Chemistry: molecular biology and microbiology – Measuring or testing process involving enzymes or... – Involving antigen-antibody binding – specific binding protein...
Patent
1989-11-03
1992-08-18
Kepplinger, Ester L.
Chemistry: molecular biology and microbiology
Measuring or testing process involving enzymes or...
Involving antigen-antibody binding, specific binding protein...
435 794, 435 795, 435975, 435968, 436507, 436513, 436518, 436808, G01N 3353, G01N 33564
Patent
active
051399326
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method for the diagnosis of IgA nephropathy using an antigen-antibody interaction, and the invention also includes a diagnostic kit for use in such a diagnosis.
Patients with primary IgA nephropathy, also known as Berger's disease, have been shown to have circulating IgA antibodies, binding to collagen IV prepared from glomerular basement membrane (GBM) (1). It was also shown that the IgA antibodies bound equally well to collagen I, II and IV and that denatured collagens bound antibodies most efficiently (1). In view of the wide distribution of the various collagens, it is of interest to note the coexistence with IgA nephropathy of symptoms from extrarenal organs (2). Thus symptoms from skin, eye and joints are of particular interest since these structures contains collagen as a major component. Indeed one study reports presence of vascular IgA deposits in skin from patients with IgA nephropathy (3).
The association of exacerbations of clinical disease with upper respiratory tract or gastrointestinal infections and the finding of IgA deposits in the glomerular mesangium is well known. The finding of increased levels of IgA-bearing peripheral lymphocytes (4) as well as decreased IgA-specific suppressor T cell activity (5) and increased IgA-specific helper T-alfa cells (6) suggests an immunological mechanism.
Fibronectin, also known as cold insoluble globulin (CIq), that is altered in many disease processes, is present both as a plasmaprotein and as a cell surface protein. The two forms differ slightly in composition but share important functions as binding to gelatin (collagen), heparin, fibrin and cell surface receptors (7). Fibronectin is the major plasma component binding to gelatin (8) and this property as well as its heparin binding properties have been utilized in its isolation (9). Interestingly fibronectin is present also in basement membranes. It can be visualised by immunofluorescense not only in the glomerular basement membrane but also in the mesangium of healthy individuals (10). Furthermore a concomitant increase of mesangial fibronectin and mesagial matrix was observed in patients with IgA nephropathy and Henoch-Schonleins purpura (10).
The present invention is based on the surprising discovery, that the IgA-antibodies are present in circulating immune complexes in patients with primary IgA nephropathy together with fibronectin, and this unexpected finding does, of course, explain the fact that the IgA-containing complexes have the ability of binding to collagen. This new finding that the circulating immune complex contains, in addition to IgA, also fibronectin, enables the provision of both a method for the diagnosis of IgA nephropathy and a diagnostic kit for use in such diagnosis.
Accordingly, one object of the present invention is to provide a method for the diagnosis of IgA nephropathy using antigen-antibody interaction, and another object of the invention is to provide a diagnostic kit for use in such diagnosis of IgA nephropathy.
The method of the present invention is characterized by the following steps: fluid drawn from a patient subject to diagnosis to bind any fibronectin-IgA-complex present in said sample to the substrate, and reaction between the exposed part of such bound complex and a corresponding antibody thereto.
In preparing such substrate capable of binding fibronectin preferred binding agents are collagen, heparin, fibrin or anti-fibro nectin. According to this aspect of the invention the substrate is prepared in such a way as to bind the fibronectin-IgA-complex through its fibronectin component. This in turn means that the IgA-component of the complex is available for determining the presence of complex bound to the substrate.
On the other hand the binding of the fibronectin-IgA-complex to the substrate can be directed to the IgA-part of the complex. In such case there can be used as a binding agent either anti-IgA or a lectin, both of which are capable of binding IgA. In this case the fibronectin part of the complex will be available f
REFERENCES:
Cederholm et al,. "Patients with IgA nephropathy have circulating anti-basement membrane antibodies reacting with structures common to collagen I, II, and IV", Proc. Natl. Acad. Sci. USA vol. 83 pp. 6151-6155 (Aug. 1986).
Rogue-Barreira et al., "Jacalin:An IgA binding lectin" J. Immuno., vol. 134(3) pp 1740-1743 (Mar. 1985).
Bygren Per
Cederholm Bo
Heinegard Dick
Wieslander Jorgen
Bidwell Carol E.
Biocarb AB
Hueschen Gordon W.
Kepplinger Ester L.
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