Figure 1142

Mixed cryoglobulinemia. Of the three types of cryoglobulins, types I and II contain monoclonal immunoglobulins (Ig). Type I cryoglobulins occur in monoclonal gammopathies and lymphomas and consist of a single monoclonal immunoglobulin. Type II cryoglobulins (also called mixed cryoglobulinemia) occur in systemic infections, autoimmune diseases, and malignancies. Type II cryoglobulins consist of two components, a monoclonal immunoglobulin, most frequently IgM, with rheumatoid factor activity directed to the polyclonal IgG component. Various patterns of glomerular injury can be found, such as a diffuse endocapillary pro-liferative glomerulonephritis with a prominent influx of monocytes, or a mesangiocapillary glomerulonephritis. Less frequently, a diffuse mesangial proliferative, sclerosing glomerulonephritis, or both can be seen. Eosinophilic aggregates along the glomerular basement membrane (GBM) or in the lumina designated as thrombi frequently are present. Type II cryoglob-ulinemia is sometimes accompanied by a vasculitis. The aggregates in the glomeruli of type I, as seen on immunofluorescence, have a composition identical to that of the cryoglobulins in the serum. The deposits in type II contain IgG, IgM, and complement. Ultrastructurally, the deposits usually demonstrate an organized or crystalline appearance. In type I, the deposits frequently are organized in closely packed fibrils, long tubules, or crystals. In type II, short tubulo-annular structures can be found. Sometimes aggregates in the glomeruli composed of a single monoclonal immunoglobulin component can be demonstrated in patients without evidence of a monoclonal immunoglobulin or cryoglobulins in the serum.

A, Diffuse endocapillary proliferative glomerulonephritis with prominent influx of mononuclear cells. B, Mixed pattern of injury in a patient with Sjogren's syndrome. Intracapillary thrombi, increase of mesangial cells and matrix, and occasionally duplication of the GBM. C, Immunofluorescence with staining for IgM. D, Electron microscopy of tubular and annular structures in the glomerular deposits. (Parts A, B, methenamine silver. Original magnification X400, X400, X200, X 120,000, respectively.)

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