Robert H. McLean

Relationship between C4 null genes, HLA-D region antigens, and genetic susceptibility to systemic lupus erythematosus in Caucasian and Black Americans

The complement components C4A, C4B, and factor B, and the HLA-A, B, C, DR, DQ, and DRw antigens were analyzed in 103 patients (66 Caucasian, 37 black) with systemic lupus erythematosus (SLE) and 98 control subjects (63 Caucasian, 35 black). Only the C4A null (silent) allele was significantly increased in SLE (0.254 versus 0.095 in Caucasians, p = 0.033; 0.200 versus 0.071 in blacks, p = 0.046). The absence of any detectable C4A gene products (homozygous C4A null or C4A*Q0,Q0) was found in 11.1 percent of Caucasian patients but in no control subjects (p = 0.006 with relative risk of 16.86). HLA-DR2 was significantly associated with Caucasian SLE (R2 = 0.63, p less than 0.0012). Multivariate analysis demonstrated that the HLA-DR2 antigen and C4A null allele contributed independently to the risk of SLE (relative risk 3.0 and 3.2, respectively); when HLA-DR2 and the homozygous C4A null phenotype were present together, the relative risk of SLE was 24.9. Both HLA-B8 and HLA-DR3 were increased in SLE, but these antigens are in linkage disequilibrium with the C4A null allele; the presence of HLA-B8 or DR3 did not contribute further to the risk of SLE. It is concluded that the HLA-DR2 antigen and the C4A null allele are independent and additive risk factors for development of SLE.

Null alleles of the fourth component of complement and HLA haplotypes in familial systemic lupus erythematosus

Eight families (121 individuals) with two or more members affected with systemic lupus erythematosus (SLE) were analyzed for histocompatibility antigens (HLA-A, B, C, DR, MT, and MB) and complement antigens (C4A, C4B, and BF). These data were correlated with serological markers (antinuclear antibodies, single- and double-stranded anti-DNA, anti-SM, anti-nRNP, anti-Ro [SS-A], anti-La [SS-B], and biological false-positive tests for syphilis and clinical features. Fifteen members had SLE, and 19 had other immune diseases (subacute cutaneous lupus erythematosus, discoid lupus erythematosus, hypothyroidism, insulin-dependent diabetes mellitus, primary, Sjogrens syndrome, immune thrombocytopenic purpura, rheumatoid arthritis, and multiple sclerosis). Twenty-three healthy relatives (seroreactors) had significant titers of circulating antibodies, as did 2 of 17 spouses. There was an increased frequency of null C4 alleles in those individuals with SLE (60%) and healthy relatives (50%) as compared with spouses (24%). Multivariate analysis showed a significant association between SLE and female sex (P=.006), whereas there was no significant association revealed between female sex and other immune diseases. Patients with SLE also had a higher frequency of either C4A or C4B null alleles (P=.01) than those with immune diseases. The C4A homozygous null phenotype was more common in SLE patients than in seroreactors (P=.02). There was a higher frequency of HLA-DR2 and DR3 in individuals with SLE than in those with immune disease (P=.08), seroreactors (P=.02) and normal relatives (P =.002). One totally C4-deficient patient with SLE was identified. These families demonstrate an important association between SLE and the C4 null allele and the HLA-DR2 and DR3. These risk factors, however, cannot account for the development of disease in all individuals.

Clinical expression of systemic lupus erythematosus in patients with C4A deficiency.

We studied 121 patients with systemic lupus erythematosus (SLE), of whom 119 were complement typed. Both black and white patients with SLE were more likely than racially matched controls to have a C4A null allotype. Patients with homozygous C4A deficiency had less proteinuria than other patients (p = 0.02) and both homozygous and heterozygous C4A-deficient patients (p = 0.05) had fewer seizures than other patients. Anti-dsDNA, anti-Sm, anti-Ro, and anticardiolipin antibodies were less common in patients with homozygous C4A deficiency, with heterozygous C4A-deficient patients intermediate in frequency between homozygous C4A-deficient and normal patients with SLE. Both homozygous and heterozygous C4A-deficient patients (p < 0.005) had higher C3 levels than other patients, and heterozygous C4A-deficient patients had higher, not lower, C4 levels (p < 0.002), compared with non-C4A-deficient patients. C4A gene deletion was found in 23.4% of patients. C4A gene deletion was associated with subacute cutaneous lupus erythematosus (p = 0.04) and Sjögren syndrome (p = 0.02) in patients with SLE. Both anti-dsDNA (p = 0.04) and anticardiolipin (p = 0.04) were found less frequently in patients with C4A gene deletion. Patients with C4A gene deletion had lower C4 levels than patients with C4A deficiency from other mechanisms. We conclude that the presence of 1 or 2 C4A null allotypes and the presence of a C4A gene deletion identify subgroups of patients with SLE that differ in clinical, laboratory, and autoantibody characteristics from other patients with SLE.

Properdin and C3 Proactivator: Alternate Pathway Components in Human Glomerulonephritis

Serological and immunopathological studies of human glomerulonephritis have suggested that alternate pathways of activation of the third component of complement may be important in some forms of glomerulonephritis. We have investigated the role of two alternate pathway proteins, properdin and C3 proactivator, in 22 patients with chronic membranoproliferative glomerulonephritis, 21 patients with systemic lupus erythematosus, 20 patients with acute poststreptococcal glomerulonephritis, and 19 patients with other forms of renal disease. C3 (measured at beta(1)A), properdin, and C3 proactivator were assayed by single radial immunodiffusion. In sera with low beta(1)A (< 2 SD), mean properdin was most significantly decreased in patients with acute poststreptococcal glomerulonephritis but was also significantly decreased in chronic membranoproliferative glomerulonephritis and in untreated systemic lupus erythematosus. Properdin levels in other renal disease, acute glomerulonephritis, and chronic membranoproliferative glomerulonephritis with normal beta(1)A levels were not significantly different from normal. A positive correlation between beta(1)A and properdin levels in individual sera was present in all diseases except systemic lupus erythematosus. Serum C3 proactivator was markedly decreased in active systemic lupus erythematosus and there was a positive correlation between beta(1)A and C3 proactivator levels in systemic lupus erythematosus and other renal diseases but not acute poststreptococcal glomerulonephritis. Properdin in fresh sera from four patients with systemic lupus erythematosus and five with chronic membranoproliferative glomerulonephritis showed increased migration toward the cathode on immunoelectrophoresis, suggesting in vivo change of the properdin molecule. The observation of reduced serum levels of properdin and C3 proactivator and altered electrophoretic migration of properdin in some patients with glomerulonephritis provide new evidence for participation of these alternate pathway proteins in glomerulonephritis.

Decreased serum factor B concentration associated with decreased opsonization of Escherichia coli in the idiopathic nephrotic syndrome

Summary: We report correlative studies of factor B, properdin, C3, and the serum opsonic activity for Escherichia coli and Staphylococcus aureus in patients with the idiopathic nephrotic syndrome (INS). Thirty-two patients with the idiopathic nephrotic syndrome were studied. Twenty-two patients were steroid responsive (Group I), of which 11 patients were steroid dependent. Ten patients were steroid resistant (Group II).The presence of the nephrotic syndrome (regardless of steroid responsiveness) was associated with a significantly reduced mean serum factor B concentration. Of the complement components studied, only factor B was significantly decreased during relapse (factor B 24.8 ± 9 μg N/ml in INS versus 46 ± 12 μg/ml in normal, P < 0.001). When the combined groups were studied during remission of INS, the mean serum factor B concentrations were not different from normal. Similar results were found when each group was examined separately. Ten patients had serum factor B determinations during both exacerbation and remission of the nephrotic syndrome. The serum factor B increased in nine patients and was unchanged in one. A highly positive correlation between serum factor B and scrum albumin concentrations was present (r = +0.805, P < 0.001).Twenty sera from 14 patients with the nephrotic syndrome, studied at various stages of the nephrotic syndrome, were evaluated for opsonization titers of E. coli employing the bacterial killing assay. Eleven sera from seven patients had reduced capacity for E. coli opsonization, i.e., bacteria were not opsonized in 2% serum. There was a significant difference between the mean factor B concentrations of sera with abnormal as compared to normal opsonization of E. coli (P < 0.001). The serum of one patient with nephrosis opsonized E. coli normally 60 min after the addition of isolated factor B. The opsonic activity of serums from three additional patients with relapse of INS were studied by determining uptake of radiolabeled E. coli by normal leukocytes. The addition of isolated factor B increased phagocytosis in the serum from two of three patients. Decreased opsonization of S. aureus was found in only 3 (two patients) of 19 sera. The complement components, C1q, C4, properdin, and C3, were normal during both periods of exacerbation and remission with the exception that C4 was significantly elevated during remission of nephrosis.These results suggest that a significant decrease of serum factor B concentration is associated with abnormal opsonization of E. coli. We do not know the cause of decreased serum factor B, but renal pathologic findings do not appear to be of etiologic importance. The high correlation of serum factor B with scrum albumin concentration suggests that factor B, with a molecular weight of 80,000, was being lost in the urine.Speculation: The increased incidence of severe infections such as peritonitis, which occurs in INS patients, may be the result of reduced serum factor B, a component of the alternative pathway. Although further work is necessary to determine the cause of factor B decrease in INS and the role of other scrum factors in this opsonic defect, the understanding of the role of factor B in the predilection of nephrotic patients to certain infections could be of great importance in the care of these patients.

Partial H (β1H) deficiency and glomerulonephritis in two families

H (β1H) controls the C3b amplification loop by its ability to displace Bb from the alternative pathway convertase, C3b,Bb, and acts as a cofactor with I (C3b inactivator) to produce inactive C3b. Serum C3 levels are dependent to a large extent on the levels of H and I. Partial H deficiency was found in two families. The index case in Family 1 had vasculitis, thrombocytopenia, proteinuria, and depressed serum H and C3 levels. The index case in Family 2 had depressed serum H and B (Factor B) levels and IgA nephropathy which progressed to renal failure. His sister also had IgA nephropathy and depressed serum H and C3 levels. The depressed serum C3 level, B level, and H level could be responsible for the development of the immune diseases found in some members of these families.

Segmental renal artery embolization for treatment of pediatric renovascular hypertension.

Selective intrarenal arterial embolization was used to treat three children with documented renovascular hypertension. Embolization resulted in complete cure (ie, elimination of all antihypertensive medicines) in all three patients and caused only minimal loss of renal parenchyma. Renal vein renin sampling, including sampling after furosemide administration, correlated well with the location of identified vascular lesions and helped direct selective angiography when lesions were not found initially. Intrarenal arterial embolization is a safe, effective alternative to surgical resection in the treatment of renovascular hypertension in children who have identifiable intrarenal arterial lesions not amenable to balloon angioplasty.

Recurrence of membranoproliferative glomerulonephritis following kidney transplantation. Serum complement component studies.

Sixteen patients with membranoproliferative glomerulonephritis who required kidney transplantation because of renal failure were evaluated for evidence of recurrence of the original disease by serologic and morphologic studies. Of the 12 patients with transplant tissue available for study, seven showed membranoproliferative glomerulonephritis by light morphology. Four of these seven also had hypocomplementemia, and this hypocomplementemia was characterized by decreased serum CH50, C3 beta1A or C3-C9 but norma serum C1, C4 and C2 by hemolytic assay. Immunofluorescent microscopy demonstrated more intense glomerular deposition of C3 and properdin in the hypocomplementemic patients. Ultrastructural studies demonstrated intramembranous deposits typical of dense deposit disease in one patient who also had marked hypocomplementemia. One patient who had two transplant biopsies and persistent hypocomplementemia showed progression from predominantly mesangial glomerular changes to both capillary wall and mesangial abnormalities. This study has shown a high rate of recurrence of membranoproliferative glomerulonephritis in the transplanted kidneys. A high death rate was noted in persistently hypocomplementemic patients. The serum C profile in hypcomplementemic patients who received translants was similar to that seen before transplantation, but the signficance of this finding remains unknown.

Recurrent haemolytic uraemic syndrome and acquired hypomorphic variant of the third component of complement

In a girl with recurrent haemolytic uraemic syndrome (HUS), persistently low serum levels of C3 were found. Analysis of complement phenotype revealed a hypomorphic variant of C3 Fast in the patient (C3fS) and a normal heterozygous pattern in both parents and the brother (C3FS). Other complement aberrations in the patient were: the presence of a null gene for C4A and C4B and low serum levels of factor H. The father also had partial factor H deficiency. It is hypothesized that the hypomorphic C3 variant may predispose to recurrent HUS. In the acquired forms the role of uraemia in alteration of C3F should be considered.

Hypomorphic variant of C3, arthritis, and chronic glomerulonephritis

Decreased synthesis (hypomorphism) of the fast variant of the third component of complement was detected in three generations of a family in which the propositus has an immune complex-type glomerulonephritis, arthritis, and a false positive test for syphilis. An affected sibling has bursitis, hematuria, and proteinuria. Decreased serum C3 protein was detected in three of four and decreased C3H50 in four of four family members with this hypomorphic variant (C3f). This is the first association between C3f and immune complex-type disease.