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.