Introduction At present, the relative contribution of the innate and adaptive cytotoxic immunity to human renal tubular epithelial cell injury (TECs) remains poorly defined. Cells of the innate immune system (NK cells) play a role in late antibody-mediated rejection and cells of the adaptive immune system (T cells) are main players during cellular rejection. Here we studied the differences in net lysis-efficacy of TECs by NK cells and CD8+ T cells during alloreactivity in vitro.

Material and Methods First, we performed europium release kill assays using FACS sorted NK and CD8 T cells. Recipient PBMCs were cocultured with donor TECs in the presence of IL-2 and IL-15. In addition,we performed autologous kill assays. Second, the proliferative response of PKH labelled lymphocytes was measured using flow cytometry.

Results Only 5-10% of TECs were lysed by CD8+ T cells at a high effector:target ratio (40:1), while NK-cell lysis of TECs reached up to 57% of TECs under the same conditions. In control experiments T cells showed 75% lysis. We also studied the expression of the surface marker CD107a which is a marker for functional cytotoxic activity. TEC activated CD8+ T cells expressed CD107a up to only 1.6%, while 14.0% of the NK cells expressed CD107a in the same setting. This refers to a more potent functional cytotoxic activity of NK cells.

Allogeneic proliferative response was induced in 6.6% ± 3.1 of CD8+ T-cell population after TEC co-culture. Autologous TEC did not lead to a CD8+ T-cell proliferative response. In addition, transwell experiments revealed that the TEC induced CD8+ T-cell proliferation was cell-cell contact dependent.

Conclusion Our data show a stronger cytolytic activity of NK cells against TECs compared to CD8 + T cells. This phenomenon may underlie the differences in clinical manifestation causing more renal tubule damage by NK rich graft infiltration during ischemia –reperfusion injury or late acute humoral rejection.

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