Project Summary Adipose tissue is a site where the immune system and metabolic pathways intersect. Adipocytes are now recognized as antigen presenting cells for lipids and likely directly activate natural killer T cells (NKT cells) via CD1d. NKT cells are potent modulators of the immune system that are able to regulate the function of other cell types largely by their capacity to rapidly produce large amounts of a wide variety of cytokines. Recent data show that adipose resident NKT cells (arNKT cells) modulate diet-induced weight gain and influence metabolism. When eating a calorically balanced diet, arNKT cells appear to encourage adipocytes to maintain a healthy tissue environment and prevent insulin resistance. Nearly all of the innate-like functions of NKT cells are dependent upon the BTB-ZF transcription factor, PLZF (zbtb16). Therefore, it is surprising that arNKT cells do not express PLZF. To our knowledge, this is the only population of NKT cells that does not continuously express the transcription factor. Chronic inflammation is associated with weight gain and subsequent metabolic disease. arNKT cells were shown to induce an anti- inflammatory response both by modulating macrophage functions and by impacting the frequency, proliferation and function of FoxP3-expressing Tregs. We propose that altered PLZF expression will impact these arNKT cell functions, which in turn, will alter the metabolism of white adipose tissue. Our studies will determine if changes in PLZF expression in arNKT cells alters their ability to control obesity and metabolic changes. We will use an innovative array of genetically modified mouse models that allow for variation in the levels of PLZF expression. We hypothesize that PLZF protein levels are essential for the control of arNKT cell functions and if the levels are altered, the onset of obesity and metabolic disease will increase. Data supporting this conclusion will lead to future studies to determine if variability in PLZF expression in humans is potentially a contributing factor to obesity. Importantly, analysis of arNKT cells that do not function correctly is expected to reveal new information about the mechanisms by which arNKT cells normally function.