Barriers: Human skin, alimentary tract, respiratory system, genital tract act as barriers.
Innate killer cells: Innate killer cells are a type of white blood cell or lymphocyte. It destroys virus infected cells and tumor cells.
Interferon: Interferon is a high molecular weight glycoprotein. It is produced by virus-infected cells and prevents the virus from multiplying.
Complement system: Complement system is a group of 20 types of plasma proteins. These inactive proteins are converted into active proteins that kill the bacteria.
Inflammatory response: Macrophages and neutrophils are activated and destroy the microbes.
Symbiotic bacteria: Symbiotic bacteria live in the body’s skin, genitals and digestive system. They destroy microbes by secreting chemicals.