Immunology for Non-Immunologists: Surface Antigen Expression

What Is Surface Antigen Expression?

Surface antigens, or cell markers, are a handy way for scientists to classify cells based on cell type and function, which is beneficial for early-stage research as well as disease diagnosis and treatment. 

The cluster of differentiation (CD) nomenclature was adopted in the early 1980s and serves as a global standard for characterizing cells based on antibody specificity. Every human leukocyte has a CD marker, ranging from widely known for T cells (CD3, CD4, CD8) and B cells (CD19, CD20) to more niche markers for endothelial cells (CD146) and epithelial cells (CD326).

Learn how to use OMIM.org to find detailed information on protein or receptor gene function and expression. 

Cell Markers as an Activation Measure

As we’ve previously discussed with cytokine measurement assays and proliferation assays, cell markers can be used to measure immune cell activation. The surface antigens that are expressed in a given assay can give you clues as to which cells are participating in the immune response. 

For example, when T cells are activated, the surface antigens expressed undergo a change. Scientists can exploit and study these changes to monitor the response of T cells to an antigen stimuli. Surface antigens that are upregulated upon activation include increases in cytokine receptors, costimulatory molecules, or receptors used in traveling to different sites. Common examples of markers that are upregulated during an immune response are CD69, CD25, and CD44. 

The table below lists some of the most commonly utilized markers, their functions, and use cases.

AntigenFunctionTiming of UpregulationComments
CD69Costimulatory moleculeAs early as one hour
CD25Part of the IL-2 receptor24-48 hours after activationCD25 is expressed on Tregs, so this may not always be specific
MHC Class IIPresentation of antigenUnknownFound on human T cells but not murine
CTLA-4Regulation of T cell activation24-48 hours after activationCheckpoint inhibitor
PD-1Regulation of T cell activation24 hours after stimulation and decreases thereafterCheckpoint inhibitor; Also used as a marker of exhaustion
CD107aLysosome associated membrane protein-1, involved in movement of lytic granules4 hours after stimulationUsed to detect degranulation; Surrogate for cytotoxicity

Ready to Learn More?

To learn more about surface antigen expression, access a recording of our webinar, 14 Ways to Measure Immune Cell Activation.

If you have specific research questions, you can always get a quick answer by asking an Astarte scientist, or by submitting a custom research request for additional help in your lab.

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