PRF1 and metabolic dysfunction-associated steatotic liver disease: However, it is known that T-bet is a key transcription factor which results in the differentiation of iNK cells to mNK cells (9, 25), and it has been demonstrated that perforin-deficient mice develop less fibrosis in a model of non-alcoholic fatty liver disease, suggesting that reduction in cNK cell cytotoxicity is protective in the steatotic liver (31).