The so called sentinel cells are located in our skin to detect invasions by e.g. microbes and viruses in terms of the innate immune response. Macrophages and dendritic cells as well as mast cells belong to the class of antigen representing sentinel cells. When an infection is caused by invaders entering our tissue through a damaged epidermis (wound), the sentinel cells respond by releasing cytokines (there are about 50 different cytokines many of them are called Interleukins). Sentinel cell cells do not recognise specific cell types but rather broad classes of invaders and destinguishes between for exapmle a virus or a bacterial infection (as opposed to the adaptive immune response that is more specific).