Hepatic interleuklin 15 (IL‐15) expression: implications for local NK/NKT cell homeostasis and development

SUMMARY Interleukin 15 (IL‐15) is critical for the development of human and murine natural killer (NK) cells and hepatic‐derived NK T cells (NKT) in mice, and for the homeostatic maintenance of NK/NKT and CD8+ memory T cells. The lymphocyte repertoire of an adult human liver includes significant populations of NK and NKT‐like cells, which may arise locally from hepatic haematopoietic stem cells (HSCs). We investigated hepatic IL‐15 levels and the expression of IL‐2/IL‐15‐receptor β‐chain (IL‐2/IL‐15Rβ ; CD122) on mature hepatic lymphocytes and HSCs. Reverse transcription‐polymerase chain reaction (RT‐PCR) was used to detect secreted/intracellular IL‐15 transcripts. IL‐15 protein was localized using immunohistochemistry; levels were measured by enzyme‐linked immunosorbent assay IL‐2/IL‐15Rβ expression by flow‐cytometry. Normal hepatic IL‐15 protein was detected at 0·43 ng/100 mg total protein (n = 11, range 0·10 ng−0·9 ng). There was a significant increase in HCV‐infected tissue (1·78 ng, P