Immune functions of phagocytic blood cells in teleost

Abstract Phagocytosis is a fundamental immune function against foreign microorganisms and abnormal cells, and it is also a bridge between innate and adaptive immunity. Blood as the direct living environment of various immune cells is a crucial site for phagocytosis. In this review, we firstly summarized the morphological structure and cytochemical characteristics of teleost peripheral blood cells, divided them into erythrocytes, leucocytes and thrombocytes, and then systematically elaborated the immune functions of phagocytic blood cells including professional and non‐professional phagocytes. The professional phagocytes consist of monocytes/macrophages and neutrophils. Monocytes/macrophages activate phagocytosis to ingest pathogens, and destroy them through respiratory burst and nitric oxide response to generate antigens, and then antigens are presented to adaptive immune cells. Neutrophils are recruited to inflammatory sites and exert phagocytosis, which is accompanied by degranulation and the production of neutrophil extracellular traps to kill pathogens. Non‐professional phagocytes including thrombocytes, B cells and erythrocytes are indispensable to exercise the phagocytosis, in addition to their main functions in the immune system. Thrombocytes participate in innate immunity and adaptive immunity. B cells carry out antigen presentation and immunoglobulin secretion in adaptive immunity. Erythrocytes perform immune regulation and infection resistance. In general, professional phagocytes play a primary role in phagocytosis and pathogen treatment, whereas non‐professional phagocytes play auxiliary role in phagocytosis and perform their unique immune functions. The functions of these two types of phagocytes jointly constitute the basis of the immune system. This review provides insights into the overall roles of phagocytic blood cells in the teleost immune system.