Innate Immune Receptor Diversity in Teleost Fishes

Teleost fishes possess an expansive array of innate immune receptors that underpin their ability to recognise and respond to pathogens in diverse aquatic environments. These receptors, which include novel immune‐type receptors (NITRs), novel immunoglobulin‐like transcripts (NILTs) and leukocyte immune‐type receptors (LITRs), exhibit extensive gene family expansion, rapid sequence diversification and varied signalling motifs. Extracellular immunoglobulin‐like domains mediate ligand binding, while cytoplasmic immunoreceptor tyrosine‐based activation motifs (ITAMs) or inhibitory motifs (ITIMs) dictate downstream signalling outcomes. Comparative analyses reveal that, although teleost receptor repertoires share structural features with mammalian natural killer and Fc receptor families, they have evolved through independent birth‐and‐death processes and domain shuffling. Functional studies in model species such as channel catfish and zebrafish demonstrate the capacity of paired activating and inhibitory receptors to fine-tune phagocytosis, degranulation and cytotoxic responses. Genomic surveys in salmonids and medaka further highlight tightly clustered multigene families that vary in copy number between species, reflecting adaptation to pathogen pressures. This receptor diversity not only informs our understanding of vertebrate immune evolution but also holds promise for selective breeding programmes in aquaculture and for the design of novel antimicrobial strategies.

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Innate Immune Receptor Diversity in Teleost Fishes publication trend

The graph below shows the total number of articles in innate immune receptor diversity in teleost fishes across all publications each year (not limited to Nature Index journals).

Technical terms

Novel immune‐type receptor (NITR): A multigene family of teleost receptors with one or two extracellular Ig-like domains that can deliver activating or inhibitory signals.

Novel immunoglobulin‐like transcript (NILT): A teleost receptor family characterised by V-type Ig domains and cytoplasmic ITIMs or ITAMs, often found in tightly clustered genomic loci.

Leukocyte immune‐type receptor (LITR): A channel catfish receptor family within the immunoglobulin superfamily that regulates innate cell responses via paired activating and inhibitory members.

Immunoglobulin‐like (Ig) domain: A protein fold common to many immune receptors, comprising two β-sheets that form a sandwich-like structure for ligand recognition.

Immunoreceptor tyrosine‐based activation motif (ITAM): A cytoplasmic signalling motif that, upon phosphorylation, recruits kinases to propagate activating immune responses.

Immunoreceptor tyrosine‐based inhibition motif (ITIM): A cytoplasmic motif that, when phosphorylated, attracts phosphatases to dampen immune cell activation.

Phagocytosis: The process by which immune cells engulf and digest pathogens or debris, often regulated by paired activating and inhibitory receptors.

References

1. A Fish Leukocyte Immune-Type Receptor Uses a Novel Intracytoplasmic Tail Networking Mechanism to Cross-Inhibit the Phagocytic Response. International Journal of Molecular Sciences (2020).
2. Genomic organisation analysis of novel immunoglobulin-like transcripts in Atlantic salmon (Salmo salar) reveals a tightly clustered and multigene family. BMC Genomics (2010).
3. Biochemical and Functional Insights into the Integrated Regulation of Innate Immune Cell Responses by Teleost Leukocyte Immune-Type Receptors. Biology (2016).
4. The medaka novel immune-type receptor (NITR) gene clusters reveal an extraordinary degree of divergence in variable domains. BMC Ecology and Evolution (2008).