Conservation of Structural and Functional Features in a Primordial CD80/86 Molecule from Rainbow Trout (Oncorhynchus mykiss), a Primitive Teleost Fish

Abstract

In mammals, interaction of CD28 with CD80 or CD86 molecules provides costimulatory signals for T cell activation that leads to increased IL-2 gene and protein expression by activated T cells. Thus far, CD80 and CD86 have been cloned and functionally characterized only in mammals and birds. To shed light into the evolution of CD80 and CD86, we have cloned and functionally characterized a rainbow trout (rt) molecule (rtCD80/86) that shows the highest degree of sequence conservation and phylogenetic relationship with CD80 and CD86 molecules. Moreover, its genomic organization was almost identical to that of human CD86. Rainbow trout possess one membrane-bound and two soluble CD80/86 transcripts, all of which are derived from the same rtCD80/86 gene. The membrane-bound form exhibited its highest degree of expression in lymphoid tissues, particularly on B cells. Incubation of trout leukocytes with LPS and bacteria leads to up-regulation of rtCD80/86 gene expression. Importantly, we show that trout and other teleost fish contain a single CD80/86 gene, thus suggesting that this gene may represent the ancestor from which CD80 and CD86 arose by gene duplication in more evolved species. To gain further insights into the function of rtCD80/86, we have identified and cloned trout IL-2 and have shown that recombinantly produced trout CD80/86 up-regulates the expression of IL-2 in trout blood leukocytes. Significantly, this finding indicates that the capacity to modulate IL-2 expression is a primordial function that has been conserved both in fish and mammalian CD80/CD86 molecules throughout 350 million years of evolution.

Molecular characterization and expression of CD2 in Nile tilapia (Oreochromis niloticus) in response to Streptococcus agalactiae stimulus

“…The BLAST analysis revealed the overall sequence homology of the CD2 proteins among different species, even among different fish species, was very poor. This finding is consistent with the result of previous studies about other costimulatory molecules in teleost, including CD28 [39,40], CD80/ CD86 [41,42] and CTLA-4 [39]. Fish are the most primitive vertebrates to possess essential components of T-cell immunity, which includes MHC, TCRs, CD3, CD4, CD8, etc, to allow the clonal selection of T-cells [27,28].…”

“…In mammals, CD2 can function as a costimulatory molecule and accelerate production of IL-2, which is the most important cytokine to promote proliferation and differentiation of T-cells [11e15]. Recent progress in evolutionary immunology supports the notion that the capacity to modulate IL-2 expression is a primordial function that has been conserved in both fish and mammals costimulatory molecules [39,41,69], suggesting On-CD2 may also possess similar function to activate T-cells. This hypothesis was supported by distinct kinetic expressions of On-CD2 in the thymus and spleen.…”

Complement C5a acts as molecular adjuvant in fish by enhancing antibody response to soluble antigen

“…Rainbow trout (100e300 g) obtained from Limestone Springs Fish Farm (Richland, PA) were maintained in our lab as previously described [31]. Trout (mean weight, 50 g) used for the immunization were maintained at Clear Springs Foods, Inc. (Buhl, Idaho).…”

“…The recombinant proteins (C5a, G, and G-C5a) were expressed and purified as previously described [31].…”

DNA vaccination against a fish rhabdovirus promotes an early chemokine-related recruitment of B cells to the muscle

“…In addition to DCs, B cells are also considered highly efficient APCs in mammals [40], and therefore it is possible that fish B cells mobilized to the muscle after DNA vaccination could play a role in antigen presentation locally in addition to other APCs, taking into account the absence of lymph nodes in teleost fish. Furthermore, the very high constitutive levels of CD80/86 in trout IgM + cells reported by Zhang et al [41], led the authors to speculate that fish IgM + B cells could be major APCs in fish. We also isolated some CD8 + cells from the vaccinated muscle, even though no CD8 transcripts were detected.…”