IgA nephropathy pathophysiology
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Pathophysiology
The disease derives its name from deposits of Immunoglobulin A (IgA) in a blotchy pattern in the mesangium (on immunofluorescence), the heart of the renal glomerulus. As a rule, this affects the whole kidney. The tissue changes gradually from being hypercellular to depositing extracellular matrix proteins, and finally fibrosis.
There is no clear known explanation for the accumulation of the IgA. Exogenous antigens for IgA have not been identified in the kidney, but it is possible that this antigen has been cleared before the disease manifests itself. It has also been proposed that IgA itself may be the antigen.
A recently advanced theory focuses on abnormalities of the IgA1 molecule. IgA1 is one of the two immunoglobulin subclasses (the other is IgD) that is O-glycosylated on a number of serine and threonine residues in a special proline-rich hinge region. Deficiency of these sugars appears to lead to polymerisation of the IgA molecule in tissues, especially the glomerular mesangium. A similar mechanism has been claimed to underly Henoch-Schönlein purpura (HSP), a vasculitis that mainly affects children and can feature renal involvement that is almost indistinguishable from IgA nephritis.
From the fact that IgAN can recur after renal transplant it can be postulated that the disease is caused by a problem in the immune system rather than the kidney itself. Remarkably, the IgA1 that accumulates in the kidney does not appear to originate from the mucosa-associated lymphoid tissue (MALT), which is the site of most upper respiratory tract infections, but from the bone marrow. This, too, suggests an immune pathology rather than direct interference by outside agents.