Innate, as the name suggests, is something that is inbuilt or natural. Innate immunity mechanisms include physical barriers such as skin, mucous membrane, mucus, chemicals in the blood, and immune system cells that attack foreign cells in the body. These special cells which form the cellular barriers of the innate immune response are macrophages, neutrophils, monocytes and natural killer cells. These cells cannot distinguish one pathogen from another, and kill almost any pathogen or infected cells by the process of phagocytosis.