Macrophages (lit. “big eaters”) are specialized eukaryotic cells found in tissues and crucial to the vertebrate immune system.
They phagocytize (lit. “eat cells”) pathogens and debris by membranous engulfment and internalization.
Joel Swanson (University of Michigan) was our visiting faculty for the Bootcamp that took place on October of 2006. He borught over several different kinds of macrophages and, most importantly, lots of questions about the forces they can exert.
We wanted to characterize the arrangement of lipid materials and the engulfed object during phagocytosis, both spatially and temporally. In order to do this we used antibody-coated microbeads controlled by optical tweezers. By bringing and orienting the beads close to the macrophage phagocytosis is triggered allowing for a real-time observation of the distribution of lipid material. In the following movie a macrophage can be seen eating an antibody-coated 5um bead.
The orientation of non-spherical objects affects the rate of phagocytosis. We were interested in how macrophages eat cigar-shaped objects such as bacteria. In the following movie we show our initial attemp at characterizing this process. A cigar-shaped bead has been fed to the macrophage .The macrophage appears reorient the bead and ingest it preferring the larger radius of curvature.
In future studies we will monitor the distribution of fluorescent proteins such as actin filaments and proteins related to curvature sensing.