What are the main methods the human body uses to prevent infection from micro-organisms?

The human body has evolved to be able to protect itself from it's external environment, especially preventing microbes entering the body, invading our cells and causing infectious diseases. Some of the common methods include:Skin acting as a mechanical barrier to the external environment. Therefore a cut or graze leaves that area of the body more exposed to entry from micro-organismsHairs in the nose are able to trap micro-organisms and act as a filter to the air we breathe from our surroundings, making it safer for us breathe in.Mucus is produced by special cells lining the windpipe which allows micro-organisms to be caught and then removed when the mucus is wafted up and out of the our bodies by microscopic hairs called cilia.