The C1q inhibitor in serum is a chondroitin 4-sulfate proteoglycan

Complementing Testicular Immune Regulation: The Relationship between Sertoli Cells, Complement, and the Immune Response

Sertoli cells within the testis are instrumental in providing an environment for spermatogenesis and protecting the developing germ cells from detrimental immune responses which could affect fertility. Though these immune responses consist of many immune processes, this review focuses on the understudied complement system. Complement consists of 50+ proteins including regulatory proteins, immune receptors, and a cascade of proteolytic cleavages resulting in target cell destruction. In the testis, Sertoli cells protect the germ cells from autoimmune destruction by creating an immunoregulatory environment. Most studies on Sertoli cells and complement have been conducted in transplantation models, which are effective in studying immune regulation during robust rejection responses. In grafts, Sertoli cells survive activated complement, have decreased deposition of complement fragments, and express many complement inhibitors. Moreover, the grafts have delayed infiltration of immune cells and contain increased infiltration of immunosuppressive regulatory T cells as compared to rejecting grafts. Additionally, anti-sperm antibodies and lymphocyte infiltration have been detected in up to 50% and 30% of infertile testes, respectively. This review seeks to provide an updated overview of the complement system, describe its relationship with immune cells, and explain how Sertoli cells may regulate complement in immunoprotection. Identifying the mechanism Sertoli cells use to protect themselves and germ cells against complement and immune destruction is relevant for male reproduction, autoimmunity, and transplantation.

Microglia as hackers of the matrix: sculpting synapses and the extracellular space

Microglia shape the synaptic environment in health and disease, but synapses do not exist in a vacuum. Instead, pre- and postsynaptic terminals are surrounded by extracellular matrix (ECM), which together with glia comprise the four elements of the contemporary tetrapartite synapse model. While research in this area is still just beginning, accumulating evidence points toward a novel role for microglia in regulating the ECM during normal brain homeostasis, and such processes may, in turn, become dysfunctional in disease. As it relates to synapses, microglia are reported to modify the perisynaptic matrix, which is the diffuse matrix that surrounds dendritic and axonal terminals, as well as perineuronal nets (PNNs), specialized reticular formations of compact ECM that enwrap neuronal subsets and stabilize proximal synapses. The interconnected relationship between synapses and the ECM in which they are embedded suggests that alterations in one structure necessarily affect the dynamics of the other, and microglia may need to sculpt the matrix to modify the synapses within. Here, we provide an overview of the microglial regulation of synapses, perisynaptic matrix, and PNNs, propose candidate mechanisms by which these structures may be modified, and present the implications of such modifications in normal brain homeostasis and in disease.

Reduced risk of placental parasitemia associated with complement fixation on Plasmodium falciparum by antibodies among pregnant women

BACKGROUND

The pathogenesis of malaria in pregnancy (MiP) involves accumulation of P. falciparum-infected red blood cells (pRBCs) in the placenta, contributing to poor pregnancy outcomes. Parasite accumulation is primarily mediated by P. falciparum erythrocyte membrane protein 1 (PfEMP1). Magnitude of IgG to pRBCs has been associated with reduced risk of MiP in some studies, but associations have been inconsistent. Further, antibody effector mechanisms are poorly understood, and the role of antibody complement interactions is unknown.

METHODS

Studying a longitudinal cohort of pregnant women (n=302) from a malaria-endemic province in Papua New Guinea (PNG), we measured the ability of antibodies to fix and activate complement using placental binding pRBCs and PfEMP1 recombinant domains. We determined antibody-mediated complement inhibition of pRBC binding to the placental receptor, chondroitin sulfate A (CSA), and associations with protection against placental parasitemia.

RESULTS

Some women acquired antibodies that effectively promoted complement fixation on placental-binding pRBCs. Complement fixation correlated with IgG1 and IgG3 antibodies, which dominated the response. There was, however, limited evidence for membrane attack complex activity or pRBC lysis or killing. Importantly, a higher magnitude of complement fixing antibodies was prospectively associated with reduced odds of placental infection at delivery. Using genetically modified P. falciparum and recombinant PfEMP1 domains, we found that complement-fixing antibodies primarily targeted a specific variant of PfEMP1 (known as VAR2CSA). Furthermore, complement enhanced the ability of antibodies to inhibit pRBC binding to CSA, which was primarily mediated by complement C1q protein.

CONCLUSIONS

These findings provide new insights into mechanisms mediating immunity to MiP and reveal potential new strategies for developing malaria vaccines that harness antibody-complement interactions.

The C1q Receptors: Focus on gC1qR/p33 (C1qBP, p32, HABP-1)1

In the past several years, a number of C1q binding surface proteins or receptors have been described. This is not of course surprising considering the complexity of the C1q molecule and its ability to bind to a wide range of cellular and plasma proteins via both its collagen-like [cC1q] region and its heterotrimeric globular heads [gC1q] each of which in turn is capable of binding a specific ligand. However, while each of these "receptor" molecules undoubtedly plays a specific function within its restricted microenvironment, and therefore merits full attention, this review nonetheless, will singularly focus on the structure and function of gC1qR-a multi-functional and multi-compartmental protein, which plays an important role in inflammation, infection, and cancer. Although first identified as a receptor for C1q, gC1qR has been shown to bind to a plethora of proteins found in plasma, on the cell surface and on pathogenic microorganisms. The plasma proteins that bind to gC1qR are mostly blood coagulation proteins and include high molecular weight kininogen [HK], Factor XII [Hageman factor], fibrinogen, thrombin [FII], and multimeric vitronectin. This suggests that gC1qR can play an important role in modulating not only of fibrin formation, particularly at local sites of immune injury and/or inflammation, but by activating the kinin/kallikrein system, it is also able to generate, bradykinin, a powerful vasoactive peptide that is largely responsible for the swelling seen in angioedema. Another important function of gC1qR is in cancer, where it has been shown to play a role in tumor cell survival, growth and metastatic invasion by interacting with critical molecules in the tumor cell microenvironment including those of the complement system and kinin system. Finally, by virtue of its ability to interact with a growing list of pathogen-associated molecules, including bacterial and viral ligands, gC1qR is becoming recognized as an important pathogen recognition receptor [PRR]. Given the numerous roles it plays in a growing list of disease settings, gC1qR has now become a potential target for the development of monoclonal antibody-based and/or small molecule-based therapies.

Moving beyond the glial scar for spinal cord repair

Traumatic spinal cord injury results in severe and irreversible loss of function. The injury triggers a complex cascade of inflammatory and pathological processes, culminating in formation of a scar. While traditionally referred to as a glial scar, the spinal injury scar in fact comprises multiple cellular and extracellular components. This multidimensional nature should be considered when aiming to understand the role of scarring in limiting tissue repair and recovery. In this Review we discuss recent advances in understanding the composition and phenotypic characteristics of the spinal injury scar, the oversimplification of defining the scar in binary terms as good or bad, and the development of therapeutic approaches to target scar components to enable improved functional outcome after spinal cord injury.

Oxidation of Some Sustainable Sulfated Natural Polymers: Kinetics and Mechanism of Oxidation of Water-Soluble Chondroitin-4-Sulfate Polysaccharide by Hexachloroiridate(IV) in Aqueous Solutions

The kinetics and mechanism of hexachloroiridate(IV) oxidation of chondroitin-4-sulfate as a sustainable coordination biopolymer macromolecule (CS) in aqueous acidic solutions at a constant ionic strength of 0.1 mol dm^-3 has been investigated spectrophotometrically. Pseudo first-order plots gave sigmoidal curves of S-shape nature, indicating that the kinetics is complex. Two distinct stages have been observed. The first stage was relatively fast corresponding to the autoacceleration period, followed by a slow stage which became linear at a longer time period called the induction period. First-order dependence with respect to the [OX] and fractional first order in [CS] was observed for both stages. Kinetic evidence for formation of the 1:1 intermediate complex within the two stages has been revealed. The influence of [H⁺] on the rate constants indicated that the oxidation was of acid inhibition nature. The kinetic parameters have been evaluated, and a suitable reaction mechanism is suggested and discussed in terms of the nature of the electron-transfer process.

Dangerous liaisons: complement, coagulation, and kallikrein/kinin cross-talk act as a linchpin in the events leading to thromboinflammation

Innate immunity is fundamental to our defense against microorganisms. Physiologically, the intravascular innate immune system acts as a purging system that identifies and removes foreign substances leading to thromboinflammatory responses, tissue remodeling, and repair. It is also a key contributor to the adverse effects observed in many diseases and therapies involving biomaterials and therapeutic cells/organs. The intravascular innate immune system consists of the cascade systems of the blood (the complement, contact, coagulation, and fibrinolytic systems), the blood cells (polymorphonuclear cells, monocytes, platelets), and the endothelial cell lining of the vessels. Activation of the intravascular innate immune system in vivo leads to thromboinflammation that can be activated by several of the system's pathways and that initiates repair after tissue damage and leads to adverse reactions in several disorders and treatment modalities. In this review, we summarize the current knowledge in the field and discuss the obstacles that exist in order to study the cross-talk between the components of the intravascular innate immune system. These include the use of purified in vitro systems, animal models and various types of anticoagulants. In order to avoid some of these obstacles we have developed specialized human whole blood models that allow investigation of the cross-talk between the various cascade systems and the blood cells. We in particular stress that platelets are involved in these interactions and that the lectin pathway of the complement system is an emerging part of innate immunity that interacts with the contact/coagulation system. Understanding the resulting thromboinflammation will allow development of new therapeutic modalities.

Serglycin proteoglycan deletion in mouse platelets: physiological effects and their implications for platelet contributions to thrombosis, inflammation, atherosclerosis, and metastasis

Serglycin is found in all nucleated hematopoietic cells and platelets, blood vessels, various reproductive and developmental tissues, and in chondrocytes. The serglycin knockout mouse has demonstrated that this proteoglycan is required for proper generation and function of secretory granules in several hematopoietic cells. The effects on platelets are profound, and include diminishing platelet aggregation responses and formation of platelet thrombi. This chapter will review cell-specific aspects of serglycin structure, its gene regulation, cell and tissue localization, and the effects of serglycin deletion on hematopoietic cell granule structure and function. The effects of serglycin knockout on platelets are described and discussed in detail. Rationales for further investigations into the contribution of serglycin to the known roles of platelets in thrombosis, inflammation, atherosclerosis, and tumor metastasis are presented.

Complement activation triggered by chondroitin sulfate released by thrombin receptor-activated platelets

BACKGROUND

Chondroitin sulfate (CS) is a glycosaminoglycan released by activated platelets.

OBJECTIVE

Here we test the hypothesis that CS released by activated platelets can trigger complement activation in the fluid phase.

METHODS AND RESULTS

Thrombin receptor-activating peptide (TRAP)-6 was used to activate platelets in platelet-rich plasma and blood, anticoagulated with the thrombin inhibitor lepirudin. TRAP activation induced fluid-phase complement activation, as reflected by the generation of C3a and sC5b-9, which could be attenuated by the C3 inhibitor compstatin. Chondroitinase ABC treatment of supernatants from activated platelets totally inhibited the activation, indicating that platelet-derived CS had initiated the complement activation. Furthermore, addition of purified CS to plasma strongly triggered complement activation. C1q was identified as the recognition molecule, as it bound directly to CS, and CS-triggered complement activation could be restored in C1q-depleted serum by adding purified C1q. TRAP activation of whole blood increased the expression of CD11b on leukocytes and generation of leukocyte-platelet complexes. It was demonstrated that these leukocyte functions were dependent on C3 activation and signaling via C5a, as this expression could be inhibited by compstatin and by a C5aR antagonist.

CONCLUSIONS

We conclude that platelets trigger complement activation in the fluid phase by releasing CS, which leads to inflammatory signals mediated by C5a.

Protection of endothelial cells by dextran sulfate in rats with thrombotic microangiopathy

The characteristic features of thrombotic microangiopathy (TMA) include glomerular and peritubular capillary endothelial cell injury in association with loss of heparan sulfate proteoglycans on the cell surface and thrombus formation, followed by subsequent ischemic tubulointerstitial damage. It therefore was hypothesized that dextran sulfate (DXS) may protect the kidney against endothelial damage in a model of TMA. TMA was induced in rats by renal artery perfusion of an antiglomerular endothelial antibody, followed by the administration of DXS or vehicle. Renal damage was assessed by histologic analysis and measurements of blood urea nitrogen and creatinine. Whereas control rats developed severe renal failure with extensive glomerular and tubular injury, administration of DXS significantly protected renal function and preserved the glomerular endothelium and peritubular capillaries. The beneficial effect of DXS could be attributed to the ability of DXS to protect endothelial cells from coagulation and complement activation, as demonstrated by the histologic analysis. In addition, binding of the administered DXS to the surface of the glomerular endothelium was confirmed in TMA rats, suggesting that DXS acts as a "repair coat" of injured glomerular endothelium. In conclusion, DXS protects the kidney from experimental TMA. This protection may be mediated by DXS's binding directly to the surface of glomerular endothelium and amelioration of coagulation, complement activation, and cellular matrix loss.

Mass spectrometry analysis of the oligomeric C1q protein reveals the B chain as the target of trypsin cleavage and interaction with fucoidan

C1q is a subunit of the C1 complex that triggers activation of the complement classical pathway through recognition and binding of immune complexes. C1q also binds to nonimmune ligands such as the sulfated polysaccharide fucoidan, a potent anticomplementary agent. C1q was submitted for the first time to mass spectrometry analysis, yielding insights into its assembly and its interaction with fucoidan. The MALDI-TOF mass spectrometry technique on membrane allowed partial preservation of noncovalent interactions, allowing precise analysis of its substructure and estimation of the C1q molecular weight at 459520-461883, with an average mass of 460793 g x mol(-1). The disulfide-linked A-B and C-C dimers as well as the noncovalent structural unit (A-B:C)-(C:B-A) were detected, providing experimental support to the C1q model based on covalent and noncovalent associations of six heterotrimers. Trypsin treatment of native C1q led to proteolysis of the B chain only, at a single cleavage site (Arg(109)) located in the globular region. Unlike DNA, fucoidan protected C1q from trypsin cleavage, indicating that this polysaccharide binds to the B moiety of the globular head. Given the involvement of the C1q globular heads in the recognition of IgG, this interaction may account for the observed anticomplementary activity of fucoidan.

Interaction of the C1 complex of complement with sulfated polysaccharide and DNA probed by single molecule fluorescence microscopy

The complex C1 triggers the activation of the Complement classical pathway through the recognition and binding of antigen-antibody complex by its subunit C1q. The globular region of C1q is responsible for C1 binding to the immune complex. C1q can also bind nonimmune molecules such as DNA and sulfated polysaccharides, leading either to the activation or inhibition of Complement. The binding site of these nonimmune ligands is debated in the literature, and it has been proposed to be located either in the globular region or in the collagen-like region of C1q, or in both. Using single molecule fluorescence microscopy and DNA molecular combing as reporters of interactions, we have probed the C1q binding properties of T4 DNA and of fucoidan, an algal sulfated fucose-based polysaccharide endowed with potent anticomplementary activity. We have been able to visualize the binding of C1q as well as of C1 and of the isolated collagen-like region to individual DNA strands, indicating that the collagen-like region is the main binding site of DNA. From binding assays with C1r, one of the protease components of C1, we concluded that the DNA binding site on the collagen-like region is located within the stalk part. Competition experiments between fucoidan and DNA for the binding of C1q showed that fucoidan binds also to the collagen-like region part of C1q. Unlike DNA, the binding of fucoidan to collagen-like region involves interactions with the hinge region that accommodate the catalytic tetramer C1r2-C1s2 of C1. This binding property of fucoidan to C1q provides a mechanistic basis for the anticomplementary activity of the sulfated polysaccharide.

Interaction of fucoidan with the proteins of the complement classical pathway

Fucoidan inhibits complement by mechanisms that so far remain to be unraveled, and the objective of this work was to delineate the mode of inhibition by this sulfated polysaccharide. For that purpose, low molecular weight fractions of algal (Ascophyllum nodosum) fucoidan containing the disaccharide unit [-->3)-alpha-L-Fuc(2SO3(-))-(1-->4)-alpha-L-Fuc(2,3diSO3(-))-(1-->](n) have been studied. Gel co-affinity electrophoresis and a new affinity capillary electrophoresis (ACE) method have been implemented to characterize fucoidan-complement protein complexes. Fucoidan binds C1q, likely to its collagen-like region through interactions involving lysine residues, and then prevents the association of the C1r(2)-C1s(2) subunit, required to form the fully active C1. In addition to C1q, fucoidan forms a complex with the protein C4 as observed by ACE. The fucoidan inhibits the first steps of the classical pathway activation that is of relevance in view of the proinflammatory effects of the subsequent products of the cascade. This study shows that a high level of inhibitory activity can be achieved with low molecular weight carbohydrate molecules and that the potential applicability of fucoidan oligosaccharides for therapeutic complement inhibition is worthy of consideration.

Complement component C1q induces endothelial cell adhesion and spreading through a docking/signaling partnership of C1q receptors and integrins

The interaction of C1q with endothelial cells elicits a multiplicity of biologic responses. Although these specific responses are thought to be mediated by the interaction of C1q with proteins of the endothelial cell surface, the molecular identity of the participant(s) has not been clearly defined. In this study, we examined the role of two C1q-binding proteins, cC1q-R/CR and gC1q-R/p33, on C1q-mediated adhesion and spreading of human dermal microvascular endothelial cells (HDMVECs). A specific and dose-dependent adhesion and spreading was observed when HDMVECs were cultured in microtiter plate wells coated with concentrations of C1q ranging from 0 to 50 microg/ml. The extent of adhesion and spreading was similar to the adhesion seen on collagen-coated wells. Furthermore, the effect of C1q was mimicked by either polyclonal anti-cC1q-R or mAb 60.11, but not with isotype- and species-matched control IgG. More importantly, however, a 100% inhibition of spreading but not adhesion to C1q-coated wells was observed when HDMVECs were cultured in the presence of 30 mM of the peptide GRRGDSP but not GRRGESP. Furthermore, while anti-beta1 integrin antibody blocked adhesion and spreading, antialpha5 integrin only blocked spreading. Since earlier studies have shown that zinc induces the exposure of hydrophobic sites in the C-terminus of gC1q-R including the putative high-molecular weight kininogen (HK)-binding site corresponding to residues 204-218, we also examined the effect of zinc on antibody binding to cell surface gC1q-R. Flow cytometric data show that the binding of mAb 74.5.2, which recognizes residues 204-218, is greatly enhanced when endothelial cells were incubated in the presence of 50 microM zinc. In summary, our data show that: (a) C1q-mediated endothelial cell adhesion and spreading requires the cooperation of both C1q receptors and 1 integrins, and possibly other membrane-spanning molecules, and (b) zinc can induce the exposure of hydrophobic sites in the C-terminal domain of gC1q-R allowing a more efficient binding of mAb 74.5.2 and HK.

Regulation of expression of megakaryocyte and platelet proteoglycans

The existence of proteoglycans in hematopoietic cells has been recognized for many years. However, elucidation of the structure and function of these molecules has only begun to be explored in recent years. This paper reviews the current status of knowledge of the structure, function and metabolism of the serglycin proteoglycan in megakaryocytes and megakaryocytic tumor cells. We have identified complex metabolic patterns of the serglycin proteoglycan in terms of regulation of overall hydrodynamic size, glycosaminoglycan chain length and disaccharide composition, and processing of the core protein in control cells or in the presence of phorbol 12-myristate 13-acetate or dimethylsulfoxide. We are currently studying the regulation of synthesis of this protein by analysis of promoter constructs in megakaryocytic and non-megakaryocytic hematopoietic cells. We have also tentatively identified a second proteoglycan, betaglycan, which is known also as the Type III transforming growth factor beta receptor. We have identified this molecule in human erythroleukemia and CHRF 288-11 cells by the presence of characteristic core proteins between 92-120 kDa, by its ability to adhere to Octyl Sepharose and by detection of mRNA. We hope to apply studies of proteoglycan metabolism in these cells to understanding the development of alpha granules and membrane elements in megakaryocytes.

Syntheses of chondroitin 4- and 6-sulfate pentasaccharide derivatives having a methyl beta-D-glucopyranosiduronic acid at the reducing end

The syntheses are reported of beta-D-GlcpA-(1-->3)-beta-D-GalpNAc-(1-->4)-beta-D-GlcpA-(1- ->3)-beta-D-GalpNAc-(1-->4)-beta-D-GlcpA-(1-->OMe), O-sulfonated at C-4 or C-6 of the aminosugar moieties, which represent structural elements of chondroitin 4- and 6-sulfate proteoglycans. Starting from a synthetic disaccharide glycosyl acceptor, the stepwise or blockwise construction of the sugar backbone with appropriate synthons led to a pentasaccharide tetraol, which was used as a common intermediate. Selective 6-O-sulfonation of this tetraol, followed by saponification, gave the 6-sulfate derivative, whereas selective 6-O-benzoylation, followed by O-sulfonation and saponification, afforded the 4-sulfate derivative as their sodium salts.

Unexpected stereochemical outcome of activated 4,6-O-benzylidene derivatives of the 2-deoxy-2-trichloroacetamido-D-galacto series in glycosylation reactions during the synthesis of a chondroitin 6-sulfate trisaccharide methyl glycoside

The synthesis of methyl (beta-D-glucopyranosyluronic acid)-(1-->3)-(2-acetamido-2-deoxy-6-O-sulfonato-beta-D-galactopyr anosyl)-(1-->4)-(beta-D-glucopyranosid)uronate trisodium salt, a chondroitin 6-sulfate trisaccharide derivative, is described. Loss of stereocontrol in glycosylation reactions involving activated 4,6-O-benzylidene derivatives of the 2-deoxy-2-trichloroacetamido-D-galacto series and D-glucuronic acid-derived acceptors was highlighted. This draw-back was overcome through the use of phenyl 3,4,6-tri-O-acetyl-2-deoxy-1-thio-2-trichloroacetamido-beta-D-gala ctopyranoside, which afforded the desired beta-linked disaccharide derivative in high yield with an excellent stereoselectivity. This later was submitted to acid-catalyzed methanolysis, followed by benzylidenation, and condensed with methyl 2,3,4-tri-O-benzoyl-1-O-trichloroacetimidoyl-alpha-D-glucopyran uronate to afford the expected trisaccharide derivative. Subsequent transformation of the N-trichloroacetyl group into N-acetyl, mild acid hydrolysis, selective O-sulfonation at C-6 of the amino sugar moiety, and saponification afforded the target molecule as its sodium salt in high yield.

Multigram syntheses of the disaccharide repeating units of chondroitin 4- and 6-sulfates

The multigram syntheses of beta-D-glucopyranosyluronic acid-(1-->3)-2-acetamido-2-deoxy-4- and 6-O-sulfo-D-galactopyranose disodium salt, the disaccharide repeating units of chondroitin 4- and 6-sulfates, are described. The disaccharide benzyl methyl 2,3,4-tri-O-benzoyl-beta-D-glucopyranosyluronate- (1-->3)-2-acetamido-2-deoxy-alpha-D-galactopyranoside was used as a common intermediate. Selective benzoylation at O-6 followed by O-sulfonation at C-4 of the aminosugar moiety, saponification and catalytic hydrogenation afforded the 4-O-sulfo derivative, whereas selective O-sulfonation at C-6 followed by similar deprotection steps provided the 6-O-sulfo derivative in high yield.

Interaction of C1q and the collectins with the potential receptors calreticulin (cC1qR/collectin receptor) and megalin

Several proteins have been identified as candidate cell-surface receptors for the complement protein C1q. Some of these also interact with the structurally-related collectin proteins. Previous descriptions of C1q-binding properties of cells, and information on the cellular distribution of candidate receptors suggest that there is more than one physiologically relevant receptor for C1q. Two such candidate receptors, cell-surface calreticulin (also referred to as cC1qR or collectin receptor) and megalin are discussed in this review.

Synthetic approach towards sulfated chondroitin di-, tri- and tetrasaccharides corresponding to the repeating unit

Chondroitin di-, tri- and tetrasaccharides, as well as their 4-, 6-mono- and 4,6-disulfates as their 4-methoxyphenyl glycosides, were systematically synthesized. Target disaccharides having beta GalNAc-(1-->4)-beta GlcA sequences were obtained starting from the corresponding pivotal chondroitin disaccharide precursor. A trisaccharide intermediate, which was synthesized by coupling of glucuronate imidate with a known disaccharide acceptor, was transformed into the sulfated and non-sulfated chondroitin trisaccharides. Chondroitin tetrasaccharide and the corresponding 4-disulfate, 6-disulfate as well as 4,6-tetrasulfate were also obtained based on the strategy developed above starting from the reported tetrasaccharide having [beta GalN3-(1-->4)-beta GlcA2] sequence.

Structural, immunological and functional comparisons of factor H, rheumatoid arthritis protein (RHP), and its apparent normal counterpart (N-RHP)

The isolation and characterization of two human serum proteins, RHP and N-RHP, are described. N-RHP appears to be the normal counterpart of RHP which is found at elevated levels in sera of patients with rheumatoid arthritis [Rosano et al. (1988b) Inflammation 12, 351 - 360]. Although both proteins crossreact with anti-Factor H and have identical N-terminal amino acid sequences, they differ from Factor H in pI, solubility at low ionic strength, and in glycosylation. RHP differs from Factor H and N-RHP in antigenicity in the rabbit, in effect on the C1q-anti-C1q precipitin reaction, and in ability to disaggregate C1, the first component of the complement system. Removal of RHP, N-RHP and Factor H from binding to C1q is a prerequesite for separation of RHP and N-RHP from Factor H by anion exchange chromatography and isoelectric focusing. The finding of uniquely demonstrable RHP activity (enhancement of C1q-anti-C1q precipitin activity) in unfractionated sera from patients with rheumatoid arthritis, but not in normal sera, suggests that RHP is not an artefact of Factor H produced during isolation.

Factor J, a human inhibitor of complement C1, is a cationic, highly glycosylated protein

Factor J (FJ) is a new inhibitor of the complement system. This work supports the fact that FJ is a cationic molecule (pI > or = 9.6 in native conditions, or pI = 8.1 in denaturing conditions) with a high sugar content (40%) that is able to interact with different lectins, suggesting a complex glycosylation. SDS impaired FJ migration in polyacrylamide gel electrophoresis. In Triton-acid-urea-polyacrylamide gel electrophoresis FJ migrated as a complex, dispersed molecule. In contrast, FJ after Smith degradation (dFJ) gave a single, smeared band of M(r) = 23.4 kDa in reducing SDS-PAGE. dFJ retained only 60% of the initial inhibitory activity of intact FJ. When digestions with different proteinases were performed, no modification of activity was observed. After beta-glucuronidase digestion, FJ lost 80% of its initial activity. Consequently, glycosylation plays an important role in the inhibitory activity of FJ.

Clustering of neutrophil leucocytes in serum: possible role of C1q-containing immune complexes

Clustering activity for neutrophil granulocytes was generated in pooled normal human serum (NHS) by incubation of the serum with preformed IgG aggregates, but not in heat-treated NHS (56 degrees C, 30 min), indicating that the function was complement-dependent. Judging from results of experiments with complement-deficient sera, and serum depleted of C1q, factor D and properdin, recruitment of the complement system beyond C1 was not required for induction of the activity. Zymosan treatment of NHS resulted in some neutrophil clustering activity, but recombinant C5a had a limited effect. C1q added to heat-treated NHS in conjunction with performed IgG aggregates supported neutrophil clustering in a dose-dependent manner. The serum C1q inhibitor, a chondroitin 4-sulphate proteoglycan known to interact with the collagenous part of C1q, clearly reduced neutrophil clustering in heat-treated NHS supplemented with C1q and IgG aggregates. The C1q inhibitor also reduced the inherent neutrophil clustering activity of some sera from patients with systemic lupus erythematosus (SLE). Neutrophil clustering activity in SLE serum was earlier shown to be inversely related to the number of circulating neutrophils in vivo. Although the precise mechanisms remain unclear, we propose that C1q-containing immunoglobulin complexes mediate neutrophil clustering through C1q receptors, and that this might contribute to pathogenesis of immune complex diseases such as SLE.

Structure of the complement-activating proteoglycan from the pilose antler of Cervus nippon Temminck

An anti-complementary polysaccharide, DWA-2, isolated from an unossified pilose antler of C. nippon Temminck by digestion with pronase, gel filtration, and affinity chromatography, consisted mainly of GalNAc, GlcA, IdoA, and sulfate in the molar ratios 1.0:0.6:0.3:0.8, and small proportions of Man, Gal, GlcNAc, and protein (4.5%). Methylation analysis, NMR spectroscopy, and degradation with enzymes indicated that DWA-2 contained chondroitin sulfate A-, B-, and C-like moieties. DWA-2 showed potent anti-complementary activity, and crossed immunoelectrophoresis indicated that it cleaved complement C3 in the absence of Ca2+ ion. Digestion of DWA-2 with chondroitinase ABC or ACI reduced the anti-complementary activity to a low level, but digestion with chondroitinase B reduced the activity by approximately 40% and the enzyme-resistant fraction still showed a significant activity.

Effect of Pseudomonas aeruginosa elastase and alkaline protease on serum complement and isolated components C1q and C3

The present study was undertaken to examine and compare the direct effect of two Pseudomonas enzymes, elastase and alkaline protease, on the serum hemolytic complement as a whole, and on the two recognition molecules of complement, C1q and C3 in particular. The results of our study show that incubation of serum with 0-50 micrograms/ml elastase or protease (60 min, 37 degrees C) resulted in a dose-dependent depletion of hemolytic complement with the protease being 3-4 times more efficient than elastase. Incubation of highly purified C3 (20 hr, 37 degrees C) with protease (2% w/w) resulted in the conversion of the 190-kDa molecule to a 120-kDa fragment. When analyzed by SDS-PAGE under reducing conditions, the 120-kDa piece yielded three distinct bands: an intact 75-kDa beta-chain and two alpha-chain pieces of approximately 41- and 26-kDa. NH2-terminal end sequence analysis localized the 26-kDa fragment within the cysteine-rich 41-kDa, COOH-terminal piece. This in turn suggests that the 70-kDa fragment which is not accounted for on SDS-PAGE is derived from the NH2-terminal end of the alpha-chain molecule which is completely degraded into small fragments. While the degradation pattern obtained with elastase is similar to that of protease, the latter enzyme was found to be more efficient. Exposure of C1q (0-5 hr, 37 degrees C) to protease or elastase on the other hand appears to reveal preferential sensitivity of the 28-kDa A-chain and 24-kDa C-chain, of the C1q molecule, with the protease being more potent than the elastase. Since both C1q and physiologic fragments of C3 (C3b, iC3b, and C3dg) are important opsonins of varying efficiencies, degradation of these molecules by Pseudomonas enzymes may, in part, facilitate the survival and proliferation of the organism in plasma. Furthermore, degradation of the key recognition molecules of complement, C1q and C3, would enhance the virulence of this organism by aborting complement-mediated bacterial killing. In addition the results imply that during Pseudomonas bacteremia, PaAP may be a much more destructive enzyme than PaE with regards to C3 and C1q but combined, the synergistic effect may overwhelm not only the proteins of the complement system, but other proteins of the humoral immune defense system as well.

Glycosaminoglycan concentrations in horse plasma and serum. Differences with other animal species and identification of affecting factors

1. The measured values of acid glycosaminoglycan (GAG) concentration in plasma or in serum show significant differences between trained and untrained horses and among sedentary horses and other animal species (cattle, rabbit, sheep). 2. Diurnal variations in serum GAG levels are reported (cattle), and changes in plasma GAG concentrations after road transport (horses) and in late pregnancy (mares, cows), while sex, age and breed do not affect them.

Proteoglycans in haemopoietic cells

Proteoglycans are produced by all types of haemopoietic cells including mature cells and the undifferentiated stem cells. The proteinase-resistant secretory granule proteoglycan (serglycin; Ref. 14), is the most prevalent and best characterised of these proteoglycans. Although its complete pattern of distribution in the haemopoietic system is unknown, serglycin has been identified in the mast cells, basophils and NK cells, in which secretion is regulated, and in HL-60 cells and a monocytoid cell line (Kolset, S.O., unpublished data) in which secretion is constitutive. Proteinase-resistant proteoglycans have been detected in human T-lymphocytes and murine stem cells (FDCP-mix) and the core proteins may be closely related to serglycin. A variety of glycosaminoglycan chains are assembled on the serglycin protein and it is likely that this class of proteoglycan can carry out a wide variety of functions in haemopoietic cells including the regulation of immune responses, inflammatory reactions and blood coagulation. There is strong evidence that in mast cells, NK cells and platelets, the proteoglycans are complexed to basic proteins (including enzymes and cytolytic agents) and amines in secretory granules and such complexes may dissociate following secretion from the cell. The stability of the complexes may be regulated by the ambient pH which may be acidic in the granules and neutral or above in the external medium. However, proteinase-proteoglycan complexes in mast cell granules seem to remain stable after secretion and it has been proposed that the proteoglycan regulates activity of proteinases released into the pericellular domain. The functions of proteoglycans which are constitutively secreted from cells are less clear. If cells have no requirement for storage of basic proteins why do they utilise the same design of proteoglycan as cells which accumulate secretory material prior to regulated release? We should stress that the so-called constitutive secretory pathway has been identified in haemopoietic cells in culture, which are usually maintained and grown in the presence of mitogenic factors (e.g., IL-2, IL-3). the cells are therefore activated and it has not been established that continuous proteoglycan secretion occurs in quiescent cells circulating in the peripheral blood. It is possible that lymphocytes, monocytes and macrophages, in which the constitutive secretion pathway operates in vitro, may store proteoglycan in vivo unless stimulated by mitogens or other activating agents.(ABSTRACT TRUNCATED AT 400 WORDS)

Inherited complement deficiency states: implications for immunity and immunological disease

The study of complement deficiency states and their influence on immune function has generated new insights and still provides a challenge to continued investigation. The association of classical pathway deficiencies (C1, C4, C2 or C3) with immunological diseases such as SLE and glomerulonephritis has contributed to current knowledge concerning complement-dependent immune complex handling and elimination. Susceptibility to systemic infection with encapsulated bacteria is encountered in most forms of inherited complement deficiency. Recurrent neisserial infection is the only clinical manifestation clearly associated with defects of the membranolytic sequence C5-C9, while deficiency of properdin, a component of the alternative activation pathway, appears to predispose to nonrecurrent meningococcal disease. Inherited complement deficiency is rare, but the perspective is widened by the more common occurence of acquired defects in immunological diseases, and the apparent requirement for efficient complement recruitment in host defense. Another aspect is the possibility that complement deficiency might alleviate or prevent inflammatory symptoms. Notably, complement deficiency has not been reported in classical rheumatoid arthritis. Considerations of this kind would be refuted or modified by findings of complement deficiency in single patients.

Syntheses of the methyl glycosides of the repeating units of chondroitin 4- and 6-sulfate

3,4,6-Tri-O-acetyl-D-galactal was transformed into methyl 6-O-acetyl-2-azido-4-O-benzyl-2-deoxy-beta-D-galactopyranoside and its 4-O-acetyl-6-O-benzyl analogue, each of which was glycosylated with activated, O-acetylated derivatives of methyl D-glucopyranosyluronate. The resulting beta-(1----3)-linked disaccharide derivatives were each reductively N-acetylated, hydrogenolysed, O-sulfated, and saponified to afford the disodium salts of methyl 2-acetamido-2-deoxy-3-O-(beta-D-glucopyranosyluronic acid)-4-O-sulfo-beta-D-galactopyranoside and the 6-O-sulfo analogue. D-Galactal was also transformed into activated derivatives of 2-azido-3,6-di-O-benzyl-2-deoxy-D-galactopyranose and their 3,4-di-O-benzyl analogues with various substituents at O-4 and O-6. These glycosyl donors were condensed with 6-O-protected derivatives of methyl 2,3-di-O-benzyl-beta-D-glucopyranoside to give the beta-(1----4)-linked disaccharide derivatives, which were selectively deprotected, then oxidised at C-6 of the gluco unit, reductively N-acetylated, selectively deprotected, O-sulfated at C-4 or C-6 of the galacto unit, and hydrogenolysed to give the disodium salts of methyl 4-O-(2-acetamido-2-deoxy-4-O-sulfo-beta-D-galactopyranosyl)-beta-D- glucopyranosiduronic acid and the 6-O-sulfo analogue.

The synthesis of proteoglycans by human T lymphocytes

We have examined the proteoglycans produced by highly-purified cultures of human T-lymphocytes. The proteoglycans were metabolically labelled with [35S]sulphate and analysed in cellular and medium fractions using DEAE-cellulose chromatography, gel filtration and specific enzymatic and chemical degradations. The results showed that the T cells synthesized a relatively homogeneous, proteinase-resistant chondroitin 4-sulphate proteoglycan that accumulated in the culture medium during a 48 h incubation period. The cellular fraction contained a significant amount of free chondroitin sulphate chains that were not secreted into the medium. These polysaccharides were formed by intracellular degradation of proteoglycan in a chloroquine-sensitive process, indicating a requirement for an acidic environment. In contrast to chondroitin sulphate derived from proteoglycan, chondroitin sulphates synthesized on the exogenous primer, beta-D-xyloside, were mainly secreted by the cells. beta-D-Xylosides caused an 8-fold stimulation in the synthesis of chondroitin sulphate, but decreased the synthesis of proteoglycan by about 50%. These proteoglycans contained shorter chondroitin sulphate chains than their normal counterparts. The results indicate that although proteoglycans are mainly secretory components in human T-cell cultures, a specific metabolic step leads to the intracellular accumulation of free glycosaminoglycans. Separate functions are likely to be associated with the intracellular and secretory pools of chondroitin sulphate.

Trimer and tetramer complexes containing C1 esterase inhibitor, C1r and C1s, in serum and synovial fluid of patients with rheumatic disease

During activation, the first component of complement C1q (C1r-C1s)2 is dissociated in conjunction with the formation of complexes containing C1 esterase inhibitor (C1-INH). Trimer complexes, with zymogen C1s associated with a firm C1-INH-C1r complex (C1-INH-C1r-C1s) can be distinguished from tetramer complexes C1-INH-C1r-C1s-C1-INH) in which C1-INH is firmly bound to both proteases. In the present study a two-stage electroimmunoassay was developed for the specific measurement of C1-INH-C1r-C1s. In the first step, C1-INH and its complexes were immunoprecipitated with anti-C1-INH during electrophoresis in the presence of Ca2+. In the second step, C1s contained in C1-INH-C1r-C1s was dissociated in the presence of EDTA and was measured by immunoprecipitation with anti-C1s. C1-INH-C1r-C1s were consistently found in normal sera. Normal sera did not contain C1-INH-C1r-C1s-C1-INH as assessed with a previously described ELISA procedure. Sera and synovial fluids from two groups of patients with inflammatory arthritis were investigated. In rheumatoid arthritis patients (n = 15) C1-INH-C1r-C1s complexes were usually found at high concentration both in serum and synovial fluid. C1-INH-C1r-C1s-C1-INH complexes were also present with values that were higher in synovial fluid than in serum, in accord with previous findings of classical pathway activation in the inflamed joints of the patients. Patients with spondylarthritic syndromes (n = 7) had serum and synovial fluid C1-INH-C1r-C1s concentrations that were comparable to those of the rheumatoid arthritis patients. If at all present, C1-INH-C1r-C1s-C1-INH were detected in trace amounts. Thus, C1 activation in patients with spondylarthritic syndromes appeared to be efficiently controlled at the C1r level. Distinguishing between C1-INH-C1r-C1s and C1-INH-C1r-C1s-C1-INH may prove of value in further studies of the activation and control of C1 in disease.

Differential sulphation of chondroitins in murine T and B lymphocytes and lymphoma cells

Splenic B and T lymphocytes metabolically labelled in vitro with [35S]-H2SO4 show differential sulphation of chondroitin sulphate, the major sulphated glycosaminoglycan in both cell-retained and secreted fractions. In B cells, 6-O-sulphation is more abundant than 4-O-sulphation, whereas in T cells sulphation occurs predominantly in the 4-O-position. The murine lymphoma lines AKTB-1b and EL-4, of B and T origin respectively, show even more marked differences. AKTB-1b follows the pattern of normal B cells, whilst in EL-4 only chondroitin 4-sulphate is synthesized.

Potential of human polymorphonuclear leukocytes to synthesize and secrete sulfated proteoglycans

To analyze the function of proteoglycans (PG) in different types of leukocytes, both the relative amounts and specific types of proteoglycans produced by cultured human peripheral blood polymorphonuclear leukocytes (PMN) were were determined and compared to mononuclear leukocytes (PBMC). Media from 3-day cultured PMN contained significantly less (less than 10%) 35SO2-4-labeled PG than media from PBMC cultures. Incorporation of 35SO2-4 into cell-associated material was comparable for both types of white blood cells. In contrast to PBMC, PMN could not increase their synthesis or secretion of PG after exposure to concanavalin A or phorbol-12-myristate-13-acetate. Various inducers of leukocyte chemotaxis also failed to enhance PG production by PMNs. Release of prelabeled PG from PMNs could be induced by exposure to either opsonized or unopsonized zymosan (yeast) as well as the bacteria S. aureus, suggesting that particle ingestion may be accompanied by PG exocytosis. Both chondroitinase ABC and AC digested greater than 90% of PMN 35S-labeled material in media and 75% in cell lysates; HNO3 treatment removed less than 5% of N-linked 35SO4 from radiolabeled media and 25% from cells. Treatment with 0.5 N NaOH released shortened glycosaminoglycan chains from 35S-labeled PMN cell lysates. beta-D-xylosides did not stimulate an increase in polysaccharide chain production by cultured PMNs. These data suggest that PMNs can produce chondroitin 4-sulfate PG whose synthesis is not affected by treatments that alter PMN functions; in contrast to PBMCs, PMNs will actively release these molecules when exposed to micro-organisms that stimulate phagocytosis.

Glycosaminoglycans enhance complement hemolytic efficiency: theoretical considerations for GAG-complement-saliva interactions

When human serum is diluted and pre-incubated at 37 degrees C in low ionic strength buffer (LIS, u = 0.07; made iso-osmotic with dextrose), a spontaneous activation of complement (C) is observed as determined by C4 and C3 electrophoretic conversion. In this paper it is postulated that most species of glycosaminoglycans (GAG) restricted non-specific fluid phase complement consumption induced by LIS, an effect which conserved complement and thereby enhanced the subsequent residual serum C mediated hemolytic activity. The capacity of glycosaminoglycans, to have modulated the hemolytic activity at low ionic strength, depended on the charge of the GAG species tested. In general, the GAG regulatory effects may have been due to GAG mediated restriction of spontaneous non-specific fluid phase C1 autoactivation, and/or restriction of activated C1 activity. Such effects would result in the subsequent reduction of the spontaneous fluid phase C4 and C3 consumption. Although the precise mechanisms responsible for the effects were not identified, it is speculated that the potentiation of C1 inhibitor function and direct effects on C1 might be involved. Overall, the relative specific activities of the glycosaminoglycans, on a weight basis, in mediating the fluid phase C regulatory effect were heparin greater than dermatan sulfate greater than chondroitin-6-sulfate greater than chondroitin-4-sulfate greater than hyaluronic acid and keratan sulfate. When much higher concns of heparin (greater than or equal 0.2 micrograms/ml) were used, complement mediated lysis of EA was inhibited, probably due to the direct inhibition of C1, even C1 which may have bound to the sensitized erythrocytes (EA). Results similar to that of heparin were obtained using greater than 1 mg/ml of dermatan sulfate or dextran sulfate. In contrast, pre-incubation of human serum in LIS with high concns (up to 10 mg/ml) of hyaluronic acid or chondroitin-4-sulfate, which are much less charged, continued to result only in the restriction of hemolytically non-specific (fluid phase) C consumption, resulting in a higher residual complement hemolytic activity. A theory is developed that the binding of polyionic GAG to C1 and to C1 INH may provide a charged local environment which simulates a relatively higher ionic strength. Chemical degradation of hyaluronic acid or chondroitin-4 or -6 sulfate resulted in lowering of this C modulating effect, indicative of the importance of the structural integrity of these charged glycosaminoglycans.(ABSTRACT TRUNCATED AT 400 WORDS)

The major human urinary trypsin inhibitor is a proteoglycan

The major urinary trypsin inhibitor (Mr 44 000), isolated from human urine, contains 35% carbohydrate. In addition to N-acetylglucosamine and neutral sugars (primarily mannose and galactose), the carbohydrate moiety contains hexuronic acid and N-acetylgalactosamine and corresponds to a glycosaminoglycan. This carbohydrate chain is an integral component of the inhibitor: it does not dissociate from the inhibitor when using dissociative conditions such as sodium dodecyl sulfate, guanidinium chloride, or by increasing ionic strength or mixing with cetylpyridinium chloride. This glycosaminoglycan chain is sensitive to chondroitinase ABC or testicular hyaluronidase digestion and corresponds to slightly sulfated chondroitin 4-sulfate or 6-sulfate. After treatment by these enzymes, the urinary inhibitor has a lower molecular mass (Mr 26 000) but still inhibits trypsin.

Inhibition of C1q binding to antigen-antibody complexes by a factor in rheumatoid arthritis serum

The sera and synovial fluids of patients with rheumatoid arthritis (RA) contain a factor which decreases the binding of C1q to antigen-antibody complex (IC). Several lines of evidence suggest that this factor is distinct from the documented C1q inhibitor which is a chondroitin sulphate. It binds to IC rather than to C1q. It is resistant to digestion with chondroitinase ABC. The addition of chondroitin sulphate to serum does not inhibit the binding of IC to C1q. The observation that three purified IgM and IgG rheumatoid factors (RF) did not reduce C1q binding to IC indicates that the factor is not RF. The ability of RA sera to reduce IC binding to C1q was inversely correlated with their ability to prevent immune precipitation (PIP), and directly with levels of an inhibitor of PIP. These data suggest that the factor which binds to IC and reduces C1q binding may be responsible for the excessive immune precipitation which occurs in RA sera.

C1 dissociation in serum: estimation of free C1q by electroimmunoassay

A two-stage electroimmunoassay was developed for measuring macromolecular C1 (C1qrs) and free C1q. The method was based on Ca2+ dependent fixation of C1qrs to agarose, followed by immune precipitation of dissociated C1s in the presence of EDTA. Free C1q was estimated from the increase in C1qrs resulting from saturation of C1q in the samples with purified C1r-C1s. The assay system was studied under various experimental conditions. Combined analysis by electroimmunoassay and crossed immunoelectrophoresis indicated that part of the free C1q in undiluted normal serum could be attributed to physiological C1 activation. Owing to concentration dependent C1qrs dissociation the proportion of free C1q increased with the dilution of serum. Results obtained with serum and with purified C1qrs were consistent with the formation of an equimolar C1q:C1r-C1s complex. However, the capacity for C1r-C1s binding appeared to be higher in the purified system than in serum. Serum concentrations of free C1q were high in some of the patients with disease conditions characterized by increased C1 activation, such as systemic lupus erythematosus or primary biliary cirrhosis.

Protein A treatment of cancer: activation of a serum component with trans-species anti-B16 melanoma activity

Mice (C57BL) succumbed to cultured B16 melanoma cells i.p. with reproducible kinetics and an MST2 of about 26 days. Serum from tumour-bearing or normal mice was treated at 0 degree C with fixed SAC cells and injected i.p. into fresh tumour-bearing mice. If serum was given 7 days or less after B16 inoculation, the MST of the mice was highly significantly increased by up to 32%. Similar activity has been generated in normal human, rabbit and guinea-pig serum, while untreated sera were ineffective. Apparently the sera contained an inactive native precursor that was activated by the SAC to produce an anti-tumour agent. Precursor and product were both relatively labile at 0 degree C. Anti-tumour activity was eluted at pH 2.5 from SAC or Sepharose-protein-A pretreated with serum, thus implicating the protein A component of SAC. The eluates contained haemolytically active C1, the first component of complement, and five crude C1 preparations made by standard methods showed good anti-tumour activity. However, seven other highly haemolytic C1 preparations had no anti-tumour effect. Similarly, two crude preparations of the subcomponent C1q had good anti-tumour activity, but eight other, more pure and highly haemolytic C1q preparations were inactive in mice. Thus the anti-tumour principle was not C1 or C1q alone, although it had some chemical properties in common with these substances. It remains unidentified, but has potential interest for cancer therapy.

The structural characterization of proteoglycans of cultured aortic smooth muscle cells and arterial wall of the pig

Aortic proteoglycans, from the growth medium of cultured smooth muscle cells and from sequential associative and dissociative extracts of the tissue of origin, the pig aorta, were isolated and purified by precipitation with cetylpiridinium chloride. After isopycnic CsCl gradient centrifugation under associative conditions 94% of the cell-secreted proteoglycans were recuperated in the bottom one fifth (rho av = 1.62 g/ml) fraction. In contrast 80% of the tissue proteoglycans of both extracts, fractionated into two fractions: the bottom one fifth (rho av = 1.60 g/ml) fraction and three fifths (rho av = 1.42 g/ml) fraction. Fractionated tissue proteoglycans were composed predominantly of chondroitin sulfate-dermatan sulfate (83-90%) with lower proportions of heparan sulfate (5-11%) and hyaluronic acid (3-6%) whilst cell-secreted proteoglycans showed a similar glycosaminoglycan composition but with a higher proportion of hyaluronic acid (11-13%). Sepharose 2B and C1-2B chromatography of tissue proteoglycans of high buoyant density showed the presence of only subunit proteoglycans whilst those of intermediate density contained a complex species, partially dissociable in 4 M guanidinium chloride, along with Kav 0.50 subunit species. The latter was also observed for cell-secreted proteoglycans although obtained at high buoyant density. The cell-secreted subunit proteoglycans became separated into two distinct populations when chromatographed on Sepharose 4B and C1-4B, half of which eluted in the column Vo and the rest at a Kav of 0.34. The majority of subunit macromolecules eluted at the Vo fractions of Sepharose 6B and C1-6B columns. Unlike the major species of cartilage proteoglycans, only approx. 20% of purified arterial proteoglycans formed complexes. This proportion could be increased by only 4-7% by interaction, of a mixture of subunit cell-secreted and tissue-extracted proteoglycans, with hyaluronic acid. These results suggest that proteoglycans secreted by cultured aortic smooth muscle cells and present in the aortic tissue possess certain similar physicochemical properties and are present in the form of complex and several subunit species.