Imaging cell trafficking and immune cell activation using PET reporter genes

MAJOR IMMUNE CELL TYPES AND THEIR FUNCTIONS. Pathogen invasion of an immunocompetent host induces a coordinated response from a network of diverse immune cell types. The interactions between these various immune cell types are spatially and temporally regulated to facilitate the acquisition of effector mechanisms that ensure pathogen clearance. This section briefly summarizes the major components of the immune network and their actions during an immune response. A more detailed description of the development and function of specific immune cell types can be found in. The immune network has two major components: the innate and adaptive immune systems. Cells of the innate immune system such as macrophages and dendritic cells generally make first contact with pathogens. Pathogen-derived molecules activate specific receptors on innate immune cells leading to the release of chemo-attractant molecules and recruitment of other inflammatory cells such as neutrophils. Furthermore, macrophages and dendritic cells ingest foreign proteins (or antigens) and migrate to nearby lymph nodes where they serve as antigen-presenting cells (APCs) in the initiation of the adaptive immune response. T and B lymphocytes are the key cell types of the adaptive immune system. Both B and T cells express dedicated and highly variable cell surface receptors for antigen. Exposure to antigen together with help from T cells activates B cells to proliferate and differentiate into plasma cells that secrete antigen-specific antibodies that, by various effector mechanisms participate in antigen clearance. Once the invading pathogen has been cleared, the expanded antigen-specific B cell population contracts through apoptosis.