In mammals, macrophages (MF) are present in virtually all tissues where they 
serve many different functions linked primarily to the maintenance of 
homeostasis, innate defense against pathogens, tissue repair and metabolism. 
Although some of these functions appear common to all tissues, others are 
specific to the homing tissue. Thus, MF become adapted to perform particular 
functions in a given tissue. Accordingly, MF express common markers but also 
sets of tissue-specific markers linked to dedicated functions. One of the 
largest pool of MF in the body lines up the wall of the gut. Located in the 
small intestine, Peyer's patches (PP) are primary antigen sampling and mucosal 
immune response inductive sites. Surprisingly, although markers of intestinal 
MF, such as F4/80, have been identified more than 30 years ago, MF of PP escaped 
any kind of phenotypic description and remained "unknown" for decades. In 
absence of MF identification, the characterization of the PP mononuclear 
phagocyte system (MPS) functions has been impaired. However, taking into account 
that PP are privileged sites of entry for pathogens, it is important to 
understand how the latter are handled by and/or escape the PP MPS, especially 
MF, which role in killing invaders is well known. This review focuses on recent 
advances on the PP MPS, which have allowed, through new criteria of PP phagocyte 
subset identification, the characterization of PP MF origin, diversity, 
specificity, location and functions.