Infiltrating Cell Types in Transplant Glomerulitis: Relationship to Peritubular Capillary C4d Deposition

Background: Transplant glomerulitis may be part of the acute rejection process in some transplant recipients. Glomerular monocytes have been shown to be the predominant cell type in transplant glomerulitis associated with peritubular capillary C4d deposition. Whether this applies to peritubular capillary C4d-negative (C4d−) biopsy specimens with transplant glomerulitis is unknown. Methods: Forty-two biopsy specimens with acute rejection and transplant glomerulitis were immunostained for monocytes, T cells, and C4d. In each biopsy specimen, glomerular monocytes and T cells were counted, and mean numbers of monocytes per glomerulus and T cells per glomerulus were determined. Results: Peritubular capillary C4d staining was present in 20 biopsy specimens (C4d-positive [C4d+] group) and negative in 22 specimens (C4d− group). There was no significant difference between mean Banff 97 glomerular scores for the 2 groups (C4d+, 1.60 ± 0.80; C4d−, 1.77 ± 0.90). Although the C4d+ group showed a significantly higher mean number of monocytes per glomerulus (3.01 ± 2.35) than the C4d− group (0.95 ± 1.00; P < 0.0001), the C4d− group showed a significantly higher mean number of T cells per glomerulus (4.05 ± 3.05) than the C4d+ group (1.36 ± 1.24; P = 0.0007). There were proportionately more C4d+ biopsy specimens with a monocyte−T-cell ratio greater than 1.0 (75%) than C4d− specimens (14%; P < 0.0001). Mean glomerular monocyte−T-cell ratio was 3.66 ± 4.24 for the C4d+ group and 0.39 ± 0.54 for the C4d− group; the difference was significant (P = 0.0009). Conclusion: In acute rejection with no peritubular capillary C4d deposition, the predominant infiltrating endocapillary cell in transplant glomerulitis is the T cell, unlike acute rejection with peritubular capillary C4d deposition, in which the predominant infiltrating glomerular cell is the monocyte.