Figure 7

Macrophage actin-pendent functions. (a) Macrophage phagocytosis and down-the-road antigen presentation depend on the actin cytoskeleton. Engulfment (phagocytosis) of foreign material, such as bacteria, viruses, dead cells, or cell debris is facilitated by the actin-myosin contractile-dependent phagosome formation at the cell surface. Once inside the cytoplasm, phagosome (containing ingested material) is then fused with the endosomes and lysosomes, leading to ingested material degradation and/or further processing into peptides through the proteasomal pathway. The resulting antigenic peptides are presented on the cell surface by major histocompatibility complex (MHC) class I and/or MHC class II molecules. (b) Macrophage migration not only depends on the formation and function of actin rich leading and trailing edge, but also on their ability to digest and degrade extracellular matrix. Extracelluar matrix degradation depends on the function of actin- and metalloproteinase-rich organelles called the podosomes. Podosomes play a role in cellular motility within tissue by coordination of degradation of the extracellular matrix with cellular movement. In macrophages the podosomes are either dispersed on the cell surface or they are clustered into higher order complex called the podosomal rosette. Podosomal metalloproteinases (shown in light green), which are used for matrix degradation, are delivered to the podosomes via microtubules emanating from microtubule organizing center (MTOC) (shown in dark green) and molecular motors.[60]