Immune-mediated glomerular diseases are characterized by infiltration of T cells, which accumulate in the periglomerular space and tubulointerstitium in close contact to proximal and distal tubuli. Recent studies described proximal tubular epithelial cells (PTECs) as renal non-professional antigen-presenting cells that stimulate CD4+ T-cell activation. Whether PTECs have the potential to induce activation of CD8+ T cells is less clear. In this study, we aimed to investigate the capacity of PTECs for antigen cross-presentation thereby modulating CD8+ T-cell responses. We showed that PTECs expressed proteins associated with cross-presentation, internalized soluble antigen via mannose receptor-mediated endocytosis, and generated antigenic peptides by proteasomal degradation. PTECs induced an antigen-dependent CD8+ T-cell activation in the presence of soluble antigen in vitro. PTEC-activated CD8+ T cells expressed granzyme B, and exerted a cytotoxic function by killing target cells. In murine lupus nephritis, CD8+ T cells localized in close contact to proximal tubuli. We determined enhanced apoptosis in tubular cells and particularly PTECs up-regulated expression of cleaved caspase-3. Interestingly, induction of apoptosis in the inflamed kidney was reduced in the absence of CD8+ T cells. Thus, PTECs have the capacity for antigen cross-presentation thereby inducing cytotoxic CD8+ T cells in vitro, which may contribute to the pathology of immune-mediated glomerulonephritis.
