A C1q Domain Containing Protein from Scallop Chlamys farreri Serving as Pattern Recognition Receptor with Heat-Aggregated IgG Binding Activity

Leilei Wang,Vinu S Siva,Zhi Zhou,Lingling Wang,Huan Zhang,Linsheng Song,Shuang-Yong Xu

doi:10.1371/journal.pone.0043289

Leilei Wang, Vinu S Siva + Show 5 more

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https://doi.org/10.1371/journal.pone.0043289

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Abstract

BackgroundThe C1q domain containing (C1qDC) proteins refer to a family of all proteins that contain the globular C1q (gC1q) domain, and participate in a series of immune responses depending on their gC1q domains to bind a variety of self and non-self binding ligands.MethodologyIn the present study, the mRNA expression patterns, localization, and activities of a C1qDC protein from scallop Chlamys farreri (CfC1qDC) were investigated to understand its possible functions in innate immunity. The relative expression levels of CfC1qDC mRNA in hemocytes were all significantly up-regulated after four typical PAMPs (LPS, PGN, β-glucan and polyI:C) stimulation. During the embryonic development of scallop, the mRNA transcripts of CfC1qDC were detected in all the stages, and the expression level was up-regulated from D-hinged larva and reached the highest at eye-spot larva. The endogenous CfC1qDC was dominantly located in the hepatopancreas, gill, kidney and gonad of adult scallop through immunofluorescence. The recombinant protein of CfC1qDC (rCfC1qDC) could not only bind various PAMPs, such as LPS, PGN, β-glucan as well as polyI:C, but also enhance the phagocytic activity of scallop hemocytes towards Escherichia coli. Meanwhile, rCfC1qDC could interact with human heat-aggregated IgG, and this interaction could be inhibited by LPS.ConclusionsAll these results indicated that CfC1qDC in C. farreri not only served as a PRR involved in the PAMPs recognition, but also an opsonin participating in the clearance of invaders in innate immunity. Moreover, the ability of CfC1qDC to interact with immunoglobulins provided a clue to understand the evolution of classical pathway in complement system.

Highlights

All these results indicated that CfC1qDC in C. farreri served as a pattern recognition receptors (PRRs) involved in the pathogen associated molecular patterns (PAMPs) recognition, and an opsonin participating in the clearance of invaders in innate immunity
The C1q domain containing (C1qDC) proteins refer to a family of all proteins that contain the globular C1q domain, and participate in a series of immune responses depending on their gC1q domains to bind a variety of self and non-self binding ligands [1,2,3,4]. gC1q is characterized by a jelly-roll topology consisting of a 10-stranded b-sandwich made up of two five-stranded antiparallel b-sheets [5,6]
Real-time PCR was used to monitor the mRNA expression of CfC1qDC transcripts in hemocytes of adult animals stimulated by four typical PAMPs (Figure 1)

Summary

Introduction

The C1q domain containing (C1qDC) proteins refer to a family of all proteins that contain the globular C1q (gC1q) domain, and participate in a series of immune responses depending on their gC1q domains to bind a variety of self and non-self binding ligands [1,2,3,4]. gC1q is characterized by a jelly-roll topology consisting of a 10-stranded b-sandwich made up of two five-stranded antiparallel b-sheets [5,6]. Depending on the structural characteristics, C1qDC proteins are classified as C1q/C1q-like proteins containing the collagen or collagen-like region in the N-terminus, and globular head C1q proteins without the collagen region [1] The members of this family are involved in several immune responses in innate immunity, such as pathogen recognition [7], activation of the complement system [8], mediating cell migration [9] and so on. The extreme versatility of C1q is due to the capacity of the gC1q domain to bind a variety of self and non-self ligands, including envelope proteins of retroviruses, b-amyloid fibrils, lipopolysaccharides (LPS), porins from Gram-negative bacteria, phospholipids and some acute phase reactants [2,3,12].

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