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.
|Antigen||Function||Timing of Upregulation||Comments|
|CD69||Costimulatory molecule||As early as one hour|
|CD25||Part of the IL-2 receptor||24-48 hours after activation||CD25 is expressed on Tregs, so this may not always be specific|
|MHC Class II||Presentation of antigen||Unknown||Found on human T cells but not murine|
|CTLA-4||Regulation of T cell activation||24-48 hours after activation||Checkpoint inhibitor|
|PD-1||Regulation of T cell activation||24 hours after stimulation and decreases thereafter||Checkpoint inhibitor; Also used as a marker of exhaustion|
|CD107a||Lysosome associated membrane protein-1, involved in movement of lytic granules||4 hours after stimulation||Used 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.