Phenotyping of macrophages derived from TpMos and Mature Ly6Chi monocytes

Monocytes are integral cells of the innate immune system that play important roles in host defence and tissue repair. It is well established that monocytes are derived from the common monocyte progenitor (cMoP) in the bone marrow (BM) before giving rise to Ly6Chi mature monocytes that enter the circulation. However, our lab has discovered that BM Ly6Chi monocytes are not homogenous, and consist of two subpopulations (CXCR4hi and CXCR4lo) in both mice and humans. In particular, the CXCR4hi subset (termed transitional pre-monocyte (TpMo) population) actively proliferates in the BM and matures into the CXCR4lo subset, which represents mature Ly6Chi monocytes. Nevertheless, how this TpMo population may behave beyond their precursor role in the BM remains undefined. While TpMos have been shown to be strictly immobilized in the BM in the steady state, our preliminary data revealed the mobilization of TpMos into the circulation during sepsis. Furthermore, TpMos were found to give rise to more macrophages than mature Ly6Chi monocytes. Our data hence suggests a critical peripheral role for TpMos that may implicate the outcome of sepsis and possible potential implications in future therapies associated with monocytes. Based on our preliminary findings, we aim to have a better understanding of these monocyte subsets and how they are transcriptionally distinct when they have become macrophages. In particular, we would like to determine if TpMo-derived macrophages are less inflammatory compared to mature monocyte-derived macrophages. BM TpMos and Mature Ly6Chi monocytes were sorted and cultured for 7 days. TpMo-derived and Ly6Chi-derived macrophages were then harvested for RNA isolation for sequencing.