IgA nephropathy - Launay et al J Exp Med 2000 191(11):1999-2009

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This disease is a glomerulonephritis and is the commonest primary glomerulonephritis worldwide. Kidney biopsies typically show deposition of IgA in the mesangium of the glomerulus and the proliferation of mesangial cells and increased amounts of mesangial matrix. There are often increases in the amount of circulating IgA in the plasma of patients. The cause of the disease is not fully understood.

Several groups now suggest that the molecule CD89 may play a role. This is a receptor for the Fc portion of IgA antibodies. The Fc portion of the molecule is the part that is not normally involved in binding to the foreign antigen. The receptors are involved in binding IgA and transporting it across cells. CD89 is also termed an FcalphaR.

A group from the famous Necker hospital in Paris now report in the Journal of Experimental Medicine, that in patients with IgA nephropathy there are high levels of soluble CD89 bound to IgA which circulate in the blood as a complex. They then put the gene for human CD89 into mice and showed that these transgenic mice developed a disease like IgA nephropathy. When serum from these affected mice was administered to unaffected mice, the serum transmitted the disease. Furthermore, if the CD89-IgA complexes were removed from this serum it was unable to transmit the disease. These finding suggest that the presence of high plasma levels of the complex formed between CD89 and IgA can cause a disease in mice similar to human IgA nephropathy. As such high levels are found in patients, but not in normal controls, these complexes may contribute to the pathology of human IgA nephropathy.

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C. A. O'Callaghan 2004