The immunoglobulins of cold-blooded vertebrates.

Helen Dooley,Rita Pettinello

doi:10.3390/biom4041045

Abstract

Although lymphocyte-like cells secreting somatically-recombining receptors have been identified in the jawless fishes (hagfish and lamprey), the cartilaginous fishes (sharks, skates, rays and chimaera) are the most phylogenetically distant group relative to mammals in which bona fide immunoglobulins (Igs) have been found. Studies of the antibodies and humoral immune responses of cartilaginous fishes and other cold-blooded vertebrates (bony fishes, amphibians and reptiles) are not only revealing information about the emergence and roles of the different Ig heavy and light chain isotypes, but also the evolution of specialised adaptive features such as isotype switching, somatic hypermutation and affinity maturation. It is becoming increasingly apparent that while the adaptive immune response in these vertebrate lineages arose a long time ago, it is most definitely not primitive and has evolved to become complex and sophisticated. This review will summarise what is currently known about the immunoglobulins of cold-blooded vertebrates and highlight the differences, and commonalities, between these and more “conventional” mammalian species.

Highlights

While most biologists know that five heavy chain (IgM, IgD, IgG, IgE and IgA) and two light chain immunoglobulin (Ig) isotypes are found in mammals far fewer are aware that the Igs of Biomolecules 2014, 4 the humoral immune system have a very long history, reaching back as far as the common ancestor of the jawed vertebrates [1]
Lymphocyte-like cells secreting somatically-recombining receptors have been identified in the jawless fishes [2,3], the mammalian-like adaptive immune system (AIS), based upon somatically-rearranging immunoglobulin superfamily (IgSF) genes is only found in jawed vertebrates
The cartilaginous fishes, which split from the common ancestor with other vertebrates ~450 million years ago (MYA) [4], are the most phylogenetically distant group relative to mammals in which bona fide Igs, recombination-activation gene (RAG)-mediated recombination and activation-induced cytidine deaminase (AID)-mediated somatic hypermutation have all been found

Summary

Introduction

While most biologists know that five heavy chain (IgM, IgD, IgG, IgE and IgA) and two light chain ( and ) immunoglobulin (Ig) isotypes are found in mammals far fewer are aware that the Igs of Biomolecules 2014, 4 the humoral immune system have a very long history, reaching back as far as the common ancestor of the jawed vertebrates [1]. Recent studies examining the Igs and humoral immune responses of the cold-blooded (ectothermic) vertebrates—cartilaginous fishes, bony fishes, amphibians and reptiles—are revealing information about the emergence and roles of the different Ig heavy and light chain isotypes and the evolution of specialised adaptive features such as isotype switching, somatic hypermutation and affinity maturation. In this review we will summarise what is known about the Igs and humoral response of cold-blooded vertebrates and try to highlight the differences, and commonalities, between these and their more familiar mammalian counterparts

Cartilaginous Fishes

Bony Fishes

Amphibians

Reptiles

Conclusions