White blood cells

There are two main groups and five main types of leucocytes.

Granulocytic polymorphs
- Contain granules of proteins for exocytosis. They are named based on their affinity for histological dyes:
- Eosinophils (take up eosin stain)- these are specialist cells involved in the immune response particularly seen in allergic disease (e.g. asthma and allergic rhinitis) and against systemic parasites (e.g. worm disease)
- Basophils (take up basal blue dye)- these contain histamine granules and are possibly involved in allergic disease although no direct role has been identified
- Neutrophils (stain neutral)- phagocytes- engulf and destroy bacteria
- These cells are released from the bone marrow and only circulate for 1-2 days before migrating to tissues where they stay for a further 3 days before dying
  - The body increases production as the body needs, particularly in response to messengers from other leukocytes (granulocyte colony-stimulating factor)
Agranulocytic mononuclear cells
- Monocytes – these are large cells with oval/kidney shaped nuclei. They are released from the bone marrow immature. Mature versions include macrophages. These are also phagocytic cells. However, these can circulate for months and can phagocytose multiple cells/organisms before undergoing autophagy.
- Lymphocytes – part of the adaptive immune system i.e. target specific things to which they are programmed
  - B-lymphocytes produce antibodies and T-lymphocytes directly destroy targets