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.

Plasma proteins and wound healing

In response to injury, the concentrations of several plasma proteins are characteristically altered. In part, these changes reflect an essential contribution of many of these proteins, acting in concert, to the processes involved in wound healing. There is evidence that plasma proteins support tissue repair by metabolic as well as functional activity. Specifically, plasma proteins may directly facilitate wound healing by: provision of carbohydrates, lipids and amino acids in a usable form as biosynthetic precursors and energetic substrates; the transport of trace metal cofactors involved in various wound repair processes; adhesion of regenerating tissue; modulation of the rate of structural protein synthesis; alignment of collagen subunits; organization of cellular elements wound repair; prevention of autoimmune reactions; hormone transport and local modulation of hormonal effects; neutralization of the potentially toxic products of the inflammatory response and the inhibition of microbial invasion and colonization.

Purified human plasma proteins of unknown function

The development of new analytic and preparative techniques in the field of protein chemistry has essentially extended our knowledge about the variety of human plasma proteins in the last 15 years. In many cases plasma proteins have been particularly determined by immunologic techniques, partially highly purified and physicochemically well characterized, before knowing the biological function. To these proteins belong among others the alpha 1-antitrypsin, Cl-inactivator, alpha 2-macroglobulin, Gc-globulin and the cold-insoluble globulin. Today we know more than 100 proteins being isolated from human plasma and among these are nearly 20, of which the biological function is not yet known. To this group are belonging proteins, which are known since many years, like the alpha 1-acid glycoprotein and the C-reactive proteins as well as proteins, which have only been described in the last years and which partially have an interesting chemical structure, e.g. the histidinerich 3,8S-alpha 2-glycoprotein and the leucine-rich 3,1S-alpha 2-glycoprotein, of which every fifth amino acid is formed by leucine. It is to be hoped that the special chemical structure of some of these human plasma proteins as well as the quantitative immunologic determination in different patient sera will give hints to their biological function.

C-reactive protein fifty years on

The discovery of C-reactive protein (CRP) half a century ago led to the description of the acute-phase reaction which is a fundamental response of the body to injury. Recent work on the structure and function of CRP has revealed the existence of a unique plasma protein family, including CRP and serum amyloid P component (SAP). These proteins have been conserved throughout vertebrate evolution. CRP binds specifically to a wide range of substances derived both from damaged autologous cells and from microorganisms. Complexed CRP can activate the complement system and, by virtue of its dramatically increased production in response to tissue injury, it probably acts primarily as a protective mechanism. However, in some circumstances CRP may also initiate or exacerbate inflammatory lesions. Clinical measurement of serum CRP is valuable as a screening test for organic disease and as a sensitive object index of disease activity and response to therapy in some inflammatory, infective, and ischaemic conditions. SAP closely resembles CRP in structure but not an acute-phase reactant in man. An apparently identical protein, amyloid P component (AP), is always found in amyloid deposits. AP is also found in normal tissues, as an integral constituent of vascular basement membranes and is located on the peripheral microfibrillar mantle of elastic fibres throughout the body.

[C-reactive protein: should it be determined in inflammatory rheumatic diseases?]

The structure, synthesis and possible functions of C-reactive protein (CRP) are discussed. CRP is a highly sensitive but non-specific indicator of tissue damage, but its diagnostic value in inflammatory rheumatic diseases is very limited. In SLE, a high level may suggest additional bacterial infection. While semiquantitative methods are of little help, the quantitative measurement of CRP can be used as both a clinical and a therapeutic parameter in patients in whom ESR does not parallel the inflammatory activity of the disease. Apart from these exceptions, CRP does not appear to offer major advantages over ESR in the day-to-day management of patients with inflammatory rheumatic diseases.

Acute phase reactant proteins as aids to monitoring disease

The plasma acute phase reactant proteins are a group consisting mainly of glycosialated proteins, whose levels rise in response to a wide variety of injuries. This review discusses how by considering several APRPs coincidentally the pattern of change can have a discriminant function which can be used alone or to enhance other biochemical tests, especially in the monitoring of disease.

Interaction of C-reactive protein with lymphocytes and monocytes: complement-dependent adherence and phagocytosis

The serum constituent C-reactive protein (CRP), which activates the classical complement (C) pathway when reacting with its substrates, was examined for its ability to mediate reactions of opsonic adherence and phagocytosis. Erythrocytes coated with C-polysaccharide (CPS) and reacted with CRP (E. CPS-CRP) failed to adhere to B cells and displayed only minimal adherence to monocytes. However, upon the addition of absorbed C or purified C components these cells were found to possess the cleavage products C4b and C3b, which in turn resulted in attachment of these cells to both human B lymphocytes and peripheral blood monocytes. E. CPS-CRP treated with C in the absence of antibody were readily phagocytosized by glass-adherent human monocytes. The phagocytosis of E. CPS-CRP-C was not only mediated by CRP but also required the presence of CRP on the surface of the red cells. The extent of ingestion was proportional to the amount of CRP on the red cell intermediate and was reduced by blocking monocyte receptors with aggregated human gamma-globulin (HGG) at concentrations which did not impair the uptake of other particles. The mediation by CRP of reactions of opsonic adherence and phagocytosis as outlined in these studies points to a significant role for CRP in reactions of host defense and inflammation.

Interactions of C-reactive protein with the complement system. III. Complement-dependent passive hemolysis initiated by CRP

Interactions of CRP with various substrates in the presence of human serum have been shown to result in efficient activation of C components C1-C5. We now report the ability of CRP to initiate C-dependent hemolysis. For this purpose CRP was isolated by affinity chromatography using pneumococcal CPS and gel filtration; its purity was established by several criteria. Erythrocytes were coated with CPS (E-CPS) and passively sensitized with CRP. C-dependent lysis of these cells was observed upon the addition of suitably absorbed human serum, and the efficiency of hemolysis compared favorably with that initiated by rabbit IgG anti-CPS antibody. CRP also sensitized E-CPS for lysis by guinea pig C; partial lysis was seen when C4-deficient guinea pig serum was used, suggesting that CRP also shares with antibody the ability of CRP to fully activate the C system and provide further evidence for a role for CRP similar to that of antibody in the initiation and modulation of inflammatory reactions via the complete system.