Basohils are the rarest type of granulocytic leukocyte, constituting less than 1% of peripheral blood white cells.
They are characterized by their large cytoplasmic granules, containing potent mediators such as histamine, leukotrienes, and cytokines, especially IL-4 and IL-13/
They can be recognized by several coarse, dark violet granules, giving them a blue hue.
The nucleus is bi- or tri-lobed, but it is hard to see because of the number of coarse granules that hide it.
They secrete two chemicals that aid in the body’s defenses: histamine and heparin.
Histamine is responsible for widening blood vessels and increasing the flow of blood to injured tissue, and makes blood vessels more permeable so neutrophils and clotting proteins can get into connective tissue more easily.
Heparin is an anticoagulant that inhibits blood clotting and promotes the movement of white blood cells into an area.
Basophils can also release chemical signals that attract eosinophils and neutrophils to an infection site.
Basophils express the high-affinity IgE receptor (FcεRI).
They are rapidly activated in IgE-dependent allergic reactions, as well as by various innate stimuli, leading to degranulation and release of their effector molecules.
Basophils play roles in the initiation and amplification of type 2 (Th2) immune responses, including allergic inflammation and defense against helminthic parasites.
Basophils contribute to tissue inflammation by promoting vascular permeability, recruiting other leukocytes, and modulating the differentiation of T cells toward a Th2 phenotype.
They are distinct from mast cells, despite some phenotypic similarities.
They are key regulators in a range of immune responses, including allergy, autoimmunity, tissue repair, and even tumor biology.
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