Specialized Subsets of Tissue-Resident Macrophages in Secondary Lymphoid Organs

The mammalian immune system has evolved to provide protection from a variety of pathogens while minimizing damage to the host. Precise evaluation of the type and location of the threat is therefore a key to an efficient immune response. Macrophages play a central role in processing and delivering such information and are often positioned in strategic locations within lymphoid organs acting as 'roadblocks' designed to meet and trap their targets at the point of entry. While macrophages can be found in essentially every tissue of the body, their phenotype and functions differ greatly and depend on the environment in which they reside, thus constituting multiple subsets with distinct tissue specific characteristics. This article will focus on specialized subsets of macrophages that occupy key niches within secondary lymphoid organs and highlight the intricate relationship between a macrophage's location, function, and phenotype.