Introduction: Early ultrastructural (US) alterations may provide valuable insights into unraveling the intricate mechanisms involved in the rejection process and may offer opportunities for intervention and therapeutic strategies. Thus, we aimed to evaluate the early US changes in renal allografts with different types of acute rejection (AR), and we compared these findings with capillary HLA-DR and VEGF expressions.
Methods: In 62 cases, acute T-cell-mediated rejection (TCMR), acute antibody-mediated rejection (ABMR), and mixed AR (MAR) were observed in 12 (19.4%), 32 (51.6%), and 18 (29%) patients, respectively. All biopsies were taken within three months after transplantation. Early US changes include endothelial cell (EC) swelling, vacuolization with fenestration loss, and EC serration in glomeruli and peritubular capillaries (PTCs). Early multilamellation of the glomerular basement membrane (BM) is diagnosed if present in ≥5% of glomerular capillaries, while early multilamellation of PTC is defined as ≥4 BM layers in at least one PTC. HLA-DR and VEGF expression were evaluated in PTCs and glomeruli. Follow-up biopsies were assessed for the development of transplant glomerulopathy (TG) and diffuse (>50%) interstitial fibrosis (IF).
Results: Early US changes in glomeruli and PTCs were highest in the MAR group and lowest in the TCMR group (p<0.001). Early US changes were positively associated with PTC destruction, PTC-itis,  glomerulitis, glomerular macrophage infiltration, C4d grade, and PTC neutrophil leukocyte infiltration (p<0.001). Contrarily, US changes are negatively associated with PTC and glomerular VEGF and HLA-DR expression. TG was developed in 12.5%, 72.4%, and 82.4% of patients with TCMR, ABMR, and MAR, respectively (P<0.001). The development of TG was 35±4.9, 21.7±10.2, and 14.6±7.7 months after the first index biopsy in TCMR, ABMR, and MAR cases, respectively. PTC and glomerular early US changes in index biopsies correlated significantly with the development of TG and IF in the follow-up biopsies (p<0.001). VEGF and HLA-DR expression in PTCs and glomeruli negatively associated with TG and IF development (P<0.001). The overall 10-year graft survival was 0%, 41%, and 53% for recipients with grade 0, 1, and 2 PTC-VEGF expression, respectively (P<0.001). It was 0%, 25%, and 64% for patients with grade 0, 1, and 2 glomerular VEGF expression, respectively (P<0.001).
Conclusion: The impact of early US changes, along with capillary VEGF expression in biopsies diagnosed with AR, extends beyond diagnostic considerations, providing a multifaceted perspective on the complexities of rejection processes. By comprehensively understanding and leveraging these changes, we can advance our ability to predict, diagnose, and intervene in AR, ultimately improving graft outcomes.