Case 2. Systemic Lupus Erythematosus
a. Type III Autoimmune Reaction
SLE is the prototype of human immune complex disease. For reasons that are unclear, autoantibodies against dsDNA are involved in the formation of immune complexes that appear to be particularly prone to become trapped in the renal glomeruli, where they can cause inflammation (glomerulonephritis). The levels of anti-dsDNA often are low during periods of disease quiecence. In this case, a flare of of disease activity was precipitated by stopping medications that keep the autoimmune response in check (prednisone and hydroxychloroquin), leading to the production of high levels of anti-dsDNA antibodies that could be detected by staining the kinetoplast (a circular DNA molecule) of Chritidia luciliae organisms. These autoantibodies formed immune complexes, resulting in the consumption of classical complement components C3 and C4 ( the classic inverse relationship between anti-DNA and complement levels). Because the immune complexes were inadequately cleared, they deposited in the renal glomeruli, resulting in the patient’s new onset of hematuria and proteinuria and the decline in her renal function (increase creatinine). With reinstitution of appropriate therapy, the anti-DNA levels declined, C3 and C4 levels recovered, and renal immune complex deposition diminished, resulting in an improvement of renal function.