T cells and in situ cryoglobulin deposition in the pathogenesis of lupus nephritis.

We discuss a 53-year-old woman with systemic lupus erythematosus who presented with vasculitis, hypocomplementemia and nephritis. Although her serum complement 4 (C4) levels were zero, she had four copies of C4 gene. Renal biopsy revealed membranoproliferative glomerulonephritis and the presence of cryoglobulins, detected by electron microscopy, and significant numbers of T cells in the interstitium. Cryoglobulins were considered responsible for the complete consumption of C4 in the serum the levels of which improved gradually after treatment. T cells in the kidney were found to express CD44 and phosphorylated ezrin/radixin/moiesin which explain why they homed to the kidney inappropriately. The contribution of cryoglobulins and T cells in the expression of kidney pathology is discussed.