The clinical and molecular significance of different types of C4d staining in renal allografts

We investigated the clinical and molecular significance of minimal peritubular capillary (PTC) and isolated glomerular C4d+ staining using microarrays. Immunohistochemistry for C4d was performed on paraffin-embedded sections. Of the 255 biopsies analyzed, 51% were C4d negative, 4% were minimal, 15% focal or diffuse PTC C4d+, and 31% isolated glomerular C4d+. Minimal and focal/ diffuse PTC C4d+ staining were associated with a higher frequency of donor-specific anti-HLA antibodies (DSA) (67% vs. 82% vs. 25%), antibody mediated rejection (AMR) (66% vs. 89% vs. 19%) and mean glomerulitis (0.88 vs. 0.65 vs. 0.25, p=0.003), interstitial inflammation (1.25 vs. 1.41 vs. 0.79; p=0.003) and peritubular capillaritis scores (1.5 vs. 1.5 vs. 0.34; p < 0.001), compared to the C4d negative group, respectively. There were no differences in the DSA frequency, AMR rate, and Banff scores between isolated glomerular C4d+ and negative patients. While both minimal and focal/diffuse C4d+ biopsies showed increased expression of genes related to the immune response, and interferon-gamma and rejection induced, cytotoxic T cell and constitutive macrophage-associated pathogenesis based transcripts, there was no activation of immune-response related genes in isolated glomerular C4d+ biopsies. In summary, minimal PTC C4d+ staining but not isolated glomerular C4d+ staining is associated with AMR.

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