Serum fibrillin–antifibrillin immune complexes among diabetic children

Abstract

The fibrillins are large glycoproteins components of 10-nm microfibrils found in the extracellular matrix of most tissues. Microfibrils play a role in elastic fiber assembly and serve to link cells to elastic fibers in the extracellular matrix. Fibrillin-1 (FBN-1) and -2 (FBN-2) are large, secreted glycoproteins known to be components of extracellular matrix microfibrils located in the vasculature, basement membrane, and various connective tissues and are often associated with a superstructure known as the elastic fiber. Anti-fibrillin antibodies found in some autoimmune diseases could form circulating immune complexes (CIC) with corresponding antigens. Type 1 (insulin-dependent) diabetes mellitus is an autoimmune disease leading to formation of different types of autoantibodies. To determine the possible presence of FBN-anti-FBN CIC (IgG and IgM) were studied by modified version of ELISA 35 children with Type 1 diabetes mellitus (mean age—12.37 ± 3.77 years, diabetes duration 4 ± 3.5 years). Eight of the diabetics had vascular complications. Twenty healthy children (mean age—11.58 ± 2.89 years) were used as controls. Diabetics showed statistically significant higher levels of FBN-anti-FBN-2 CIC — IgG (0.303 ± 0.076 vs. 0.252 ± 0.029; p = 0.029) and IgM (0.415 ± 0.085 vs. 0.348 ± 0.069; p = 0.018) compared to the control group. FBN-anti-FBN-1 CIC IgM correlate with diabetes duration ( r = 0.52; p = 0.0015) and BMI ( r = 0.33, p = 0.053) while FBN-anti-FBN-1 CIC IgG correlate with serum Zinc ( r = 0.49, p = 0.006). FBN-anti-FBN-2 CIC IgG correlate with microalbuminuria ( r = 0.65, p = 0.0046) and retinopathy ( r = 0.61, p = 0.0001). This study suggests that there may be a relationship of levels of FBN-anti-FBN-2 CIC IgG with the development of diabetic microangiopathy. Of course the number of the tested patients is limited for definitive conclusions. Although the meaning of these results is still being determined, the measurement of FBN-anti-FBN CIC may represent immunologic markers of FBN metabolism.