Expression of interleukin-15 and its receptor by human fetal retinal pigment epithelial cells

Purpose. IL-15 and IL-15 receptor expression was measured in retinal pigment epithelial (RPE) cells to support a possible role of IL-15 in ocular inflammatory and immune responses. Methods. Reverse transcription-coupled polymerase chain reaction (RT-PCR) and Northern blot analysis of IL-15 mRNA in previously characterized non-transformed and simian virus (SV)-40 transformed human fetal RPE cells were carried out. Biological activities of IL-15 produced by the RPE cells were assayed by co-culture with IL-15 responsive cells. Expression of the IL-15 receptor (IL-15R) alpha, IL-2R beta and gamma chains were examined by RT-PCR. Results. Both non-transformed and SV-40 transformed human fetal RPE cells express IL-15, a T cell growth factor which has similar biological activities to IL-2, and the expression of IL-15 is enhanced by interferon-gamma (IFN-gamma) or tumor necrosis factor-alpha (TNF-alpha) stimulation. In addition, transcripts for all three IL-15 receptor components (IL-15R alpha, IL-2R beta and IL-2R gamma) were detected in these cells. Conclusions. RPE cells produce IL-15, which may play an important role in ocular immune and inflammatory responses by stimulating infiltrated T cells and RPE cells via paracrine and autocrine loops, respectively.