F2R and acute monocytic leukemia: To investigate the potential mechanism of CatG-induced MHC I expression, human acute monocytic leukemia cell line (THP-1), which only expresses PAR1 and PAR4 [21], was incubated with the PAR1 antagonist (FR171113, FR) [22] or the PAR4 antagonist (tcY-NH2) [23] in the presence or absence of CatG.