Hidden Granzyme B-Mediated Injury in Chronic Active Antibody-Mediated Rejection

Antibody-mediated injury in chronic active antibody-mediated rejection, possibly with other effector T cells, may play a role in graft injury. The role of inflammatory cells in the inflammation and fibrosis and tubular atrophy region has been recently advocated in the progression of injury. Cytotoxic T cells play a prominent role in T-cell-mediated rejection; however, the possible role of cytotoxic T cells in circulation and the intragraft compartment in chronic active antibody-mediated rejection, a common immunological cause of long-term graft failure, has not been well-studied.

We measured the frequency of circulating cytotoxic T cells with flow cytometry, serum granzyme B level by enzyme-linked immunosorbent assay and intragraft granzyme B+ cell, and mRNA by immunohistochemistry and real-time polymerase chain reaction in biopsy tissue from living donor renal allograft recipients with stable graft function and chronic active antibody-mediated rejection.

The frequency of CD3+ and CD3+CD8+ T cells was similar in both stable graft function patients and chronic active antibody-mediated rejection patients. The frequency of CD3+CD8+granzyme B+ cytotoxic T cells was significantly lower in peripheral blood. Serum granzyme B level and intragraft number of granzyme B+ cells (counts/mm²) were also significantly higher in the chronic active antibody-mediated rejection group compared with that of patients with stable graft function. The intragraft granzyme B+ T cell count was positively correlated with serum creatinine and 24-hour urine proteinuria but negatively correlated with estimated glomerular filtration rate.

Granzyme B mediates covert graft injury in patients with chronic active antibody-mediated rejection in addition to antibody-mediated injury.