Increased immunoglobulin-secreting cells in the blood of patients with active idiopathic IgA nephropathy.

Peripheral blood lymphocytes from 33 patients with idiopathic IgA nephropathy (IgAN) and 15 healthy controls were stimulated in vitro by Protein A from Staphylococcus Cowan I; immunoglobulin (Ig) production was measured by a reverse hemolytic plaque assay to evaluate the quantity of cells secreting Ig. In addition, serum Ig levels, circulating IgG, IgA and IgM immune complexes (ICs) and the Fc and C3b receptor mediated phagocytosis of peripheral monocytes were measured. The laboratory findings in different phases of the disease were compared. The mean level of IgA-plaque forming cells (IgA PFC) in IgAN patients with normal renal function was significantly higher (p less than 0.001) than the mean control value. In contrast, they were reduced significantly in those patients who were subjected to periodic hemodialysis (p less than 0.001). Disease activity produced a significant increase in IgG PFC and IgA PFC, high IgG and IgM serum levels, high circulating IgG ICs, and low C3b-mediated phagocytic function of the peripheral macrophages. These findings demonstrate that IgAN is associated with an increased number of IgG and IgA-secreting cells in the peripheral blood of patients during the active phase of the disease and that the concurrent presence of high levels of circulating Ig ICs may be responsible for the gross hematuria, as their deposition in the glomeruli could activate the complement system.