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Subject - Immunology

Making up about two thirds of the total population, granulocytes make up the majority of the leukocytes (white blood cells). They are characterized by a large number of cell inclusions (granules) that contain messenger and effector substances, which can be released on demand. Different types of granulocytes are:

Basophil granulocytes, also called basophils, are specialized in the defence against parasites, and patrol the blood stream. They make up less than 1 % of the granulocytes. Basophils display receptors for immunoglobuline E (IgE) on their cell surface. If these receptors are cross linked by IgE antibodies bound to an allergen, the basophils degranulate and secrete imunnomodulating mediators, e.g. histamine. Via this pathway, they are involved in immediate allergic reactions.

Mast cells are similar to basophil granulocytes, but they are found in tissues. They play a critical role in immediate allergies (type 1). Vesicles containing immunomodulating substances are incorporated inside the mast cells. Mast cells also display receptors for IgE antibodies on their surfaces. Upon crosslinking of these receptors by an allergen, the mast cells degranulate and release these mediators inside their granules.

Eosinophil granulocytes, also called eosinophils are also involved in defence against parasites and allergic reactions. They comprise 2-4 % of the granulocytes.

Neutrophil granulocytes, also called neutrophils or neutrophil phagocytes, are the largest group of granulocytes (over 90 %). They are small scavenger cells in the blood and are specialized in targeting viruses, bacteria, and fungi.

See also: macrophages , mast cells , phagocytes , antibodies