A Comparison of the Innate and Adaptive Immune Systems in Cartilaginous Fish, Ray-Finned Fish, and Lobe-Finned Fish

Abstract

The immune system is composed of two subsystems—the innate immune system and the adaptive immune system. The innate immune system is the first to respond to pathogens and does not retain memory of previous responses. Innate immune responses are evolutionarily older than adaptive responses and elements of innate immunity can be found in all multicellular organisms. If a pathogen persists, the adaptive immune system will engage the pathogen with specificity and memory. Several components of the adaptive system including immunoglobulins (Igs), T cell receptors (TCR), and major histocompatibility complex (MHC), are assumed to have arisen in the first jawed vertebrates—the Gnathostomata. This review will discuss and compare components of both the innate and adaptive immune systems in Gnathostomes, particularly in Chondrichthyes (cartilaginous fish) and in Osteichthyes [bony fish: the Actinopterygii (ray-finned fish) and the Sarcopterygii (lobe-finned fish)]. While many elements of both the innate and adaptive immune systems are conserved within these species and with higher level vertebrates, some elements have marked differences. Components of the innate immune system covered here include physical barriers, such as the skin and gastrointestinal tract, cellular components, such as pattern recognition receptors and immune cells including macrophages and neutrophils, and humoral components, such as the complement system. Components of the adaptive system covered include the fundamental cells and molecules of adaptive immunity: B lymphocytes (B cells), T lymphocytes (T cells), immunoglobulins (Igs), and major histocompatibility complex (MHC). Comparative studies in fish such as those discussed here are essential for developing a comprehensive understanding of the evolution of the immune system.

Epidermal Club Cells in Fishes: A Case for Ecoimmunological Analysis

“…The two main cell types that mediate adaptive immune responses are T and B lymphocytes. While jawless fish only possess T- and B-like cells, gnathostomes have T and B lymphocytes—most similar to the ones found in mammals [ 99 , 100 ]. Components of the adaptive immune system are relatively slow responders compared to innate immune system components.…”

“…Besides mucus-producing goblet cells, the cellular components of innate immunity in fish comprise tissue resident cells, such as dendritic cells, mast cells, and recruited cells such as monocytes/macrophages, neutrophils, and natural killer cells. These cells are produced in the primary lymphoid organs of fish, namely the head kidney and thymus [ 100 ]. Dendritic cell subsets in teleosts, as in mammals, function as professional antigen-presenting cells, thereby bridging innate and adaptive immune systems [ 103 ].…”

Development of Fish Parasite Vaccines in the OMICs Era: Progress and Opportunities

“…Teleosts are the lowest vertebrates that elicit both innate and adaptive immune responses against pathogen invasion [ 47 ]. However, compared to higher vertebrates, innate immunity plays a major role than the adaptive immune response in aquatic organisms, irrespective of the nature of the pathogen [ 48 ].…”

Terminal deoxynucleotidyl transferase-mediated formation of protein binding polynucleotides

“…At the heart of the process of clonal selection in the development of lymphocytes, is the V(D)J recombination which involves DNA editing of the variable regions in both the exons of immunoglobulins and T-cell receptors of the developing lymphocyte ( 2 ). Terminal deoxynucleotidyl transferase (TDT) enzyme plays an important role in producing genetic variation in the variable region of the DNA by incorporating random nucleotides into the V, D and J exon regions of both B and T cells ( 3 ).…”