Natural killer cells in peripheral blood and lung tissue are associated with chronic rejection after lung transplantation

Background: Natural killer (NK) cells have the capacity to recognize and respond to alloantigen, yet their role in lung transplant rejection is not well defined. The aim of this study was to correlate NK cell numbers and immunophenotype in peripheral blood and tissue with graft function after lung transplantation. Methods: NK cell subsets were immunophenotyped in peripheral blood (n = 41). Lung tissue was stained for NK cells via CD16 and morphologic assessment (n = 30). Results: Peripheral blood NK cells were activated in patients with chronic rejection, but the overall number of cells was lower in these patients when compared with stable patients. Furthermore, there was significantly more CD 16(+) NK cells in the lung compartment of patients with bronchiolitis obliterans syndrome compared with stable patients (p = 0.001). Conclusions: In patients with chronic rejection, peripheral blood NK cells are activated but their numbers decrease, while the number of NK cells in the lungs increases. This suggests NK cells systemically activate and migrate to the lung during the progression of chronic rejection after lung transplantation.