Innate immunity is the first line of defence of the body against any invading pathogen and provides immediate immunity to the body. It comprises of the physical barriers and their secretions such as the skin and the mucous lining of the gastrointestinal tract and the respiratory tract that prevents any foreign pathogen from invading the body and the cells such as the macrophages, neutrophils, monocytes, mast cells etc. that are involved in phagocytosis of the pathogen, activation of the complement system, secreting cytokines or histamines etc. which in turn help attack or destroy the invading pathogen and initiate repair processes.