Isolation and characterization of two major serum proteins from the dogfish, Mustelus canis, C-reactive protein and amyloid P component

Pentraxins in invertebrates and vertebrates: From structure, function and evolution to clinical applications

The immune system is divided into two broad categories, consisting of innate and adaptive immunity. As recognition and effector factors of innate immunity and regulators of adaptive immune responses, lectins are considered to be important defense chemicals against microbial pathogens, cell trafficking, immune regulation, and prevention of autoimmunity. Pentraxins, important members of animal lectins, play a significant role in protecting the body from pathogen infection and regulating inflammatory reactions. They can recognize and bind to a variety of ligands, including carbohydrates, lipids, proteins, nucleic acids and their complexes, and protect the host from pathogen invasion by activating the complement cascade and Fcγ receptor pathways. Based on the primary structure of the subunit, pentraxins are divided into short and long pentraxins. The short pentraxins are comprised of C-reactive protein (CRP) and serum amyloid P (SAP), and the most important member of the long pentraxins is pentraxin 3 (PTX3). The CRP and SAP exist in both vertebrates and invertebrates, while the PTX3 may be present only in vertebrates. The major ligands and functions of CRP, SAP and PTX3 and three activation pathways involved in the complement system are summarized in this review. Their different characteristics in various animals including humans, and their evolutionary trees are analyzed. The clinical applications of CRP, SAP and PTX3 in human are reviewed. Some questions that remain to be understood are also highlighted.

Serum amyloid P-component/C-reactive proteins in fugu (Takifugu rubripes) egg with binding ability to disease-causing bacteria by carbohydrate-recognition

Two galactose-binding proteins were purified from the eggs of Takifugu rubripes by affinity chromatography. These proteins were detected at 26 and 23 kDa under reducing and at 40 and 45 kDa under non-reducing conditions at SDS-PAGE. The peptide sequences from both proteins matched to short-type pentraxin. The 26-kDa lectin was glycosylated, while the other one was not, indicating that these could be glycoforms of pentraxin. Messenger RNA of pentraxin was detected in eggs and embryos at 1-cell stage, was undetectable till blastula, and finally detected again after gastrula, suggesting that the mRNAs in eggs and 1-cell embryos were maternal in origin, and autologous transcription of the gene occurred after blastula. Since they bind to pathogenic bacteria, egg pentraxins may have immunological functions during embryogenesis. This is the first study to show the presence of short-type pentraxin in fish eggs and the diversity of fish egg lectins.

A Comparison of the Innate and Adaptive Immune Systems in Cartilaginous Fish, Ray-Finned Fish, and Lobe-Finned Fish

The immune system is composed of two subsystems-the innate immune system and the adaptive immune system. The innate immune system is the first to respond to pathogens and does not retain memory of previous responses. Innate immune responses are evolutionarily older than adaptive responses and elements of innate immunity can be found in all multicellular organisms. If a pathogen persists, the adaptive immune system will engage the pathogen with specificity and memory. Several components of the adaptive system including immunoglobulins (Igs), T cell receptors (TCR), and major histocompatibility complex (MHC), are assumed to have arisen in the first jawed vertebrates-the Gnathostomata. This review will discuss and compare components of both the innate and adaptive immune systems in Gnathostomes, particularly in Chondrichthyes (cartilaginous fish) and in Osteichthyes [bony fish: the Actinopterygii (ray-finned fish) and the Sarcopterygii (lobe-finned fish)]. While many elements of both the innate and adaptive immune systems are conserved within these species and with higher level vertebrates, some elements have marked differences. Components of the innate immune system covered here include physical barriers, such as the skin and gastrointestinal tract, cellular components, such as pattern recognition receptors and immune cells including macrophages and neutrophils, and humoral components, such as the complement system. Components of the adaptive system covered include the fundamental cells and molecules of adaptive immunity: B lymphocytes (B cells), T lymphocytes (T cells), immunoglobulins (Igs), and major histocompatibility complex (MHC). Comparative studies in fish such as those discussed here are essential for developing a comprehensive understanding of the evolution of the immune system.

Evolution of C-Reactive Protein

C-reactive protein (CRP) is an evolutionarily conserved protein. From arthropods to humans, CRP has been found in every organism where the presence of CRP has been sought. Human CRP is a pentamer made up of five identical subunits which binds to phosphocholine (PCh) in a Ca²⁺-dependent manner. In various species, we define a protein as CRP if it has any two of the following three characteristics: First, it is a cyclic oligomer of almost identical subunits of molecular weight 20–30 kDa. Second, it binds to PCh in a Ca²⁺-dependent manner. Third, it exhibits immunological cross-reactivity with human CRP. In the arthropod horseshoe crab, CRP is a constitutively expressed protein, while in humans, CRP is an acute phase plasma protein and a component of the acute phase response. As the nature of CRP gene expression evolved from a constitutively expressed protein in arthropods to an acute phase protein in humans, the definition of CRP became distinctive. In humans, CRP can be distinguished from other homologous proteins such as serum amyloid P, but this is not the case for most other vertebrates and invertebrates. Literature indicates that the binding ability of CRP to PCh is less relevant than its binding to other ligands. Human CRP displays structure-based ligand-binding specificities, but it is not known if that is true for invertebrate CRP. During evolution, changes in the intrachain disulfide and interchain disulfide bonds and changes in the glycosylation status of CRP may be responsible for different structure-function relationships of CRP in various species. More studies of invertebrate CRP are needed to understand the reasons behind such evolution of CRP. Also, CRP evolved as a component of and along with the development of the immune system. It is important to understand the biology of ancient CRP molecules because the knowledge could be useful for immunodeficient individuals.

Pentraxins CRP-I and CRP-II are post-translationally deiminated and differ in tissue specificity in cod (Gadus morhua L.) ontogeny

Pentraxins are fluid phase pattern recognition molecules that form an important part of the innate immune defence and are conserved between fish and human. In Atlantic cod (Gadus morhua L.), two pentraxin-like proteins have been described, CRP-I and CRP-II. Here we show for the first time that these two CRP forms are post-translationally deiminated (an irreversible conversion of arginine to citrulline) and differ with respect to tissue specific localisation in cod ontogeny from 3 to 84 days post hatching. While both forms are expressed in liver, albeit at temporally differing levels, CRP-I shows a strong association with nervous tissue while CRP-II is strongly associated to mucosal tissues of gut and skin. This indicates differing roles for the two pentraxin types in immune responses and tissue remodelling, also elucidating novel roles for CRP-I in the nervous system. The presence of deimination positive bands for cod CRPs varied somewhat between mucus and serum, possibly facilitating CRP protein moonlighting, allowing the same protein to exhibit a range of biological functions and thus meeting different functional requirements in different tissues. The presented findings may further current understanding of the diverse roles of pentraxins in teleost immune defences and tissue remodelling, as well as in various human pathologies, including autoimmune diseases, amyloidosis and cancer.

Ayu C-reactive protein/serum amyloid P agglutinates bacteria and inhibits complement-mediated opsonophagocytosis by monocytes/macrophages

The short-chain pentraxins (PTXs), including C-reactive protein (CRP) and serum amyloid P (SAP), are soluble pattern recognition molecules (PRMs) that exhibit calcium-dependent binding to bacterial surface molecules. They opsonize pathogens or other particles by phagocytic clearance. However, the detailed functions of short-chain PTXs in teleosts remained unclear. In this study, we identified a short-chain PTX gene from ayu, Plecoglossus altivelis, and tentatively named as PaCRP/SAP. Sequence analysis revealed that PaCRP/SAP has typical characteristics of fish CRP/SAP and is mostly closely related to rainbow smelt (Osmerus mordax) SAP. PaCRP/SAP transcripts were detected in all tested tissues, with the highest level in the liver, and its expression significantly upregulated following Vibrio anguillarum infection. The active recombinant mature PaCRP/SAP (rPaCRP/SAPm) agglutinated Gram-negative bacteria (Escherichia coli, V. anguillarum, Aeromonas hydrophila, and Vibrio parahaemolyticus) and Gram-positive bacteria (Staphylococcus aureus and Listeria monocytogenes) in a calcium-dependent manner in vitro, and it correspondingly bound peptidoglycan and lipopolysaccharide in a dose-dependent manner. The binding of rPaCRP/SAPm to E. coli and S. aureus resulted in a clear inhibition of the deposition of ayu complement 3 (PaC3) on the bacteria. Furthermore, rPaCRP/SAPm decreased phagocytosis of rPaCRP/SAPm-bound E. coli and S. aureus cells by ayu monocytes/macrophages (MO/MΦ) in a complement-dependent way. However, rPaCRP/SAPm alone had no significant influence on phagocytosis. These results provided the first evidence that PaCRP/SAP might function in ayu immune responses via agglutinating bacteria and inhibiting complement-mediated opsonophagocytosis by MO/MΦ.

PLASMA PROTEIN ELECTROPHORESIS AND SELECT ACUTE PHASE PROTEINS IN HEALTHY BONNETHEAD SHARKS (SPHYRNA TIBURO) UNDER MANAGED CARE

Preventative health care of elasmobranchs is an important but understudied field of aquatic veterinary medicine. Evaluation of inflammation through the acute phase response is a valuable tool in health assessments. To better assess the health of bonnethead sharks ( Sphyrna tiburo ) under managed care, normal reference intervals of protein electrophoresis (EPH) and the acute phase proteins, C-reactive protein (CRP) and haptoglobin (HP), were established. Blood was collected from wild caught, captive raised bonnethead sharks housed at public aquaria. Lithium heparinized plasma was either submitted fresh or stored at -80°C prior to submission. Electrophoresis identified protein fractions with migration characteristics similar to other animals with albumin, α-1 globulin, α-2 globulin, β globulin, and γ globulin. These fractions were classified as fractions 1-5 as fractional contents are unknown in this species. Commercial reagents for CRP and HP were validated for use in bonnethead sharks. Reference intervals were established using the robust method recommended by the American Society for Veterinary Clinical Pathology for the calculation of 90% reference intervals. Once established, the diagnostic and clinical applicability of these reference intervals was used to assess blood from individuals with known infectious diseases that resulted in systemic inflammation and eventual death. Unhealthy bonnethead sharks had significantly decreased fraction 2, fraction 3, and fraction 3:4 ratio and significantly increased fraction 5, CRP, and HP. These findings advance our understanding of elasmobranch acute phase inflammatory response and health and aid clinicians in the diagnosis of inflammatory disease in bonnethead sharks.

CsPTX1, a pentraxin of Cynoglossus semilaevis, is an innate immunity factor with antibacterial effects

Pentraxin 1 (PTX1) is a member of the pentraxin protein family, which plays important roles in the innate immunity of vertebrates. In fish, the biological function of PTX1 is essentially unknown. In this study, we examined the expression and function of a PTX homologue (CsPTX1) from the tongue sole, Cynoglossus semilaevis. CsPTX1 contains 223 amino acids and shares 49.3%-38.8% overall sequence identity with other known fish pentraxins. CsPTX1 is expressed in multiple tissues and is upregulated by bacterial and viral infection. CsPTX1 contains a pentraxin domain, which is known to bind extracellular antigens, and recombinant CsPTX1 (rCsPTX1) bound a wide range of Gram-positive and Gram-negative bacteria. rCsPTX1 also agglutinated all the bacteria tested in a Ca(2+)-dependent manner and the agglutinating capacity of rCsPTX1 was abolished in the absence of calcium. As well as its ability to agglutinate bacterial cells, rCsPTX1 displayed apparent bacteriostatic activity against Pseudomonas fluorescens in vitro by influencing the permeability of the microbial envelope. When introduced in vivo, rCsPTX1 enhanced the host's resistance to bacterial infection. These results indicate that CsPTX1 is a classic pattern recognition molecule that defends C. semilaevis against bacterial infection.

CsSAP, a teleost serum amyloid P component, interacts with bacteria, promotes phagocytosis, and enhances host resistance against bacterial and viral infection

Serum amyloid P component (SAP) is a member of the pentraxins family that plays important roles in innate immunity in vertebrates. In fish, the biological function of SAP is essentially unknown. In this study, we examined the expression and function of a SAP homologue (CsSAP) from tongue sole Cynoglossus semilaevis. CsSAP shares 46%-58% overall sequence identities with known fish SAP and was upregulated in expression by bacterial and viral infection. Recombinant CsSAP (rCsSAP) exhibited differential binding capacities to a wide range of Gram-positive and Gram-negative bacteria and promoted uptake of the bound bacteria by host phagocytes. When introduced in vivo, rCsSAP enhanced host resistance not only to bacterial infection but also to viral infection. Consistently, antibody blockage of CsSAP significantly weakened the ability of tongue sole to clear invading bacteria. These results provide the first evidence that fish SAP contributes significantly to both antibacterial and antiviral immunities.

Gene expression and functional characterization of serum amyloid P component 2 in rock bream, Oplegnathus fasciatus

Mammalian serum amyloid P component (SAP) recognizes a wide range of exogenous pathogenic substances and activates a complementary pathway leading to pathogen clearance. To determine the potential roles of SAP in the fish immune system, SAP (RbSAP2) gene was cloned from ESTs analysis of rock bream (Oplegnathus fasciatus), which consisted of a signal peptide and pentraxin domain. Phylogenetic analysis revealed that the RbSAP2 gene was classified with other known fish SAPs. RbSAP2 was highly expressed in the liver of healthy rock bream. Overall, pathogen exposure led to an induction of RbSAP2 in the liver and spleen, although this effect was not observed in the spleen following infection with Edwardsiella tarda. A high concentration of recombinant RbSAP2 (rRbSAP2) showed lower growth Streptococcus iniae than control in the absence of Ca(2+), whereas E. tarda growth was decreased by high concentration of rRbSAP in the presence of the Ca(2+). These results suggest that RbSAP plays an important role in the immune response against invading pathogens.

Functional characterisation and expression analysis of recombinant serum amyloid P isoform 1 (RbSAP1) from rock bream (Oplegnathus fasciatus)

Lectins are carbohydrate-binding proteins that play important roles in the recognition and elimination of pathogens via the innate immune system. Pentraxins (PTX) are humoral lectins, which are multifunctional proteins in vertebrates. Pentraxins can be divided into two groups based on their primary structure: short (C-reactive protein and serum amyloid P [SAP]) and long pentraxins (PTX3 and neuronal pentraxins). Previously, SAP was shown to have Ca(2+)-dependent binding specificity for various ligands and to be a major acute phase protein. In this study, we identified and characterised the gene encoding SAP isoform 1 in rock bream (Oplegnathus fasciatus) (RbSAP1) and analysed its expression in various tissues after a pathogen challenge. An alignment analysis conducted based on the deduced amino acid sequence of RbSAP1 (1918 bp full-length cDNA with a 699 bp open reading frame encoding 232 amino acids) and SAPs and PTXs isolated from other organisms, revealed that the pentraxin domain and cysteine residues of the deduced protein are conserved. RbSAP1, which was ubiquitously expressed in all tissues examined, was predominantly detected in head kidney, trunk kidney, peripheral blood leukocytes, and gills. RbSAP1 expression was dramatically up-regulated in the kidney and liver after infection with Edwardsiella tarda, Streptococcus iniae, or red seabream iridovirus. Purified rRbSAP1 was able to bind Gram-negative bacteria, Gram-positive bacteria, and pathogen-associated molecular patterns. Interestingly, rRbSAP1 aggregated Gram-negative bacteria in the presence of Ca(2+). The anti-pathogen activity of rRbSAP1 suggests that SAP functions in innate immunity in the rock bream.

The C-reactive protein of tongue sole Cynoglossus semilaevis is an acute phase protein that interacts with bacterial pathogens and stimulates the antibacterial activity of peripheral blood leukocytes

Pentraxins are a family of evolutionarily conserved proteins that play an important part in innate immunity. C-reactive protein (CRP) is a member of the pentraxin family and in humans is known to be the major acute phase protein. In this work, we report the identification and analysis of a CRP, CsCRP, from half-smooth tongue sole (Cynoglossus semilaevis). CsCRP is composed of 228 amino acid residues and possesses a Pentraxin/CRP domain. Expression of CsCRP occurred in a wide range of tissues and was upregulated by pathogen infection in kidney, spleen, blood, and, in particular, liver. Following bacterial infection, CsCRP level in blood rose rapidly within 12 h and was approximately 3.8 fold of that of the basal level. Purified recombinant CsCRP (rCsCRP) was able to interact with Gram-negative and Gram-positive bacteria including those of pathogenic nature in a dose-dependent manner. When peripheral blood leukocytes (PBL) were infected with bacterial pathogen in the presence of rCsCRP, the respiratory burst and phagocytic capacity of the cells were increased to significant extents. Taken together, these results indicate that CsCRP is an acute phase protein that plays a role in innate immune defense against bacterial infection.

Molecular characterization and expression analysis of two new C-reactive protein genes from common carp (Cyprinus carpio)

C-Reactive protein (CRP) plays an important role in the acute phase response. Transcripts encoding two new CRP-like molecules (ccCRP1 and ccCRP2) from European common carp have been characterized which has enabled seven CRP-like genes to be identified in zebrafish. 79.3% (ccCRP1) and 74.5% (ccCRP2) identity to CRP from East-Asian common carp occurs and fish CRP genes form a distinct clade. ccCRP2 gene organization comprises four exons and three introns, in contrast to the two exons/one intron organization of mammalian CRP genes. Gene expression assays showed both ccCRP-like molecules are constitutively expressed in liver, skin, gill, gut, muscle, kidney, spleen and blood. Protein levels of ccCRP in serum and spleen were significantly different from other organs analyzed, and levels were greatest in the liver. It is proposed that the two carp CRP genes defined differ in their expression profiles which may suggest differences in their biological activities.

Isolation of two C-reactive protein homologues from cod (Gadus morhua L.) serum

Pentraxins are important molecules in innate defence and play a role in the acute phase response of both mammals and fish. Isolation of cod pentraxins by affinity chromatography using phosphorylcholine agarose revealed two pentraxin-like proteins, referred to as PI and PII proteins. These varied in their overall charge, pentameric and subunit molecular size, glycosylation and N-terminal amino acid sequences. The PI protein was homologous with the CRP-like pentraxin previously described in cod whereas the PII protein was a new CRP homologue, which was characterized by substantial individual heterogeneity with regard to subunit size and relative density. The results indicate considerable genetic variations in the cod pentraxins.

Serum CRP-like protein profile in common carp Cyprinus carpio challenged with Aeromonas hydrophila and Escherichia coli lipopolysaccharide

The potential of C-reactive protein (CRP)-like proteins to be used as a biomarker of health status in cultured carp obtained from various European fish lines has been assessed. Varying CRP-like protein levels in the serum of carp were monitored using an indirect competitive enzyme-linked immunosorbent assay. CRP-like protein basal levels in normal fish varied between carp lines, ranging on average from 2.9+/-0.15 to 12.57+/-1.19 microg ml(-1). Serum levels of CRP-like protein in carp were observed to increase several fold in fish infected with the pathogen Aeromonas hydrophila. However, carp injected with Escherichia coli lipopolysaccharide (LPS) serotype 0111:B4 did not exhibit an increase in CRP-like proteins levels.

The innate immune response of finfish--a review of current knowledge

The decline in the fisheries of traditional marine species has been an incentive for the diversification of today's aquaculture sector into the intensive rearing of many finfish species. The increasing interest in commercial farming of different finfish species is expected to result in similar environmental and husbandry-related problems as have been experienced in the development of the salmonid farming industry. An understanding of the biology of the fish species being cultured, in particular the immune response is important for improved husbandry and health management of the species. The innate immune system of fish has generated increasing interest in recent years and is now thought to be of key importance in primary defence and in driving adaptive immunity. This review focuses on key components (cellular and humoral) of the innate immune responses of different fish species of commercial importance.

Effect of turpentine oil on C-reactive protein (CRP) production in rainbow trout (Oncorhynchus mykiss)

The effect of turpentine oil on C-reactive protein (CRP) production was studied in rainbow trout (Oncorhynchus mykiss). Serum CRP concentration was estimated by sandwich enzyme-linked immunosorbent assay using anti-rainbow trout CRP monoclonal antibody (mAb) AC4 and polyclonal antibody. Intracellular CRP was demonstrated by flow cytometry using anti-trout CRP mAb. Hepatocytes, head kidney macrophages, spleen lymphocytes and peripheral blood lymphocytes showed reaction against AC4, but RTG-2 fibroblastic line cells, derived from rainbow trout gonad did not. This is the first report on the detection of intracellular CRP in fish. CRP levels decreased significantly 1 day after intramuscular injection of turpentine oil and remained low for 14 days. Significant decreases in the expression of CRP in hepatocytes, head kidney macrophages and spleen lymphocytes after injection of turpentine oil were found. The reduction of serum CRP concentration after turpentine oil injection may be attributed to decreases in intracellular CRP synthesis.

c-Reactive protein levels as a biomarker of inflammation and stress in the Atlantic sharpnose shark (Rhizoprionodon terraenovae) from three southeastern USA estuaries

Circulating c-reactive protein (CRP) levels can be used as a bioindicator of the acute phase inflammatory response and as a possible biomarker of inflammation and neurogenic stress in vertebrates. Currently, there are no data describing the ranges of CRP levels in sharks living in different habitats, especially habitats of differing degrees of pollution. Developing antibodies against CRP is a first and critical step towards developing sensitive methods for quantifying CRP, and thus inflammatory and stress responses in sharks. Sharpnose shark, Rhizoprionodon terraenovae, serum C-reactive protein was purified sequentially over AH-sepharose 4B-PC and sepharose CL-4B columns and used to immunize balb/c mice for generating stocks of polyclonal anti-sera. Serum samples from 131 sharpnose sharks were collected from three different geographical regions along the coast of SC and GA, USA between June and November 2002. Total CRP concentrations were quantified by ELISA and found to be highest in the sharpnose shark population collected in the summer from Charleston, SC, compared to Beaufort, SC and Brunswick, GA. Seasonal comparisons indicated a higher CRP concentration in the summer of the Charleston, SC population compared to the fall. These data suggest that sharks living in the Charleston, SC harbor estuary may be exposed to a suite of pathogens or other stressors that are different than those found in the Beaufort, SC and Brunswick, GA estuaries. These data support the use of CRP as a bioindicator of health status in elasmobranchs.

Changes of C-reactive protein levels in rainbow trout (Oncorhynchus mykiss) sera after exposure to anti-ectoparasitic chemicals used in aquaculture

Changes of serum C-reactive protein (CRP) levels in rainbow trout (Oncorhynchus mykiss) were studied after exposure to formalin, metriphonate or potassium permanganate, which are used in aquaculture as anti-ectoparasitic chemicals. The CRP level in normal trout sera is 88+/-5 microg ml(-1) according to sandwich enzyme-linked immunosorbent assay. CRP levels increased to a maximum at six or nine days after exposure to formalin for 3.5 h at 300 ppm or 9.5 h at 30 ppm, respectively; these levels are 4.3 and 18 times higher than normal. At 18 days after treatment, the CRP level had decreased to significantly below the normal level. After exposure to metriphonate (0.4 ppm for 30 min), the CRP level increased significantly to a maximum at three days after exposure (9.9 times higher than normal), then decreased to below normal. With exposure to potassium permanganate at 40 ppm for 45 min, fish showed significantly lower CRP levels than the normal level at 14 days after exposure. Fish reared at a water temperature of 16.5-19.5 degrees C showed significantly higher CRP levels than those reared at 13 degrees C. Measurement of CRP levels in trout serum can be used as a bioindicator of the health condition of the fish.

Inflammatory interactions in fish exposed to pollutants and parasites: a role for apoptosis and C reactive protein

Although previous studies have highlighted the inflammatory responses of fish infected with parasites and exposed to pollutants, very little is known about how these two stressors interact within the fish. In this review, which also contains original data, the effect of these two parameters on the fish inflammatory response is assessed and, in particular, the role of apoptosis and the acute phase protein, C reactive protein, is evaluated. InCyprinus carpioexposed to 0·5 mg NH4+l−1or 0·1 mg Cd2+l−1and experimentally infected with the blood fluke,Sanguinicola inermis, the pollutant type and the order in which the fish experiences the parasite and toxicant, significantly affects the ultrastructural appearance and cellular content of the pronephros and thymus. This is reflected in the intensity of infection where the pollutant appears to have less effect on an established infection. Both stressors, pollutant and infection, may mediate their effects via the endocrine system. Studies have revealed that cortisol at 100 ng ml−1is able to induce apoptosis in pronephric cells of carp and that an increase in apoptosis is associated with an increase in phagocytosis in this immune organ. In addition, C reactive protein, which is used as a biomarker of the inflammatory response in humans and other mammals, is evaluated as a possible indicator of physiological states in fish exposed to pathogens and pollutants.

Complete cDNA sequence of SAP-like pentraxin from Limulus polyphemus: implications for pentraxin evolution

The serum amyloid P component (SAP)-like pentraxin Limulus polyphemus SAP is a recently discovered, distinct pentraxin species, of known structure, which does not bind phosphocholine and whose N-terminal sequence has been shown to differ markedly from the highly conserved N terminus of all other known horseshoe crab pentraxins. The complete cDNA sequence of Limulus SAP, and the derived amino acid sequence, the first invertebrate SAP-like pentraxin sequence, have been determined. Two sequences were identified that differed only in the length of the 3' untranslated region. Limulus SAP is synthesised as a precursor protein of 234 amino acid residues, the first 17 residues encoding a signal peptide that is absent from the mature protein. Phylogenetic analysis clusters Limulus SAP pentraxin with the horseshoe crab C-reactive proteins (CRPs) rather than the mammalian SAPs, which are clustered with mammalian CRPs. The deduced amino acid sequence shares 22% identity with both human SAP and CRP, which are 51% identical, and 31-35% with horseshoe crab CRPs. These analyses indicate that gene duplication of CRP (or SAP), followed by sequence divergence and the evolution of CRP and/or SAP function, occurred independently along the chordate and arthropod evolutionary lines rather than in a common ancestor. They further indicate that the CRP/SAP gene duplication event in Limulus occurred before both the emergence of the Limulus CRP variants and the mammalian CRP/SAP gene duplication. Limulus SAP, which does not exhibit the CRP characteristic of calcium-dependent binding to phosphocholine, is established as a pentraxin species distinct from all other known horseshoe crab pentraxins that exist in many variant forms sharing a high level of sequence homology.

Acute phase response of C-reactive protein of Labeo rohita to aquatic pollutants is accompanied by the appearance of distinct molecular forms

Different forms of C-reactive proteins have been purified to electrophoretic homogeneity by calcium dependent affinity chromatography on a phosphorylcholine (PC)-Sepharose column from the sera of Labeo rohita confined in fresh water (CRP(N)) and water polluted with sublethal doses of cadmium (CRP(Cd)), mercury (CRP(Hg)), phenol (CRP(Ph)), and hexachlorocyclohexane (CRP(Hx)), which elevate serum CRP levels by three- to fivefold. On native PAGE, induced forms of CRP show remarkable differences in their electrophoteric mobility indicating differences in molecular mass, charge, and/or shape. Kinetic studies reveal the appearance of a pollutant specific molecular variant, which replaces the normal form at the peak of induction. Studies on amino acid and carbohydrate compositions, isoelectric focusing, binding to PC, C-polysaccharide (CPS) & lectins, and secondary structures of the purified CRPs, indicate, that, they differ significantly from each other, but grossly share the common properties of a CRP, including pentraxin, structure revealed by electron microscopy.

The acute phase response and innate immunity of fish

Tissue trauma or invasion by pathogens or parasites induce changes in the quantities of several macromolecules in animal body fluids. These changes comprise one aspect of the acute phase response (APR), which in toto involves metabolic changes in several organ systems. One clear indication of the response is the increase in synthesis and secretion by the liver of several plasma proteins, with simultaneous decreases in others. These acute phase proteins (APP) function in a variety of defense-related activities such as limiting the dispersal of infectious agents, repair of tissue damage, inactivation of proteases, killing of microbes and other potential pathogens, and restoration of the healthy state. Some APP are directly harmful to microbes, while others modify targets thus marking them for cell responses. Some work alone while others contribute to cascades. Proteins that are APP in mammals, and that have been identified in both teleosts and elasmobranchs include C-reactive protein, serum amyloid P, and several components of the Complement system. Others reported in teleosts include transferrin and thrombin. Of these, only CRP has been reported to increase in acute phase plasma. In trout, a precerebellin-like protein is an APP with unknown functions. A cDNA library enriched in fragments of transcripts that were more abundant in livers from fish undergoing an APR recently yielded sequences resembling 12 additional known APP, and as many others either not known to be APP, or not similar to others yet in public databases. It appears that, as in mammals, hepatocytes are the prime source of APP in fish, and that pro-inflammatory cytokines induce transcription of their genes.

Evolution of effectors and receptors of innate immunity

The bony fishes are derived from one of the earliest divergent vertebrate lineages to have both innate and acquired immune systems. They are considered by some to be an ideal model to study the underpinnings of immune systems precisely because of their phylogenetic position and the fact that their adaptive immune systems have not been elaborated to the extent seen in mammals. By the same token, examination of innate immune systems in invertebrates and early chordates can provide insight into how homologous systems operate in fish and higher vertebrates. Herein, we provide an overview of the molecular evidence that we hope helps clarify the evolutionary relationships of innate immune molecules identified in bony fishes. The innate immune systems being considered include select chemokines (CC and CXC chemokines and their receptors), cytokines (IL-1, IL-8, interferons, TGF-beta, TNF-alpha), acute phase proteins (SAA, SAP, CRP, alpha2M, and the complement components--C3-C9, MASP, MBL, Bf), NK cell receptors, and molecules upstream and downstream of the Toll signaling pathways.

C-reactive protein in the hemolymph of Achatina fulica: interrelationship with sex steroids and metallothionein

C-reactive protein in Achatina fulica (ACRP) is a normal component of the hemolymph. Its concentration varied from 1mg/ml in the newly hatched male, 3-5 mg/ml in the most active hermaphrodite and 1.5-2.8 mg/ml in the sedentary female showing a direct relationship of the protein with the active phase of the animal. ACRP has a molecular mass of 400 kDa and showed high absorbance in the region of 200-230 nm. It has four subunits with relative molecular masses of 110, 90, 62 and 60 kDa, respectively. Interestingly, rat platelet aggregation in vitro was significantly enhanced by ACRP in presence of 10 microM ADP and 2 mM Ca(2+) suggesting a probable role of ACRP in the aggregation of amoebocytes during the formation of plug in injured tissue. Like other vertebrate CRPs, ACRP also acts as a scavenger of chromatin fragments as evidenced by its binding to poly-L-arginine. Among the sex steroids, 4-androstenedione induces ACRP synthesis in the newly hatched male reaching the level found in the most active hermaphrodite phase (4 mg/ml). A very high molar ratio (5) of mercury binding to ACRP confirmed its sequestration property of heavy metals as observed in vertebrates. The level of metallothionein (MT) in the hemolymph gradually increased from the male to the hermaphrodite to the female, a pattern distinctly different from that of the ACRP titer. Since both MT and ACRP can sequester inorganic mercury, the high level of MT compensates functionally for the low titer of ACRP in the sedentary female.

C-reactive protein and SAP-like pentraxin are both present in Limulus polyphemus haemolymph: crystal structure of Limulus SAP

C-reactive protein and serum amyloid P component are members of the pentraxin family of oligomeric serum proteins which has been conserved through evolution. In humans both have pentameric structures and both play complex roles in the immune response, C-reactive protein being the classical acute-phase reactant produced in response to tissue damage and inflammation. An invertebrate SAP-like pentraxin has not previously been identified and it has been postulated that C-reactive protein and serum amyloid P component are products of a gene duplication event within vertebrate evolution. We have isolated serum amyloid P component from the haemolymph of the phylogenetically ancient "living fossil", the horseshoe crab Limulus polyphemus and determined the three-dimensional structure by X-ray crystallography. The structure of the previously undiscovered Limulus serum amyloid P component, the first invertebrate lectin structure to be determined, reveals the pentraxin fold and a novel doubly stacked octameric ring. The crystal structure and the discovery that both prototypic pentraxins are present in Limulus raises the possibility that both were present in the common ancestors of arthropods and chordates over 500 million years ago. The impact of the results on our understanding of the origins and evolution of pentraxins and innate immunity is discussed.

Effect of environmental pollutants on the C-reactive protein of a freshwater major carp, Catla catla

C-reactive proteins (CRP) have been affinity purified to electrophoretic homogeneity from the sera of major carp, Catla catla before and after exposure to environmental pollutants. Exposure to these pollutants elevate the levels of circulating CRPs to 2.8-3.5 times the normal values. Kinetic studies of metal intoxication indicate that a unique molecular variant of CRP is present in the serum at the peak level of acute phase induction, and this variant coexists with normal CRPs. Carbohydrate analysis and lectin binding reveals that these CRPs are glycoproteins differing significantly in total carbohydrate contents. Their electrophoretic mobilities in native gel are different but become identical on desialylation and deglycosylation implying that the molecular variants vary in the glycan parts. All these forms of CRP contain two nonidentical subunits of Mr 22 and 29 kDa. Examination of their immunological crossreactivity demonstrate their similarity in overall molecular topology but their differences in the quantitative extent of binding are reflected.

A comparative study of pentraxin-like proteins in different fish species

Pentraxins are a family of pentameric serum proteins that have been conserved in evolution and share sequence homology, similar subunit assembly and the capacity for calcium-dependent ligand binding. The classical pentraxins are human C-reactive protein (CRP) and serum amyloid P component (SAP). The sequence homology and gene organization indicate that they arose from a gene duplication of an ancestral pentraxin gene. They are usually isolated based on their affinity for phosphorylcholine and agarose, respectively. We have used this method for isolation of pentraxin-like proteins from normal serum of Atlantic salmon (Salmo salar), common wolffish (Anarhichas lupus), cod (Gadus morhua) and halibut (Hippoglossus hippoglossus). Although pentraxin structures have not been verified, the isolated proteins all appear to be pentraxin-like based on their binding specificity, molecular weight of subunits, cross-reactivity with antibodies to human pentraxins and N-terminal amino acid sequences. However, with the described method only one pentraxin-like protein was detected in each of the fish species.

Atypical phosphorylcholine-reactive protein from Atlantic salmon, Salmo salar L

A phosphorylcholine-reactive protein was isolated from serum of Atlantic salmon (Salmo salar L.) by affinity chromatography on a phosphorylcholine-conjugated Sepharose column followed by elution with phosphorylcholine. Based on the method used we describe the isolated protein as salmon phosphorylcholine-reactive protein (salmon PRP). Salmon PRP has calcium-independent binding to phosphorylcholine. The protein exists in a monomeric and dimeric form with molecular weight of approximately 80 and 160 kD, respectively. Separation of the protein preparation on SDS-PAGE under reducing conditions resulted in disappearance of the 80 and 160 kD bands and appearance of a major protein band of approximately 100 kD. The N-terminal amino acid sequences of the non-reduced 80 and 160 kD bands and the reduced 100 kD band were identical. Apart from the dimeric form, the molecular weight of salmon PRP and its appearance on SDS-PAGE is similar to human plasminogen. Comparison of the sequence in a protein database resulted in approximately 50% identity with human and bovine plasminogen. In addition, cross-reactivity between antibodies to human plasminogen and salmon PRP was demonstrated. Thus, salmon PRP appears to be different from other phosphorylcholine-reactive proteins which are mostly reported to be CRP-like proteins with calcium-dependent binding to phosphorylcholine, pentameric ring-structure and sequence homology between species. Whether salmon PRP is a new type of phosphorylcholine-binding protein with an unknown function or a plasminogen-like protein with binding specificity for phosphorylcholine calls for further investigation.

Multimer formation and ligand recognition by the long pentraxin PTX3. Similarities and differences with the short pentraxins C-reactive protein and serum amyloid P component

PTX3 is a prototypic long pentraxin consisting of a C-terminal 203-amino acid pentraxin-like domain coupled with an N-terminal 178-amino acid unrelated portion. The present study was designed to characterize the structure and ligand binding properties of human PTX3, in comparison with the classical pentraxins C-reactive protein and serum amyloid P component. Sequencing of Chinese hamster ovary cell-expressed PTX3 revealed that the mature secreted protein starts at residue 18 (Glu). Lectin binding and treatment with N-glycosidase F showed that PTX3 is N-glycosylated, sugars accounting for 5 kDa of the monomer mass (45 kDa). Circular dichroism analysis indicated that the protein consists predominantly of beta-sheets with a minor alpha-helical component. While in gel filtration the protein is eluted with a molecular mass of congruent with900 kDa, gel electrophoresis using nondenaturing, nonreducing conditions revealed that PTX3 forms multimers predominantly of 440 kDa apparent molecular mass, corresponding to decamers, and that disulfide bonds are required for multimer formation. The ligand binding properties of PTX3 were then examined. As predicted based on modeling, inductive coupled plasma/atomic emission spectroscopy showed that PTX3 does not have coordinated Ca2+. Unlike the classical pentraxins CRP and SAP, PTX3 did not bind phosphoethanolamine, phosphocholine, or high pyruvate agarose. PTX3 in solution, bound to immobilized C1q, but not C1s, and, reciprocally, C1q bound to immobilized PTX3. Binding of PTX3 to C1q is specific and saturable with a Kd 7.4 x 10(-8) M as determined by solid phase binding assay. The Chinese hamster ovary cell-expressed pentraxin domain bound C1q when multimerized. Thus, as predicted on the basis of computer modeling, the prototypic long pentraxin PTX3 forms multimers, which differ from those formed by classical pentraxins in terms of protomer composition and requirement for disulfide bonds, and does not recognize CRP/SAP ligands. The capacity to bind C1q, mediated by the pentraxin domain, is consistent with the view that PTX3, produced in tissues by endothelial cells or macrophages in response to interleukin-1 and tumor necrosis factor, may act as a local regulator of innate immunity.

Isolation of a pentraxin-like protein from rainbow trout serum

Serum amyloid P-component (SAP) is a glycoprotein consisting of five or ten noncovalently associated identical subunits of molecular weight 19,000-30,000. Herein we report the isolation and partial characterization of a SAP-like protein from rainbow trout serum. The protein was isolated by calcium-dependent binding to Sepharose followed by ion-exchange and size-exclusion chromatography. Rabbit antibody against human SAP reacted with the trout protein and the NH2-terminal sequence of 16 amino acids showed 60% identity with the first 15 residues of human SAP. SDS-PAGE and endoglycosidase treatment indicated that the trout protein is a glycoprotein in which five or six subunits are linked by disulphide bonds. The subunits have a molecular weight of 37,000 of which approximately 13% is due to carbohydrate. We propose to name the trout protein sulphide linked SAP (SL-SAP).

Molecular characterization of Limulus polyphemus C-reactive protein. I. Subunit composition

The molecular mass of whole native C-reactive protein (CRP) from Limulus polyphemus, the horseshoe crab, was precisely determined for the first time, by analytical ultracentrifugation after measurement of its absorption coefficient, A1cm, 1% at 280 nm (15.49) and its partial specific volume (0.72 +/- 0.003 ml/g). The apparent weight-average molecular mass, in the range over which it was independent of the concentration, was 300 kDa. Limulus CRP, isolated from an individual animal, was also analyzed by electrospray mass spectrometry after dissociation into its subunits, and nine components were detected in the mass range 24935-25617 Da. Four of these components corresponded precisely to one of the previously reported protein sequences of Limulus CRP subunits which is glycosylated by a single oligosaccharide chain of composition, Man2GlcNAc2, Man3GlcNAc2, Man4GlcNAc2 or Man5GlcNAc2, the structures of which are elucidated in the accompanying paper [Amatayakul-Chantler, S., Dwek, R. A., Tennent, G. A., Pepys, M. B. & Rademacher, T. W. Molecular characterization of Limulus polyphemus C-reactive protein. II. Asparagine-linked oligosaccharides (1993) Eur. J. Biochem. 214, 99-110]. All the remaining components, except one minor component, corresponded to the analogous glycoforms of peptides of molecular mass 24281 +/- 2 Da and 24523 +/- 1 Da, neither of which have previously been characterized. These results are consistent with the presence of 12 subunits in the Limulus CRP molecule, in contrast to the number of subunits in vertebrate members of the CRP family. The CRP family members in vertebrates are known as pentraxins because of the symmetrical pentameric arrangement of their subunits. The concentration of Limulus CRP in hemolymph from 20 individual animals, measured precisely by specific electroimmunoassay, covered the wide range 0.275-6.64 mg/ml, mean (SD) = 1.83 (2.06) mg/ml. It remains to be determined whether this protein is an acute-phase reactant, like its human and some other mammalian homologues.

Cell surface C-reactive protein of rainbow trout lymphocytes

C-reactive protein (CRP) expressed on rainbow trout (Oncorhynchus mykiss) lymphocytes was investigated to determine what role CRP might have on lymphocyte function. C-reactive protein was detected on the surface (S-CRP) of 25% of peripheral blood lymphocytes (PBL) and 4% of head kidney lymphocytes (HKL) by flow cytometry of cells labelled with biotinylated rabbit anti-rainbow trout CRP IgG and fluorescent-coupled avidin. Purified CRP, when added to cells in culture, bound to both PBL and HKL. Stimulation of PBL and HKL by concanavalin A, phytohemagglutinin, or lipopolysaccharide increased the percentage of S-CRP-positive cells, which suggests the production of CRP by lymphocytes. Treatment of lymphocytes with anti-rainbow trout CRP IgG and complement decreased the number of S-CRP-positive cells.

Isolation of an acute-phase phosphorylcholine-reactive pentraxin from channel catfish (Ictalurus punctatus)

1. Channel catfish (Ictalurus punctatus) serum contains a protein that precipitates pneumococcal C-polysaccharide (CPS) in a calcium-dependent fashion. 2. The serum titer of this protein follows an acute-phase pattern in catfish injected with turpentine. 3. A non-glycosylated, phosphorylcholine (PC)-reactive protein (PRP) with molecular mass ca 100 kDa, was isolated from channel catfish acute-phase sera by affinity chromatography on PC-Sepharose 4B. 4. Contaminating proteins with molecular masses ca 700 kDa and ca 20 kDa that co-eluted with PRP from PC-Sepharose appear to be aggregated and native low-molecular weight factors (LMFs), respectively. 5. Purified PRP has gamma mobility but in serum samples PRP has gamma-beta mobility. 6. Electron microscopy confirmed that PRP has planar, pentagonal symmetry. 7. The amino terminus of PRP is blocked, but based on comparison of amino-acid compositions channel catfish PRP is clearly similar to human CRP and is most like CRPs from the dogfish (Mustelus canis) and rainbow trout (Oncorhynchus mykiss).

Studies in vivo and in vitro of serum amyloid P component in normals and in a patient with AA amyloidosis

Pure serum amyloid P component (SAP) was isolated from a normal donor pool, from individuals with the different genotypes of an MspI restriction fragment length polymorphism (RFLP) linked to the SAP gene, and from a patient with AA amyloidosis. The SAP preparations were all identical and all behaved as a single homogeneous species in polyacrylamide gel electrophoresis, isoelectric focussing, reverse-phase chromatography, binding in vitro to phosphoethanolamine-Sepharose (binding constant 2.4 x 10(7) l/mol) and AL amyloid fibrils (1.6 x 10(8) l/mol), and binding to amyloid deposits in vivo in mice with casein-induced amyloidosis. The in vivo metabolism of 125I-SAP from a single donor was normal and identical in three healthy individuals representing the three different MspI RFLP genotypes. There is thus no frequent polymorphism of SAP in normal subjects, and SAP altered with respect to the characteristics studied here is not a necessary condition for pathogenesis of systemic AA amyloidosis.

C-reactive protein in eel: purification and agglutinating activity

C-reactive protein was highly purified from Japanese eel (Anguilla japonica) serum by precipitation with phosphatidyl-choline and Ca2+. On SDS-PAGE, eel C-reactive protein (eCRP) migrated as a single band with a molecular weight of 24,000 under reducing and 23,500 under non-reducing conditions. The molecular weight of native eCRP was estimated to be 120,000 by Sephacryl S-300 gel filtration. The eCRP was detected within the albumin region on immunoelectrophoresis. The eCRP showed an agglutinating activity against Streptococcus pneumoniae in the presence of Ca2+, and the activity was inhibited by 1 mM EDTA or 1 mM phosphorylcholine (PC). The eCRP also agglutinated rabbit red blood cells (RRBC), but not human and five other kinds of red blood cell. The hemagglutinating activity was inhibited by glucosamine or mannose. The eCRP formed a precipitin line with histone, protamine, poly(L-lysine) and poly(L-arginine) in agarose gel. The serum levels of eCRP were distributed in 6.8 ng/ml-5.3 mg/ml, n = 187, the mean value being 834 ng/ml.