Basophil vs. Eosinophil

What's the Difference?

Basophils and eosinophils are both types of white blood cells, specifically granulocytes, that play important roles in the immune system. Basophils are characterized by their large, dark-staining granules and make up a small percentage of the total white blood cell count. They are involved in allergic reactions and release histamine, which causes inflammation and helps to attract other immune cells to the site of infection or injury. On the other hand, eosinophils have smaller, bright-staining granules and are also present in low numbers. They are primarily responsible for combating parasitic infections and play a role in allergic reactions as well. Eosinophils release toxic substances that help to kill parasites and modulate the immune response. Overall, while both basophils and eosinophils are involved in immune responses, they have distinct functions and characteristics.


Cell TypeGranulocyteGranulocyte
Size12-15 μm12-17 μm
Nucleus ShapeBilobedBilobed
GranulesLarge, dark-staining granulesLarge, bright-staining granules
FunctionAllergic reactions, immune responseParasitic infections, allergic reactions
LocationBloodstream, tissuesBloodstream, tissues

Further Detail


White blood cells, also known as leukocytes, play a crucial role in our immune system by defending our body against harmful pathogens and foreign substances. Among the various types of white blood cells, basophils and eosinophils are two important components. While both basophils and eosinophils are granulocytes, they have distinct characteristics and functions. In this article, we will delve into the attributes of basophils and eosinophils, exploring their structure, function, role in the immune response, and associated disorders.


Basophils are a type of granulocyte that make up only a small percentage of the total white blood cell count. They are characterized by their large, irregularly shaped nuclei and abundant granules in their cytoplasm. These granules contain various substances, including histamine, heparin, and cytokines, which are released upon activation.

Basophils primarily function in allergic reactions and immune responses against parasites. When an allergen enters the body, basophils release histamine, which triggers an inflammatory response. This response leads to vasodilation, increased blood flow, and the recruitment of other immune cells to the site of infection or injury. Basophils also play a role in the defense against parasites by releasing substances that are toxic to these organisms.

Despite their relatively low numbers, basophils are essential for maintaining homeostasis and initiating immune responses. However, abnormalities in basophil count or function can lead to various disorders. Basophilia, an increase in basophil count, may be seen in conditions such as chronic myeloid leukemia, polycythemia vera, and certain allergic reactions. On the other hand, basopenia, a decrease in basophil count, can occur in severe infections, stress, or during certain drug treatments.


Eosinophils, like basophils, are granulocytes with a bilobed nucleus and prominent cytoplasmic granules. These granules contain enzymes, major basic protein, eosinophil peroxidase, and other substances involved in the immune response. Eosinophils are primarily associated with allergic reactions, asthma, and defense against parasites.

One of the key functions of eosinophils is their involvement in allergic reactions. When an allergen is encountered, eosinophils are recruited to the site of inflammation. They release their granules, which contain histaminase, an enzyme that breaks down histamine, thereby reducing the allergic response. Eosinophils also play a role in asthma, as their activation can lead to airway inflammation and constriction.

Additionally, eosinophils are crucial in the defense against parasites, particularly helminths. These white blood cells release toxic substances that can kill or immobilize parasites, aiding in their elimination. Eosinophils also modulate the immune response by interacting with other immune cells and releasing cytokines.

Similar to basophils, abnormalities in eosinophil count or function can indicate underlying health conditions. Eosinophilia, an increase in eosinophil count, may be observed in allergic disorders, parasitic infections, certain autoimmune diseases, and some types of cancers. Conversely, eosinopenia, a decrease in eosinophil count, can occur during acute stress, severe infections, or as a result of corticosteroid therapy.


While basophils and eosinophils share some similarities, such as being granulocytes and participating in immune responses, they also have distinct attributes that set them apart.

  • Structure: Basophils have large, irregularly shaped nuclei, while eosinophils have bilobed nuclei.
  • Granules: Basophils contain granules that release histamine, heparin, and cytokines, whereas eosinophils have granules containing enzymes, major basic protein, and eosinophil peroxidase.
  • Function: Basophils primarily function in allergic reactions and defense against parasites, while eosinophils are involved in allergic reactions, asthma, and defense against parasites.
  • Allergic Response: Basophils release histamine to trigger an inflammatory response, while eosinophils release histaminase to break down histamine and reduce the allergic response.
  • Parasite Defense: Basophils release substances toxic to parasites, while eosinophils release toxic substances and interact with other immune cells to eliminate parasites.


Basophils and eosinophils, two types of granulocytes, play vital roles in our immune system. While basophils primarily function in allergic reactions and defense against parasites, eosinophils are involved in allergic reactions, asthma, and parasite defense. Understanding the attributes and functions of these white blood cells helps us appreciate their significance in maintaining our health and combating infections. Monitoring basophil and eosinophil counts can also aid in diagnosing and managing various disorders. By unraveling the complexities of these cells, researchers continue to uncover new insights into the immune response and potential therapeutic targets.

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