Page 976 - Veterinary Immunology, 10th Edition

VetBooks.ir Basophils

Basophils, the least common type of blood leukocyte, are
functionally similar to mast cells, although their origins and gene

expression profiles are very different. Basophils are
polymorphonuclear granulocytes (10–14 µm in diameter) whose
cytoplasmic granules stain intensely with basic dyes, such as
hematoxylin (Fig. 29.13). These granules are fewer and smaller than
those in mast cells and they contain histamine as well as a restricted

protease profile. Basophils constitute about 0.5% of blood
leukocytes. Unlike mast cells they have a very short lifespan of
about 60 hours in mice and are actively replenished by stem cells.

They are not normally found outside the bloodstream and only
enter tissues under the influence of some T cell–derived
chemokines.

FIG. 29.13 Photomicrographs of peripheral blood basophils from a
horse, a cat, and a dog. These cells are about 10 µm in diameter;
all were photographed at the same magnification. Giemsa stain.
(Courtesy Dr. M.C. Johnson.)

Basophils bind IgE through FcεRI. Antigens binding to this IgE
will cause basophil degranulation and the release of their granule
contents. Basophil granules contain a mixture of molecules similar
to those in mast cells including proteases, amines, and cytokines

such as IL-4 and lipid mediators. When activated, they produce IL-
4, IL-6, IL-13, and TSLP. Basophils release platelet-activating factor
(PAF), a lipid, in response to IgG1-mediated stimulation. PAF is
about 10,000 times more effective than histamine in increasing

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