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H Gewurz

Publications and source records attributed to H Gewurz.

At least 37 records · Page 2Linked to original sources
PubMed1991

Preferential binding and aggregation of rabbit C-reactive protein with arginine-rich proteins.

Human and rabbit C-reactive proteins (CRP) are similar in mol. wt, structure and amino acid sequence. In addition to the characteristic phosphoryline (PC)-binding specificity, both CRP molecules bind arginine- and lysine-rich proteins. The human CRP-cationic protein reactivity has been reported to be inhibited by calcium and promoted by PC in the presence of calcium. The present study compares binding and precipitation reactions of rabbit CRP (raCRP) with arginine- and lysine-rich proteins, and demonstrates the differential modulation of these interactions by calcium and acidic pH. Rabbit CRP shows preferential binding and precipitation reactivities with arginine-rich cationic molecules. Binding of raCRP to poly-L-arginine (PLA) and arginine-rich histone (ARH) occurs at pH 6.0, in the presence of calcium and is inhibitable by phosphorylcholine (PC) suggesting an interaction at or near the calcium-modulated PC binding site. The in vitro precipitation of raCRP and arginine-rich cationic molecules is significantly inhibited at pH 6.0, by the non-precipitating lysine-rich ligand PLL, and by physiological levels of calcium, and may reflect the participation of distinct "self-aggregation" sites on CRP in the precipitation response. The significance of the preferential arginine reactivity of raCRP to in vivo functions as a scavenger of chromatin during cell death and/or as a modulator of lipoprotein metabolism during the acute phase response is discussed.

Animals↗
PubMed1991

Direct binding of complement component C1q to human immunodeficiency virus (HIV) and human T lymphotrophic virus-I (HTLV-I) coinfected cells.

Previous studies have shown that coinfection of the human T lymphotrophic virus type I (HTLV-I) chronically infected cell line MT4 with human immunodeficiency virus type 1 (HIV-1) results in cells which spontaneously activate complement via the classical pathway. This complement activation was antibody independent, yet required C2, suggesting either direct C1, C4, or C2 activation. Because some animal retroviruses have been shown to bind human C1q directly, the present study investigated the possible direct binding of C1q by HIV coinfected MT4 cells. Coinfected cells bound both C1q present in serum and highly purified C1q. Binding of C1q resulted in formation of active C1 on the cell surface, which could in turn activate complement as shown by C4 consumption. The C1q binding was not HIV-isolate specific since infection of MT4 cells with any of three diverse isolates all induced C1q binding. Purified collagen-like region (CLR) and globular region (GR) fragments of C1q both bound to coinfected cells, suggesting a mechanism of binding by C1q similar to that of fibronectin-C1q binding. However, culture of coinfected cells in serum-free (fibronectin-free) medium did not reduce C1q binding. A second HTLV-I chronically infected line, SLB-1, also displayed increased binding of C1q after HIV infection. The H9 cell line, which is not HTLV-I infected, did not bind C1q after HIV infection. These results suggest that a retrovirus protein expressed by coinfected cells directly binds C1q resulting in classical complement activation. This type of activation may have profound biological effects in persons coinfected with HIV-1 and HTLV-I.

Cell Line↗
PubMed1991

Defined chemically cross-linked oligomers of human C-reactive protein: characterization and reactivity with the complement system.

Chemically cross-linked C-reactive protein (CRP) oligomers were prepared and characterized, and C1q binding and C activation were investigated. Purified human CRP was polymerized in the presence of both non-cleavable and cleavable cross-linking agents and further separated by Superose 12 analytical FPLC column chromatography into fractions of 110 KDa (pentameric monomers), 220 KDa (dimers) and 330 KDa (trimers); virtually no larger oligomers were formed under a variety of experimental conditions. CRP subunits were cross-linked both within and between CRP pentamers. CRP trimers retained native CRP antigenicity without expression of neo-CRP epitopes. CRP trimers showed maximal binding and CRP dimers showed partial binding of solid phase C1q while CRP monomers bound virtually no C1q at all; CRP trimers also bound to fluid phase C1q. Binding was Ca++ independent and increased as the ionic strength or pH were lowered, characteristics comparable to binding of aggregated IgG to C1q; it was not inhibited by phosphorylcholine. CRP trimers consumed total C, C1 and C2 haemolytic activities upon incubation in fresh human serum, but much less efficiently than did CRP-protamine complexes or Agg-IgG. CRP trimers failed to deplete alternative C pathway haemolytic activity at all. The stable, chemically defined CRP oligomers described in this report, which bind C1q efficiently but display poor ability to activate the classical C pathway in the absence of an appropriate ligand, should be valuable in further studies of the interactions between CRP and the C system.

C-Reactive Protein↗
PubMed1989

Elucidation of a protease-sensitive site involved in the binding of calcium to C-reactive protein.

C-reactive protein (CRP) is a Ca2+-binding protein composed of five identical 23-kDa subunits arranged as a cyclic pentamer, present in greatly elevated concentration in the blood during the acute phase of processes involving tissue injury and necrosis. In the present work, it was found that treatment of human CRP with Pronase or Nagarse protease produces two major fragments which remain associated in physiological buffers but are separable under denaturing conditions. To localize the cleavage site(s), the fragments were characterized according to molecular mass, amino acid composition, partial amino acid sequence, and reactivity with monoclonal antibodies specific for the fragments and for defined CRP epitopes including residues 147-152 and 199-206. Nagarse protease cleaves the CRP subunit between residues 145 and 146, producing two fragments, 16 and 6.5 kDa (calculated molecular mass). Pronase cleaves the CRP subunit between residues 146 and 147, producing a 16-kDa fragment (A1) and a 6.5-kDa fragment (B); an additional fragment (A2) approximately 1 kDa smaller than fragment A1 is also apparently produced due to a secondary cleavage site in fragment A1. Cleavage appears to be completely inhibited in the presence of 1 mM CaCl2. Ca2+ does not protect cleaved CRP from heat-induced aggregation (i.e., precipitation) as it does the intact protein. Protease-cleaved CRP loses the ability to bind to the Ca2+-dependent ligand phosphorylcholine but remains the ability to bind to the Ca2+-independent ligand arginine-rich histone. Equilibrium dialysis indicates that intact CRP binds 2 mol of Ca2+/mol of subunit with a Kd of 6 X 10(-5) M.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1989

Identification and partial characterization of multiple native and neoantigenic epitopes of human C-reactive protein by using monoclonal antibodies.

Multiple mAb to human C-reactive protein (CRP) were prepared which reacted preferentially with either native CRP, modified CRP (expressing "neo-CRP" determinants) or both forms of the molecule. These mAb were divided into four groups according to their binding characteristics to various CRP preparations and CRP peptides by using a combination of ELISA, dot blot, and Western blot assays; they were further characterized based upon their reactivity with CRP in the presence of calcium and inhibition by phosphorylcholine. The first group consisted of mAb that reacted only with native CRP, and served to define four distinct native CRP epitopes. The second group consisted of mAb that reacted with native CRP and also with CRP modified by direct immobilization on polystyrene plates, urea-chelation or SDS treatment in the absence of calcium, thus identifying a fifth native CRP epitope; these mAb displayed significantly greater reactivity with native than with modified CRP. The third group included mAb that reacted only with modified CRP and with the larger amino-terminal fragment (residues 1-146) of pronase-cleaved CRP. The fourth group included mAb that reacted only with modified CRP and with the smaller carboxyl-terminal fragment (residues 147-206) of pronase-cleaved CRP; most of these antibodies also reacted with the carboxyl-terminal octapeptide (residues 199-206) of CRP. These experiments have identified mAb that react preferentially with distinct conformational and sequence-determined epitopes of native and modified forms of the CRP molecule, respectively; provide partial identification of the epitopes with which they interact; point to the presence of at least five epitopes on native CRP and at least three epitopes on modified CRP; and provide antibodies suitable for identification and quantitation of native and modified forms of CRP. The mAb directed against neo-CRP epitopes may help identify the presence of this pentraxin and antigenically-related proteins at previously unappreciated sites.

Animals↗
PubMed1989

Binding sites for C-reactive protein on human monocytes are distinct from IgG Fc receptors.

Previous investigations have provided evidence to suggest that C-reactive protein (CRP), an acute-phase reactant, binds to human monocytes at a membrane site that is either identical to or physically associated with IgG Fc receptors. To characterize further the relationship between monocyte CRP binding sites and IgG Fc receptors, monocytes were allowed to attach to surfaces coated with IgG or CRP and binding-site redistribution was assessed. Binding was measured by using protein-coated sheep erythrocytes (E). When attached to control (gelatin or albumin) surfaces, greater than 60% and 43% of monocytes formed rosettes with E-IgG and E-CRP, respectively. Following adherence to surface immobilized CRP, the proportion of cells binding E-IgG was unchanged; however, fewer than 20% of monocytes bound E-CRP. When attached to IgG-coated surfaces, fewer than 20% of monocytes formed rosettes with either E-IgG or E-CRP. In order to determine whether the unidirectional modulation of CRP and IgG binding sites was the result of CRP binding directly to a subclass of IgG Fc receptors, fluid-phase IgG-blocking studies were performed. When monocyte monolayers were preincubated with either monomeric or heat-aggregated IgG, a dose-dependent reduction in E-IgG binding was observed. In contrast, all concentrations of fluid-phase IgG failed to inhibit monocyte binding of E-CRP. These data indicate that CRP binds to human monocytes at a site physically associated with but distinct from IgG Fc receptors.

Antigens, Differentiation↗
PubMed1988

Preferential expression of neo-CRP epitopes on the surface of human peripheral blood lymphocytes.

Antibodies specific for C-reactive protein (CRP) have been reported to react with certain human peripheral blood lymphocytes (PBL); however, the nature of the antigen has not been clearly defined. In the present study we identified the CRP antigenicity on PBL as a CRP neoepitope not seen on the native-CRP molecule. Neo-CRP epitopes are expressed when the native pentameric form of CRP is dissociated into free subunits. Commercial anti-CRP antisera were found to possess a significant proportion of specificities (up to 16% of the total reactivity) directed against neo-CRP antigenicity. Since similar reagents had been used in previous studies on the reactivity of anti-CRP antisera with PBL, we set out to determine if either native- or neo-CRP epitopes were preferentially expressed on PBL. We prepared antisera monospecific for native-CRP and neo-CRP, respectively, and characterized these reactivities in both direct and indirect enzyme immunoassays. When analyzed by flow cytometry, anti-neo-CRP but not anti-native-CRP antiserum was found to react with normal PBL. F(ab')2 fragments of affinity-purified anti-neo-CRP had identical activity, and the reactivity against CRP was absorbed by reagents expressing neo-CRP but not native-CRP epitopes. Flow cytometric analyses of monocyte-depleted PBL from 25 normal donors detected a mean of 23.8 +/- 5.8% anti-neo-CRP-positive cells, a higher proportion of PBL expressing the CRP antigen than previously reported. Our findings indicate that a molecule identical to, or cross-reactive with, a neo-antigenic form of CRP is present on the surface of a significant proportion of normal human PBL.

Antigens, Surface↗
PubMed1988

C-reactive protein antigenicity on the surface of human peripheral blood lymphocytes. Characterization of lymphocytes reactive with anti-neo-CRP.

Previously, we have shown that antibodies specific for C-reactive protein determinants, not present on the native molecule, termed neo-CRP, also react with a significant percentage of PBL. In the present study, cells were evaluated by flow cytometry using alpha-neo-CRP antisera and mAb specific for lymphocyte subsets. With use of either monocyte-depleted PBL or Percoll-enriched large granular lymphocytes, we observed an overlap between cells reactive with alpha-neo-CRP and cells bearing the surface markers CD16, CD11b, Leu-7, and/or Leu-19, which are expressed on NK cells. In addition, we showed co-expression of the neo-CRP antigen with CD19, CD20, and HLA-DR, cell surface markers which are expressed on B lymphocytes. The major proportion of CD3+ cells failed to exhibit co-expression of neo-CRP. Single parameter flow cytometric analyses demonstrated that cells reactive with alpha-neo-CRP exhibited a bimodal staining pattern based on fluorescence intensity: high intensity neo-CRPbright and low intensity neo-CRPdim. Two-color analysis revealed that neo-CRPbright cells co-expressed CD19, CD20, and HLA-DR, whereas neo-CRPdim cells co-expressed CD16, CD11b, Leu-7, and Leu-19. Anti-neo-CRP also reacted with PBL obtained from patients with CD16+ lymphoproliferative disorders and from patients with chronic lymphocytic leukemia of B cell origin, but not with cells from patients with T cell or myeloid leukemias. The alpha-neo-CRP cells from patients with NK cell expansions showed dim fluorescence, whereas patients with B cell expansions showed bright fluorescence, consistent with the staining patterns observed with normal PBL. In addition, cell lines of T cell, B cell, NK cell, myeloid, and erythroid origin were evaluated for reactivity with alpha-neo-CRP. The cloned NK cell line NK 3.3 reacted as neo-CRPdim, but the B cell lines BL41, BL41/95, T1, T2, and CESS all reacted as neo-CRPbright. The cell lines K562, Molt-4, Hut-78, HL-60, U-937, and THP-1-0, which lack characteristic NK and B cell markers, did not react with alpha-neo-CRP. Additional study of the two-color histograms revealed a distinct diagonal staining pattern that was observed only when cells were co-stained with alpha-neo-CRP and either alpha-CD16 (alpha-Fc gamma RIII) or antibody IV3 (alpha-CDw32; alpha-Fc gamma RII). This finding suggests a 1:1 relationship between Fc gamma R on both NK and B cells and determinants recognized by alpha-neo-CRP.(ABSTRACT TRUNCATED AT 400 WORDS)

Antigen-Antibody Reactions↗
PubMed1988

Stimulation of human neutrophils, monocytes, and platelets by modified C-reactive protein (CRP) expressing a neoantigenic specificity.

C-reactive protein (CRP) can be structurally modified by heat, acid, or urea-chelation to express a neoantigen designated by us as neo-CRP. This antigen is also expressed on the in vitro primary protein translation products of both human and rabbit CRP. Unmodified CRP and CRP complexed with pneumococcal C-polysaccharide (CPS) do not express neo-CRP. Forms of CRP expressing neo-CRP but not native CRP antigenicity (even in the presence of CPS) consistently and in a dose-dependent manner potentiated the respiratory burst response of human polymorphonuclear leukocytes and peripheral blood monocytes to heat-modified IgG. Forms of CRP expressing neo-CRP antigenicity also induced reactions of aggregation and secretion from isolated platelets and potentiated platelet activation stimulated by ADP in platelet-rich-plasma, while native CRP alone or complexed with CPS again did not. Unlike CRP-CPS complexes, forms of CRP expressing neo-CRP were not able to activate the complement system. These data emphasize the biologic potential inherent in this humoral acute-phase reactant, particularly in the activation of the formed elements of the blood important in the inflammatory response. Since these cell-activating properties are preferentially observed when CRP is structurally modified to express the neo-CRP antigen, such a molecular conversion may be central to the structure-function relationships of CRP at local sites of inflammation and tissue injury.

Blood Platelets↗
PubMed1988

Expression of a C-reactive protein neoantigen (neo-CRP) in inflamed rabbit liver and muscle.

We have reported that human C-reactive protein (huCRP) can exist in two antigenically distinct forms which are observed as the native, pentameric, phosphorylcholine (PC)-binding CRP ("native-huCRP antigen"), and as a conformationally and physicochemically distinct free huCRP subunit ("neo-huCRP antigen"), respectively. We have demonstrated that forms of huCRP which preferentially express neo-huCRP antigenicity are naturally present on the surface of both normal human peripheral blood B lymphocytes and lymphocytes with natural killer cell activity. We have also reported that forms of huCRP expressing the neo-huCRP antigen have potent in vitro activities in platelet, polymorphonuclear leukocyte, and monocyte assays. In this study, we demonstrate a rabbit-CRP (raCRP) neoantigen can be expressed when isolated PC-binding raCRP is modified in analogy to huCRP. This "neo-raCRP" is cross-reactive with the neo-huCRP antigen and occurs naturally in acute phase but not normal rabbit liver and muscle. The relative distribution and localization of both antigens were comparable in tissue sections taken at 24 and 48 hr postinflammation elicited with typhoid vaccine. These data support the concept that CRP molecules expressing a structure and antigenicity which are distinct from native, pentagonal CRP do occur in vivo, and that such molecules accumulate at tissue sites of inflammation and necrosis.

Acute-Phase Reaction↗
PubMed1988

Evidence that serum amyloid P component binds to mannose-terminated sequences of polysaccharides and glycoproteins.

Serum amyloid P component (SAP) is a normal human serum protein with pentraxin structure that has morphological and immunochemical identity to the amyloid P component found in normal tissue and amyloid deposits. In the presence of calcium, SAP binds to certain complex polysaccharides, including agarose and zymosan. While the binding of SAP to agarose involves interaction with a galactose pyruvate acetal, the ligand in zymosan has not been defined. In the present study we determined that SAP binds to ligand(s) in a soluble extract of zymosan prepared by alkaline hydrolysis, which contains the mannose oligosaccharide sequences alpha DMan1----3DMan and alpha DMan1----6DMan. SAP did not bind to the alkali-insoluble fraction of zymosan, which is predominantly a glucan polymer, and its binding to zymosan extract which had been absorbed with concanavalin A was markedly reduced, suggesting that mannose residues are involved in the binding of SAP to zymosan. We also demonstrated that SAP binds to the glycoproteins ovalbumin, thyroglobulin, beta-glucuronidase and C3bi, which contain mannose-terminated sequences, while it did not bind to native and desialized preparations of ovomucoid, alpha 1-acid glycoprotein and glycophorin, which lack terminal mannose residues. SAP did not bind to pneumococcal C polysaccharide or to N-acetylglucosamine oligosaccharides covalently linked to a protein carrier. The binding of SAP to ligand(s) in zymosan extract or ovalbumin was inhibited by the preincubation of SAP with either zymosan extract or ovalbumin glycopeptides, both of which share similar mannose oligosaccharide sequences. All of the SAP binding reactions required calcium, were maximal at approximately 1 mM calcium, and gave similar results whether purified SAP or SAP in serum was used. These findings indicate that mannose-terminated oligosaccharides of polysaccharides and glycoproteins represent a new class of ligands for SAP and suggest that SAP may function as a mannose-binding protein.

Calcium↗
PubMed1988

Identification of multiple forms of the P component of amyloid isolated from human serum.

We examined isolated serum amyloid P component (SAP), the circulating counterpart of the amyloid P component, and established a previously unreported heterogeneity for SAP by immunological and biochemical methods. Highly purified SAP had a gel filtration Mr of 255,000, a Stokes radius of 57 A, a calculated frictional coefficient of 1.4, and 10 subunits of Mr of approximately 25,000. We present evidence suggestive of varying affinities of SAP for agarose, to which SAP is known to adsorb in the presence of calcium, by fused rocket immunoelectrophoresis. We resolved SAP subunits by isoelectric focusing into multiple species with isoelectric points of 6.08 (two forms), 6.02, and 5.95; three of these forms were delineated by high resolution two-dimensional SDS gel electrophoresis to have an Mr = 25,500, while a fourth (pI = 6.08) had an Mr = 24,500. The observed isoelectric charge heterogeneity could not be eliminated by neuraminidase treatment event though the electrophoretic migration of native desialized SAP was impeded (alpha 1 to beta) when examined by crossed immunoelectrophoresis, being consistent with the removal of anionic charges. Further, an additional neuraminidase-generated component was detected at the beta-position which could be removed by concanavalin A affinity. These data suggest SAP may exist in microheterologous or allotypic forms, the significance of which is under investigation.

Chromatography, Gel↗
PubMed1987

Expression, detection and assay of a neoantigen (Neo-CRP) associated with a free, human C-reactive protein subunit.

It has previously been reported that human C-reactive protein (CRP) can exist in at least two molecular conformations distinguished by antigenic, electrophoretic and ligand-binding reactivities. In the present study we describe the formation, detection and distinctiveness of a conformation expressing a CRP neoantigen (neo-CRP), and report that this form is characteristic in vitro of a free CRP subunit. Soluble native-CRP was found to express neo-CRP antigenicity upon treatment with acid; upon urea-chelation or heating in the absence of calcium; and upon adsorption onto uncoated polystyrene plates. Native-CRP bound by capture ELISA to phosphorylcholine-containing ligand or anti-native-CRP did not express neo-CRP antigenicity, suggesting that PC ligand- or antibody binding is not sufficient to induce expression of the neoantigen. Human CRP which expressed neo-CRP antigenicity had limited solubility and tended to aggregate in buffers of ionic strength 0.15, but remained soluble when the ionic strength was reduced to 0.015. Soluble urea-chelated or acid-treated CRP molecules expressing neo-CRP antigenicity chromatographed and electrophoresed as a single protein with a Mr of approx. 22,000, indicating that the CRP neoantigen can be expressed on free CRP subunits and this expression need not require proteolysis. Further, molecules expressing neo-CRP antigenicity were detected in the plasma of patients with rheumatoid arthritis. The identification and characterization of this CRP neoantigen should serve as a useful marker in studies of CRP subunits and biologically relevant forms of CRP, and should contribute to the elucidation of the role of CRP in the acute inflammatory response.

C-Reactive Protein↗
PubMed1986

Cleaved forms of C-reactive protein are associated with platelet inhibition.

C-reactive protein (CRP) is the prototypic acute phase reactant and serves clinically as a marker of inflammation and tissue destruction. When native CRP pentamer was incubated with Streptomyces griseus protease, a newly formed and transient ability to inhibit platelet aggregation stimulated by adenosine diphosphate or collagen was often elicited early during the course of enzymatic digestion. Sodium dodecyl sulfate polyacrylamide gel electrophoresis analyses of the digests revealed that platelet inhibitory activity correlated with altered electrophoretic mobility and reductions in subunit and pentameric m.w. Minimally degraded forms of CRP were also isolated "de novo" from inflammatory fluids and, like their enzyme degraded counterparts, inhibited platelet activation. Dissociation of degraded CRP with SDS followed by the removal of SDS resulted in the separation fragments which inhibited platelet function. We propose that in a degradative environment, such as at sites of inflammation/tissue damage or through the action of serum proteases, CRP may transitorily down-regulate the platelet.

C-Reactive Protein↗
PubMed1986

Binding of C-reactive protein to nucleated cells leads to complement activation without cytolysis.

C-reactive protein (CRP) is an acute-phase reactant that is found bound to cells at sites of inflammation. We have passively sensitized HEp-2 cells for CRP binding and examined the effect of this treatment on complement activation and cell lysis. When cells were treated with protamine sulfate and CRP and were incubated with normal human serum in a 4-hr 51Cr-release assay, no significant lysis was noted. In contrast, HEp-2 cells treated with antibody and normal human serum were lysed. The consumption of complement components in normal human serum after incubation with cells treated with protamine and CRP was measured by hemolytic assays. CRP-treated cells consumed over 80% of C1, C4, and C2 and about 40% of C3 present. No significant consumption of C5 through C9 components was observed. Cells treated with antibody and complement showed consumption of C1 through C9. Cells were also sensitized for CRP binding by using diazophenylphosphocholine. This treatment also led to CRP binding and activation of the early classical pathway (C1, C4, C2, and to a lesser extent C3). The components of the membrane attack complex (C5 through C9) were not activated. Both a mouse monoclonal IgM and a human IgG antibody to phosphocholine activated the entire classical pathway. These results indicate that CRP activation of the classical complement pathway is restricted to the early part of the pathway. In the absence of activation of the membrane attack complex, complement-mediated cell lysis cannot occur.

Animals↗
PubMed1986

The effects of C-reactive protein on human cell-mediated cytotoxicity.

C-reactive protein (CRP) is a trace serum protein that increases markedly in concentration during inflammatory reactions. Although CRP, in the presence of a multivalent ligand, binds in vitro to a small percentage of peripheral blood lymphocytes from normal donors and is present on natural killer (NK) cells, exogenous addition of CRP has few effects on human lymphocytes. CRP causes minimal enhancement of proliferation in a mixed lymphocyte culture and a slight increase in 3H-thymidine uptake by unstimulated cells. The most significant effect of CRP is a substantial increase in cell-mediated cytotoxicity (CMC). In this publication, we show that CRP dramatically enhances the alloantigen-activated cytotoxic response only when it is present at the initiation of culture and that pretreatment of responder cells with CRP will not produce enhancement. Although the CMC enhancement generated the presence of CRP is not antigen specific, it is mediated by a T cell, and neither NK-like cells nor monocytes are involved in mediating CRP enhanced killing.

Animals↗
PubMed1986

Enhancement of human peripheral blood monocyte respiratory burst activity by aggregated C-reactive protein.

We had previously demonstrated that C-reactive protein (CRP), an acute phase reactant, when aggregated or coupled to a ligand, interacts with monocytes and certain human peripheral blood lymphocytes. The purpose of the present study, after further characterizing the binding interaction of CRP with human monocytes, was to focus on the biological response of monocytes to CRP binding. Flow cytometric analysis of human mononuclear leukocytes, following incubation with fluoresceinated heat-aggregated CRP (Agg-CRP), revealed that while greater than 70% of monocytes bound Agg-CRP, only 8% of lymphocytes demonstrated positive fluorescence. Furthermore, mean channel fluorescence values indicated that monocytes bound greater amounts of Agg-CRP per cell than did lymphocytes. Luminol-enhanced chemiluminescence (CL) was used as a measure of monocyte respiratory burst activity. Monocytes were stimulated only minimally by Agg-CRP alone; however, Agg-CRP substantially enhanced the CL response to heat-aggregated IgG. This Agg-CRP enhancing effect was selective for IgG-initiated monocyte activation, as no augmentation in CL was observed following cell stimulation with phorbol myristate acetate or serum-opsonized zymosan. These results demonstrate that aggregated CRP binds to the major proportion of human monocytes and selectively augments Fc receptor-mediated stimulation of monocyte oxidative metabolism.

C-Reactive Protein↗