Linkage of Chido and HL-A

Early Components of the Complement Classical Activation Pathway in Human Systemic Autoimmune Diseases

The complement system consists of effector proteins, regulators, and receptors that participate in host defense against pathogens. Activation of the complement system, via the classical pathway (CP), has long been recognized in immune complex-mediated tissue injury, most notably systemic lupus erythematosus (SLE). Paradoxically, a complete deficiency of an early component of the CP, as evidenced by homozygous genetic deficiencies reported in human, are strongly associated with the risk of developing SLE or a lupus-like disease. Similarly, isotype deficiency attributable to a gene copy-number (GCN) variation and/or the presence of autoantibodies directed against a CP component or a regulatory protein that result in an acquired deficiency are relatively common in SLE patients. Applying accurate assay methodologies with rigorous data validations, low GCNs of total C4, and heterozygous and homozygous deficiencies of C4A have been shown as medium to large effect size risk factors, while high copy numbers of total C4 or C4A as prevalent protective factors, of European and East-Asian SLE. Here, we summarize the current knowledge related to genetic deficiency and insufficiency, and acquired protein deficiencies for C1q, C1r, C1s, C4A/C4B, and C2 in disease pathogenesis and prognosis of SLE, and, briefly, for other systemic autoimmune diseases. As the complement system is increasingly found to be associated with autoimmune diseases and immune-mediated diseases, it has become an attractive therapeutic target. We highlight the recent developments and offer a balanced perspective concerning future investigations and therapeutic applications with a focus on early components of the CP in human systemic autoimmune diseases.

Relationships between the bovine major histocompatibility system and commonly recognized erythrocyte and serum polymorphisms

Linkage at a recombination frequency of 0.10 or less between the bovine major histocompatibility system and the B, C and L red blood cell groups and the albumin, haemoglobin and transferrin loci was excluded by Morton's lod score method. The white blood cell antigen CA19, which is independent of the bovine major histocompatibility system, is the J blood group.

HLA and disease

Many human diseases are associated with HLA class I, class II and class III antigens. It appears that the class III antigen disease associations can be explained by a direct defect operating at the level of either the class III gene or its gene product. The mechanism underlying class I and class II antigen disease associations is at present unknown. In this review we have considered thirty diseases which have been ranked according to their relative risk as defined by the frequency of a given HLA antigen in patient and control populations. The chronic inflammatory disorder, ankylosing spondylitis and its association with HLA B27 has been used as a model to study the HLA linked diseases. We have suggested that the disease may be caused by the Gram-negative microorganism Klebsiella which has antigenic similarity to HLA B27. It is proposed that some antibodies made against Klebsiella bind to HLA B27, thereby acting as autoantibodies leading to the pathological sequelae of chronic inflammatory arthritis. This is the crosstolerance hypothesis or molecular mimicry model and it has been compared to the receptor model. It is further suggested that the crosstolerance hypothesis can be utilised as a general theory to explain the association of other diseases with the class I and class II antigens, and offer a possible explanation for the polymorphism of HLA.

The saga of cystatin C gene mutation causing amyloid angiopathy and brain hemorrhage--clinical genetics in Iceland

Firstly, we review investigations of hereditary cystatin C amyloid angiopathy, which is caused by a mutation in the cystatin C gene. Symptoms of brain haemorrhages, which lead to death in young adults, are the hallmark of this disorder. The mutation can now be detected by the RFLP method using Alu I restriction enzyme and cystatin C cDNA probe. Secondly, we give an overview of other clinical genetic studies in Iceland with emphasis on activities initiated or sponsored by the Genetical Committee of the University of Iceland. The list of references covers most publications on genetic studies of Icelanders.

High-titer, low-avidity (HTLA) antibodies and antigens: a review

Antibodies that react to HTLA characteristics cause difficulties in serologic testing because of the weak reactions they produce in the indirect antiglobulin test. Those specificities that are more frequently encountered (anti-Yka, -McCa, -Kna, -Ch) are directed toward antigens of high incidence in both the white and black populations. They have not been shown to cause significant destruction of transfused antigen-positive red cells. The antibodies create problems in serologic tests because the reactions they produce interfere with the identification of reactions due to other, clinically significant antibodies.

An immunoblotting technique for direct visualization of Chido and Rodgers reactivity on C4 variants after electrophoresis

An immunoblotting technique allows direct visualization of Chido and Rodgers antigenic determinants on intact C4 proteins. C4 molecules separated by electrophoresis are selectively transferred to nitrocellulose membranes saturated with goat antiserum to human C4. The membranes are then incubated in alloanti-Chido or anti-Rodgers followed by enzyme-conjugated goat antihuman IgG. Molecules with Chido or Rodgers reactivity are visualized by incubation with an indicator substrate for the bound enzyme.

Allo-anti-Chido in a Ch-positive patient

Allo-anti-Chido (Ch) was detected in a patient whose red cells typed as Ch+. The C4 allotype of the patient was A4,B2 which associates strongly with the Ch phenotype Ch:1,-2,3,4,-5,6. Anti-Ch2 + Ch5 were the Ch specificities identified. Absence of only Ch2 and Ch5 determinants on the C4B protein allowed this unique immune response to blood transfusion.

The molecular genetics of components of complement

Rapid progress has been made in establishing linkages and in chromosome allocation of the genes of some 9 complement components. In the MHC, C2, Factor B, and two C4 or C4 related genes have been placed in some detail in both man and mouse. The gene coding for the cytochrome P-450 21-hydroxylase has been shown to be duplicated and immediately 3' to the two C4 genes, though it appears to be functionally and structurally unrelated to the complement components. Thus six genes have been mapped to this region where particular haplotypes are associated with increased susceptibility to a number of diseases, some of which are autoimmune in character. The complete gene structure of Factor B has been solved in man and rapid progress is being made with the C2 and C4 genes. The structural basis of the polymorphisms of these genes is being established. In C4, the polymorphism is exceptionally complex with varying numbers of loci and probably more than 50 allotypes occurring in man. A structural basis has also been found for the big differences in the biological activity of some of the C4 allotypes in man. Apart from the genes in the MHC, linkage has been found between the genes coding for C4bp, CR1, and Factor H. Remarkably there are sequence homologies between these proteins and C2 and Factor B, probably related to the ability to bind to one or other of the structurally similar proteins C3b and C4b. The complete cDNA sequences of C3 and C4 in mouse and man have given much information on the many posttranslational modifications of these proteins. A partial structure has been obtained for the C3 gene and the homology shown between C3, C4, C5, alpha 2-macroglobulin, and pregnancy zone protein. Although the amount of detailed information in the molecular genetics of complement components is accumulating rapidly, there appears to be a reasonable prospect that linkages and homologies will classify the data into a comprehensible form.

Adverse transfusion reactions associated with a precipitating anti-C4 antibody of anti-Rodgers specificity

A patient suffering from chronic hepatitis exhibited severe transfusion reactions after administration of fresh frozen plasma and a plasma fraction: PPSB (prothrombin complex concentrate). 1 month before these reactions, she received fresh frozen plasma during plasma exchange therapy. The patient's serum obtained 1 week and 6 months after the second reaction gave a precipitation arc against PPSB preparations when examined by double-diffusion technique in agarose gel. An antibody of IgG class present in these sera reacted with a purified preparation of the fourth complement component (C4). This was demonstrated by various experiments (protein A radioimmunoassay and passive hemagglutination) using purified C4 as antigen. The antibody had a limited specificity and reacted only with C4 of Rodgers specificity. Phenotype determination of the patient's C4 group showed that she was Chido positive and Rodgers negative. Her HLA group was A1, Aw30; B8,-; DR3,-. The patient had neither detectable anti-IgA nor other anti-immunoglobulin antibodies. She had not received blood or plasma transfusion before her hepatitis. The coexistence of a precipitating anti-C4 antibody and adverse transfusion reactions to plasma fractions containing large amounts of C4 indicates that in the absence of antibodies of other specificities, this antibody can be considered as the cause of the transfusion reaction.

An international reference typing for Ch and Rg determinants on rare human C4 allotypes

Red cells, serum and plasma samples of 20 individuals, selected for their C4 allotypes, were distributed from Bonn to five laboratories, for investigation of their Chido (Ch) and Rodgers (Rg) determinants. One anti-Ch (M.H.) and one anti-Rg(Prest.) were distributed, but the individual laboratories also used their own reagents and their own typing methods. There was general agreement in interpretation of the majority of samples. Partial inhibition for Ch and Rg was detected. Two samples gave anomalous results; one sample with C4 A1,3 BQO, QO had Ch determinants on the red cells and in plasma (partial inhibition), and another sample with C4 A3,4 B5, QO apparently lacked Ch determinants on the red cells and in plasma. Heterogeneity of anti-Ch and anti-Rg was suggested in testing red cells, perhaps, reflecting a quantitative effect. This heterogeneity was confirmed by inhibition studies. The capacity of some reagents to detect partial inhibition probably reflects qualitative as well as quantitative differences.

Genetics of human C4 polymorphism: detection and segregation of rare and duplicated haplotypes

Applying a combined technology for the detection of allotypic variation of the fourth component of human complement (C4), including immunofixation with anti-C4 and C4-dependent lysis after agarose electrophoresis, sodium dodecyl sulfate-polyacrylamide gel electrophoresis of C4 to separate the C4A and B alpha-chains, and the determination of Rodgers (Rg) and Chido (Ch) determinants of C4 in serum and at the blotted C4 alpha-chains, we detected rare human C4 allotypes and studied the genetic linkage. Partial inhibitors (p.i.) of anti-Rg and anti-Ch sera were found; the C4A51 allotype characterized as Rg p.i. and the C4A1 and C4B51 allotypes as Ch p.i. were genetically inherited. The C4A1 allotype has a unique Rg- Ch+ C4A alpha-chain. Duplicated C4A loci, A*3, A*2, and A*5, A*2 were both associated with a C4BQO and the HLA haplotype A3-Cw4-Bw35-DR1. These additions to the already known extensive C4 polymorphism may help to sort out their significance for the biological functions of human C4.

The significance of complement in immunohematology

In vitro detection of red cell-bound complement can be important in the differential diagnosis of autoimmune and drug-induced immune hemolytic anemias; it can also be a sensitive test for the detection of complement-binding alloantibodies, e.g., in compatibility testing. Red cell-bound complement can be detected by the antiglobulin test if suitable antiglobulin sera (AGS) are utilized. In 1971, the Federal Standards for AGS were criticized because so-called broad spectrum AGS used routinely in blood banks were shown to often be deficient in anticomplement reactivity. In the new few years commercial regents changed with regard to the quantity and specificity of their anticomplement components. A great deal of controversy developed as to the true importance of detecting red cell-bound complement, the particular fragments of complement that should be detected, and the causes of nonspecific reactions that seemed to be occurring, especially with the increasing usage of new techniques utilizing low ionic strength media. When monospecific anti-IgG and anti-C3 became available commercially, the controversy regarding diagnostic testing was resolved as direct antiglobulin testing could be performed with these reagents rather than the broad spectrum reagents. Two main questions remained: how rare are alloantibodies that are only detectable by the anticomplement component of AGS? How clinically significant are such antibodies? The results of our 3-year study indicated that such antibodies (usually anti-Kidd) occurred with a incidence of 1/8000 sera tested. Some of these antibodies seemed capable of shortening the life span of transfused red cells, as determined by 51Cr survival studies; some showed negligible cell destruction. Severe transfusion reactions due to such antibodies would seem unlikely. Individual laboratories will have to balance the risk of missing some complement-dependent antibodies of possible clinical significance with the increased nonspecificity encountered in their own laboratory with AGS containing anticomplement.

The MHC in human bone marrow allotransplantation

In this chapter, we have considered the theoretical and practical background of bone marrow transplantation. The immune response and its regulation by genes within the major histocompatibility complex, particularly of the I region of the mouse and of the HLA-D/DR region in man, is of central importance in both graft acceptance (rejection) and graft-versus-host disease. Methods which are available for typing alleles at the HLA-A, -C, -B, -DR and complotype (BF, C2, C4A, C4B) loci, have been considered in detail. The extent to which recombination affects specific alleles on haplotypes within families is discussed, as is the occurrence of linkage disequilibrium and extended haplotypes in populations of unrelated individuals. Because the HLA-DR and complotype region in man is thought to be critical for the success of bone marrow transplantation, methods for typing of HLA-D by both the HTC and PLT approaches have been examined. Although HLA-D/DR assignments are easily made in normal subjects, they are ambiguous in about 50 per cent of candidates for bone marrow transplantation, including, particularly, patients with aplastic anaemia, leukaemia, and severe combined immunodeficiency. In this setting, it is particularly important to obtain additional information by modification of HLA-D typing procedures and through complotype and GLO allele determinations in all family members. Finally, we can hope that there will be an increased possibility of using non-family donors through methods for removing cytotoxic T cells from donor marrow and through the identification, in the general population, of individuals who are genotypically similar or identical to the recipient. In this regard, the recognition that some 30 per cent of chromosome 6 in caucasians (50 per cent of individuals) bear extended haplotypes, which include a relatively fixed set of alleles particularly in the HLA-B, -DR, complotype and GLO regions, offers considerable promise.

A molecular basis for the two locus model of human complement component C4

The major histocompatibility complex(MHC)-linked fourth component of complement (C4) shows a high degree of polymorphism in several animal species. In man C4 polymorphism was detected by distinct charge differences of the variants. O'Neill et al. showed that this C4 polymorphism was controlled by two closely linked genetic loci, F (C4A) and S (C4B) and these results were extended by Awdeh et al. with an improved typing method. Biochemical analysis of human C4 has revealed that it consists of three polypeptide chains, alpha, beta and gamma. In all reports so far on the molecular analysis of human C4, no molecular weight differences between the A and B locus-encoded molecules have been noticed. Here we demonstrate that the C4A and C4B locus-encoded alpha-chains have a molecular weight (MW) of 96,000 and 94,000, respectively, presenting for the first time a molecular basis for the difference between all C4A and C4B variants tested. Even rare variants that are difficult to allocate to the A or B locus on the basis of charge differences could be identified as C4A or C4B variants in this way, thereby providing new insights into the relationships between the C4A and C4B loci.

BF types and the mode of inheritance of insulin-dependent diabetes mellitus (IDDM)

Insulin-dependent diabetes mellitus (IDDM) has been found to be highly associated with a rare allele of the complement protein, properdin factor B (BF). Assuming that there is a susceptibility gene for IDDM tightly linked to the genetic locus for BF and the major histocompatibility complex (MHC), the distribution of BF types in more than 1100 North American IDDM patients strongly argues for the rejection of dominant, epistatic, and overdominant modes of inheritance. Other evidence suggesting complex modes of inheritance for IDDM is reviewed and it is concluded that our observations and published data are consistent with the idea of susceptibility to IDDM being inherited as a simple autosomal recessive trait. C4 and C2 types, also linked to BF and the MHC, were investigated too. C4 Fs0 was found to be increased in association with BF F1, while C4 f0S and C2 b were each found to occur twice as frequently as in a control population and will be of value in defining haplotypes associated with susceptibility to IDDM.

The location of C2, C4, and BF relative to HLA-B and HLA-D

The loci for HLA-A,B,C,D, and DR are known to be closely linked to the structural loci for the complement components C2, BF, and the duplicated loci for C4, C4A and C4B. Conflicting evidence has been presented for the order of these genes. However, new techniques have made possible identification of markers in the HLA-D and C4 region for nearly all identified haplotypes. In our population we have confirmed five HLA-B-D crossovers and in each case informative allotypes of C2, BF, or C4A and C4B segregated with HLA-D or DR suggesting that the loci for these proteins lie close to HLA-D and DR. These findings may be of importance for resolving problems encountered in the assignment of HLA-D alleles.

Complement-human histocompatibility antigen haplotypes in C2 deficiency

C4 allotyping 13 homozygous C2-deficient individuals demonstrated 23 of 25 haplotypes to be of the relatively rare type C4A4 B2. This is of the same magnitude as the association of C2Q0 with HLA-DW2/DR2.

On the significance of C2, C4, and factor B polymorphisms in disease

In this review article, recent evidence is presented that some diseases like insulin-dependent diabetes mellitus, multiple sclerosis, and idiopathic membranous nephropathy, which are primarily associated with HLA-D,DR, are also related to the rare C2, C4, and Factor B alleles. Circumstantial evidence is available that at least some of these rare variants may be functionally deficient. Based on the concept of functionally interacting gene clusters, mutant complement genes may lead to impaired effector mechanisms in virus neutralization or lysis of virus-infected cells. Other mechanisms such as alteration of vascular permeability may be involved in the development of proliferative retinopathy and familial hypertension. In lepromatous lepra, an impaired cell-mediated lysis of M. leprae may be related to the hemolytically inactive C4F1 allelic product.

Murine antigen H-2.7: localization of its antigenic determinant to the Ss (C4) molecule

Murine blood group antigen H-2.7 is encoded by a locus mapping in the vicinity of the S locus which codes for the Ss antigen carried by the fourth component of the complement pathway (C4). Normal mouse serum of H-2.7-positive strains contains a substance which inhibits anti-H-2.7 hemagglutination. This substance cannot be removed by passage of the serum through an anti-Ss immunoabsorbent column indicating that the Ss and H-2.7 antigens are present on separate molecules or molecular fragments in the serum. In contrast, fresh plasma either does not contain the H-2.7-bearing substance at all or it contains it at a far lower concentration than normal serum, although it has a normal level of the Ss-antigen-bearing substance. However, the H-2.7-positive substance appears when the plasma is allowed to stand for several hours, or when it is dialyzed and treated subsequently in a manner favoring spontaneous degradation of complement components. Removal of the Ss substance from the fresh plasma prevents the appearance of the H-2.7 antigen at any time thereafter. These findings indicate that the Ss and H-2.7 antigens are carried by the same molecule or molecular complex. The intact molecule expresses only the Ss antigen; the H-2.7 antigen is either hidden or masked so that it is inaccessible or poorly accessible to H-2.7 antibodies. Degradation of these molecules results in the generation of two fragments, a large fragment carrying the Ss antigen and a smaller H-2.7-positive fragment. The data are consistent with the interpretation that the H-2.7 antigen is encoded by the S locus, and that it is carried by that portion of the C4 molecule split off during complement activation.

Association between the electrophoretically-determined C4M haplotype product and partial inhibition of anti-Cha

C4-coated Ch(a+) red blood cells (RBC) were used as indicator cells in a serum inhibition reaction of anti-Ch(a), for the determination of the Ch group of serum. This serological study, combined with electrophoretic studies of C4 in a family material, showed that the C4M haplotype product was associated with partial inhibition of anti-Ch(a).

Different HLA antigen associations for the functionally active and inactive products of the complement C4F1 allele

The genetic polymorphism of the fourth component of human complement, C4, was studied in 945 unrelated Caucasian individuals. A third allele of the C4F (Rodgers) locus, termed C4F1 was demonstrated. This allele is characterized using immunofixation electrophoresis, by the presence of an additional fast-moving anodal band of C4 which distinguishes it clearly from the common C4F variant. The allelic frequencies fit the Hardy-Weinberg equilibrium assuming three alleles at the C4F locus: C4F, C4Fo, and C4F1. The functional activity of the C4F variants was investigated using a specific hemolytic overlay technique for C4. It was found that in almost all individuals (75 out of 78), the C4F1 allele codes for a functionally inactive C4 product only when it occurs on an HLA-B17 positive haplotype but that the same allele codes for a functionally active fast variant of C4 when it occurs on an HLS-B37 positive haplotype (18 out of 18). Very strong genetic linkage disequilibrium was observed for the C4F1 allele with HLA-B17 and B37. The active and inactive C4F1 variant also has marked nonrandom gametic association to different alleles of the Bf locus and to HLA-C locus determinants. No further variants of the C4S (Chido) locus have been identified so far. Rodgers (Rg) typing by the plasma inhibition test of anti-Rg antiserum has shown that plasma from individuals homozygous for the C4F1 allele is only able to partially inhibit anti-Rg whereas all C4F positive individuals totally inhibited the reaction.

Inherited structural polymorphism of the fourth component of human complement

Human fourth component of complement (C4) was found to be highly polymorphic by agarose gel electrophoresis of neuraminidase-treated plasma. The system allows clear-cut separation of the products of the two C4 genetic loci, C4A (acidic or Rodgers) and C4B (basic or Chido). There are at least six structural variants and a deletion allele at the C4A locus and two structural variants and a deletion allele at the C4B locus. Close linkage with no crossovers was found between the two C4 loci, allowing the definition of C4AB haplotypes, and between C4 haplotypes and the C2 and BF loci of the human histocompatibility complex. Nine C4 haplotypes, each with a frequency of 0.005 or more in Caucasians, were found. These studies provide direct evidence for two distinct but closely linked genetic loci for human C4 in the major histocompatibility complex on the short arm of chromosome 6.

Strong linkage disequilibrium between HLA-Dw2 and and BfS in multiple sclerosis and in the normal population

An increased frequency of the S allele of Properdin factor B (BfS) was found amongst 162 patients with multiple sclerosis (MS) compared with 470 normal controls. This increase was shown to be due to a strong linkage disequilibrium (LD) between BfS and HLA-Dw2 in 77 patients typed for both systems (delta = 3.84%, P = .0002). The same LD was demonstrated amongst 100 normal controls (delta = 2.24%, P = .0049) and 31 patients with idiopathic demyelination of the peripheral nervous system (IDPN). A total of 70 haplotypes with HLA-Dw2 were encountered (40 MS, seven IDPN and 23 normal controls) and all contained BfS. In the MS patient group, a much weaker association was noted between BfS and HLA-B7 suggesting either that the Bf locus is musch closer to the HLA-D than the HLA-B locus or (and) that HLA-D and Bf products selectively interact (perhaps on the surface of B lymphocytes) with evolutionary advantage or disadvantage resulting from certain allelic combinations. Strong associations between BfS1 and HLA-Bw21 (P = .0000) and BfF1 and HLA-B18 (P = .0001), both previously reported, were confirmed in the current study. No increase in the frequency of a glyoxalase (GLO) allele was found amongst the MS patients and no LD was encountered between HLA-Dw2 and a GLO allele. The possibility that the HLA-Dw2, BfS disequilibrium has resulted from a selective advantage conferred on the general community but at the expense of increasing susceptibility to MS should be considered.

Association between HLA and red cell antigens. V. A further study of the nature and behaviour of the HLA antigens on red blood cells and their corresponding haemagglutinins

The variation in the reactivity of red blood cells (RBC) with HLA haemagglutinins was studied, and the influence of some variable factors evaluated. A comparison of the HLA reactivity of RBC with automated and manual methods, showed the superiority of the Auto-Analyzer technique. The similarity in the nature and behaviour of HLA RBC antigens and the related Chido and Rg antigens is discussed. Inhibition/adsorption experiments were performed, and the results did not support the theory that HLA antigens on RBC originate from serum-HLA-active substance. The strength of the HLA reactivity of RBC from a donor was shown to vary from time to time without evidence of clinical disease.

The HLA linkage group and disease susceptibility

The HLA linkage group, located on chromosome 6, is composed of serologically defined (SD-) loci (HLA-A, -B and -C) and of a MLC (= mixed lymphocyte culture-) or lymphocyte defined (LD-) locus (HLA-D). Different alleles of these loci are linked together as well as with loci for the synthesis of some complement components and the properdin factor B (= Bf-system) by strong positive linkage disequilibria (gametic association). The indication of a HLA linked genetic control of immunoresponsiveness makes the HLA system one of the biologically most important immunogenetic systems in man. The associations, found between single HLA determinants and diseases, can be explained in different ways, but may contribute to a better understanding of the etiopathogenesis of diseases and of the biological role of the HLA linkage group.

Linkage relationships of the loci of the major histocompatibility complex in families with a recombination in the HLA region

A number of families with an established recombination in the major histocompatibility complex has been investigated for markers known to be coded by genes of this linkage group. The results provide further data on the relative position of the loci for HLA-A, HLA-B, HLA-C, HLA-D, Bf, Chido, Rodgers and PGM3 on chromosome 6. A positive lodscore for linkage between HLA and blood group P was found; lodscores between HLA and nineteen other markers were negative.

A new antibody specificity, anti-Rga, reacting with a red cell and serum antigen

A new antibody specificity, anti-Rga, which detects an inherited antigen on red cells and in serum, reacts with 97% of individuals in the British population.

The HL-A type of Rg(a-) individuals

The investigation of 2 examples of anti-Rga led to the observation that the phenotype HL-A 1,8 occurs very frequently among Rg(a-) individuals.