Anti-CD36 autoantibodies in thrombotic thrombocytopenic purpura and other thrombotic disorders: identification of an 85 kD form of CD36 as a target antigen.

The presence of anti-CD36 antibodies in plasma of patients with thrombotic thrombocytopenic purpura (TTP), idiopathic thrombocytopenic purpura (ITP), and heparin-induced thrombocytopenia without/with thrombosis (HIT/HITT) has been examined by immunoblots, and a monoclonal antibody capture assay, the platelet-associated IgG characterization assay (PAICA). Results with PAICA showed that 73% (8/11) of patients with TTP were positive, and 71% (10/14) by immunoblots. With ITP, 20% (6/30) were positive by PAICA and 19% (3/16) by immunoblots; HIT, 30% (3/10) were positive by PAICA and 60% (6/10) by immunoblot; HITT, 50% (2/4) by PAICA and 100% (4/4) by immunoblot. Purification of CD36 by fast protein liquid chromatography (FPLC) from Triton X-100 extracts of normal platelet membranes resulted in the isolation of two different forms: the classic 88 kD form, and a second, lighter 85 kD form. Our data indicated that the patients' plasma autoantibodies reacted strongly with the 85 kD form. Conventional monoclonal and polyclonal antisera produced to the 88 kD form reacted strongly with the 88 kD form but weakly with the 85 kD form. These results confirm the possible importance of anti-CD36 antibodies in the pathophysiology of TTP and other thrombocytopenias and demonstrate the presence of a previously unrecognized target antigen for these antibodies.

Antibody-independent binding of complement component C1q by Legionella pneumophila.

Incubation of Legionella pneumophila Philadelphia 1 in normal human serum depleted of either classical-pathway component C1q or alternative-pathway component factor B resulted in activation of the complement system. Experiments focused on the role of the classical pathway in complement activation revealed that legionellae bound C1q independently of antibody. Purified preparations of L. pneumophila major outer membrane protein but not serogroup 1 lipopolysaccharide bound C1q independently of antibody. This suggests that antibody-independent binding of C1q by L. pneumophila can result in activation of the classical pathway in normal human serum and that major outer membrane protein may be a C1q acceptor on the L. pneumophila cell surface.

Heat shock (stress) proteins and autoimmunity in rheumatic diseases.

The rheumatic diseases (RDs) are characterized by acute and chronic inflammation, and autoimmunity plays a major role in their pathogenesis. RDs are for the most part of unknown etiology, but recent evidence indicates that heat shock or stress proteins (HSPs) may have an important role in the etiology/pathogenesis of RDs. HSPs are produced by prokaryotic and eukaryotic cells and are grouped according to molecular weight. Phylogenetically, HSPs are very old and are remarkably conserved molecules in evolution from bacteria to humans. HSPs are induced by a variety of cellular stresses in addition to heat; cognates are expressed constitutively and are essential in a number of normal functions. Some HSPs serve as molecular chaperones, the latter defined as proteins that mediate folding of other polypeptides and either promote their assembly into oligomeric structures or disassemble the final product. Conservation of structure and function of many HSPs may provide a link between immunity to infection and the autoimmune features of RDs. Evidence is reviewed from clinical and laboratory observations that diverse microbial agents, including viruses, bacteria, and parasites, may have putative roles in the development and pathogenesis of some RDs. HSPs also are discussed in relation to the major histocompatibility complex, HLA antigens, and disease associations and how they may alter the balance between tolerance and autoimmunity. Studies are reviewed that are supportive or nonsupportive of the concept of microbial infection associated with autoimmunity; individuals first react to microbial immunizations or infections with enhanced cellular/humoral responses to the agent's HSPs. With the enhanced immune response, cross-reactivity may occur with an HSP of the stressed host because of structural similarities to the microbial HSP. If all of these events occur, the host's homologous HSP or stressed cells now become true autoantigen(s). This sequence has implications for the etiology of immune-mediated RDs, the concept of epitope sharing, and the accompanying autoimmunity. A recurring theme emphasized in some reports to understand better the role of HSPs in autoimmunity is the need to select patients with early-onset disease. A minor subpopulation of T lymphocytes express a CD3-associated T-cell receptor (TCR) heterodimer composed of gamma and delta polypeptide chains. The gamma delta + T cells have several unique features. When analyzed by the polymerase chain reaction, lymphocytes with TCR-gamma delta appear to reflect the polyclonal expansion of preexisting gamma delta clones. They are found in peripheral lymphoid tissue in very low percentage (< 5%) but may represent the majority of T cells within epithelial tissue.(ABSTRACT TRUNCATED AT 400 WORDS)

Legionella pneumophila lipopolysaccharide activates the classical complement pathway.

Legionella pneumophila is a gram-negative bacterium capable of entering and growing in alveolar macrophages and monocytes. Complement and complement receptors are important in the uptake of L. pneumophila by human mononuclear phagocytes. The surface molecules of L. pneumophila that activate the complement system are unknown. To identify these factors, we investigated the effects of L. pneumophila lipopolysaccharide (LPS) on the classical and alternative complement pathways of normal human serum by functional hemolytic assays. Although incubation of LPS in normal human serum at 37 degrees C resulted in the activation of both pathways, complement activation proceeded primarily through the classical pathway. Activation of the classical pathway by LPS was dependent on natural antibodies of the immunoglobulin M class that were present in various quantities in sera from different normal individuals but were absent in an immunoglobulin-deficient serum obtained from an agammaglobulinemic patient. Additional studies using sheep erythrocytes coated with LPS suggested that the antibodies recognized antigenic sites in the carbohydrate portion of LPS. The ability of LPS to interact with the complement system suggests a role for LPS in the uptake of L. pneumophila by mononuclear phagocytes.

Functional properties of heterogeneous human asialo-C4 and its isotypes C4A and C4B.

The fourth component of human complement (C4) is encoded at two separate but closely linked loci within the MHC on the short arm of chromosome 6. Thus, there are two types of C4 protein in most individual and pooled normal human sera (NHS): C4A and C4B. Incubation of individual sera, pooled NHS, or purified heterogeneous C4 (C4A/C4B) with bacterial sialidase at 37 degrees C increased C-mediated hemolysis of antibody-sensitized sheep erythrocytes 1.54- to 1.93-fold. Comparative studies of Tmax of human C2, using asialo-C4 or buffer-treated C4 on EAC1gp and extrapolation to time 0 indicated a z value 4-fold higher with asialo-C4. This indicated that more hemolytically active C42 complexes are available with sialidase-treated C4 compared to untreated C4. There was no appreciable difference in the % 125I-C4 bound to EAC1gp (sialidase- or buffer-treated). Sera from two different blood donors with C4A3 phenotype (C4BQ0), two different donors with C4B1 phenotype (C4AQ0), and serum from an individual heterozygous deficient at both C4A3 and C4B1 regions (A3, AQ0; B1, BQ0) were investigated. The C4 allotypes, purified from these sera, were treated with sialidase; the C4A3 was enhanced in hemolytic assays by sialidase-treatment (1.52- to 2.3-fold), whereas the C4B1 allotype was not enhanced. Fluorometric determinations revealed that approximately the same percentage of sialic acid was released from sialidase-treated C4A3 and C4B1. Therefore, the increase in hemolytic titer observed after treatment of NHS or purified heterogeneous C4 with sialidase is a property of C4A3 but not a property of C4B1.

Properties of four acute phase proteins: C-reactive protein, serum amyloid A protein, alpha 1-acid glycoprotein, and fibrinogen.

Four plasma proteins, referred to as positive acute phase proteins because of increases in concentration following inflammatory stimuli, are reviewed: C-reactive protein (CRP), serum amyloid A protein (SAA), alpha 1-acid glycoprotein (AAG), and fibrinogen. The CRP and SAA may increase in concentration as much as 1000-fold, the AAG and fibrinogen approximately twofold to fourfold. All are synthesized mainly in the liver, but each may be produced in a number of extrahepatic sites. The role of cytokines in induction of the acute phase proteins is discussed, particularly the multiple functional capabilities of interleukin-6 (IL-6). Other cytokines that regulate acute phase gene expression and protein synthesis include IL-1, tumor necrosis factor alpha, interferon gamma, as well as other stimulatory factors and cofactors. The physicochemical characteristics of each protein are reviewed together with the molecular biology. For each protein, the known biological effects are detailed. The following functions for CRP have been described: reaction with cell surface receptors resulting in opsonization, enhanced phagocytosis, and passive protection; activation of the classical complement pathway; scavenger for chromatin fragments; inhibition of growth and/or metastases of tumor cells; modulation of polymorphonuclear function; and a few additional diverse activities. The role of plasma SAA is described as a precursor of protein AA in secondary amyloidosis; other functions are speculative. AAG may play an immunoregulatory role as well as a role in binding a number of diverse drugs. In addition to clot formation, new data are described for binding of fibrinogen and fibrin to complement receptor type 3. Finally, the concentration of each protein is discussed in a wide variety of noninfectious and infectious disease states, particularly in connective tissue diseases. The quantification of the proteins during the course of various acute and chronic inflammatory disorders is useful in diagnosis, therapy, and in some cases, prognosis.

Functional properties of the asialo-fifth component of human complement.

Removal of exposed, terminal sialic acid (SA) from carbohydrate chains N-glycosidically linked to asparagine residues of highly pure human C5 with bacterial sialidase increased C-mediated hemolysis of antibody-sensitized sheep E maximally 2.77-fold. Sialidase-treated C5 used as a reagent for the titration of C6, C7, C8, and C9 resulted in increased titers of all these components compared to buffer-treated C5. As determined by a fluorometric method, ca. 65% of the SA was enzymically hydrolyzed under optimal conditions. Endoglycosidase F incubated with C5 followed by monosaccharide analyses by anion exchange chromatography with pulsed amperometric detection revealed both high mannose and complex (terminate in SA) oligosaccharides were hydrolyzed; no effect was found on the functional activity of C5. Approximately 4% of the complex oligosaccharides were hydrolyzed from C5. Comparison of sialidase- and buffer-treated C5 decay rates from EAC1gp(4b,oxy2a,3b)hu resulted in two linear components of the decay curve with sialidase-treated C5, but one linear component with buffer-treated C5. Of the sialidase-treated 125I-C5 15% was bound to EAC1gp(4b,oxy2a,3b)hu compared to 9.3% of buffer-treated 125I-C5. Furthermore, 27% of sialidase-treated 125I-C5 was bound to EAC1gp,4bhu compared to 16.6% of buffer-treated 125I-C5, but no lysis occurred after the addition of C6-C9. The mechanism of increased hemolytic activity after removal of SA from C5 is: the Tmax is prolonged at 30 degrees C (ca. 15 min vs 9 min), and a higher percentage of C5 binds to cellular intermediates compared to buffer-treated C5.

Complement activation and corticosteroid therapy in the development of the adult respiratory distress syndrome.

Fifty-nine patients in septic shock were observed for the development of the adult respiratory distress syndrome (ARDS) prior to and after receiving either 30 mg/kg methylprednisolone sodium succinate, 6 mg/kg dexamethasone sodium phosphate or no steroid. Serum levels of C3, C4 and Factor B allowed classification of 42 patients by activation of complement pathways. Despite a trend toward patients with severe septic shock who activate the alternative pathway being protected from the development of ARDS, complement pathway determination did not allow prediction of the development of ARDS and steroid pretreatment did not influence complement levels or prevent ARDS.

Complement activation in septic shock patients.

To evaluate the status of the complement system and to determine the effects of corticosteroids on complement component levels in septic shock, C3, C4, and Factor B were measured in 42 patients with severe late septic shock. Serum levels of C4 and Factor B correlated with C3 levels (r = 0.48 and 0.64, respectively; p less than .01) in patients in shock for more than 4 h, but only Factor B correlated with C3 (r = 0.85; p less than .01) in patients in shock for 4 h or less. C3 and Factor B levels were significantly (p less than .05) lower in patients who died (12,174 +/- 1,524 CH50 U/ml and 14 +/- 1 mg/dl, respectively) than in patients who survived (18,418 +/- 2,833 CH50 U/ml and 21 +/- 2 mg/dl, respectively). Corticosteroids did not alter complement component levels. The alternative pathway appears to be activated early in septic shock, whereas the classical pathway is activated later. C3 and Factor B levels may predict survival of patients in septic shock. In this study, corticosteroids did not change the complement component levels of patients in late severe septic shock.

The effects of a partially purified fraction of an ant venom in rheumatoid arthritis.

A partially purified extract of an ant venom from the South American tree ant Pseudomyrmex sp. was tested in a double-blind, controlled study of patients with rheumatoid arthritis. Venom treated patients demonstrated an improvement in global efficacy and a decrease in the number of tender/painful joints and swollen joints. Swollen joint index improved in 60% of venom treated patients. Other parameters did not demonstrate significant change. Reduction of joint swelling was followed by symptomatic improvement that was sometimes delayed by weeks. Reactions were limited to erythema at the injection site (all patients), local pruritus (two-thirds of the patients), and fever with malaise (one-third of the patients). Further study of this venom in rheumatoid arthritis appears warranted in view of its apparent favorable efficacy-to-toxicity ratio.

Separation of functionally or highly pure C2 from human plasma with Sepharose and a lectin of Euonymus europeus.

A method is described for isolating both functionally and highly pure C2 from normal human serum or plasma. Functionally pure C2 was obtained by a two-step method of ammonium sulfate (AS) fractionation of plasma or serum and chromatography on AH-Sepharose containing a bound lectin of Euonymus europeus. The functionally pure C2 can be isolated in 2 days, and is used routinely as a reagent for functional hemolytic titrations of C3 and C4 in the Clinical Immunology Laboratory. Highly pure C2 was isolated by the two-step fractionation with AS followed by chromatography on CM-cellulose, aged CNBr-activated Sepharose 4B, and AH-Sepharose-lectin. The major difficulty for isolating highly pure C2 was its separation from Factor B of the alternative complement pathway. The yield of C2 varied from 30 to 40 per cent. Following electrophoresis and staining on polyacrylamide gels, the single band was hemolytically active C2.

Effect of sequential glycolysis of the lectin of Euonymus europaeus on activation of the classical complement pathway in normal human serum.

The lectin of Euonymus europaeus at concentrations of 5-21 micrograms/ml causes activation of the classical complement (C) pathway (C1, C4, C2) when added to normal human serum at 37 degrees C. At higher concentrations, C3 is also consumed. The effect is dependent on a 'natural antibody' in serum of the IgM class which reacts with an epitope of the lectin. With physicochemical methods, the carbohydrate of the lectin was shown to be involved in the activation of C, but not involved in the agglutination of group B erythrocytes. Removal of N-acetyl-D-glucosamine from the lectin with an exoglycosidase greatly reduced the activation of C in serum, but it did not affect erythroagglutination. Using competitive binding studies with various sugars, it was confirmed that N-acetyl-D-glucosamine is the dominant specificity of a determinant for activation of the classical C pathway in serum.

The first component of human complement: on the mechanism of activation by some carbohydrates.

Four synthetic saccharides (mono-, di-, tri-, tetra-) linked to the carrier 8-methoxycarbonyloctanol were used in the presence or absence of a polysaccharide (PS) purified from ant venom to study the activation of C1 and the consumption of C4 in normal serum. The carrier was essential for the recorded activities of the saccharides. The alpha D mannose-O-carrier did not cause C1 activation and C4 consumption by itself, but it enhanced these activities when combined with the venom PS. The alpha L fuc(1 leads to 4)beta D glc-NAc-O-carrier caused C1 activation but no C4 consumption by itself at a high concentration (1.4 mg/ml), and enhanced C1 activation and C4 consumption in combination with the venom PS. The beta D gal(1 leads to 3)alpha L fuc(1 leads to 4)beta D glc-NAc-O-carrier caused both C1 activation and C4 consumption in normal human serum by itself. The alpha L fuc(1 leads to 2)beta D gal[alpha L fuc(1 leads to 4)]beta D glc-NAc-O-carrier neither caused C1 activation and C4 consumption by itself, nor did it enhance these activities when combined with the venom PS. Neither EAC1hu nor EAC1hu bound 3H-PS or 3H-beta D gal(1 leads to 3)alpha L fuc(1 leads to 4)beta D glc-NAc-O-carrier. Also, the precursor human C1 on EA (EAC1) was not activated by the venom PS. Thus, the overall evidence shows that human precursor C1 is activated by these carbohydrates solely by an interaction with C1q subunit of macromolecular C1.

Activation of first component of complement (C1) in guinea pig serum by a polysaccharide is prevented by C1 inhibitor.

A polysaccharide (PS) purified from venom of the ant Pseudomyrmex sp. causes the activation of the classical complement (C) pathway in normal serum, but not in guinea pig serum. To investigate why C was not activated in guinea pig serum, we partially purified guinea pig C1 in the presence of the protease inhibitor p-nitrophenyl, p'-guanidinobenzoate (NPGB). This C1 preparation was activated (mu = 0.15, pH 7.5) by the PS in a dose-dependent reaction after NPGB was eliminated by dilution. The PS decreased the action of the C1 inhibitor for C1 in diluted guinea pig serum, and it also inhibited the activity of highly purified guinea pig C1 inhibitor for C1. There was a direct correlation between the concentration of the guinea pig C1 inhibitor and the loss of ability of the PS to activate C1 in mixtures of constant concentrations of purified guinea pig C1 and purified venom PS, and increasing concentrations of purified guinea pig C1 inhibitor. The activity of the human C1 inhibitor, either in diluted serum or highly purified, was not decreased by the PS. These results show that the PS does not activate guinea pig C1 in serum because its action is blocked by the C1 inhibitor.