C4 glomerulopathy overview
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Ali Poyan Mehr, M.D. [2]; Associate Editor(s)-in-Chief: Olufunmilola Olubukola M.D.[3]
Overview
Historical Perspective
Classification
Pathophysiology
- The generation of the classical pathway of complement occurs by the immune complex.
- Immune complex glomerulonephritis, such as lupus, frequently activates the classical pathway by binding C1q to the antibody-containing immune complexes, which can result in glomerular deposition of immunoglobulins, C3, C1q, and C4d.
- C4 activation can also ensue by the lectin pathway of complement.
- In the lectin pathway, mannose-binding lectins bind to mannose located on the carbohydrates structure or microbial membranes, which activate C4 (and therefore bypass C1q), resulting in the formation of the classical pathway C3 convertase.
- Glomerular C4d, is a split creation of C4, is suggestive of C4 activation as a result of activation of either the lectin pathway of the classical complement pathway.
- In C4 glomerulopathy, bright streak for C4d indicates mesangial/capillary wall deposits. C4d deposits are present in a few cases of IgA nephropathy and post-streptococcal glomerulonephritis.