The Scaffold Immune Microenvironment: Biomaterial-Mediated Immune Polarization in Traumatic and Nontraumatic Applications<sup/>.

The immune system mediates tissue growth and homeostasis and is the first responder to injury or biomaterial implantation. Recently, it has been appreciated that immune cells play a critical role in wound healing and tissue repair and should thus be considered potentially beneficial, particularly in the context of scaffolds for regenerative medicine. In this study, we present a flow cytometric analysis of cellular recruitment to tissue-derived extracellular matrix scaffolds, where we quantitatively describe the infiltration and polarization of several immune subtypes, including macrophages, dendritic cells, neutrophils, monocytes, T cells, and B cells. We define a specific scaffold-associated macrophage (SAM) that expresses CD11b ⁺ F4/80 ⁺ CD11c ^+/- CD206 ^hi CD86 ⁺ MHCII ⁺ that are characteristic of an M2-like cell (CD206 ^hi ) with high antigen presentation capabilities (MHCII ⁺ ). Adaptive immune cells tightly regulate the phenotype of a mature SAM. These studies provide a foundation for detailed characterization of the scaffold immune microenvironment of a given biomaterial scaffold to determine the effect of scaffold changes on immune response and subsequent therapeutic outcome of that material.