Innate Immune Responses in Fish: Antigen Presenting Cells and Professional Phagocytes

Similar to higher vertebrates, the immune system of fish is composed of two major components, innate (non-specific) and adaptive (specific) immune responses. However, the innate immune system in fish has a fundamental importance in preventing pathogen entry as the adaptive immune responses are less efficient compared to mammals. The components of the innate immune system in fish are commonly divided into three compartments: physical parameters, humoral parameters, and cellular factors. Recently, the fish professional APCs received more attention resulting in the increased numbers of studies on their morphology and function. Following a lengthy gap, in the last decades, considerable progress has been made in the mechanistic understanding of fish APC-dependent immune responses. Dendritic cells (DCs), the universal APCs and the major players in bridging and shaping both innate and adaptive immune responses have been characterized in several teleost fish based on their morphology and function. In addition to innate immunity, macrophages have been demonstrated as essential in initiation of adaptive immunity as another professional APCs in teleost fish. Like in mammals, teleost B cells were characterized as important APCs that activate naive T cells and initiate adaptive immunity. In this study, we provide an overview of innate immune responses in teleost fish and discuss the current status of the field of teleost fish DCs, macrophages and B cells as professional APCs.