Abstract
Receptors interacting with the constant domain of immunoglobulins (Igs) have a number of important functions in vertebrates. They facilitate phagocytosis by opsonization, are key components in antibody-dependent cellular cytotoxicity as well as activating cells to release granules. In mammals, four major types of classical Fc receptors (FcRs) for IgG have been identified, one high-affinity receptor for IgE, one for both IgM and IgA, one for IgM and one for IgA. All of these receptors are related in structure and all of them, except the IgA receptor, are found in primates on chromosome 1, indicating that they originate from a common ancestor by successive gene duplications. The number of Ig isotypes has increased gradually during vertebrate evolution and this increase has likely been accompanied by a similar increase in isotype-specific receptors. To test this hypothesis we have performed a detailed bioinformatics analysis of a panel of vertebrate genomes. The first components to appear are the poly-Ig receptors (PIGRs), receptors similar to the classic FcRs in mammals, so called FcRL receptors, and the FcR γ chain. These molecules are not found in cartilagous fish and may first appear within bony fishes, indicating a major step in Fc receptor evolution at the appearance of bony fish. In contrast, the receptor for IgA is only found in placental mammals, indicating a relatively late appearance. The IgM and IgA/M receptors are first observed in the monotremes, exemplified by the platypus, indicating an appearance during early mammalian evolution. Clearly identifiable classical receptors for IgG and IgE are found only in marsupials and placental mammals, but closely related receptors are found in the platypus, indicating a second major step in Fc receptor evolution during early mammalian evolution, involving the appearance of classical IgG and IgE receptors from FcRL molecules and IgM and IgA/M receptors from PIGR.
Highlights
Immunoglobulins (Igs) are only found in jawed vertebrates and there are strong indications that the complexity of the adaptive immune system has increased gradually during vertebrate evolution
The results presented in this communication show that the transport receptor for IgA and IgM, the poly-Ig receptors (PIGRs), the Fc receptor-like (FcRL) family and the signaling component the common c chain appeared with the bony fish, indicating a major event in the evolution of these receptors at the base of the bony fish
Based on our screening of a large panel of vertebrate genomes, we can conclude that the first components to appear within the Fc receptors (FcRs) locus are the PIGRs, the FcRL molecules and the signaling subunit, the c chain as they are found in all bony fish species analyzed
Summary
Immunoglobulins (Igs) are only found in jawed vertebrates and there are strong indications that the complexity of the adaptive immune system has increased gradually during vertebrate evolution. Mammals express up to six different Ig classes: IgM, IgD, IgG, IgE, IgA and IgO, and the total number of isotypes can sometimes exceed 15 (Figure 1) [1]. The gene for IgD has probably been lost in this lineage (Figure 1) [17] These findings indicate that the number of Ig classes and isotypes has increased during vertebrate evolution from two to three in fish, to sometimes more than fifteen in mammals (Figure 1). This seems to have occurred at the emergence of the tetrapods, The second step was most likely a duplication of IgM, forming the ancestor of IgA/X This isotype is first observed in amphibians. How this increase has occurred is still only partly understood
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
