CD8 (TCR, Leu2, T8)

CD8 (cluster of differentiation 8), also known as Leu-2 and T8, is a ~68 kDa transmembrane glycoprotein primarily expressed on the surface of cytotoxic (CD8⁺) T cells, as well as some populations of thymocytes, dendritic cells and NK cells. As a T cell co-receptor, CD8 plays a pivotal role in T cell signaling, assists CD8⁺ T cells in the recognition of antigen presenting MHC class I molecules, and can serve as a cell adhesion molecule. While the full functionality of CD8 is yet to be determined, it has been shown to be a potent co-receptor capable of enhancing T cell activation and differentiation.

CD8 Isoforms

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CD8 can be expressed as either a CD8αα homodimer or as a CD8αβ heterodimer on the surface of T cells, and each is encoded by a different gene. Although both isoforms act as T cell co-receptors for T cell activation and differentiation, they have their own unique characteristics. For example, CD8αβ is primarily expressed on the surface of TCRαβ thymocytes and peripheral T cells, as well as certain dendritic cells and double negative thymocytes (e.g. CD4⁺CD8⁺). CD8αα, can be found on intestinal intraepithelial cells, NKT cells and is known to have a broader expression pattern in tissue section. While the function of CD8αα is not fully understood, CD8αβ however, is required for positive selection of CD8⁺ T cells and for the activation of CD8⁺ T cells in periphery.

The extracellular domain of CD8α and CD8β is comprised of an IgG variable domain and an intracellular tail which is joined together by a thin stalk region approximately 30-45 amino acids long. In both isoforms, the extracellular domain of CD8α is responsible for interacting with tyrosine kinase p56 Lck, and through this association modulates T cell activation and development, as well as down regulate cytokine production in T helper cells.

CD8 Antibodies

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The HIT8a, OKT-8 and SK1 monoclonal CD8 antibodies are designed to recognize and react with the human CD8? chain, a component found in both CD8 isoforms. Anti-CD8 antibodies are frequently used in flow cytometry, immunoblotting (WB) and immunofluorescence applications to identify immune cell subsets expressing CD8 and examine the role of CD8 in cytotoxic T cell activation. In clinical research studies, CD8 has shown to play a key part in regulating HIV replication during the inital phases of infection. During HIV infection, CD8⁺ T cells can recognize and eliminate infected cells through interactions with MHC class I molecules.

AAT Bioquest offers a comprehensive catalog of CD8 antibodies purified by affinity chromatography and conjugated to a variety of fluorophores under optimal conditions that minimize unconjugated fluorophore and antibody. Available fluorophores include:

• iFluor® dyes - bright, photostable dyes with optimized flow cytometry (FACS), fluorescence imaging and in vivo imaging applications.
• mFluor™ dyes - bright, photostable dyes with optimized for flow cytometry (FACS) applications.
• Alexa Fluor^® dyes - suitable for flow cytometry (FACS) and fluorescence imaging applications.
• Classic dyes - suitable for flow cytometry (FACS) and fluorescence imaging applications.
• Phycobiliproteins and Tandem dyes - intensely bright dyes for flow cytometry (FACS) and multiparametric analysis.

1. FC = Flow Cytometry; ELISA = Enzyme-linked immunosorbent assay; IF = Immunofluorescence; IHC-F = Immunohistochemistry (Frozen); WB = Western Blot.

iFluor® Dyes Labeled to CD8 Antibodies

The following table outlines the fluorescence properties of available iFluor® dye labeled anti-human CD8 antibodies for use in flow cytometry (FACS), immunoblotting (WB) and fluorescence imaging applications. Conjugates made with iFluor® dyes exhibit superior brightness and photostability, outperforming Alexa Fluor^® conjugates and other spectrally similar conjugates. For additional information on iFluor® dye-labeled CD8 antibodies and availability of other clones click on any label in the table below.

1. ε = molar extinction coefficient at their maximum absorption wavelength (Units = cm^-1M^-1).
2. Φ = fluorescence quantum yield in aqueous buffer (pH 7.2).
3. CF at 260 nm is the correction factor used for eliminating the dye contribution to the absorbance at 260 nm (for oligo and nucleic acid labeling).
4. CF at 280 nm is the correction factor used for eliminating the dye contribution to the absorbance at 280 nm (for peptides and protein labeling).

mFluor™ Dyes Labeled to CD8 Antibodies

The following table outlines the fluorescence properties of available mFluor™ dye labeled anti-human CD8 antibodies for use in flow cytometry (FACS). Each mFluor™ dyes is optimally excited by one of the major laser lines commonly equipped in flow cytometers, such as the 405 nm, 488 nm, 532 nm, 561 nm or 633 nm laser lines. For additional information on mFluor™ dye-labeled CD8 antibodies and availability of other clones click on any label in the table below.

1. ε = molar extinction coefficient at their maximum absorption wavelength (Units = cm^-1M^-1).
2. Φ = fluorescence quantum yield in aqueous buffer (pH 7.2).
3. CF at 260 nm is the correction factor used for eliminating the dye contribution to the absorbance at 260 nm (for oligo and nucleic acid labeling).
4. CF at 280 nm is the correction factor used for eliminating the dye contribution to the absorbance at 280 nm (for peptides and protein labeling).

Alexa Fluor^® Dyes Labeled to CD8 Antibodies

The following table outlines the fluorescence properties of available Alexa Fluor^® dye labeled anti-human CD8 antibodies for use in flow cytometry (FACS) and fluorescence imaging applications. For additional information on Alexa Fluor^® dye-labeled CD8 antibodies and availability of other clones click on any label in the table below.

1. ε = molar extinction coefficient at their maximum absorption wavelength (Units = cm^-1M^-1).
2. Φ = fluorescence quantum yield in aqueous buffer (pH 7.2).
3. CF at 280 nm is the correction factor used for eliminating the dye contribution to the absorbance at 280 nm (for peptides and protein labeling).

Classic Dyes Labeled to CD8 Antibodies

The following table outlines the fluorescence properties of available classic dye labeled anti-human CD8 antibodies for use in flow cytometry (FACS) and fluorescence imaging applications. For additional information on classic dye-labeled CD8 antibodies and availability of other clones click on any label in the table below.

1. ε = molar extinction coefficient at their maximum absorption wavelength (Units = cm^-1M^-1).
2. Φ = fluorescence quantum yield in aqueous buffer (pH 7.2).
3. CF at 280 nm is the correction factor used for eliminating the dye contribution to the absorbance at 280 nm (for peptides and protein labeling).

PE, APC, PerCP and Tandem Dyes Labeled to CD8 Antibodies

The following table outlines the fluorescence properties of available phycoerythrin (PE), allophycocyanin (APC), PerCP and tandem dye labeled anti-human CD8 antibodies for use in flow cytometry (FACS). Phycobiliproteins are uncharacteristically bright due to their high molar extinction coefficients and quantum yields, an enviable quality when imaging low-abundance targets. However, since phycobiliprotiens photobleach rapidly, they are not recommended for microscopy. For additional information on phycobiliprotein-labeled CD8 antibodies and availability of other clones click on any label in the table below.

1. ε = molar extinction coefficient at their maximum absorption wavelength (Units = cm^-1M^-1).

References

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1. Clement, M., Ladell, K., Ekeruche-Makinde, J., Miles, J. J., Edwards, E. S., Dolton, G., Williams, T., Schauenburg, A. J., Cole, D. K., Lauder, S. N., Gallimore, A. M., Godkin, A. J., Burrows, S. R., Price, D. A., Sewell, A. K., & Wooldridge, L. (2011). Anti-CD8 antibodies can trigger CD8+ T cell effector function in the absence of TCR engagement and improve peptide-MHCI tetramer staining. Journal of immunology (Baltimore, Md. : 1950), 187(2), 654-663. https://doi.org/10.4049/jimmunol.1003941
2. Gulzar N, Copeland KF. CD8+ T-cells: function and response to HIV infection. Curr HIV Res. 2004;2(1):23?37. doi:10.2174/1570162043485077.
3. Li, Y., Yin, Y., & Mariuzza, R. A. (2013). Structural and biophysical insights into the role of CD4 and CD8 in T cell activation. Frontiers in immunology, 4, 206. https://doi.org/10.3389/fimmu.2013.00206
4. Sun, J., Leahy, D. J., & Kavathas, P. B. (1995). Interaction between CD8 and major histocompatibility complex (MHC) class I mediated by multiple contact surfaces that include the alpha 2 and alpha 3 domains of MHC class I. The Journal of experimental medicine, 182(5), 1275-1280. https://doi.org/10.1084/jem.182.5.1275.
5. Wang, R., Natarajan, K., & Margulies, D. H. (2009). Structural basis of the CD8 alpha beta/MHC class I interaction: focused recognition orients CD8 beta to a T cell proximal position. Journal of immunology (Baltimore, Md. : 1950), 183(4), 2554-2564. https://doi.org/10.4049/jimmunol.0901276