Granulocyte markers

Granulocytes are a vital class of white blood cells that form an essential part of the innate immune system, acting as the body’s first responders to invading pathogens. Produced in the bone marrow, these cells are characterized by the presence of large cytoplasmic granules, which are visible under a microscope and give granulocytes their name. These granules are packed with antimicrobial proteins and effector molecules, such as eosinophil cationic protein, eosinophil peroxidase, and major basic protein, which play a crucial role in neutralizing bacteria, viruses, and parasites. Once matured, granulocytes circulate in the blood and can be rapidly recruited to tissues at sites of infection or inflammation, where they help eliminate pathogens and regulate immune responses. Their ability to store and release potent antimicrobial proteins makes them indispensable for the body’s defense against a wide range of infections, including viral and parasitic infections.

Types of Granulocytes

There are four main types of granulocytes, each with distinct features and functions: neutrophils, eosinophils, basophils, and mast cells. Neutrophils are the most abundant type, making up 50-70% of circulating leukocytes in human blood. They are easily recognized by their multilobed nuclei and the presence of granules in their cytoplasm. Eosinophils, which have a characteristic bilobed nucleus, are especially important in the regulation of immune responses to parasitic infections and in modulating inflammation. Basophils are the least common granulocyte in peripheral blood but play a significant role in allergic reactions and immune regulation. Mast cells, while similar to basophils, are primarily found in tissues rather than circulating in the blood and are key players in allergic responses and inflammation. All these cell types share the defining feature of granules in their cytoplasm, which are critical for their immune functions.

Functions of Granulocytes

Granulocytes are central to the innate immune system, where they perform a variety of functions to protect the body from infection and maintain immune balance. These cells can engulf and destroy pathogens through phagocytosis, release cytokines to coordinate immune responses, and secrete granules filled with antimicrobial proteins that directly attack bacteria, viruses, and parasites. Neutrophils are particularly effective against bacterial infections, rapidly migrating to sites of infection and releasing their granule contents to neutralize pathogens. Eosinophils are specialized for combating parasitic infections and also help regulate inflammation. Basophils and mast cells are involved in the activation and regulation of allergic reactions, releasing histamine and other mediators that contribute to inflammation. Additionally, granulocytes can present antigens to T cells, bridging innate and adaptive immunity and ensuring a coordinated immune response.

Neutrophils are a key component of the innate immune system, often identified by their expression of specific surface markers. Among these, CD11b plays a role in adhesion and migration, while CD14 is involved in recognizing bacterial components. CD15 is commonly used to distinguish granulocytes in flow cytometry, and CD54 contributes to cell–cell interactions during inflammation. These markers help researchers and clinicians monitor immune responses, study disease progression, and develop targeted therapies. Their expression levels can vary depending on activation state, tissue environment, and pathological conditions. By analyzing combinations of these markers, scientists gain insights into neutrophil function and behavior across different biological contexts. This approach supports ongoing efforts in immunology, oncology, and infectious disease research, offering a practical framework for cell identification and characterization.

CD11b

CD11b, also known as integrin alpha M, is widely used to identify granulocytes in flow cytometry and immunohistochemistry. Expressed on neutrophils, monocytes, and macrophages, CD11b plays a role in cell adhesion and migration. Its surface presence increases during inflammation, making it a reliable indicator of immune activation. Researchers studying innate immunity and inflammatory responses often use CD11b to track granulocyte behavior. This marker supports investigations into autoimmune conditions, infectious diseases, and cancer immunology, contributing to a deeper understanding of immune cell dynamics.

Figure 1. Flow Cytometry - Anti-CD11b antibody [M1/70] (ab8878).

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CD14

CD14 is a membrane glycoprotein commonly used to identify monocytes and granulocytes in immunological studies. It binds lipopolysaccharides and plays a role in recognizing bacterial components, making it useful in tracking innate immune responses. CD14 expression varies across cell types and activation states, offering insights into inflammation and infection. Researchers often use CD14 in flow cytometry to distinguish granulocyte subsets and monitor immune cell behavior. Its presence supports studies in immunopathology, vaccine development, and host–pathogen interactions.

Figure 2. Immunohistochemistry (Formalin/PFA-fixed paraffin-embedded sections) - Anti-CD14 antibody [SP192] (ab183322).

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CD15

CD15, also known as Lewis x antigen, is a carbohydrate marker expressed on the surface of granulocytes, particularly neutrophils. It is commonly used in flow cytometry and immunohistochemistry to identify and isolate these cells. CD15 plays a role in cell–cell interactions and migration during immune responses. Its expression helps distinguish granulocytes from other leukocyte populations, supporting studies in inflammation, infection, and hematologic disorders. Researchers often rely on CD15 to explore immune cell behavior and to refine diagnostic and therapeutic strategies in immunology and oncology.

Figure 3. Multiplex immunohistochemistry - Anti-CD15 antibody [SP159] (ab135377).

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CD54

CD54, also known as intercellular adhesion molecule-1 (ICAM-1), is expressed on granulocytes and other immune cells. It facilitates leukocyte adhesion and migration during inflammatory responses. CD54 expression increases under cytokine stimulation, making it a useful marker in studies of immune activation and cell trafficking. Researchers use CD54 to investigate granulocyte behavior in conditions such as autoimmune diseases, infections, and cancer. Its role in cell–cell interaction supports applications in flow cytometry, immunohistochemistry, and therapeutic development targeting immune modulation.

Figure 4. Western blot - Anti-ICAM1 antibody [EPR24639-3] (ab282575).

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Basophils are a rare type of granulocyte involved in immune regulation and allergic responses. Their identification relies on a combination of surface markers that distinguish them from other leukocytes. CD45 is a pan-leukocyte marker that confirms hematopoietic origin, while CD123, the interleukin-3 receptor alpha chain, is highly expressed on basophils and aids in their functional analysis. CD294, also known as CRTH2, is associated with type 2 immune responses and helps differentiate basophils from other CD123-positive cells. These markers are commonly used in flow cytometry and immunophenotyping to study basophil activation, migration, and cytokine production. Understanding their expression patterns supports research in immunology, allergy, and inflammation, offering a practical approach to cell identification and functional profiling. This marker combination continues to be a valuable tool for scientists investigating basophil biology in both health and disease.

CD45

CD45, a protein tyrosine phosphatase, is expressed on most hematopoietic cells including basophil granulocytes. It plays a role in signal transduction and cell activation. In flow cytometry, CD45 helps distinguish basophils from other leukocytes based on expression intensity and scatter properties. Its use in combination with other markers enhances basophil identification in allergy, inflammation, and immunotherapy research. CD45 supports studies exploring basophil function, cytokine release, and immune regulation, contributing to a more refined understanding of granulocyte subsets.

Figure 5. Flow Cytometry - Anti-CD45 antibody [EPR27167-58] (ab303670).

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CD123

CD123, the alpha chain of the interleukin-3 receptor, is a surface marker commonly used to identify basophil granulocytes. It is expressed at high levels on basophils, making it useful in flow cytometry for distinguishing these cells from other leukocytes. CD123 supports research into allergic responses, cytokine signaling, and hematologic profiling. Its application in immunophenotyping helps researchers explore basophil function in inflammation, hypersensitivity, and immune regulation. CD123 is often used alongside other markers to refine cell population analysis in both clinical and research settings.

Figure 6. Immunocytochemistry/ Immunofluorescence - Anti-IL3RA/CD123 antibody [EPR24481-20] - BSA and Azide free (ab280370).

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CD294

CD294, also known as CRTH2, is a G protein–coupled receptor expressed on basophils and other type 2 immune cells. It binds prostaglandin D2 and plays a role in chemotaxis and immune signaling. CD294 is commonly used in flow cytometry to identify basophils, especially in studies of allergic inflammation and asthma. Its selective expression supports research into basophil activation, cytokine production, and immune regulation. CD294 helps researchers explore pathways involved in hypersensitivity and contributes to profiling basophil responses in clinical and experimental settings.

Figure 7. Immunohistochemistry (Formalin/PFA-fixed paraffin-embedded sections) - Anti-CRTH2 antibody (ab150632).

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Eosinophils are granulocytes involved in immune defense and allergic inflammation. Their identification relies on a distinct set of surface markers that help differentiate them from other leukocytes. CD49b, an integrin subunit, contributes to cell adhesion and migration. CD66b is commonly associated with granulocyte activation and is useful in distinguishing eosinophils from neutrophils. CD125, the interleukin-5 receptor alpha chain, plays a role in eosinophil development and survival. CD193, also known as CCR3, is a chemokine receptor that guides eosinophil trafficking to inflamed tissues. These markers are widely used in flow cytometry and immunophenotyping to study eosinophil behavior in various biological and clinical contexts. By analyzing their expression, researchers gain insights into eosinophil function in allergy, asthma, and parasitic infections, supporting broader investigations into immune regulation and disease mechanisms.

CD49d

CD49d, also known as integrin alpha-4, is a surface protein expressed on eosinophils and other leukocytes. It plays a role in cell adhesion and migration by interacting with vascular cell adhesion molecule-1 (VCAM-1). In immunophenotyping, CD49d is used to identify eosinophil granulocytes and study their behavior in allergic inflammation, asthma, and autoimmune conditions. Its expression pattern helps distinguish eosinophils from other granulocytes, supporting research into immune cell trafficking and tissue infiltration. CD49d is often used in combination with other markers for detailed immune profiling.

Figure 8. Western blot - Anti-Integrin alpha 4/CD49D antibody [EPR1355Y] (ab81280).

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CD66b

CD66b, a member of the carcinoembryonic antigen family, is primarily expressed on granulocytes, including eosinophils and neutrophils. It plays a role in cell adhesion, activation, and migration during immune responses. In flow cytometry and immunohistochemistry, CD66b is used to identify eosinophil subsets and monitor their activity in allergic reactions, parasitic infections, and chronic inflammation. Its expression helps differentiate eosinophils from other leukocytes, supporting research into immune regulation and disease progression. CD66b contributes to detailed profiling of granulocyte behavior in both clinical and experimental settings.

Figure 9. Flow Cytometry - Anti-CD66b antibody [GM-2H6] (ab48589).

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CD125

CD125, the alpha chain of the interleukin-5 receptor, is a surface marker prominently expressed on eosinophil granulocytes. It plays a role in eosinophil growth, activation, and survival, making it valuable in studies of allergic inflammation and parasitic infections. CD125 is commonly used in flow cytometry to identify eosinophils and monitor their response to cytokine signaling. Its expression supports research into immune regulation, asthma, and other eosinophil-associated conditions. CD125 helps researchers explore targeted therapies and refine immune cell profiling in both clinical and experimental settings.

Figure 10. Immunohistochemistry (Formalin/PFA-fixed paraffin-embedded sections) - Anti-IL-5RA antibody [CAL40] (ab237716).

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CD193

CD193, also known as CCR3, is a chemokine receptor expressed on eosinophil granulocytes and other type 2 immune cells. It plays a role in cell migration by binding eotaxins, guiding eosinophils to sites of inflammation. CD193 is widely used in flow cytometry to identify eosinophils and study their involvement in allergic diseases, asthma, and parasitic infections. Its selective expression supports investigations into immune cell trafficking and cytokine signaling. CD193 helps researchers explore eosinophil function and refine diagnostic approaches in immunological studies.

Figure 11. Flow Cytometry - Alexa Fluor® 488 Anti-CCR3 antibody [5E8] (ab270656).

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References

1. Wood, B. Multicolor Immunophenotyping: Human Immune System Hematopoiesis  Methods Cell Biol.   75  ,559-576 (2004)
2. Elghetany, M., Elghetany, M. Surface Antigen Changes during Normal Neutrophilic Development: A Critical Review  Blood Cells, Mol. Dis.   28  ,260-274 (2002)
3. Mantovani, A., Cassatella, M. A., Constantini, C., Jaillon, S. Neutrophils in the activation and regulation of innate and adaptive immunity  Nat. Rev. Immunol.    11  ,519-531 (2011)
4. Behnen, M., et al. Immobilized Immune Complexes Induce Neutrophil Extracellular Trap Release by Human Neutrophil Granulocytes via Fc RIIIB and Mac-1. J  Immunol.   193 ,1954-1965 (2014).