A Guide to Basophil Markers

Basophils are granulocytic white blood cells that represent about 0.5%–1% of circulating white blood cells. They are a critical component of the immune response against allergens, parasites, and pathogens, releasing histamine and heparin during allergic reactions and eliminating foreign invaders via phagocytosis. Their rarity, lack of genetically homogenous cells and animal models for their study, and historical difficulty isolating them have made basophils a relatively under-studied population of white blood cells. 

Techniques such as flow cytometry have simplified the identification of basophils, however, and the basophil activation test (BAT) is used regularly in the clinic to diagnose allergies. Further optimization and development of the BAT is expanding the utility of basophil identification in other conditions, including autoimmune urticaria and leukemia. This guide summarizes the most commonly used markers used to identify basophils.

This diagram highlights general basophil markers and markers during basophil activation.

Markers Used to Identify Basophils

Often, basophils are physically separated from other white blood cells after confirming expression of basophil-specific markers, but flow cytometry can identify basophil populations whether they will be physically separated from other cells or not. Most of the markers discussed in this article are appropriate for both physical separation and flow cytometry-based identification of basophils.

Basophils are most similar to mast cells, which are white blood cells also involved in allergic reactions. Both express a variety of different adhesion receptors, cytokine receptors, and other cell surface markers. Basophil-specific markers that can be used to differentiate them from the closely related mast cells include CD18, CD31, and CD123 (IL-3Rɑ).

CD203c is an additional basophil-specific marker often used to differentiate basophils from other white blood cells, including mast cells, eosinophils, and neutrophils. CCR3 is another basophil-specific marker that can be used alone or in combination with other markers to positively identify basophils. Cytokine receptors expressed by basophils include IL-2R, CD116, and IL-8R; however, their use in identifying basophils, while it has been reported, is limited.

CD170, CD172a (SIRP-α), and CD184 (CXCR4) are also expressed to varying degrees by basophils; however, because they are expressed by other white blood cells, they must be used in combination with other markers to positively identify basophils. Although basophils express a number of MHC class II receptors, they do not express HLA-DR, which is often used in combination with any of the aforementioned markers to identify basophils (always HLA-DR negative).

Markers for Activated Basophils

The basophil activation test was developed after initial reports of CD63 as an activation marker expressed by basophils. As CD63 is also expressed by the highly related mast cells, it cannot be used as an independent marker. Anti-IgE has been routinely used to identify activated basophil populations; however, newer protocols suggest CD203c, CD123, and CCR3 (CD193) may be more reliable markers of activated basophils.

Stimulating whole blood to activate basophils in an IgE-FcɛRI (IgE receptor) dependent manner during the BAT impacts the expression of several of the typical markers used for basophil identification, including CD203c (increases), CD123 (decreases), and CCR3 (decreases). Therefore, a variety of gating strategies for successfully identifying basophils via the BAT have been reported.

CD123 is one of the most commonly used markers in these assays; CD123/CCR3, CD123/HLDAR-, and CD123/FcɛRI are successful gating strategies for identifying activated basophils. Combining FcɛRI with CD203c or CCR3 also yields clearly identified basophil populations. CD13 is an additional marker that can be used in combination with CD203c.

Additional marker combinations used to successfully identify activated basophils include CCR3/CD203c/IgE/, CRTH2/IgE, and CD203c/IgE. Negative staining for CD3 is also often used in combination with several of the aforementioned markers/marker combinations to exclude activated Th2 lymphocytes and ensure the identification of pure basophil populations.

Table of Basophil Markers

The table below lists human and murine markers of basophils as described by recent literature. Accompanying each marker are links to relevant antibodies and ELISA kits, as these immunodetection tools are routinely used in cell characterization studies via flow cytometry and immunostaining. The associated products are offered by a variety of manufacturers and can serve as a useful reference for identifying and isolating basophils.

Note: *Some markers are protein isoforms, multi-subunit protein complexes, or protein families composed of several distinct genes. Information on Protein Type, Localization, and Size (kDa) obtained from UniProt.org (for human genes only). 

References

1. Sonder SU, Plassmeyer M, Loizou D et al. Towards standardizing basophil identification by flow cytometry. Front Allergy. 2023; 4:1133378. doi: 10.3389/falgy.2023.1133378

2. Eberlein B, Hann R, Eyerich S et al. Optimizing of the basophil activation test: Comparison of different basophil identification markers. Cytometry B Clin Cytom. 2015; 88(3):183-9. doi: 10.1002/cyto.b.21203

3. Ghannadan M, Hauswirth AW, Schernthaner GH et al. Detection of Novel CD Antigens on the Surface of Human Mast Cells and Basophils. Int Arch Allergy Immunol. 2002; 127(4):299-307. doi: 10.1159/000057747

4. Hoffmann HJ, Santos AF, Mayorga C et al. The clinical utility of basophil activation testing in diagnosis and monitoring of allergic disease. Allergy. 2015; 70(11):1393-405. doi: 10.1111/all.12698

5. Chirumbolo S. State-of-the-art review about basophil research in immunology and allergy: is the time right to treat these cells with the respect they deserve? Blood Transfus. 2012; 10(2): 148–168. doi: 10.2450/2011.0020-11

6. Hennersdorf F, Florian S, Jakob A et al. Identification of CD13, CD107a, and CD164 as novel basophil-activation markers and dissection of two response patterns in time kinetics of IgE-dependent upregulation. Cell Res. 2005; 15(5):325-35. doi: 10.1038/sj.cr.7290301