Background: C4d staining in peritubular capillaries is a well-established feature of antibody-mediated rejection (AMR). The relevance of C4d staining outside peritubular capillaries is not well understood. We investigated the significance of arteriolar C4d staining in chronic-active AMR (c-aAMR).
Methods: All for-cause renal allograft biopsies performed in 2007-2014 at the Erasmus MC and meeting the criteria for suspicious/diagnostic c-aAMR using the Banff Classification 2015 were included. For comparison, renal allograft biopsies from a matched control group and native renal biopsies were analyzed. Arteriolar C4d staining was semiquantitatively scored as negative (0), small deposits in 1 arteriole (1+), small/large deposits in >1 arterioles (2+), or at least extensive deposits in most arterioles (3+).
Results: Thirty-four of 40 (85%) patients with c-aAMR showed arteriolar C4d staining. A significant difference in arteriolar C4d score was observed between cases and matched controls (P = 0.01) and a trend toward significance difference between cases and native renal biopsies (P = 0.05). In the cases, arteriolar C4d staining was significantly associated with severity of arteriolar hyalinosis (P = 0.004) and ≥2 arteriolar C4d staining was independently associated with better graft outcome in a multivariate Cox regression analysis (hazard ratio, 0.260; 95% CI, 0.104-0.650; P = 0.004).
Conclusions: This pilot study shows that arteriolar C4d staining is more common in biopsies with c-aAMR compared with those without and that it is associated with arteriolar hyalinosis and ≥2 arteriolar C4d staining is associated with superior graft outcome. However, larger studies are needed to examine these findings in more detail to asses if arteriolar C4d staining is truly related to antibody-mediated injury.