The human endoplasmic reticulum aminopeptidase (ERAP) 1 and 2 proteins were 
initially identified as homologues of human placental leucine 
aminopeptidase/insulin-regulated aminopeptidase. They are categorized as a 
unique class of proteases based on their subcellular localization on the luminal 
side of the endoplasmic reticulum. ERAPs play an important role in the 
N-terminal processing of the antigenic precursors that are presented on the 
major histocompatibility complex (MHC) class I molecules. ERAPs are also 
implicated in the regulation of a wide variety of physiological phenomena and 
pathogenic conditions. In this review, the current knowledge on ERAPs is 
summarized.