Abstract
Blood feeding provides essential nutrients for development and reproduction in hematophagous arthropods yet also initiates significant other physiological alterations in immune function. Immune cells, or hemocytes, are integral components of the arthropod innate immune system with notable roles in defining vector competence. Evidence suggests that both blood feeding and infection drive substantial changes in hemocyte phenotypes, including proliferation, immune activation, and differentiation, which directly and indirectly influence pathogen infection outcomes. These dynamics have fueled extensive research into hemocyte biology in recent years, which aided by emerging single-cell technologies and methods of phagocyte depletion, have provided novel molecular insights into hemocyte populations and additional support for their important contributions to parasite, virus, and bacterial infections. Despite this progress, many aspects of arthropod immune cell biology remain unclear. Focusing on mosquitoes and ticks as two of the most prominent and well-studied arthropod vectors, this review summarizes the effects of blood feeding and infection on mosquito and tick hemocytes, highlighting hemocyte classifications, and the known mechanisms by which hemocytes can have positive or negative impacts on vector-borne pathogen infection.