In vitro effects of C-reactive protein on phagocytosis

An overview on human serum lectins

An extensive literature survey done on the various naturally occurring lectins in human serum upon its salient features such as methods of detection, level and sites of synthesis, binding specificity, cation dependency, modes of isolation, molecular and functional characterization way back from 1930s to till date was presented in a tabulated section. In addition, the generation of lectin and other immune molecules in vertebrates upon treatment with exogenous elicitors has also been framed in a tabular form. Furthermore, ANEW lectin induced in human serum for the very first time by an exogenous elicitor was detected, isolated and characterized by us whose features are also tabulated explicitly.

Pentraxins: structure, function, and role in inflammation

The pentraxins are an ancient family of proteins with a unique architecture found as far back in evolution as the Horseshoe crab. In humans the two members of this family are C-reactive protein and serum amyloid P. Pentraxins are defined by their sequence homology, their pentameric structure and their calcium-dependent binding to their ligands. Pentraxins function as soluble pattern recognition molecules and one of the earliest and most important roles for these proteins is host defense primarily against pathogenic bacteria. They function as opsonins for pathogens through activation of the complement pathway and through binding to Fc gamma receptors. Pentraxins also recognize membrane phospholipids and nuclear components exposed on or released by damaged cells. CRP has a specific interaction with small nuclear ribonucleoproteins whereas SAP is a major recognition molecule for DNA, two nuclear autoantigens. Studies in autoimmune and inflammatory disease models suggest that pentraxins interact with macrophage Fc receptors to regulate the inflammatory response. Because CRP is a strong acute phase reactant it is widely used as a marker of inflammation and infection.

The protective function of human C-reactive protein in mouse models of Streptococcus pneumoniae infection

Human C-reactive protein (CRP), injected intravenously into mice or produced inside mice by a human transgene, protects mice from death following administration of lethal numbers of Streptococcus pneumoniae. The protective effect of CRP is due to reduction in the concentration of bacteria in the blood. The exact mechanism of CRP-dependent killing of pneumococci and the partners of CRP in this process are yet to be defined. The current efforts to determine the mechanism of action of CRP in mice are directed by four known in vitro functions of CRP: 1. the ability of pneumococcal C-polysaccharide-complexed CRP to activate complement pathways, 2. the ability of CRP to bind to Fcgamma receptors on phagocytic cells, 3. the ability of CRP to bind to immobilized complement regulator protein factor H which can also be present on pneumococci, and, 4. the ability of CRP to interact with dendritic cells. CRP-treated dendritic cells may well be as host-defensive as CRP alone. An interesting condition for the protective function of CRP is that CRP must be given to mice within a few hours of the administration of pneumococci. CRP does not protect mice if given later, suggesting that CRP works prophylactically but not as a treatment for infection. However, full knowledge of CRP may lead to the development of CRP-based treatment strategies to control pneumococcal infection. Also, because CRP deficiency in humans has not yet been reported, it becomes important to investigate the deficiency of the mechanism of action of CRP in CRP-positive individuals.

SOLUBLE BIO-MARKERS IN VASCULAR DISEASE: MUCH MORE THAN GAUGES OF DISEASE?

1. In recent years demonstration of a direct association between slightly elevated serum levels of soluble proteins including the acute phase response proteins, selectins and intercellular adhesion molecules and the risk of developing vascular disease have been widely reported. These studies may provide the clinician with an insight into disease diagnosis, prognosis and disease activity. 2. The simplest interpretation of this data is that soluble proteins are just sensitive markers of inflammation. However, they may in fact be modulating inflammation directly through interaction with circulating cells. 3. Recent work has shown that these soluble proteins do indeed remain active and can bind to functional ligands expressed by circulating leucocytes. The current review focuses on the soluble proteins C-reactive protein and soluble P-selectin and describes previous studies characterizing their interaction with immune cells to modulate the pathogenesis of vascular disease. 4. The current review focuses on the soluble proteins C-reactive protein and soluble P-selectin and describes previous studies characterizing their interaction with immune cells to modulate the pathogenesis of vascular disease.

The antimicrobial activity of C-reactive protein

Recent studies in transgenic mice confirmed that C-reactive protein is protective against microbial pathogens. This is consistent with its ability in vitro to bind microbes, activate the complement classical pathway, and engage FcgammaRI and FcgammaRII. However, in transgenic mice protection also requires the alternative pathway of complement, and FcgammaRI is dispensable.

The role of C-reactive protein in the resolution of bacterial infection

C-reactive protein is an acute phase protein in man and an important component of the innate immune system. C-reactive protein activates the classical pathway of complement, which is one of its main mechanisms in providing host defense. It has recently been recognized that C-reactive protein interacts with the cells of the immune system by binding to Fc gamma receptors. It may thus bridge the gap between innate and adaptive immunity and provide an early, effective antibacterial response. Furthermore, as it protects against the damaging inflammatory response to lipopolysaccharide and cytokines, it may prevent the lethal side-effects of bacterial products. The recent identification of the interaction of C-reactive protein with Fc gamma receptors will lead to an enhanced understanding of C-reactive protein and its role in both the innate and acquired immune systems.

C-reactive protein binding to murine leukocytes requires Fc gamma receptors

Human C-reactive protein (CRP) is an acute phase protein that binds to receptors on human and mouse leukocytes. We have recently determined that the high and low affinity receptors for CRP on human leukocytes are Fc gamma RIIa and Fc gamma RI, respectively. Previous work by others suggested that CRP receptors on mouse macrophages are distinct from Fc gamma R. We have taken advantage of the availability of mice deficient in one or more Fc gamma R to reexamine the role of Fc gamma R in CRP binding to mouse leukocytes. Three strains of Fc gamma R-deficient mice were examined: gamma-chain-deficient mice that lack Fc gamma RI and Fc gamma RIII, Fc gamma RII-deficient mice, and mice deficient in both gamma-chain and Fc gamma RII that lack all Fc gamma R. No binding of CRP was detected to leukocytes from double-deficient mice, indicating that Fc gamma R are required for CRP binding. CRP binding to leukocytes from gamma-chain-deficient and Fc gamma RII-deficient mice was reduced compared with binding to leukocytes from wild-type mice. Further analysis of CRP binding to macrophages, neutrophils, and lymphocytes provides direct evidence that Fc gamma RIIb1, Fc gamma RIIb2, and Fc gamma RI are the receptors for CRP on mouse leukocytes. These findings may have important implications in understanding the physiological function of CRP.

The major receptor for C-reactive protein on leukocytes is fcgamma receptor II

C-reactive protein (CRP) is an acute phase serum protein that shares several functions with immunoglobulin (Ig)G including complement activation and binding to receptors on monocytes and neutrophils. The identity of the receptor for CRP has been the target of extensive research. We previously determined that CRP binds to the high affinity receptor for IgG, FcgammaRI (CD64). However, this interaction could not account for the majority of binding of CRP to neutrophils or monocytic cells. We now determine that CRP also interacts with FcgammaRIIa (CD32), the low affinity receptor for IgG on monocytes and neutrophils. COS-7 cells were transfected with a construct containing the human FcgammaRIIA cDNA. CRP binding and the presence of CD32 were detected by mAb and analyzed by two-color flow cytometry. Cells expressing CD32 bound CRP in a dose-dependent and saturable manner consistent with receptor binding. CRP bound to transfectants and K-562 cells with similar kinetics, and in both cases binding was completely inhibited by aggregated IgG. On monocytic cell lines, treatment with Bt(2)cAMP increased FcgammaRII expression and enhanced CRP binding. CRP also specifically precipitated FcgammaRI and FcgammaRII from the monocytic cell line, THP-1. It is suggested that the major receptor for CRP on phagocytic cells is FcgammaRII.

C-reactive proteins, limunectin, lipopolysaccharide-binding protein, and coagulin. Molecules with lectin and agglutinin activities from Limulus polyphemus

In 1964, Levin and Bang discovered that gram-negative bacterial endotoxin could rapidly induce gelation of Limulus amebocyte lysate. This observation has led to the development of the most sensitive and specific method for the detection of bacterial endotoxin in pharmaceuticals and drugs intended for human use. Over 10 years ago, Bang injected endotoxin into young horseshoe crabs and observed a time and dose-dependent coagulation of the whole hemolymph. Limunectin, LEBP-PI, and Limulus CRP are found together with coagulin as part of the hemolymph clot at the time of endotoxin-induced exocytosis of amebocytes. In this manner, these molecules with agglutinin/lectin activities could work in concert to assist in the recognition and eventual removal of invading microorganisms from the circulating system. Although the mechanism of endotoxin-induced clot formation is to a large extent understood, the mechanism of clot dissolution and removal in the Limulus hemolymph remains to be clarified.

A hypothesis resolving the apparently disparate activities of native and altered forms of human C-reactive protein

Although C-reactive protein (CRP) has been studied for over 60 years, the in vivo function of this acute-phase reactant has not been clearly defined. The literature on CRP has been divided here into three categories: the cyclic, pentameric blood-borne form of CRP termed 'native' CRP which has activities mainly associated with the resolution of inflammation, conformationally altered and aggregated forms of CRP which display pro-inflammatory properties, and proteolytic forms of CRP exhibiting mixed activities. Since the activities of certain forms of CRP in some cases contradict others, a hypothesis has been developed which reconciles these differences. It is proposed that distinct species of CRP are formed which have unique activities at an inflammatory site; conformationally altered and proteolytic forms of CRP are created in succession from bound native CRP at the inflammatory site due to local conditions (e.g. lowered pH, oxygen radicals, or possibly enzymes). Aggregated and/or conformationally altered forms of CRP initially promote inflammation, and subsequently produced peptide products either up or down regulate different leukocyte activities to aid in the progression of the inflammatory event. As the local conditions favoring the conversion of native CRP to altered forms begin to subside, native CRP then predominates at the site, facilitating the removal of cellular debris and resolution of the lesion.

Crystallization and preliminary X-ray diffraction studies of dogfish C-reactive protein

Crystals of dogfish (Mustelus canis) C-reactive protein were obtained through vapor phase equilibration using the sitting drop rod technique with ammonium sulfate as the precipitating agent. The space group was determined to be P1 (triclinic lattice) with unit cell dimensions of a = 82.91, b = 92.25 and c = 103.40 A; alpha = 83.36 degrees, beta = 89.76 degrees, and gamma = 81.30 degrees. These crystals diffract to about 2.6 A resolution and contain two hexamers in the asymmetric unit.

Rotation function studies of human C-reactive protein

Rotation function studies of two tetragonal crystal forms of human C-reactive protein have confirmed the pentameric structure of the molecule. The two crystal forms have space groups P4122 (I) and P4222 (II) with closely similar unit cells and are often twinned together. Investigation of the crystallization conditions indicates that dissociation heterogeneity has been a major limiting factor in the reproducible growth of good single crystals. The orientation of the pentameric molecule is shown to be almost identical in both forms, about the axial direction omega = 57 degrees, phi = 45 degrees, i.e. 57 degrees away from c in the (110) plane.

Preliminary crystallographic study of C-reactive protein from Limulus polyphemus

Crystals of C-reactive protein from Limulus polyphemus have been grown both with and without calcium. The space group for the calcium-free crystals is I422 or I4(1)22, and the cell parameters are a = b = 173.33 (4) A, c = 98.81 (3) A. The crystals diffract to at least 2.8 A resolution and are suitable for detailed structural studies.

Purification of human C-reactive protein by barium sulfate and preparative agarose electrophoresis

A procedure is described for the purification of C-reactive protein (CRP) from human serum. The methods described take advantage of the barium sulfate adsorption property of CRP and the unique biophysical property of CRP migration during electrophoresis in agarose gels containing Ca2+. The purified CRP had an apparant molecular weight of 28,000 as determined by migration of the reduced protein during SDS polyacrylamide gel electrophoresis. The described procedure has the advantage of not requiring either molecular sieve or affinity chromatography for purification of homogenous CRP from human sera.

CRP and neutrophils: functional effects and complex uptake

The uptake of C-reactive protein (CRP)-pneumococcal C-polysaccharide (CPS) complexes by neutrophils was studied. A specific CRP dependent mechanism of uptake was demonstrated. This promoted CPS (complexed to CRP) clearance which was further enhanced by additional complement activation. Physiological concentrations of low density lipoprotein inhibited entry of complexed CPS into neutrophils but had no effect on entry of CRP alone. Pure human CRP was shown to have no effect on neutrophil chemotaxis and oxidative metabolism.

C-reactive protein mediates the solubilization of nuclear DNA by complement in vitro

We have studied the interaction of C-reactive protein (CRP)-chromatin complexes with serum. The amount of chromatin solubilized by serum is directly proportional to the amount of CRP present. Serum minus C3 did not appreciably solubilize chromatin within the time allowed in these experiments regardless of the amount of CRP present. This indicates that, in addition to CRP, complement is critical to the solubilization process. Studies using genetically C2-deficient serum and purified C2 indicate that the classical complement pathway is primarily involved in the solubilization, however, there may be minor involvement by the alternative pathway. We used an enzyme-linked immunosorbent assay to determine the amounts of CRP in plasma from eight patients with systemic lupus erythematosus; two of the eight had levels of CRP far lower than previously reported for normal individuals, and an additional sample had antibodies reactive with CRP. Together, these results suggest that one of the functions of CRP is to mediate the removal of exposed nuclear DNA by complement-dependent solubilization of chromatin. A defect in this mechanism could (a) facilitate the production of antibodies against chromatin components exposed due to tissue damage or (b) contribute to immune complexes containing the chromatin components released from damaged tissue because they are not rapidly cleared.

The role of the spleen in the protective effect of C-reactive protein in Streptococcus pneumoniae infection

C-reactive protein (CRP) is an acute phase serum protein in man which activates complement and has opsonic activity. We have reported that prior injection of CRP into mice can increase their survival following intravenous challenge with Streptococcus pneumoniae type 3 or 4. In this study the conditions required for protection, and the role of hepatic and splenic clearance of bacteria have been examined. Protection against lethal infection was observed with a minimum dose of 25-50 micrograms CRP per mouse. CRP was most effective when administered between 6 h before and 2 h after challenge. CRP treated mice were not protected against infection with Salmonella typhimurium, LT-2, an organism which does not bind CRP. Mice depleted of C3 by treatment with cobra venom factor were protected against S. pneumoniae infection by CRP. Pre-treatment of mice with CRP did not increase the rate of clearance of viable S. pneumoniae from the bloodstream but did increase splenic and decrease hepatic clearance of radiolabelled bacteria in both normal and complement depleted mice. Although these findings suggest a role for the spleen in CRP protection, mice which had been splenectomized were also protected against lethal pneumococcal infection by CRP treatment.

Effect of C-reactive protein on the complement-mediated stimulated of human neutrophils by Streptococcus pneumoniae serotypes 3 and 6

C-reactive protein (CRP) has long been known to appear in the sera of individuals with inflammatory processes, but its role in host defense against bacterial infection is unclear. We have recently demonstrated that CRP in the presence of the classical complement pathway markedly enhances the opsonization of Streptococcus pneumoniae serotype 27 by polymorphonuclear leukocytes (Edwards et al., J. Immunol. 128:2493-2496). In this report we have extended these studies to characterize the role of CRP in the opsonization of other S. pneumoniae serotypes. Two clinically important serotypes, 3 and 6, were tested along with the nonpathogenic rough strain R36a. All strains were found to bind radiolabeled CRP in the presence of calcium and to activate the classical complement pathway in normal human serum. However, the opsonophagocytic response of polymorphonuclear leukocytes to the strains, measured by chemiluminescence, was quite different. In contrast to the marked enhancement by CRP of the chemiluminescent response to serotype 27 in normal human serum, CRP had no effect on the opsonization of serotype 6 or R36a and inhibited opsonization of serotype 3 in normal serum. In serum from a hypogammaglobulinemic patient, CRP enhanced the lowered chemiluminescent response to serotype 3 and 6 organisms but did not restore the response to normal. The greater opsonic effect of CRP on serotype 27 may be related to the ability of CRP to bind to the capsule as well as to the cell wall of this serotype or to differences in the amount of CRP bound to the different strains.

C-reactive protein reactivity with complement and effects on phagocytosis

In the studies described here we have attempted to evaluate the hypothesis that CRP may function in host defense using two systems in which CRP in the presence of C appears to have opsonic properties. In the first, CRP and C were found to stimulate ingestion of erythrocytes by human monocyte or mouse macrophages in vitro, and to alter clearance patterns in vivo. In the second, we have studied opsonization of S. pneumoniae by CRP and C. Experiments with human neutrophils indicate that although CRP and C can enhance opsonization of S. pneumoniae, this effect is more pronounced in the absence of antibody. In vivo CRP was found to protect mice against intravenous infection with S. pneumoniae.

C-reactive protein is protective against Streptococcus pneumoniae infection in mice

C-reactive protein (CRP) has several properties that suggest that it may function as a bacterial opsonin. CRP shows binding reactivity with pneumococcal C-polysaccharide, the cell wall carbohydrate of Streptococcus pneumoniae. In this study we have demonstrated protection of mice against serotypes 3 and 4 of S. pneumoniae infection by a single prior injection of CRP. This effect was seen both in mice that lacked antibody to phosphocholine and in normal mice. Thus the opsonic properties of CRP previously described may be related to protection against pneumococcal infection.

Synthesis, transport, and secretion of plasma proteins by the livers of control and Streptococcus pneumoniae-infected rats

The synthesis, intracellular transport, and secretion of plasma proteins by the liver was studied in both control and Streptococcus pneumoniae-infected rats. Rats were injected with [3H]leucine; at various time intervals, the components of the intracellular secretory system were isolated. The isolation and partial characterization of rough microsomes, smooth microsomes, and Golgi from both control and infected animals are described. After infection, the specific activity of the label in the homogenate and in all isolated cell fractions was significantly increased. In both control and infected animals, the kinetics of labeling suggested that the secretory pathway of the newly synthesized protein was from the rough endoplasmic reticulum to the smooth endoplasmic reticulum to the Golgi and finally to the circulation. Even though infected animals synthesized, transported, and secreted significantly more plasma protein, infection did not significantly alter the secretion time (time between injection of isotope and appearance of labeled protein in the circulation). It is concluded that, after S. pneumoniae infection, the liver still maintains its capability to perform the basic functions of protein synthesis, intracellular transport, and secretion and that newly synthesized plasma protein follows the same intracellular pathway in both control and S. pneumoniae-infected rats.

Acute phase proteins and C9 in patients with Behcet's syndrome and aphthous ulcers

Estimation of the concentration of C9, C-reactive protein (CRP) and alpha1-antitrypsin in forty sera from patients with Behcet's syndrome and recurrent oral ulcers showed significantly increased amounts of C9 and CRP in Behcet's syndrome. The concentration of C9 was also significantly raised in recurrent oral ulceration, though to a lesser extent than in Behcet's syndrome. The assay C9 and CRP might be useful in the differential diagnosis of Behcet's syndrome, especially from recurrent oral ulcers. It is suggested that during epithelial inflammation in recurrent oral ulcers some of the acute phase proteins are increased and in some patients these may modulate the immunological mechanism in such a way as to induce a transition from focal oral ulceration to the multifocal Behcet's syndrome.

Effects on C-reactive protein on the lymphoid system. I. Binding to thymus-dependent lymphocytes and alteration of their functions

C-reactive protein (CRP) is an acute phase protein which shares with the immunoglobulins the ability to induce precipitation and agglutination reactions and activate the complement system. We report here that purified human CRP binds selectively to human T lymphocytes, inhibits their ability to form spontaneous rosettes with sheep erythrocytes and inhibits their response to allogeneic cells in mixed lymphocyte culture reactions; it fails to inhibit phytohemagglutinin- or concanavalin-A-induced mitogenesis. CRP does not bind to human B lymphocytes, nor does it alter the following B-cell functions: binding to activated complement components or the Fc portion of immunoglobulins, mediation of antibody-dependent cytotoxicity reactions or the ability of allogeneic cells to stimulate a mixed lymphocyte culture reaction. Human CRP shows similar selective binding with murine T lymphocytes. It therefore seems that binding of CRP is a property of T lymphocytes or a subpopulation thereof, and can result in modulation of certain of the T-cell functional characteristics in vitro. We suggest that CRP may play a role in modulating T-cell functions during the inflammatory state.

In vitro binding of human C-reactive protein by some pathogenic bacteria and zymosan

C-reactive protein (CRP) in serum from patients with an acute disease was adsorbed not only to Diplococcus pneumonia, but also to E. coli, and could be eluted highly purified.

The finding suggests a specific interaction between CRP and bacteria, an interaction possibly playing an important role in the stimulating effect of CRP on phagocytosis of several bacterial species.

Stimulating effect of C-reactive protein on phagocytosis of various species of pathogenic bacteria

In an investigation of the relationship between the presence of C-reactive protein (CRP) and the promoting effect of the phagocytosis of leucocytes in an in vitro phagocytosis system containing living pathogenic bacteria, it was found that CRP stimulated phagocytosis of Diplococcus pneumoniae, Staph. aureus, E. coli and Klebsiella aerogenes. It appears that CRP is related to non-specific immunity.