C4 null alleles in a Swedish population

Circulating immune complexes induced by food proteins implicated in precocious myocardial infarction

BACKGROUND

Circulating immune complexes (CIC) are frequently found in postinfarction patients. The constituents of these CIC are mostly unknown.

AIM

The objective of the current study was to assess whether CIC containing alimentary proteins and antibodies against these proteins are implicated in precocious myocardial infarction (MI).

METHODS

Seventy-six survivors (67 men and 9 women, mean age 39 years) of a first MI before the age of 45 years were enrolled in this study. Two control groups were included. One group consisted of age-matched, randomly selected, population-based healthy individuals, 79 men and 11 women, without features of coronary heart disease. An additional control group was used only for the determination of serum antibodies against some of the alimentary proteins and consisted of 139 healthy blood donors, 95 men and 44 women, with a mean age of 42 years. Sucrose density gradient centrifugation, gel filtration and precipitation by polyethylene glycol were used for the isolation of CIC, and enzyme-linked immunosorbent assay (ELISA) was used to measure the immunoglobulin levels and specific antibodies against alimentary proteins in both sera and isolated CIC. Sodium dodecylsulfate (SDS) polyacrylamide gel electrophoresis and Western blotting were used to determine alimentary proteins in the CIC.

RESULTS

Alimentary antigens/antibodies were present in immune complex form in seven out of 14 (50%) postinfarction patients who had persistent high concentrations of CIC, the latter constituting 18% of the entire group. Antibodies of the IgG isotype predominated. A rise in CIC, signs of activation of the classical complement pathway, and a rise in plasma concentrations of von Willebrand factor antigen (vWFAg) were evident within 1 week in four patients subjected to a 2-week elimination diet followed by a single challenge with cow's milk.

CONCLUSION

This study suggests that dietary proteins occasionally give rise to persistent CIC, which may predispose to MI at a young age.

Circulating immune complexes and complement C4 null alleles in patients in patients operated on for premature atherosclerotic peripheral vascular disease

Circulating immune complexes can lead to vascular inflammation and premature atherosclerosis and the fourth component of complement, C4, plays an important role in the removal of immune complexes. The objective of this study was to analyze the relation between circulating immune complexes and C4 null alleles in patients operated on for peripheral vascular disease before the age of 50. The prevalence of circulating immune complexes and null alleles of C4 (C4Q0) was determined in 62 patients with peripheral atherosclerosis requiring surgery before 50 years of age and in a matched control group. C4A and C4B null alleles (C4A*Q0, C4B*Q0) were determined by electrophoresis of plasma, followed by immunofixation. C4A and C4B concentrations were measured by ELISA. Circulating immune complexes were determined by sucrose density gradient centrifugation and gel filtration. There was no difference in the distribution of C4Q0 between patients and controls. The patients had higher prevalences and levels of circulating immune complexes. This was correlated with the presence of C4Q0, especially C4A*Q0. There was an inverse correlation of concentration of circulating immune complexes with C4A levels and with ratio of C4A/B levels. Thus, a significant proportion of patients with premature peripheral atherosclerosis had circulating immune complexes and C4A*Q0 enhanced the propensity to immune complex formation. This might represent one mechanism for vascular damage in this patient group.

Homozygous deletion of the CYP21A-TNXA-RP2-C4B gene region conferring C4B deficiency associated with recurrent respiratory infections

The central class III region of the human major histocompatibility complex contains highly polymorphic genes that are associated with immune disorders and may serve as susceptibility factors for viral infections. Many HLA haplotype specific rearrangements, duplications, conversions and deletions, occur frequently in the C4 gene region. Genetic deficiencies of complement components are associated with recurrent occurrence of bacterial infections. We have studied the complement profile and the class III genes 5'-RP1-C4A-CYP21A-TNXA-RP2-C4B-CYP21B-TNXB -3' in a 4-year-old Caucasian patient. He has suffered from several pneumonias caused by respiratory viruses, eight acute otitis media, prolonged respiratory infections and urinary tract infection. Complement C4 was constantly low, but the other complement components, from C1 to C9, C1INH, factor B and properdin, were within normal limits. Immunological evaluation gave normal lymphocyte numbers and functions with the exception of subnormal T cell response to pokeweed mitogen. Molecular studies of the C4 gene region in the patient revealed homozygous deletion of CYP21A-TNXA-RP2-C4B generating total deficiency of C4B and the flanking 5' region up to C4A, and in the father a missing CYP21A gene. Further investigations are needed to elucidate the relationship between C4B deficiency and susceptibility to infections.

Anti-cardiolipin antibodies and circulating immune complexes in type 1 diabetes mellitus: increased prevalence and relation to vascular complications

Anti-cardiolipin antibodies, oxidatively modified low-density lipoproteins (oxLDL) and circulating immune complexes are humoral factors that have been linked to vascular damage. To analyse their possible role in the vascular complications in type 1 diabetes mellitus, we investigated patients with and without vascular complications (retinopathy, nephropathy, polyneuropathy, foot ulcers). The patients were matched for age, sex and duration of diabetes. The patients were also compared with 102 healthy individuals. Anti-cardiolipin antibodies of IgG and IgA type were more common in patients compared with healthy individuals. There was no difference between patients with and without vascular complications. There was no increased prevalence of IgM anti-cardiolipin antibodies, but the levels of these antibodies were higher in patients with vascular complications compared with patients without complications and controls. Eighty-three percent of patients had circulating immune complexes in comparison with 5% of healthy individuals. Such complexes were more common in patients with complications. Both the prevalence and the levels of immune complexes were higher in patients with null alleles of complement factor C4. Patients with vascular complications had higher prevalence of C4A than of C4B null alleles. Anti-cardiolipin antibodies were present in higher relative concentrations in immune complex form than in serum in all six patients analysed. There was no increased prevalence of antibodies against oxidatively modified LDL in the patients. The higher prevalence and levels of anti-cardiolipin antibodies and circulating immune complexes in patients with vascular complications suggests that these humoral factors might be involved in the vascular complications of type 1 diabetes mellitus.