The Innate Immune system covers three areas
1. The skin and mucosal membranes
The skin and the lining of the body cavities that open to the outside must provide a protective barrier. The entrance to the organs like the gut and the reproductive tract needs to prevent invasion by any pathogenic micro organisms. The oil or ‘sebum produced by the skin keeps its pH slightly acidic which controls the growth of any organisms on the skin. The mucosal membranes secrete a variety of fluids, such as saliva by the gastro-intestinal tract and mucus in the respiratory tract, which provide a defence against pathogenic micro-organisms. The body carries its own natural ‘flora’ of micro-organisms that we happily live with, which also prevent other more dangerous bugs from taking over.
2. Secreted soluble proteins
These proteins and enzymes, such as lysozyme, c-reactive protein, interferons and the complement system, are present in the body secretions and fluids and attack different micro-organisms in a variety of ways, often by dissolving their protective layer.
3. Cells
Most of the white blood cells, called granulocytes (including neutrophils, basophils and eosinophils), alongside others called macrophages, mast cells and natural killer (NK) cells, have a role in initial defence. They arrive at the site of damage or infection and either eat up the invading organisms (known generally as ‘antigens’) by a process called phagocytosis, or release chemicals toxic to the invader. Some of them also play a part in killing abnormal cells or tidying up the debris after such a fight.
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