Basophils are a type of white blood cell produced in the bone marrow. As granulocytes, they are characterized by the large granules visible within their cellular structure. While they are the largest of the granulocytes, they are the least common, making up less than one percent of all circulating white blood cells in the bloodstream.
Primary Function in Allergic Responses
Basophils play a part in the body’s immediate allergic reactions. Their cell surface contains protein receptors that bind to an antibody known as Immunoglobulin E (IgE). When a person has an allergy, their immune system produces an excess of IgE in response to otherwise harmless substances, such as pollen, dust mites, or certain foods. This IgE then attaches to the surface of basophils and similar immune cells called mast cells.
Upon subsequent exposure to the same allergen, the substance binds to the IgE antibodies coating the basophils. This connection triggers a process called degranulation, where the basophil rapidly releases the contents of its internal granules into the surrounding tissues. This process is a driver of the symptoms experienced during an allergic reaction.
A primary substance released from these granules is histamine. Histamine acts on local blood vessels, causing them to widen and become more permeable, which leads to increased blood flow and leakage of plasma into the tissues. This causes the immediate symptoms of an allergy, such as swelling, hives on the skin, a runny nose, and itching. Basophils also release other compounds like leukotrienes, which contribute to inflammation and bronchoconstriction, the tightening of airways seen in asthma.
Broader Roles in the Immune System
Beyond their involvement in allergies, basophils contribute to the body’s defense against parasites, particularly larger organisms like parasitic worms (helminths). When the immune system detects these invaders, basophils are recruited to the site and release substances that help expel the parasites. This response, sometimes called a “weep and sweep” reaction, involves creating an inflammatory environment that makes it difficult for the parasite to remain attached to host tissues.
Basophils also release heparin, a substance that acts as an anticoagulant to prevent blood from clotting too quickly. At a site of inflammation or infection, maintaining blood flow is important for allowing other immune cells to reach the area. By releasing heparin, basophils help ensure that small clots do not obstruct the movement of these responding cells, facilitating a more effective immune response.
The release of cytokines, which are signaling proteins, is another function of basophils. One such cytokine, interleukin-4 (IL-4), plays a part in modulating the activity of other immune cells, including B-cells and T-cells. This signaling helps coordinate the broader immune response, influencing the direction and intensity of the defense mounted by the body.
Significance of Basophil Count in Blood Tests
A complete blood count (CBC) with differential is a common blood test that measures the levels of different types of blood cells, including basophils. An abnormally high count of basophils is a condition known as basophilia. Basophilia can be an indicator of chronic inflammation in the body and may be associated with autoimmune conditions like rheumatoid arthritis or inflammatory bowel disease.
Certain blood-related disorders can also lead to basophilia. For example, myeloproliferative neoplasms, conditions where the bone marrow produces too many blood cells, can result in elevated basophil levels. Chronic myelogenous leukemia is one such condition where basophilia is often observed. Hypothyroidism, a condition where the thyroid gland is underactive, has also been linked to an increased number of basophils.
Conversely, an abnormally low basophil count, or basopenia, can also be informative. Basopenia may be seen during acute infections, severe allergic reactions, or periods of physiological stress. An overactive thyroid gland (hyperthyroidism) can also lead to a decrease in basophil numbers. An abnormal basophil count is not a diagnosis on its own but a signal for a healthcare provider to investigate the underlying cause.