Natural killer (NK) cells play an important role in the first-line defense against tumor and virus-infected cells. Although “missing-self” suggests NK cells would target foreign organ allografts, the prevailing dogma has been that NK cells are not important in the rejection of solid organ allografts. However, studies now suggest NK cells participate in both acute and chronic rejection while paradoxically also facilitating tolerance to an allograft. In clinical studies, however, a clear relationship between predicted NK cell alloreactivity and graft survival was not observed suggesting NK cell function in response to alloantigen is complex. NK cell activity is tightly regulated by a repertoire of inhibitory and activating receptors. The goal of this study was to determine the functional and NK cell receptor responses to alloantigen.

To assess the ability of NK cells to recognize and respond to allogeneic targets, we generated B lymphoblastoid cell lines (LCL), from a cohort (n=10) of healthy donors. Primary human NK cells (CD3^–CD14^–CD19^–CD56⁺) from the same cohort, were isolated by negative selection, and co-cultured with autologous (control) or allogeneic LCLs. NK cells were then assayed by flow cytometry for the degranulation protein CD107a, the NK cell marker CD56, the NK cell maturation marker CD57, the NK cell receptors NKG2A, NKG2C, NKG2D, 2B4, and CD16, and intracellular IFNγ.

NK cells from 9 of 10 donors specifically recognized and responded to the panel of allogeneic LCLs and this was not specifically correlated to KIR ligand mismatches. NK cells from 7 donors showed both cytolytic and IFNγ responses whereas the other 2 donors had either a cytolytic or IFNγ response. Visualization of the frequencies of 64 different NK receptor combinations on NK cells co-cultured with allogeneic LCL from each of the 10 donors indicate that 2B4 and NKG2D were highly expressed (>90%) on NK cells that produced IFNγ, CD107a or were polyfunctional (IFN⁺CD107a⁺) while expression of the inhibitory receptor, NKG2A and activating receptor, NKG2C were highly variable.

Our study, using a multi-parameter approach to examine NK cells suggests diversity in the NK receptors responding to alloantigen. These findings may provide insight into the varied role of NK cells in alloimmunity and will lead to novel strategies to prevent graft rejection and promote tolerance to an allograft.

CITATION INFORMATION: Hatton O, Shawler T, Blish C, Martinez O, Krams S. Natural Killer Cells Display Functional and Receptor Diversity in Response to Alloantigen. Am J Transplant. 2016;16 (suppl 3).

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