Hereditary deficiency of the second component of complement (C'2) in man

Human inborn errors of immunity to infection affecting cells other than leukocytes: from the immune system to the whole organism

Studies of vertebrate immunity have traditionally focused on professional cells, including circulating and tissue-resident leukocytes. Evidence that non-professional cells are also intrinsically essential (i.e. not via their effect on leukocytes) for protective immunity in natural conditions of infection has emerged from three lines of research in human genetics. First, studies of Mendelian resistance to infection have revealed an essential role of DARC-expressing erythrocytes in protection against Plasmodium vivax infection, and an essential role of FUT2-expressing intestinal epithelial cells for protection against norovirus and rotavirus infections. Second, studies of inborn errors of non-hematopoietic cell-extrinsic immunity have shown that APOL1 and complement cascade components secreted by hepatocytes are essential for protective immunity to trypanosome and pyogenic bacteria, respectively. Third, studies of inborn errors of non-hematopoietic cell-intrinsic immunity have suggested that keratinocytes, pulmonary epithelial cells, and cortical neurons are essential for tissue-specific protective immunity to human papillomaviruses, influenza virus, and herpes simplex virus, respectively. Various other types of genetic resistance or predisposition to infection in human populations are not readily explained by inborn variants of genes operating in leukocytes and may, therefore, involve defects in other cells. The probing of this unchartered territory by human genetics is reshaping immunology, by scaling immunity to infection up from the immune system to the whole organism.

Quantification of human complement C2 protein using an automated turbidimetric immunoassay

BACKGROUND

The measurement of complement components is clinically useful where a deficiency is suspected, or where excessive activation and consumption are present in disease. C2 deficiency carries an increased risk of developing systemic lupus erythematosus, recurrent infections and atherosclerosis. In this study, we have evaluated The Binding Site's Human Complement C2 SPAPLUS® assay.

METHODS

Linearity was tested using 13 sample dilutions covering the standard measuring range. Within- and between-assay variabilities were calculated using five samples with different C2 concentrations. The correlation between C2 concentrations in EDTA-plasma and serum was assessed, as was the correlation between C2 measurements by the automated assay and radial immunodiffusion. C2 concentrations were compared with CH50 activity, and quantified in individuals with homozygous or heterozygous C2 deficiency, acquired angioedema and patients with chronic inflammatory conditions.

RESULTS

The assay was linear across the measuring range (3.8-42.3 mg/L). Intra- and interassay variability were 2.3%-3.8% and 0%-3.3%, respectively. Comparison between C2 measurements in EDTA-plasma and serum provided a strong correlation (p<0.0001, R2=0.82, slope 0.92), as did the correlation between the automated and radial immunodiffusion methods (p<0.0001, R2=0.89, slope 1.07). A positive correlation between C2 concentration and CH50 activity was demonstrated (p<0.0001, R2=0.48). Significant differences were observed between the median C2 concentrations obtained in healthy controls and the patient clinical samples, with homozygous C2-deficient patients giving below detectable results.

CONCLUSIONS

This C2 SPAPLUS® assay allows the automated, rapid and precice quantification of complement C2 protein and could therefore be considered as a replacement for older, more time-consuming methods.

Rare autoimmune disorders with Mendelian inheritance

Autoimmune diseases represent a heterogeneous group of common disorders defined by complex trait genetics and environmental effects. The genetic variants usually align in immune and metabolic pathways that affect cell survival or apoptosis and modulate leukocyte function. Nevertheless, the exact triggers of disease development remain poorly understood and the current therapeutic interventions only modify the disease course. Both the prevention and the cure of autoimmune disorders are beyond our present medical capabilities. In contrast, a growing number of single gene autoimmune disorders have also been identified and characterized in the last few decades. Mutations and other gene alterations exert significant effects in these conditions, and often affect genes involved in central or peripheral immunologic tolerance induction. Even though a single genetic abnormality may be the disease trigger, it usually upsets a number of interactions among immune cells, and the biological developments of these monogenic disorders are also complex. Nevertheless, identification of the triggering molecular abnormalities greatly contributes to our understanding of the pathogenesis of autoimmunity and facilitates the development of newer and more effective treatment strategies.

Complement deficiencies in humans and animals: links to autoimmunity

Complement is involved in the pathogenesis of systemic lupus erythematosus (SLE) in multiple ways and may act as both friend and foe. Inherited homozygous deficiency of one of the earliest components of the classical pathway is strongly associated with susceptibility to the development of SLE. However, complement is also implicated in the effector inflammatory phase of the autoimmune response that characterizes the disease. A further paradox in the links between complement and SLE is the observation that autoantibodies to some complement proteins, especially to C1q, develop as part of the autoantibody response. In this chapter, the role of the complement system in SLE is reviewed and hypotheses advanced to explain the complex relationships between complement and lupus.

A history of pediatric immunology

Immunology has played a prominent role in the history of medicine. Pediatric immunologists have focused on immune aberrations in pediatric disorders, particularly those involving host defense mechanisms. These efforts have paid rich dividends in terms of fundamental knowledge of the immune system and major therapeutic advances, including 1) i.v. immunoglobulin therapy, 2) hematopoietic stem cell transplantation, and 3) gene therapy. Pediatric immunology as an organized discipline emerged in the early 1950s, when pediatricians and their basic scientist colleagues began to focus on clinical and basic research related to immunodeficiency. Since then, key organizations and infrastructure have been developed to support this research and the clinical care of immunodeficient patients. We review here the evolution of contemporary pediatric immunology, particularly in North America, from its roots in 19th-century Europe to its current expression as one of the fundamental scientific and clinical disciplines of pediatrics.

Immunoglobulin deficiencies and susceptibility to infection among homozygotes and heterozygotes for C2 deficiency

About 25% of C2-deficient homozygotes have increased susceptibility to severe bacterial infections. C2-deficient homozygotes had significantly lower serum levels of IgG2, IgG4, IgD, and Factor B, significantly higher levels of IgA and IgG3 and levels of IgG1 and IgM similar to controls. Type 1 (28 bp deletion in C2 exon 6 on the [HLA-B18, S042, DR2] haplotype or its fragments) and type II (non-type I) C2-deficient patients with increased susceptibility to bacterial infection had significantly lower mean levels of IgG4 (p < 0.04) and IgA (p < 0.01) than those without infections (who had a higher than normal mean IgA level) but similar mean levels of other immunoglobulins and Factor B. Of 13 C2-deficient homozygotes with infections, 85% had IgG4 deficiency, compared with 64% of 25 without infections. IgD deficiency was equally extraordinarily common among infection-prone (50%) and noninfection-prone (70%) homozygous type I C2-deficient patients. IgD deficiency was also common (35%) among 31 type I C2-deficient heterozygotes (with normal or type II haplotypes), but was not found in 5 type II C2-deficient heterozygotes or 1 homozygote. Thus, C2 deficiency itself is associated with many abnormalities in serum immunoglobulin levels, some of which, such as in IgG4 and IgA, may contribute to increased susceptibility to infection. In contrast, IgD deficiency appears not to contribute to increased infections and appears to be a dominant trait determined by a gene or genes on the extended major histocompatibility complex (MHC) haplotype [HLA-B 18, S042, DR2] (but probably not on type II C2-deficient haplotypes) similar to those previously identified on [HLA-B8, SC01, DR3] and [HLA-B18, F1C30, DR3].

A restriction fragment of the C2 gene is a unique marker for C2 deficiency and the uncommon C2 allele C2*B (a marker for type 1 diabetes)

There are three common C2 protein alleles in caucasians, C2*C, C2*B, and C2*Q0, with allele frequencies of 0.96, 0.03, and 0.01, as well as Sst I RFLP variants of 2.75, 2.7, 2.65, 2.55, and 2.4 kb, with frequencies of 0.017, 0.533, 0.358, 0.017, and 0.075. Thus, C2*C is informatively split by the RFLP. Of 94 nonrandomly ascertained caucasian complotypes, 77 contained C2*C, four contained C2*Q0, and 13 had C2*B. None of the C2*C-containing complotypes carried the 2.75 kb Sst I fragment and all of the complotypes with C2*B or C2*Q0 carried it. All of the C2*Q0 alleles were associated with C4A*4, C4B*2 in the complotype S042 as previously reported. C2*B was usually (9/13) in the complotype SB42, occasionally (1/13 each) in SB45, SB41, SB(4,3)0, and SB31. Thus, the association of the C2 2.75-kb fragment was with C2*B and C2*Q0, not with C4A*4, C4B*2, or even C4A*4 alone. The complotype SC42 was associated with the 2.65-kb Sst I fragment in four of five instances and in a single example with the 2.7-kb fragment. C2*B and C2*Q0 possibly had a common evolutionary ancestor complotype which carried the 2.75-kb Sst I fragment, and BF*S, C4A*4, and C4B*2. C2*B (particularly as the haplotype HLA-Bw62, SB42, DR4) is associated with type 1 diabetes but C2*Q0 is protective.

Defective activation of the alternative pathway of complement in patients with homozygous C2 deficiency: studies in two unrelated families

Selective homozygous deficiency of the second component of complement, C2, with increased susceptibility to infection was detected in five children of two unrelated families. Because the haemolytic activity of the alternative complement pathway (AP) was in the low normal range, we evaluated the AP activation pattern. Serum levels of factor B measured immunochemically and the haemolytic function of factor B were low normal. Levels of C3d were not increased. Activation products of factor B were undetectable indicating the absence of in vivo activation of AP. Activation of C3 in vitro by activators of the AP (zymosan A and lipopolysaccharide) was profoundly deficient in homozygous C2 deficiency while heterozygous carriers exhibited intermediate values. There was no correlation between serum levels of factor B and in vitro C3 activation. We conclude that defective AP activation may contribute to increased susceptibility to bacterial infections in some patients with homozygous C2 deficiency.

Inherited deficiencies of complement components in man

Isolated inherited deficiency states of almost every complement protein have been recognized. Almost all are autosomal recessive traits. Deficiency of the early-acting components C1, C4 and C2 is associated with increased risk of immune complex disease, particularly systemic lupus erythematosus. Patients with deficiency of C3, factor I or factor H have increased susceptibility to infection by pyogenic bacteria, whereas those with deficiencies of properdin, C5, C6, C7 or C8 are prone to systemic neisserial infection. Inherited deficiency of C1 inhibitor is transmitted as an autosomal dominant trait, is genetically heterogeneous, and is associated with attacks of angioedema and consumption of C4 and C2. There is evidence that a plasmin-modified fragment of C2 is responsible for the angioedema in this disorder. Administration of androgens tends to correct the biochemical abnormalities of hereditary angioedema and to prevent attacks.

Inherited disorders of complement

Isolated complement component deficiencies are uncommon. Deficiencies of all eleven components and two inhibitors of the classical pathway have been described. Complete absence of the components of the alternative pathway has not been described. The consequences of a single defect in complement are often predictable from an understanding of the biologic activities associated with activation of the complement system. Deficiency of C1 esterase inhibitor gives rise to the disease, hereditary angioedema; deficiency of the early components of the classical pathway are associated with lupus erythematosus; C3 and C3 inactivator deficiencies with pyogenic infections; C5 dysfunction with Leiner's disease; deficiencies of the terminal components with recurrent Neisseria bacteremia; and C9 deficiency with normal health. The complement system and its associated biologic activities are reviewed. The present knowledge of the inherited complement deficiencies and associated diseases, with particular emphasis on the dermatologic manifestations, genetics, and diagnosis, is summarized.

Heat production in different populations of human blood cells exposed to immune complexes in vitro: the importance of the Fc parts of immunoglobulins and the influence of active complement

By use of a batch microcalorimeter of the thermopile type, heat production was measured in isolated populations of human peripheral blood cells exposed to defined immune complexes formed in vitro. It was found that most of the heat production recorded in whole blood after admixture of immune complexes occurs in the granulocytes. Under these conditions small but constantly higher activation values were found in the absence of active complement. It was shown that complexes consisting of antigen and F(ab)2 fragments prepared from the specific antibodies were able to initiate heat production in the cells only in the presence of active complement. These experiments indicate that immune complexes are able to induce increased heat production in the cells either by binding to Fc receptors or by activation of complement through the alternative pathway and subsequent binding of the generated C3b to C3b receptors on the heat-producing cells.

Deficiency of the second complement component association with the HLA haplotype A10, B18 in a normal population

Serum C2 activity was measured in 135 individuals drawn from a panel of 418 tissue-typed blood donors. The study group included all donors with HLA antigens A10 and B18. Heterozygote C2 deficiency (C2Dhet) was defined by reference to the range of C2 activity in previously studied obligate heterozygotes. Five donors were C2Dhet. Family studies confirmed that C2Dhet was associated in all instance with an A10, B18 haplotype. The minimum frequency for C2Dhet was 1.2% in the panel of 418 donors and 62.5% in those donors with an A10, B18 haplotype.

Recurrent bacterial meningitis in patients with genetic defects of terminal complement components

Isolated genetic deficiencies of complement components in man are rare. We describe two kindreds with inborn deficiencies of either C5 or C6 in which both propositi presented with recurrent bacterial meningitis. Neisseria meningitidis was isolated from the cerebrospinal fluid of the C5-deficient patient and bactericidal activity against his autologous meningococcus was absent from whole fresh patients' serum despite a rising titre of complement-fixing antibody. The stimulated movement of normal leucocytes was impaired in the presence of C5-deficient serum but not in the presence of C6-deficient serum; neither deficiency reduced significantly the complement-dependent opsonization of Saccharomyces cerevisiae. HLA typing and complement component phenotyping showed no segregation with the complement defect in either the C5- or C6-deficient families. Normal individuals and apparent heterozygotes with approximately half the normal levels of the relevant component were found in both families, in keeping with an autosomal codominant inheritance of the defects.

Studies on the C2-deficiency gene in man

A one-step haemolytic assay using cellular intermediates was used to determine C2 levels in 50 HLA-A25 and B18 positive blood donors and four families suspected to have the C2-deficiency gene. The method clearly discriminated between homozygous normals and heterozygous deficient individuals, and it was found that approx. 50% of individuals with the haplotype HLA-A25, B18 had low levels of functional C2. In the four families studied, the close linkage of the C2-deficiency gene and the haplotype HLA-A25, B18 was confirmed. Furthermore, the C2-deficiency gene was shown to be a silent or null allele at the structural locus.

Hereditary complement (C2) deficiency with discoid lupus erythematosus and idiopathic atrophoderma

A family with hereditary deficiency of the second component of complement was studied. Three siblings were homozygous for C2 deficiency and two of them had associated skin diseases. One sister presented with idiopathic atrophoderma and the other had clinical and pathological manifestations of discoid lupus erythematosus. This is the first description of an association between idiopathic atrophoderma and C2 deficient state.

Polymorphism of the second component of human complement (C2). Observation of the rare phenotype (C2 2 (= C2 B) and data on the localization of the C2 locus in the HLA region

The polymorphism of the second component of human complement was studied by means of isoelectric focusing in polyacrylamide gels with subsequent complement-dependent lysis of sensitized sheep erythrocytes in an agarose overlay containing C2-deficient or normal human serum. In a material of 289 unrelated individuals the following gene frequencies were observed: C21=0.965 and C22=0.035. The rare phenotype C2 2 (=C2 B) could be seen once in a child of a C2 1--2 heterozygous mother. The investigation of the C2/HLA relationship revealed a very close linkage: Among 62 informative meiotic divisions one recombination between HLA-B and C2 was found (i.e. 1.61%); in addition, C2(2) was significantly associated with HLA-B15 and -Cw3. In a family with an HLA-B/D(DR) crossover C2 segregated together with HLA-D(DR). This supports the assumption of a C2 structural locus outside HLA-B, probably near HLA-D(DR).

Association of low C2 and C4 serum levels with the HLA-DW2 allele in healthy individuals

HLA typed unrelated healthy individuals (HLA-DW2 positive n = 64, and HLA-DW2 negative n = 72) were investigated for their C2 functional activity and C4 serum protein levels. For the C2 and C4 levels a bimodal distribution was found in HLA-DW2 positive and HLA-DW2 negative individuals. HLA-DW2 positive persons had a significantly higher incidence of low C2 and C4 serum levels. Our data support the concept that genes governing C2 as well as C4 serum levels are in linkage disequilibrium with the HLA-DW2 allele of the major histocompatibility complex.

Genetics of complement deficiencies associated with lupus-like syndromes

There appears to be an association between deficiencies of a number of complement components, particularly of the second component (C2), and rheumatic diseases, especially lupus. The meaning of this association is not clear, but the linkage of deficiency of C2 with HLA, especially HLA-A10, B18, Dw2, as well as with BfS, suggests a possible linkage to immune response genes.

[Demonstration of total complement in normal cerebrospinal fluid]

Até o presente momento, todos os autores afirmam que o líquido cefalorraqueano (LCR) normal do homem não apresenta atividade hemolítica do complemento total. Alguns pesquisadores verificaram, entretanto, a presença de todos os quatro componentes em muitas amostras de LCR normal sem conseguir, porém, demonstrar a atividade hemolítica do complemento total. Este fato parecia indicar que o LCR normal era desprovido da atividade hemolítica do complemento total provavelmente por motivo da concentração insuficiente de suas proteínas. Para investigar esta hipótese foi feita uma prova preliminar, concentrando 10 amostras de LCR normal, dividindo-se o concentrado em duas partes, uma das quais foi inativada à temperatura de 56°C, durante 20 minutos. Esta prova revelou hemólise das hemácias sensibilizadas somente em relação com o LCR concentrado ativo. Em prosseguimento foram feitas pesquisas em 108 amostras de LCR normal obtidas por punção cisternal, selecionadas de pacientes sem doença de ordem geral, porém com perturbações neurológicas ou psíquicas que, em geral, não costumam determinar alterações do LCR. As amostras de LCR foram concentradas vinte vezes o seu volume, pelo método da diálise sob pressão negativa em camisa de colódio, segundo o processo de Mies. Esta pesquisa proporcionou resultados que permitiram concluir que o líquido cefalorraqueano normal concentrado apresenta atividade hemolítica do complemento total em 98% dos casos. O título do complemento total variou de 0 a 23 unidades de hemólise 50% em 1 ml de líquido concentrado.

Hereditary C2 deficiency and systemic lupus erythematosus associated with severe glomerulonephritis

Although an unusually high incidence of immunological diseases has been described in patients with hereditary C2 deficiency, the severity of these illnesses has been relatively mild, suggesting that blocking complement activation beyond C4 may protect against significant complement-mediated inflammation. This report describes studies in a C2-deficient patient with severe systemic lupus erythematosus (SLE) and diffuse proliferative glomerulonephritis. An immunopathological study of the kidney revealed the deposition of properdin, properdin factor B, C3 and C5 in a pattern similar to immunoglobulin G deposits. Serum properdin and properdin factor B levels were low at various times during the patient's course. In vitro complement fixation studies showed C3 fixation by glomerular deposits could occur via the alternative pathway. Studies of the immune deposits in the patients' skin revealed similar results. These studies suggest that inflammation may be effectively mediated via the alternative complement pathway in the C2 deficiency-lupus syndrome.

Severe systemic lupus erythematosus with nephritis in a boy with deficiency of the fourth component of complement

A young boy with severe systemic lupus erythematosus was found to be totally deficient in the fourth component of complement. Family studies were consistent with an autosomal recessive mode of transmission and with linkage of the gene(s) determining C4 deficiency to the major histocompatibility complex; no disease states were associated with heterozygosity. This patient has had severe multisystem disease and immune complex glomerulonephritis presumably the alternative pathway of complement was utilized in the pathogenesis of his nephritis.

Hypocomplementaemic and normocomplementaemic multiple sclerosis. Genetic determinism and association with specific HLA determinants (B18 and B7)

Seventy-five patients with multiple sclerosis (MS) were treated for complement components C3, after factor B, C4, and tested for HLA-A and B-determinants. Levels of IgG, IgA, IgD, IgE and titres of measles antibodies were also determined. Correlations between these immunological values and HLA determinants could be obtained in siblings, parents and/or children of the patients in 13 families. B18 frequency is strongly associated with the hypocomplementaemic group (x2 = 8.9). An association of B18 with the population of cases with low B levels is also found (x2 = 8.02). Familial data showed that low C3 and/or low B levels are associated with the HLA haplotyes, especially with those containing B18. A "complement abnormality susceptibility gene", linked to the HLA genes, is postulated. Infections are significantly more frequent in families of hypocomplementaemic MS, the existence of a genetic immunodeficiency affecting the synthesis of the complement components, linked to the HLA determinants. In 1 case studied in this article, a heterozygous C2 deficiency linked to HLA-A10, B18 was found and might confirm this hypothesis.

Cutaneous manifestations of defective host defenses

Those caring for children should recognize that cutaneous findings are common in children with host defense defects. Atopic dermatitis, recurrent or persistent pyodermas, candidiasis and lupus-like syndromes, should signal the possibility of host defense deficiencies. Particularly the findings of atopic dermatitis and recurrent skin abscesses should alert the clinician to determine serum IgE levels and neutrophil chemotaxis in such patients. The triad of generalized seborrheic dermatitis, failure to thrive, and diarrhea in an infant should bring to mind Leiner disease or severe combined immunodeficiency disease.

Linkage between the gene (or genes) controlling synthesis of the fourth component of complement and the major histocompatibility complex

In an attempt to map the gene (or genes) controlling the synthesis fo the fourth component of complement (C4), we performed linkage studies in a family with hereditary C4 deficiency. The proband, a seven-year-old boy with lupus erythematosus, consistently lacked deteftable serum C4 by both functional and protein measurements. The complement defect was transmitted as an autosomal recessive disorder. Eight of 15 family members were considered to be heterozygotes, seven because of low C4 levels and one because of genetic data (obligate heterozygote). The gene (or genes) coding for C4 deficiency appeared to be linked to the major histocompatibility complex (A2,B12,DW2 on the maternal side and A2,BW15,LD108 on the paternal side) and to other markers known to be in close proximity to the histocompatibility complex on chromosome 6 (phosphoglucomutase-3, glyoxalase-1 and properdin factor B).

Inherited deficiency of the second component of complement. Rheumatic disease associations

The prevalence of homozygous and heterozygous deficiency of the second component of complement (C2) was determined in patients with rheumatic disease including 137 with systemic lupus erythematosus (SLE), 274 with juvenile rheumatoid arthritis, and 134 with rheumatoid arthritis. 1 C2 homozygous deficient and 19 possible heterozygous deficient individuals were identified by using both immunochemical and functional assays to determine C2 levels. Of the 20, 8 had SLE (5.9%), 10 had juvenile rheumatoid arthritis (3.7%), and 2 had rheumatoid arthritis (1.4%), the homozygous deficient individual having SLE. The prevalence of C2 deficiency in the SLE and juvenile rheumatoid arthritis patients was significantly increased (P = 0.0009 and P = 0.02, respectively) when compared with controls, 6 (1.2%) of 509 blood donors having C2 levels consistent with heterozygous deficiency. 15 of the 20 C2 deficient patients were HLA typed and found to have antigens A10(Aw25), B18, or both. The patients with C2 deficiency and SLE had earlier age of onset of disease and less antinuclear antibody when compared with the C2 normal SLE patients. 11 families of the propositi were studied and found to have one or more C2 heterozygous deficient individuals. The family members had an equal distribution of rheumatic disease and antinuclear antibody in the C2 deficient and C2 normal groups. C2 deficient individuals were found to have significantly lower levels of properdin Factor B (242 mug/ml+/-54) when compared with the non-C2 deficient family members (282 mug/ml+/-73). These data support the concept that inherited deficiency of C2 is significantly associated with both SLE and juvenile rheumatoid arthritis.

[The importance of serum components, particularly complement factors, properdin and transferrin, in inhibition of bacterial growth by human serum (author's transl)]

In this study human serum was broken down of column chromatography into its protein components, which were than examined singly and in comnination for antibacterial activity. The bactericidal effect of serum was retained to an apperciable extent in only one of six fractions. Antibacterial inhibitory activity could be restored fully by combining the fractions however. There was no correlation with the specific antibody titers. Complement had an essential part in this unspecific defence. In the absence of C'9 all other combinations of the remanining complement components exhibited no appreciable inhibitory effect. Not all complement componets are required, however, for unspcific bacterial growth inhibition. In contrast to this all complement components are necessary in the antigen-antibody reaction. Futhermore, properdin displays bactericidal activity which is related to the presence of complements. A great deal of the antibacterial activity of human serum thus arises only from the combined action of several components. These do not include proteins with a molecular weight between 100,000 and 70,000, whereby transferrin plays a part.

Hereditary C2 deficiency: association with skin lesions resembling the discoid lesion of systemic lupus erythematosus

Two patients with hereditary homozygous C2 deficiency are described. They showed many similar clinical features. Both had discoid-like skin rashes and serologic abnormalities consistent with SLE, but neither had evidence of involvement of any organ other than skin. Although biopsy of these lesions revealed expected changes by light microscopy, typical immunofluorescent findings were not present. The presence of the HL-A haplotype 10, W18 was seen in both families and was associated with the C2 deficiency gene. The 2 patients were mutually nonreactive in MLC tests and both were found to be homozygous for the LD7a type.

C3 metabolism in a patient with deficiency of the second component of complement (C2) and discoid lupus erythematosus

A patient with a hereditary deficiency of the second component of complement and discoid lupus erythematosus with features of systemic lupus erythematosus was studied. The propositus had a 9-year history of rash and arthralgia. Transient renal disease had completely resolved; there was a history of seizures. Examination of his serum disclosed antinuclear antibodies but no total haemolytic complement activity. C2 was absent. Serum concentrations of C1s, C3, C5 and C9 were elevated; other complement components were present in normal concentration, including C3 pro-activator. The patient's C3 pro-activator was electrophoretically converted by inulin and four of five lipopolysaccharides, but was poorly converted by aggregated human IgG. Two separate turnover studies with radiolabelled C3 showed fractional catabolic rates of 3-03 and 2-48% of the remaining plasma pool/hr (range of three normals: 1-62-2-18%/hr); and estimated C3 synthetic rates of 2-74 and 2-31 mg/kg/hr (range of three normals: 0-89-1-40 mg/kg/hr). Serum complement profiles of the patient's family demonstrated that the C2 deficiency was inherited as an autosomal codominant. One sibling, homozygous for C2 deficiency, and three other siblings, both parents and one daughter, all heterozygous for C2 deficiency, are in good health. Immunofluorescent studies of the patient's diseased skin exhibited substantial deposits of IgG, IgM, C1q, and C4 but not of later acting complement components, properdin, or C3 proactivator. These studies do not support the notion that inflammation in C3-deficient individuals with lupus erythematosus is mediated by the alternative complement pathway.

Genetic independence between the HL--A system and deficits in the first and sixth components of complement

From two families, one with Clr deficiency and the other with C6 deficiency, evidence was obtained suggesting genetic independence between the transmission of a 50% deficit in the functional activity of these two complement components and the inheritance of the HL--A system, the ABO system, and the sex of individuals.