A 52-year-old man presents with nephrotic syndrome: proteinuria 12 g/day, serum albumin 2.1 g/dL, and hyperlipidemia. Renal biopsy with silver stain shows diffusely thickened glomerular basement membrane with the characteristic finding marked **A** — silver-positive spikes projecting between subepithelial dense deposits. Serology is positive for anti-PLA2R antibodies. Which of the following best explains the pathogenesis of this morphologic finding?