IL18 and infection: However, in response to a foreign antigen such as SARS-CoV2, peripheral blood monocytes are recruited into the alveoli where they differentiate into M1 macrophage which produce inflammatory cytokines such as IL-1, IL-6, and IL-18 which in turn attract neutrophils cells into the alveoli to fight the infection, leading to infection clearance through reactive oxygen species (ROS) and phagocytosis.