Immune complexes are putatively deposited in the glomerular subendothelium, resulting in activation of complement, chemoattraction of leukocytes, and an inflammatory reaction that leads to disruption of the glomerular basement membrane with enlargement of glomerular barrier pores, thus permitting passage of high molecular weight (HMW) macromolecules such as IgG to which the basement membrane is normally impermeable. The increased load of HMW macromolecules in the tubular lumen leads to saturation of the re-absorptive mechanism by tubular cells. In addition, the reabsorption capacity of the epithelial cells of the proximal tubules may also be impaired.