Structural and Functional Characterization of Complement C4 and C1s-Like Molecules in Teleost Fish: Insights into the Evolution of Classical and Alternative Pathways

Abstract

There is growing evidence that certain components of complement systems in lower vertebrates are promiscuous in their modes of activation through the classical or alternative pathways. To better understand the evolution of the classical pathway, we have evaluated the degree of functional diversification of key components of the classical and alternative pathways in rainbow trout, an evolutionarily relevant teleost species. Trout C4 was purified in two distinct forms (C4-1 and C4-2), both exhibiting the presence of a thioester bond at the cDNA and protein levels. C4-1 and C4-2 bound in a similar manner to trout IgM-sensitized sheep erythrocytes in the presence of Ca2+/Mg2+, and both C4 molecules equally restored the classical pathway-mediated hemolytic activity of serum depleted of C3 and C4. Reconstitution of activity was dependent on the presence of both C3-1 and C4-1/C4-2 and on the presence of IgM bound to the sheep erythrocytes. A C1s-like molecule was shown to cleave specifically purified C4-1 and C4-2 into C4b, while failing to cleave trout C3 molecules. The C1s preparation was unable to cleave trout factor B/C2 when added in the presence of C3b or C4b molecules. Our results show a striking conservation of the mode of activation of the classical pathway. We also show that functional interchange between components of the classical and alternative pathway in teleosts is more restricted than was anticipated. These data suggest that functional diversification between the two pathways must have occurred shortly after the gene duplication that gave rise to the earliest classical pathway molecules.

Multiple tissue transcriptomic responses toPiscirickettsia salmonisin Atlantic salmon (Salmo salar)

“…Complement C3 is one of the components of the complement system and plays a role in host immune surveillance and immune response against infection (50,53). Complement C1q is the ligand recognition subcomponent of the classical complement pathway and is considered as a bridge between innate and adaptive immunity (4,66).…”

Recent advances on the complement system of teleost fish

“…Since the primary sequences of C1r/C1s/MASP-like molecules in fish cannot predict their true identities, functional characterization of their gene products will be required to resolve their roles in the lectin and/or classical pathways and thus, draw their definitive assignment. In this regard, a recent study has shown that rainbow trout possesses a C1s-like molecule capable of cleaving trout C4 into C4a and C4b fragments [33]. This molecule however did not have the capacity to cleave any of the trout C3 or Bf/C2 isoforms.…”

RNA-seq profiles from grass carp tissues after reovirus (GCRV) infection based on singular and modular enrichment analyses

“…The complement system of teleost fish consists of three pathways, making it similar to of the system found in higher vertebrates (Boshra et al, 2004;Nonaka and Smith, 2000). Many complement proteins have been isolated from various teleost species (Holland and Lambris, 2002;Dodds and Petry, 1993;Endo et al, 1998;Yeo et al, 1997), and it has been suggested the complement system of fish may have wider recognition functions than in mammals (Sunyer and Tort, 1995) due to the larger diversity of complement proteins (Nakao et al, 2002).…”