Catalytic activity of antibodies against factor VIII in patients with hemophilia A.

Hemophilia A is an X chromosome-linked recessive disorder resulting in defective or deficient factor VIII (FVIII) molecules, which, in its severe form, is a life-threatening and crippling hemorrhagic disease. Infusion of homologous FVIII to patients with severe hemophilia A results, in 25% of patients, in the emergence of alloantibodies against FVIII (inhibitors)( ref. 1) that inhibit FVIII procoagulant activity by steric hindrance of the interaction of FVIII either with stabilizing molecules, with molecules essential for its activity or with activating molecules. Here, we report on the proteolysis of FVIII by alloantibodies of two patients with severe hemophilia A, demonstrating a previously unknown mechanism by which FVIII inhibitors may prevent the pro-coagulant function of FVIII. The kinetic parameters of FVIII hydrolysis indicate a functional role for the catalytic immune response in the inactivation of FVIII in vivo. The characterization of alloantibodies against FVIII as site-specific proteases may provide new approaches to the treatment of FVIII inhibitors.

Surface-associated heparin inhibits zymosan-induced activation of the human alternative complement pathway by augmenting the regulatory action of the control proteins on particle-bound C3b.

Discrimination by the human alternative pathway between activating and nonactivating particles occurs after deposition of C3b by the continuous low-grade interaction of the alternative pathway components in biologic fluids and is dependent on the modulation by surface constituents of the interaction of bound C3b with the control proteins, beta 1H, and C3b inactivator (C3bINA). When heparin glycosaminoglycan was coupled to activating particles, such as zymosan or Sepharose, by cyanogen bromide activation, their capacity to activate the human alternative pathway was inhibited. The loss of alternative pathway-activating capacity was directly correlated to the number of heparin molecules bound/zymosan particle, whether the ratio was varied by increasing the amounts of heparin in the initial coupling reactions or by treating a fully inhibited particle with incremental concentrations of heparinase. Analysis by linear regression of the inhibitory effect of each procedure (r = 0.97, r = 0.98, respectively) for adjusting the number of heparin molecules/particle revealed that the dose-response relationships were identical and that complete inhibition occurred with greater than 12 X 10(8) molecules of heparin/zymosan particle. The coupling of heparin to zymosan did not impair the uptake of C3b from the fluid-phase interaction of C3, B, and D, and did not alter the capacity of bound C3b to associate with B so as to permit its inactivation by D. Although the regulatory proteins present in normal serum chelated with EDTA or presented as a combination of purified C3bINA and beta 1H were relatively inefficient in inactivating C3b function on an activating particle of the alternative pathway such as zymosan or zymosan-cyanogen bromide, the control proteins rapidly inactivated C3b on a nonactivating particle wuch as a sheep erythrocyte or zymosan with coupled heparin. The increased numbers of C3b sites susceptible to inactivation by C3bINA in the presence of beta 1H were significantly correlated to the number of molecules of heparin/particle. By linear regression analysis of the correlation (r = 0.99) the number of heparin molecules/particle required to promote total inactivation of bound C3b by purified control proteins was 13.8 X 10(6). This molecular analysis suggests that the action of heparin coupled to an activating particle of the alternative pathway is to promote the interaction between particle-bound C3b and the regulatory proteins, thereby preventing particle-associated amplified C3 cleavage. It is noteworthy that both surface constituents known to maintain a particle as a nonactivator of the alternative pathway, sialic acid and N-sulfated mucopolysaccharide, act by facilitating the inactivation by regulatory proteins of the function of particle-bound C3b.

Complement mediates human immunodeficiency virus type 1 infection of a human T cell line in a CD4- and antibody-independent fashion.

Incubation of the human T cell lymphotropic virus (HTLV)-IIIB and HTLV-RF strains of human immunodeficiency virus type 1 (HIV-1) with normal seronegative human serum under conditions that allow complement activation resulted in enhancement of infection of the MT2 human T cell line cultured in the presence of low amounts of virus. Infection of MT2 cells was assessed by measuring reverse transcriptase activity in supernatants at day 9 of culture. Complement activation by viral suspensions occurred through the alternative pathway. Opsonization of HTLV-RF viral particles with complement was sufficient to allow a productive infection to occur in cells exposed to suboptimal amounts of virus. Infection of MT2 cells with suboptimal amounts of serum-opsonized HIV-1 was suppressed by blocking the C3dg receptor (CR2, CD21) on MT2 cells with monoclonal anti-CR2 antibody and rabbit F(ab')2 anti-mouse immunoglobulin antibodies. Blocking of the gp120-binding site on CD4 under similar experimental conditions had no inhibitory effect on infection of MT2 cells with opsonized virus. Opsonization of HIV-1 with seronegative serum also resulted in a CR2-mediated enhancement of the infection of normal peripheral blood mononuclear cells and T lymphocytes. These results indicate that complement in the absence of antibody may enhance infection of C3 receptor-bearing T cells with HIV-1, and that the interaction of opsonized virus with the CR2 receptor may result by itself in the infection of target T cells in a CD4- and antibody-independent fashion.

[Intravenous immunoglobulins in autoimmune and inflammatory disorders: beyond a simple substitution]. / Immunoglobulines intraveineuses dans les maladies auto-immunes et inflammatoires: au-delà d'une simple substitution.

Despite their widespread use since many years in autoimmune and inflammatory disorders, the mechanisms of action of IVIg have not been completely understood. These mechanisms depend on Fc and/or F(ab')2. IVIg interacts with the different components of the immune system: Fc receptors, complement, cytokines, T and B lymphocytes, dendritic cells, granulocytes and NK cells. Here, we discuss the recent advances in the understanding of the mechanisms of action of IVIg, in particular the importance of the sialylated Fc fragment. These advances maybe help us conceive better therapeutic strategies against autoimmune and inflammatory disorders.

Normal immunoglobulin G (IgG) for therapeutic use (intravenous Ig) contain antiidiotypic specificities against an immunodominant, disease-associated, cross-reactive idiotype of human anti-thyroglobulin autoantibodies.

Pooled normal polyspecific IgG for therapeutic use (IVIg) contain anti-idiotypes against idiotypic determinants expressed by autoantibodies from patients with a variety of autoimmune diseases. In the present study, antiidiotypes in IVIg are shown to recognize a cross-reactive idiotype on human anti-thyroglobulin (TG) autoantibodies, that was defined by heterologous antiidiotypic antibodies, termed anti-T44 antibodies. The T44 idiotype is located outside the antibody-combining site of anti-TG autoantibodies. F(ab')2 fragments from anti-T44 antibodies inhibited the binding of IVIg to affinity-purified F(ab')2 anti-TG autoantibodies. Anti-T44 antibodies bound to F(ab')2 fragments of patients' antibodies, which were retained on an affinity column of Sepharose-bound F(ab')2 fragments from IVIg, but not to F(ab')2 fragments from the effluent of the column. The T44 idiotype was expressed on antibodies that bound to IVIg from eight of nine patients with autoimmune thyroiditis, but not on IVIg-binding Igs from healthy individuals. A small amount of the T44 idiotype was also expressed on the fraction of IVIg that bound to itself upon affinity chromatography. The T44 idiotype was cross-reactive between antibodies from patients with autoimmune thyroiditis. Thus, IVIg contain antiidiotypic antibodies directed against an immunodominant disease-associated cross-reactive alpha-idiotype of human anti-TG autoantibodies. These results support the concept that IVIg may be beneficial in selected autoimmune diseases by modulating the function of the idiotypic network.

Membrane-bound hemagglutinin mediates antibody and complement-dependent lysis of influenza virus-treated human platelets in autologous serum.

Influenza A virus-treated human platelets were lyzed in autologous serum. Lysis required the presence of antibody and occurred predominantly through activation of the classical complement pathway. Binding of the virus followed by its elution at 37 degrees C resulted in a dose-dependent desialation of the cells with a maximal release of 45% of total platelet sialic acid. In contrast, platelets that had been treated with Vibrio cholerae neuraminidase and from which 55% of total sialic acid had been removed were not lyzed in autologous serum and did not bind C3 as shown in binding assays using radiolabeled monoclonal anti-C3 antibody. Thus, the immune-mediated lysis of virus-treated platelets in autologous serum did not involve neoantigens expressed by desialated cells. To assess the effect of viruses on the platelet surface, treated platelets were incubated with galactose oxidase and sodium [3H]borohydride prior to separation and analysis of the labeled glycoproteins by SDS-PAGE. Viral treatment resulted in a desialation of each of the surface glycoproteins. At the same time, a labeled component of Mr 72,000 (nonreduced) and Mr 55,000 (reduced) was observed that was not present when V. cholerae-desialated platelets were examined in the same way. Immunoblotting experiments performed using antiwhole virus and anti-hemagglutinin antibodies demonstrated this component to be viral hemagglutinin. Involvement of membrane-bound hemagglutinin in antibody and in complement-mediated lysis of virus-treated platelets in autologous serum was supported by the increased lytic activity of a postvaccinal serum containing an elevated titer of complement fixing anti-hemagglutinin antibodies. Binding of a viral protein to the platelet surface provides a model for immune thrombocytopenias occurring during acute viral infections at the time of the specific immune response.

Immunohistochemical study of the human glomerular C3b receptor in normal kidney and in seventy-five cases of renal diseases: loss of C3b receptor antigen in focal hyalinosis and in proliferative nephritis of systemic lupus erythematosus.

The presence and distribution of C3b receptors in normal human kidneys and in biopsies from 75 patients with renal disease were investigated by immunohistochemical techniques using monospecific rabbit antibody to the 205,000-mol wt glycoprotein that is the C3b receptor of human peripheral blood cells. Anti-C3b receptor bound exclusively to podocytes in normal renal cortex, and was homogeneously distributed on the plasma membrane of these cells. Biosynthesis of the receptor by the podocyte was suggested by the presence of antigenic activity in the Golgi apparatus. Although occupancy of receptor sites following the interaction of kidney sections with aggregated IgG preincubated with normal serum inhibited binding to glomeruli of C3b coated cells, the C3b receptor remained accessible to anti-C3b receptor antibody. No staining of podocytes was found in extra-capillary proliferating cells in rapidly progressive glomerulonephritis (GN). Segmental loss of staining was found in focal hyalinosis, nodular diabetic glomerulosclerosis, and amyloidosis while no detectable C3b receptor antigen was found in severe proliferative nephritis of systemic lupus erythematosus (SLE). Normal staining of podocytes was found in other nephropathies with endocapillary proliferation such as acute GN and mesangial GN and in renal diseases associated with immune deposits containing C3 such as mesangial proliferative and membranous SLE nephritis, idiopathic membranous GN, membranoproliferative GN types I and II, mesangial GN with IgA or C3 deposition and Henoch Schönlein's purpura. Loss of C3b receptor antigen in the diffuse proliferative nephritis of SLE distinguishes it both from nonproliferative lupus nephritis and other immunologically mediated proliferative GN.

Antibodies to a conserved region of HLA class I molecules, capable of modulating CD8 T cell-mediated function, are present in pooled normal immunoglobulin for therapeutic use.

Intravenous immunoglobulin (IVIg) is increasingly used for the treatment of autoimmune diseases and the prevention of infections and of graft versus host reactions in recipients of allogeneic bone marrow transplants. The immunomodulatory effects of IVIg are largely dependent on their ability to interact with membrane molecules of lymphocytes. We report here that IVIg recognizes the B07.75-84 peptide, corresponding to a conserved region of the alpha I helix of the first domain of HLA-B7 01, which represents a nonpolymorphic determinant of HLA class I molecules. Intact IVIg and its F(ab')2 fragments bound to the peptide as well as to purified soluble HLA and to HLA on a human T cell line. Binding of IVIg to HLA was assessed by ELISA, immunofluorescence, and real-time analysis of the interaction using the BIAlite system. The binding of antipeptide antibodies to HLA was inhibited by free peptide. Antipeptide antibodies isolated from IVIg by affinity chromatography inhibited CD8 cell-mediated cytotoxicity of an influenza virus-specific human T cell line. The presence in IVIg of antibodies to critical regions of HLA class 1 molecules suggests a possible role for IVIg in modulation of class-I-restricted cellular interactions in the immune response.

Structural determinants of the capacity of heparin to inhibit the formation of the human amplification C3 convertase.

The ability of heparin glycosaminoglycan to prevent formation of the properdin-stabilized amplification C3 convertase is independent of antithrombin binding activity and requires substitution of the amino sugar and a degree of oxygen (O)-sulfation which could be on the uronic acid or the amino sugar. Preparations of heparin glycosaminoglycan isolated by different techniques from different species (rat, human, and porcine) exhibited an equivalent capacity to inhibit generation of the amplification C3 convertase. Hyaluronic acid, which is devoid of O-sulfation, had no inhibitory activity; chondroitin 4-sulfate of rat and whale origins, chondroitin 6-sulfate of rat and shark origins, and dermatan sulfate from porcine skin are O-sulfated on the galactosamine and had minimal activity. Porcine heparin glycosaminoglycan, isolated on the basis of affinity for antithrombin III, had no greater anticomplementary activity than porcine glycosaminoglycan, which failed to bind antithrombin III and had essentially no anticoagulant activity. Nitrogen (N)-desulfation of porcine heparin reduced anticomplementary activity to the level of the other sulfated mucopolysaccharides, and both N-resulfation and N-acetylation restored the original activities, thereby indicating a requirement for N-substitution, but not N-sulfation. N-resulfation of N-desulfated and O-desulfated heparin did not restore any activity, thus indicating that O-sulfation and N-substitution represent independent, critical structural requirements for the anticomplementary activity of heparin glycosaminoglycan. Inasmuch as N-desulfated-N-acetylated heparin had no anticoagulant activity, the nature of the N-substitution completely distinguishes the plasma-protein effector pathway that is inhibited.

Natural autoantibodies.

Autoantibodies of the IgM, IgG and IgA classes, reactive with a variety of serum proteins, cell surface structures and intracellular structures, are 'naturally' found in all normal individuals. Present in human cord blood and in 'antigen-free' mice, their variable-region repertoire is selected by antigenic structures in the body and remains conserved throughout life. Encoded by germline genes with no, or few, mutations, natural autoantibodies are characteristically 'multireactive' and do not undergo affinity maturation in normal individuals. Natural autoantibodies may participate in a variety of physiological activities, from immune regulation, homeostasis and repertoire selection, to resistance to infections, transport and functional modulation of biologically active molecules.

Immunomodulation of autoimmune and inflammatory diseases with intravenous immunoglobulin.

Intravenous immunoglobulin (IVIg) has been used in the treatment of primary and secondary antibody deficiencies for over two decades. Since the early 1980s, the therapeutic efficacy of IVIg has been established in idiopathic thrombocytopenic purpura, Guillain-Barré syndrome, chronic inflammatory demyelinating polyneuropathy, myasthenia gravis, dermatomyositis and Kawasaki syndrome, and the prevention of graft versus host disease in recipients of allogeneic bone marrow transplants. Its use has also been reported in a large number of other autoimmune and systemic inflammatory conditions. In this review, we discuss the mechanisms by which IVIg exerts immunomodulatory effects in immune pathologies.

Generation of complement anaphylatoxins and C5b-9 by crystalline cholesterol oxidation derivatives depends on hydroxyl group number and position.

Cholesterol crystals activate the human alternative complement pathway. Loss of Factor B hemolytic activity in C2-deficient serum was comparable to that in normal human serum after incubation with cholesterol crystals. Consumption of Factor B hemolytic activity in normal serum incubated with cholesterol occurred in a time- and dose-dependent manner. The reduced capacity of crystals-absorbed serum to activate C2, but not Factor B, on fresh crystals, indicated that cholesterol mediates antibody-dependent classical pathway activation in addition to alternative pathway activation in whole serum. Cholestane triol, an oxidation derivative of cholesterol which bears three hydroxyl groups, cleaved 5-fold more C3 than cholesterol in normal human serum. Three cholesterol derivatives, each bearing two hydroxyl groups, were intermediate activators between cholesterol and cholestane triol. The compounds differed, however, in their complement-activating ability, indicating that hydroxyl position as well as number exerts an influence on complement activation. Measurements of C3adesArg and C5adesArg antigens in cholesterol crystal treated serum revealed that approx. 10% of total serum C3 was cleaved and that, on a molar basis, only 3% C5 cleavage occurred relative to C3 cleavage. For 1 mole of C5a generated, 0.1 moles of fluid-phase C5b-9 was detected. Although the extent of C3 cleavage varied with each cholesterol derivative depending on the position and number of hydroxyl groups, the relative coupling efficiency of C3 and C5 cleavage and C5a and C5b-9 generation was similar for all compounds. The ability of cholesterol and its oxidation products to generate anaphylatoxins and C5b-9 complexes may be of importance in mediating inflammatory processes involved in atherogenesis.

Structure-function relationships in the inhibitory effect of heparin on complement activation: independency of the anti-coagulant and anti-complementary sites on the heparin molecule.

Fluid phase heparin inhibits formation of the classical and alternative pathway C3 convertase of complement in assays performed either with purified complement proteins or in whole serum. Experiments using oligosaccharides of homogeneous mol. wt obtained by mild nitrous hydrolysis of heparin, demonstrated that the inhibitory activity of heparin increased exponentially with mol. wt for fragments containing between 4 and 14 saccharidic units and that fragments of mol. wt above 4700 (greater than 14 saccharidic units) had a similar anti-complementary activity to that of native heparin. Fragments of homogeneous mol. wt (octasaccharides) separated by ion exchange chromatography on the basis of negative charges, exhibited increasing inhibitory activity with increasing sulfate content. Over-sulfation of fragments of defined mol. wt resulted in a constant enhancement of the relative capacity of each fragment species to inhibit formation of the classical and alternative pathway C3 convertases. A synthetic pentasaccharide representing the minimal critical sequence responsible for the binding of heparin to anti-thrombin III exhibited a similar inhibitory capacity on formation of the C3 convertases as another synthetic pentasaccharide that was devoid of anti-Xa activity. These studies contribute to define a minimal structure of the heparin molecule with C3b- and C4b-binding capacity and definitively establish the independency of the anti-coagulant and anti-complementary sites on the heparin molecule.

The ability of Sephadex to activate human complement is suppressed in specifically substituted functional Sephadex derivatives.

The capacity of Sephadex and of chemically substituted Sephadex derivatives to activate human complement was examined by incubating polymer particles in normal human serum (NHS) under conditions that allow classical and/or alternative pathway activation, and by determining complement consumption or generation of C3a antigen in serum. Sephadex was found to activate complement in NHS, mainly through the alternative pathway. The complement-activating capacity of Sephadex was directly related to the surface area of polymer that could interact with serum. Substitution of hydroxyl groups of Sephadex with carboxymethyl (CM) groups suppressed the complement-activating capacity of the polymer in a dose-dependent fashion so that Sephadex bearing an average of one or more CM groups per saccharidic unit exhibited no complement-activating ability. Blocking of CM groups on CM sephadex with amide bonds did not restore a complement-activating capacity to the polymer, indicating that intact hydroxyl groups of the sugar units are required for complement activation by Sephadex. CM Sephadex was also found to adsorb C3adesArg which bound to the polymer with a calculated affinity of 1 x 10(6) l x M-1. Substitution of Sephadex with carboxymethyl and benzylamide sulphonate groups which confers to the polymer the capacity to catalyse thrombin inactivation on its surface also suppressed the complement-activating capacity of Sephadex. Sephadex derivatives that lack complement-activating properties and adsorb anaphylatoxins may provide useful models for the design of cellulosic membranes and biomaterials with blood compatible properties.

Heparin prevents formation of the human C3 amplification convertase by inhibiting the binding site for B on C3b.

Fluid-phase heparin prevents generation of the C3 amplification convertase of human complement, C3b, Bb most likely by inhibiting the formation of the bimolecular complex between cell-bound C3b and B. The effect of heparin on the binding of B to C3b was examined using 125I-labelled B and C3b-bearing sheep erythrocytes (EsC3b). In the absence of heparin, B bound to EsC3b with an affinity of 0.5-1 X 10(6) M-1 in the presence of 5 mM Mg2+. Incremental amounts of heparin (100-700 micrograms/10(7) EsC3b) inhibited the binding of 125I-B to C3b in a dose-dependent manner. Scatchard analysis of the binding data in the presence of four inhibitory concns of heparin revealed that heparin did not affect the binding affinity of B for C3b but decreased the number of C3b sites recognized by B on the cells. No inhibition of binding occurred in the presence of totally (N- and O-) desulfated heparin which has no anticomplementary activity. These results demonstrate that heparin prevents generation of the C3 amplification convertase by binding to cell-bound C3b and masking the binding site for B on C3b.

Sulfonated dextran inhibits complement activation and complement-dependent cytotoxicity in an in vitro model of hyperacute xenograft rejection.

In the present study, we demonstrate that a substituted soluble dextran derivative bearing 73% carboxylic groups and 15% benzylamide sulfonate groups, termed CMDBS25, inhibits complement activation and complement-mediated damage in an in vitro model of xenogeneic rejection. Incubation of porcine aortic endothelial cells with normal human serum resulted in time-dependent complement consumption as assessed by C3a generation in the fluid phase and deposition of activated complement fragments C3, C5 and of C5b-9 on target cells. The presence of C5b-9 membrane attack complex was associated with 51Cr release from prelabelled endothelial cells. The addition of 5-25 mg of CMDBS25/ml under the experimental conditions used, inhibited complement activation and C3a generation in a dose-dependent fashion. CMDBS25 (25 mg/ml) totally suppressed iC3b, C5 and C5b-9 cytolytic complex deposition on cells and inhibits by 42% lysis of target endothelial cells. Native dextran had no effect. Our observations document the anti-complementary properties of sulfonated dextran derivatives and their potential as therapeutic agents for the prevention of complement-dependent hyperacute xenograft rejection.

Inhibition of complement activation by natural sulfated polysaccharides (fucans) from brown seaweed.

In the present study, we demonstrate that natural sulfated polysaccharides (fucans) isolated from brown seaweed are potent inhibitors of human complement activation. A fucan fraction of chromatographic molecular weight 22,600, termed BS8, was found to inhibit classical and alternative pathway activation in whole serum in a dose-dependent fashion. Fucan BS8 inhibited formation of the classical pathway C3 convertase by interfering with C1 activation or by inhibiting C4 cleavage and the interaction between C4b and C2. The fucan also inhibited formation/function of the alternative pathway C3 convertase by suppressing the binding of B to C3b and by interfering with the stabilizing function of Properdin. The inhibitory effect of fucans on formation of the C3 convertases was dependent on the molecular weight of the polysaccharide for compounds of chromatographic molecular weight below 16,600. Fucan had no effect on the function of the terminal complex. Since fucans were more efficient than heparin in inhibiting activation of the classical pathway in whole serum and exhibited a lesser specific anticoagulant activity on a molar basis, our results suggest that these natural sulfated polysaccharides have a potential for use as anti-complementary and anti-inflammatory agents.

Mouse monoclonal antibodies to the human C3b receptor.

Mouse monoclonal antibodies were raised against the human C3b receptor (CR1) molecule that had been purified from solubilized erythrocytes membranes. Four hybridomas were selected, cloned and expanded because their supernatants reacted strongly with insolubilized CR1 by ELISA and intensely stained B-dependent areas of the spleen and glomerular podocytes by indirect immunofluorescence. The four monoclonal antibodies, named J3D3, J8B10, J3B11 and J7C2, were IgG1 immunoglobulins. J3D3 immunoprecipitated two protein bands of apparent mol. wts 200,000 and 220,000 from 125I-surface-labeled human erythrocytes, which correspond to the two major allotypic forms of CR1. By indirect immunofluorescence, monoclonal antibodies stained polymorphonuclear leucocytes (PMN), most peripheral blood B-cells and a small subset of peripheral blood T-cells. J3D3 bound to CR1 on erythrocytes, PMN and lymphocytes with an affinity of 1-3 X 10(9) M-1 and recognized 170-1330 antigenic CR1 sites with an average of 740 sites/erythrocyte in 100 healthy individuals, approx. 50,000 sites/PMN and 15,000 sites/lymphocyte. There was a bimodal distribution of CR1 numbers on erythrocyte in the normal population. The four monoclonal antibodies similarly inhibited CR1-mediated decay of preformed cell-bound alternative- and classical-pathway C3 convertase sites. Two antibodies, J3D3 and J3B11, inhibited C3b-dependent rosette formation with lymphocytes, although much less efficiently than F(ab')2 polyclonal anti-CR1 antibody. Differences that were observed in the relative capacity of the antibodies to inhibit some of the functions of CR1 and in their ability to compete for binding of 125I-J3D3 to CR1 on erythrocytes, suggested that they are directed against different epitopes on CR1. Monoclonal antibodies provide useful means to assess and analyze the biological and immunoregulatory functions of the C3b receptor.

Genetic analysis of CR1 (the C3b complement receptor, CD35) expression on erythrocytes of HIV-infected individuals.

The number of C3b receptor (CR1) molecules on erythrocytes is genetically determined by two codominant autosomal alleles. The genetic polymorphism of CR1 expression correlates with a Hind III restriction fragment length polymorphism (RFLP) of the CR1 gene. The relative frequency of individuals homozygous for the allele coding for low CR1 numbers is approximately 5% of the normal population. CR1 numbers/erythrocytes are significantly decreased in symptomatic HIV-infected individuals. Decreased CR1 expression correlates with the severity of disease. The present study investigated the CR1 genomic Hind III RFLP-related polymorphism in 79 HIV-infected individuals and 84 healthy subjects. Allele frequencies were found to be similar in both populations. Thus, there is no susceptibility nor resistance to HIV-infected linked to the CR1 gene. Defective expression of CR1 in HIV-infected patients is acquired through central and/or peripheral mechanisms.