2 – insect hemocytes and their role in immunity

TL;DR: In this chapter I review the classification of hemocytes, their origins, and functions, and reveal evidence of crosstalk between hemocytes and other components of the immune system.

Abstract: The cellular immune response of insects refers to defense responses mediated by hemocytes such as phagocytosis, encapsulation, and clotting. In this chapter I review the classification of hemocytes, their origins, and functions. Although hemocytes have similar functions across all insects, the naming of different hemocyte types varies among species. However, comparative studies across different taxa suggest hemocytes are produced during two stages of insect development: embryogenesis from head or dorsal mesoderm and during the larval or nymphal stages in mesodermally derived hematopoietic organs. Studies in model species like Drosophila melanogaster have identified several signaling pathways regulating hemocyte proliferation and differentiation. Studies in different taxa have also provided important insights into the regulation of hemocyte-mediated defense responses. These include the identification of multiple receptors involved in recognition or opsonization of foreign targets, cytokines that regulate hemocyte function, adhesion proteins, and effector molecules involved in killing foreign invaders. Studies in different insect models also reveal evidence of crosstalk between hemocytes and other components of the immune system. In summary, hemocytes perform diverse functions and comprise an essential arm of the insect immune system.