The
immune system is a complex network of cells and proteins that defends
the body against infection. The immune system keeps a record of every
germ (microbe) it has ever defeated so it can recognise and destroy the
microbe quickly if it enters the body again.
The
immune system is spread throughout the body and involves many types of
cells, organs, proteins, and tissues. Crucially, it can distinguish our
tissue from foreign tissue — self from non-self.
- White blood cells circulate in the body in blood vessels and the lymphatic vessels that parallel the veins and arteries. When they find a target, they begin to multiply and send signals out to other cell types to do the same.
Our
white blood cells are stored in different places in the body, which are
referred to as lymphoid organs. so recognized and cleared away by the
immune system.
These include the following:
- Thymus — a gland between the lungs and just below the neck.
- Spleen — an organ that filters the blood. It sits in the upper left of the abdomen.
- Bone marrow — found in the center of the bones, it also produces red blood cells.
- Lymph nodes —small glands positioned throughout the body, linked by lymphatic vessels.
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