Immune Functions of Erythrocytes in Osteichthyes

Abstract

Red blood cells (RBCs)-erythrocytes-of Osteichthyes are primarily known for their involvement in the process of gas exchange and respiration. Currently, physiological properties of RCBs in fish should also include their ability to participate in defense processes as part of the innate and adaptive immune mechanisms. In response to viruses, bacteria, and fungi or recombinant nanoparticles, they can modulate expression of genes responsible for immune reactions, influence activity of leukocytes, and produce cytokines, antimicrobial peptides, and paracrine intercellular signaling molecules. Via the complement system (CR1 receptor) and owing to their phagocytic properties (erythrophagocytosis), RBCs of Osteichthyes can eliminate pathogens. In addition, they are probably involved in the immune response as antigen-presenting cells via major histocompatibility complex class II antigens.

Immune functions of phagocytic blood cells in teleost

“…SOD in erythrocytes can remove ROS produced in phagocytosis process, thus protecting phagocytes. 186 Likewise, teleost erythrocytes also show immune regulation. CR1 on teleost erythrocytes can also recognize and bind to the immune complexes containing complement, and these immune complexes are cleared by the phagocytic system after they are transported to such tissues as liver and spleen with blood flow.…”

“…174 In addition, when viruses and bacteria invade and infect organisms, teleost erythrocytes can produce a variety of cytokines (including ILs and IFNs) and AMPs to regulate the activity of leucocytes so that erythrocytes and leucocytes jointly resist the invasion. 186 Moreover, omics analysis indicates that tilapia erythrocytes can express a variety of genes in various processes, such as cytokine signalling pathway, platelet activation, T cell receptor signalling pathway and leucocyte transendothelial migration, indicating that fish erythrocytes potentially regulate the immune function of leucocytes. 187…”

“…CR1 on teleost erythrocytes can also recognize and bind to the immune complexes containing complement, and these immune complexes are cleared by the phagocytic system after they are transported to such tissues as liver and spleen with blood flow 174 . In addition, when viruses and bacteria invade and infect organisms, teleost erythrocytes can produce a variety of cytokines (including ILs and IFNs) and AMPs to regulate the activity of leucocytes so that erythrocytes and leucocytes jointly resist the invasion 186 187 …”

“…CR1 on the surface of erythrocytes degrades C3b in the immune complex into iC3b (a protein fragment when complement factor I cleaves C3b) to expand the binding site between the immune complex and phagocytes. SOD in erythrocytes can remove ROS produced in phagocytosis process, thus protecting phagocytes 186 . Likewise, teleost erythrocytes also show immune regulation.…”

Partial immune responses in Sichuan bream (Sinibrama taeniatus) after starvation

“…There are a variety of cell types involved in innate immune response, including monocytes (or macrophages), non-specific cytotoxic cells and granulocytes, and lymphocytes were mainly involved in specific immunity in fish. In recent reports, erythrocytes and thrombocytes of fish were reported to be functional in immune function as well ( 9 , 10 ). Besides the immune cells, plasmatic antibodies, complements, antibacterial peptides and other immune factors constitutes the humoral immune system Among them, lysozyme, complement and tumor necrosis factor are mainly involved in innate immune response, while immunoglobulins produced by B cells are mainly involved in adaptive immunity.…”