White blood cells are the key players in your immune system. They are made in your bone marrow and are part of the lymphatic system.

White blood cells move through blood and tissue throughout your body, looking for foreign invaders (microbes) such as bacteria, viruses, parasites and fungi. When they find them, they launch an immune attack.
White blood cells include lymphocytes (such as B-cells, T-cells and natural killer cells), and many other types of immune cells.

Antibodies help the body to fight microbes or the toxins (poisons) they produce. They do this by recognising substances called antigens on the surface of the microbe, or in the chemicals they produce, which mark the microbe or toxin as being foreign. The antibodies then mark these antigens for destruction. There are many cells, proteins and chemicals involved in this attack.

The complement system is made up of proteins whose actions complement the work done by antibodies.

• manage the fluid levels in the body
• react to bacteria
• deal with cancer cells 
• deal with cell products that otherwise would result in disease or disorders
• absorb some of the fats in our diet from the intestine. 

• lymph nodes (also called lymph glands) — which trap microbes
• lymph vessels — tubes that carry lymph, the colourless fluid that bathes your body’s tissues and contains infection-fighting white blood cells
• white blood cells (lymphocytes).

Bone marrow is the spongy tissue found inside your bones. It produces the red blood cells our bodies need to carry oxygen, the white blood cells we use to fight infection, and the platelets we need to help our blood clot.

The spleen is a blood-filtering organ that removes microbes and destroys old or damaged red blood cells. It also makes disease-fighting components of the immune system (including antibodies and lymphocytes).

The thymus filters and monitors your blood content. It produces the white blood cells called T-lymphocytes.