Genetic deficiency of the second component of complement (C2) associated with systemic lupus erythematosus. Relation of the complement abnormality and disease manifestations

Sex influences transmission of the supratype associated with the C2 deficiency allele: a possible mechanism for the maintenance of heterozygosity and disease susceptibility

We have examined the transmission of the supratype associated with C2 deficiency (C2Q0) using our own and many published pedigrees in order to determine whether nonrandom transmission may contribute to the stability of disease-associated supratypes. Unexpectedly, we found that C2Q0 may be preferentially transmitted to the opposite sex and therefore propose that such "zig-zag" transmission may result in the preservation of recessive disease susceptibility genes and in the maintenance of heterozygosity. Further pedigrees are required to verify our findings.

Complement depletion accelerates the clearance of immune complexes from the circulation of primates

Binding of immune complexes (IC) to erythrocytes in vitro is the result of interaction between C3b sites on the IC, and complement receptors type I (CRI) expressed on primate erythrocytes. Recent evidence indicates that primate erythrocytes can also rapidly bind large, preformed IC in vivo. This study was undertaken to determine if the binding of IC to baboon erythrocytes in vivo is complement dependent and to examine the effect of complement depletion on IC clearance from the circulation. The results indicate that complement depletion in vivo reduced the binding of IC to erythrocytes. There was relatively little binding of IC to leukocytes in both the complement-depleted and complement-repleted condition. Thus, the majority of IC not bound to erythrocytes remained free in the plasma and, consequently, IC infusion during the complement-depleted state resulted in increased plasma IC concentrations. This was associated with a rapid disappearance of IC from the circulation. By contrast, in the normal or complement-repleted state, a large fraction of the IC became bound to erythrocytes during IC infusion, which resulted in lower plasma IC concentrations. Under these conditions, a more gradual rate of disappearance of IC from the circulation was observed. The relatively abrupt clearance of IC from the circulation in the complement-depleted state could not be accounted for by increased hepatic or splenic uptake. These data indicate that, in contrast to previous studies in nonprimates, complement depletion in primates results in accelerated removal of IC from the circulation. This suggests that factors such as hypocomplementemia and deficient expression of erythrocyte CRI, which are known to occur in certain IC-mediated diseases, may promote IC uptake by organs vulnerable to IC-mediated injury.

Complement biosynthesis by the human hepatoma-derived cell line HepG2

The human hepatoma-derived cell line, HepG2, synthesized and secreted functional complement proteins C1r, C1s, C2, C3, C4, C5, factor B, C1 inhibitor, C3b inactivator, a small amount of C6, and trace amounts of C8; but failed to produce detectable C1q, C7, or C9. Immunochemically, C2, C3, C4, C5, and B were isolated from culture medium as proteins with molecular sizes and subunit structures identical to the corresponding components isolated from serum. C2 and factor B from cellular lysates had slightly lower molecular weights than the corresponding proteins in culture medium. C3, C4, and C5 were detected as single chain precursor molecules in cellular lysates. These results demonstrate that human C5, like C3 and C4, is synthesized as a single chain precursor that is converted by limited proteolysis to the native two-chain molecule. It also establishes the precursor-product relationship for human pro-C4 and native C4, pro-C5, and native C5.

Systemic lupus erythematosus in hereditary deficiency of the fourth component of complement

Three patients from two families with complete hereditary deficiency of the fourth component of complement (C4) and systemic lupus erythematosus are described. The syndrome presented by these patients is characterized by early onset in life; exquisite sensitivity to sunlight and to cold exposure, the latter resulting Raynaud's phenomenon; and skin lesions involving not only exposed areas of the body but also palms and soles and presenting as butterfly rashes, maculopapular eruptions, and lesions similar to those of chronic discoid lupus erythematosus, with marked scaling, atrophy, and scarring. Lupus erythematosus (LE) cell tests were negative and antinuclear antibody (ANA) titers low or negative. The male patient of our series died at the age of 31/2 years from septicemia, whereas the two girls, aged 18 and 11 years, respectively, were alive at the time of writing. The C4-deficient gene is associated with HLA-Aw32, Bw38, and Bf S in one family and with HLA-A30, B18, DR7, and Bf S1 in the other family; the latter is the second family in which this HLA haplotype has been found to be associated with hereditary C4 deficiency.

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.

Bactericidal antibody and susceptibility to otitis media caused by nontypable strains of Haemophilus influenzae

We have developed a bactericidal antibody assay to determine the role of circulating antibody to nontypable strains of Haemophilus influenzae in children with otitis media. Antibody infecting strain was present in the acute sera of 2/20 children with otitis media caused by H. influenzae NT; 15/18 of these patients had covalescent specimens with titers greater than or equal to 1:2 (X2 = 13.0, P < 0.001). The acute sera of 95 children with otitis media caused by various organisms were screened for bactericidal activity against a randomly selected H. influenzae NT stain. Antibody was present in 0/28 acute sera of patients whose infection was caused by H. influenzae NT and in 18/67 (26.9% of those whose middleear exudates were sterile or contained other bacterial species (X2 = 9.95, P < 0.01). A bactericidal antibody response generally follows infection of the middlw ear with H. influenzae NT. The absence of antibody to a single strain in the sera of some children appears to be associated with susceptibility to this infection.

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).

Abnormalities of the complement system in Reye syndrome

Sixteen patients with Reye syndrome had diminished concentration of serum complement proteins and/or hemolytic activity in the earliest blood sample. All 12 studied with hemolytic methods had significantly reduced C1 activity; total hemolytic complement activity was reduced in only three. Low Cl activity was accompanied by equivalent reduction of Cls in 11 of 12 patients; Clq was less than normal in only two of 12. Decreased levels of at least one other classical pathway complement hemolytic activity or protein concentration were found in 13 patients, whereas factor B or the alternate complement pathway was normal or elevated in the ten patients studied. The consistent reduction of Cls protein concentration in Reye syndrome suggests that early metabolic abnormalities regularly affect the production or catabolism of this protein. Although normal serum Clq concentration in the majority of these patients does not support an immune pathogenesis, decreased Clq, C4, and C2 in three patients does suggest that immune mechanisms may be responsible for the serum complement abnormalities in this latter group of patients.