Q.How do cytokine barriers provide innate immunity in humans?

Non-specific, or innate, immunity is the immune system's general-purpose, always-ready defence. It does not need to recognise a specific pathogen in advance, and it is traditionally described as acting in two lines, built on a broader set of four kinds of barrier.

The first line of defence consists of external barriers that try to stop a pathogen from ever entering the body at all — the skin, mucus lining the respiratory and digestive tracts (which traps particles before they can penetrate deeper), and secretions such as saliva and tears, which contain the enzyme lysozyme that breaks down bacterial cell walls.

The second line of defence comes into play once a pathogen has actually breached the first line: phagocytic cells that engulf the invader, natural killer (NK) cells that destroy infected or abnormal cells, the inflammatory response (localised redness, heat, swelling and pain as blood vessels dilate and immune cells are recruited to the site), and fever (a body-wide rise in temperature that makes conditions less favourable for many pathogens and speeds up immune cell activity). …