Resident Tissue Leukocytes: Underappreciated Guards of the Body

Inflammatory reactions occurring in different milieu follow common phases with major highlights being local changes in vascular permeability and influx of inflammatory leukocytes that eliminate the source of inflammation while subsequent resolution is completed by tissue repair. The main inflammatory cells consist of blood-derived neutrophils and macrophages that arrive to the inflammatory site in response to a chemotactic signal. However, their arrival to the loci is initiated by a special set of leukocytes already present in various places of the body such as skin or body cavities that are called tissue or resident leukocytes. The cells consist of mast cells, macrophages and lymphocytes. Although the presence of resident leukocytes is commonly recognized their actual involvement in subsequent stages of inflammation is underappreciated while the cells are critical for all phases of the reaction. The current mini-review describes the role of resident leukocytes in the initiation, the course, and the termination of exemplary acute inflammatory reaction, namely zymosan-induced peritonitis. Additionally, facts on human resident peritoneal leukocytes are presented and discussed.