerosis, sustained low grade inflammatory signaling by innate immune cells can promote further immune cell recruitment and activation, leading to worsened disease pathogenesis. To treat atherosclerosis and other chronic inflammatory diseases like it, more research must be performed to understand the natural mechanisms in place to suppress rampant inflammation and why these mechanisms fail during disease. In this study, we seek to define a signature low grade inflammatory phenotype for monocytes challenged with free cholesterol, as well as uncover a mechanism for this phenotype. The peroxisome is an organelle with a variety of immunomodulatory functions within the cell, and its dysfunction can increase the risk of cardiovascular disease. Here, we establish that peroxisome dysfunction as caused by deletion of peroxisomal transport protein PEX5 exacerbates the low grade inflammatory monocyte phenotype caused by treatment with free cholesterol, indicating a potential protective role for this organelle in the context of chronic inflammatory disease. To do this, bone marrow-derived monocytes from PEX5^+/+ and PEX5^-/- mice were cultured for 5 days and repetitively stimulated with free cholesterol, then harvested for analysis by flow cytometry or Western blot. It was found that immune enhancing marker CD86 and adhesive marker CD49d were elevated after cholesterol treatment and more so in PEX5^-/- cells, while resolving, anti-inflammatory markers such as CD163 and CSF1R were dramatically decreased. Additionally, mTORC1 signaling is upregulated in cholesterol-treated monocytes and more so in PEX5^-/- monocytes as measured by relative protein levels of SYK, PRAS40, and S6K, indicating a potential role for this signaling pathway in promoting peroxisome dysfunction-mediated pathogenic inflammation. Downstream, inflammatory transcription factor STAT5 expression is also induced by cholesterol and elevated in the absence of PEX5, potentially leading to the expression of the signature low grade inflammatory surface markers. Together, these data suggest that PEX5 deficiency could aggravate the progression of atherosclerosis by removing a key protector against pathogenic inflammation.