Abstract : The immune system has evolved to protect the host from invading pathogens and to eliminate disease, and the innate and adaptive immune systems work together to provide this protection. The innate immune system, which includes physical (e.g. skin), biochemical (e.g. complement system, lysozymes, interferons), and cellular components, is the first line of defence against invading pathogens (antigens) (e.g. neutrophils, monocytes, macrophages, natural killer cells "NK", natural killer-T cells "NKT"). When the barrier to infection is breached, biochemical components such as lysozymes (which break down the protective peptidoglycan cell wall) and the split products resulting from complement activation destroy the pathogen (e.g. bacteria, fungi, parasites).
