The Biochemical and Biophysical Mechanisms of Macrophage Migration

The ability of macrophages to migrate is critical for a proper immune response. During an innate immune response, macrophages migrate to sites of infection or inflammation where they clear pathogens through phagocytosis and activate an adaptive immune response by releasing cytokines and acting as antigen-presenting cells. Unfortunately, improper regulation of macrophage migration is associated with a variety of dieases including cancer, atherosclerosis, wound-healing, and rheumatoid arthritis. In this thesis, engineered substrates were used to study the chemical and physical mechanisms of macrophage migration. We first used microcontact printing to generate surfaces specifically functionalized with fibronectin and functionally blocked against cell adhesion to study the migration of RAW/LR5 murine macrophages. Using these surfaces we found that macrophage migration is biphasic with respect to increasing surface ligand or soluble chemokine concentration, and that RAW/LR5 migration is dependent on PI3K and ROCK signaling. We then used traction force microscopy to measure the force generation capabilities of primary human macrophages and found that these cells generate strong forces at their leading edge in a stiffness-dependent manner. Through the use of chemical inhbitors we showed that force generation is dependent on myosin II contraction, PI3K signaling, and Rac signaling downstream of the GEF Vav1, but not the GEF Tiam1. Finally, we investigated the motility and force generation of M1 and M2 polarized primary human macrophages. We found that M1 macrophages are less motile and generate less force than M0 or M2 macrophages, and that M2 macrophages are more motile but do not have any change in force generation compared to M0 macrophages. We have been able to show that both chemical signals and mechanical mechanisms contribute to macrophage migration. This work contributes to the growing understanding of the mechanisms that govern macrophage migration and demonstrates the importance of mechanics when studying leukocyte migration