IgA fibronectin collagen complexes in IgA nephropathy
Thomas, M., Hollingsworth, P.N., Mallal, S., Saker, B. and Dawkins, R.L. (1989) IgA fibronectin collagen complexes in IgA nephropathy. In: 25th Annual Scientific Meeting of the Australasian Society of Nephrology, 26 February - 1 March 1989, Newcastle, N.S.W.
The antigen in the circulating immune complexes in IgA GN remains unspecified. Sera from some IgA Gn patients can bind to the FN-binding fractions of intact and denatured collagens I, II & IV, and plasma FN contains collagen-binding domains. Serum IgA FN complexes (<1% of total IgA) binding to collagen have recently been demonstrated in IgA GN patients. To determine the specificity of this observation, stored serum from patients with mesangial proliferative GN with (N = 24) or without (N = 14) IgA deposition, patients with high serum IgA without ON (N = 5), patients with rheumatoid factor or antinuclear antibodies (N = 3) and normal subjects (N = 2) were assayed for IgA FN collagen-binding complexes by ELISA (kit courtesy of Dr. B. Cederholm, Sweden). Results were expressed as median (m) and ranges (r) of optical densities (OD); normal range < 3 x OD of negative control; marked elevation = OD > 0.40. IgA ON patient's sera showed a bimodal distribution with 11 patients showing normal-moderate OD elevation (m = 0.10, r = 0.02 to 0.25) and 13 patients showing marked OD elevations (m = 0.47, r = 0.40 to 0.65). Patients with non lgA ON had only normal-moderate OD elevations (m = 0.11, r 0.01 to 0.23). Patients with high serum IgA concentrations showed mild-marked OD elevation, (m = 0.28, r = 0.12 to 0.60). Patients with autoantibodies did not differ from normal subjects. Elevations in serum IgA FN complexes binding to collagen are not specific to IgA nephropathy; mild-moderate elevations are found in other non lgA proliferative ON. Marked elevations in concentrations of this complex were limited to IgA GN in all but one sample. Correlations with clinical features of IgA GN are in progress.
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