Expression of IFI 16 in epithelial cells and lymphoid tissues.

IFI 16 is a member of the HIN-200 protein family named for their haemopoietic expression, interferon-inducibility and nuclear localisation. These proteins have been characterised as transcriptional regulators that modulate the cell cycle. IFI 16 is expressed in some haemopoietic lineages including CD34+ progenitor cells, mature lymphocytes and monocytes, but is absent from granulocytes, erythrocytes and megakaryocytes. We present a wider study of IFI 16 expression in normal human tissues using a monoclonal antibody specifically recognising the C-terminus of IFI 16. As expected, IFI 16 was detected in the nuclei of lymphocytes in the spleen, thymus, lymph node and palatine tonsil, but was also found in epithelial cells in these tissues. Interestingly, IFI 16 protein was also expressed in non-lymphoid tissues including trachea, gastrointestinal tract, skin and testis, but was absent from others including heart and brain. In each tissue, IFI 16 was predominantly expressed in surface epithelial cells and staining was strongest in basal epithelial layers. Therefore, IFI 16 expression is not restricted to cells of the immune system, but is also expressed in epithelial cells. In contrast to the perceived role of HIN-200 proteins as suppressors of cell growth, maximal expression of IFI 16 was in cells with high proliferative potential.