Two Divergent Isotypes of the Fourth Complement Component from a Bony Fish, the Common Carp (Cyprinus carpio)

Abstract

Duplication and diversification of several complement components is a striking feature of bony fish complement systems. It gives an interesting insight into an evolutionary strategy for the possible enhancement of the repertoire of innate immunity. The present study is aimed at examining diversity in bony fish C4, a member of the thioester-containing complement components. Two diverged cDNA sequences sharing only ∼32% identity at the amino acid level were isolated from the common carp and designated C4-1 and C4-2. C4-1 and C4-2 share a number of C4-like structural signatures, such as the thioester site and a disulfide-linked three-chain structure. Interestingly, they differ at the residue corresponding to the thioester-catalytic histidine, as seen in the human C4A and C4B isotypes, suggesting their distinct substrate specificities in the binding reaction of the thioester. Phylogenetic analysis indicates that the divergence of C4-1 and C4-2 predated the separation of the cartilaginous and bony fish lineages. Genomic Southern hybridization suggests the presence of single copy genes each encoding C4-1 and C4-2 in the carp genome. An activation fragment, C4a, was shown to be released from each isotype in carp serum activated via the classical and/or lectin pathways. Synthetic peptides representing a putative C2 binding site on C4-1 and C4-2 inhibited the classical pathway-mediated hemolytic activity of carp serum in a dose-dependent manner. The results suggest that C4-1 and C4-2 represent two major lineages of C4 that are present in carp serum, have distinct binding specificities, and are functional in the classical/lectin pathways of complement activation.

Effects of dietary carbohydrate sources on growth performance, immunity and glycometabolic enzyme activity ofRhynchocypris lagowskiiDybowski

“…Lysozyme plays an important role in the non-specific immunity of fish, which can help organisms to improve disease resistance (Bergljót, 2006). C3 is an important component in the activation of the complement system and plays a critical role in eliminating invasive pathogens (Ichiki et al, 2012;Kuroda et al, 2000). ACP is a marker enzyme of lysosomes in macrophages and plays a vital role in body metabolism.…”

Effects of Aflatoxin-Contaminated Feed on Immunological Parameters of Common Carp (Cyprinus Carpio)

“…Complement component 4 (C4) is a glycoprotein produced by macrophages and, monocytes. Complement C4 identifies some inflammatory agents with the help of other proteins of the immune system, then this complement makes them interact and removes the inflammatory agents [34]. A decrease in C4 in aflatoxin-treated fish may be due to a decrease in macrophages and monophages or a reduced synthesis level of C4 in such cells.…”

Diversified Components of the Bony Fish Complement System: More Genes for Robuster Innate Defense?

“…On the other hand, C4A isotype, in which His 1106 is replaced by Asp, binds predominantly to the amino-group 18 . Similarly, carp C4-1 has a His, and C4-2 possesses an Asp at the equivalent position, suggesting their difference in the binding specificity of the thioester 15 . In the bony fish complement system, the presence of C2 has not been proven either at the cDNA or protein level 8 .…”

“…If C1r/s-A and C1r/s-B are C1r-equivalent, as predicted by phylogenetic analysis, C1r/s-B isotype with the predicted substrate specificity to Lys-X would be less active than C1r/s-A to cleave C1r/s-A or C1r/s-B itself, because both isotypes share an Arg-Val segment at the putative cleavage site into H-and Lchains of their active forms 10 . Even if the two isotypes were C1s-equivalent, C1r/s-B could again be poorly active as an enzyme to cleave carp C4, because two carp C4 isotypes share Arg-X at the cleavage site to yield C4a and C4b fragments 15 . Therefore, it seems likely that C1r/s-A and C1r/s-B are functionally differentiated.…”

“…C4 has been purified and cloned from trout 11,12 , fugu 16 , and carp 15 . Trout C4 and fugu C4 have been reported to be encoded by a single gene in respective Figure 2.…”