Your body has a defence system in place to protect it from foreign invaders like bacteria, viruses and parasites. This exquisite system has many working parts involving many organs throughout the body but the soldiers of this defence system are your white blood cells (WBC). There are a number of different types of WBC that circulate throughout your blood stream:
- Neutrophil: Most abundant WBC. They eat bacteria and fungi and when they die they form pus.
- Eosinophils: Deal with parasitic infections but also play a role in allergies.
- Basophils: Least abundant WBC. Responsible for recognizing foreign invaders and in allergic response.
- Lymphocytes: Come in three varieties: T-cells, B-cells and natural killer cells. They are important in your immune memory.
- Monocyte: Generally move into tissues where they eat up invaders and display them to other members of the immune system for education.
There are also WBC that don’t circulate but instead reside in certain tissues in the body. These include:
- Dendritic cells: Found in tissues that are in contact with the outside environment.
- Mast cells: Important in wound healing.
- Macrophage: Found in almost all tissues to eat up foreign invaders to destroy them.
- Microglia: Only present in the brain and spinal cord. Important in keeping the brain safe from invaders.
The number of WBC circulating in your blood is often an indicator of infection or disease. Most WBC only live for a short time, between 6 hours to a couple days. However, the lymphocytes (T, B and Natural killer cells) survive for years in order to retain a memory of the infection you fought off. When you are vaccinated, it is the T-cells and B-cells that retain the memory of the vaccine in order to fight off the invader next time.