Cluster of differentiation (CD) are cell surface molecules expressed on the cells of the immune system, which play key roles in immune cell-cell communication, sensing the microenvironment and in adaptive immunity. During lymphocyte maturation, immune cells will express complex variations of CD antigens on its cell surface, some of which are lost, while others are acquired at various stages either by interactions with antigen presenting cells (APC) or with other cells of the immune system. In flow cytometric immunophenotyping, monoclonal antibodies targeting CD antigens are extensively used for the identification and characterization of leukocyte populations, subpopulations and differentiation stages. AAT Bioquest features purified anti-human CD antibodies and fluorescently labeled CD antibody conjugates applicable for a wide range of research disciplines including, flow cytometry, immunohistochemistry and immunoblotting applications.

Since immune cells express CD antigens at various stages of development or cell activation, they serve as reliable biomarkers for differentiating leukocyte populations and subpopulations, a technique referred to as immunophenotyping. For example, CD3 is a T cell co-receptor exclusively expressed on the surface of all mature T cells, while CD4 and CD8 antigens are expressed on the surface of T helper cells and cytotoxic T cells, respectively.

In addition, CD antigen expression can be influenced by certain disease conditions, and as such are often used as diagnostic or prognostic factors for the identification of leukemia's and lymphomas. For example, multiple myeloma is generally characterized by cells expressing CD38 but not CD19 and CD20. Because CD antigens are expressed at varying degrees and cell types, multiparameter flow cytometric analysis utilizing two or more combinations of fluorescently labeled CD antibodies enables clear resolution of particular cell type or subtype.

The CD nomenclature is a universally adopted designation system sanctioned by the World Health Organization (WHO). This system was designed for the classification of monoclonal antibodies (mAbs) directed against epitopes on the surface molecules of leukocytes. For difficult to characterize cell surface molecules, or ones only recognized by a single mAb, they are given the designation 'CDw' (e.g. CDw60 or CDw156). If the surface molecule is well characterized (recognized by two or more mAbs), then they are assigned an arbitrary value, such as CD4, CD8 or CD45.

CD nomenclature is also used to describe lymphocyte and leukocyte subtypes. The presence or absence of a specific antigen from the surface of the particular cell population is denoted with "+" or "-" respectively. A "+" symbol added to a CD number indicates the presence of that molecule on a cell or cell population, whereas a "-" indicates its absence. For example, a 'CD45+/CD20-' cell is one that expresses CD45, but not CD20. Cell populations can also be defined as hi or low indicating an overall variability in CD expression, particularly when compared to other cells being studied.

AAT Bioquest offers a comprehensive selection of purified CD antibodies and fluorescently labeled CD antibody conjugates for multicolor flow cytometry, immunohistochemistry and functional assays. Available fluorophores include:

The following table outlines the fluorescence properties of available iFluor™ dye labeled anti-human CD antibodies for use in flow cytometry (FACS) 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 CD antibodies and availability of other clones click on any label in the table below.

The following table outlines the fluorescence properties of available mFluor™ dye labeled anti-human CD 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 CD antibodies and availability of other clones click on any label in the table below.

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

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

The following table outlines the fluorescence properties of available phycoerythrin (PE), allophycocyanin (APC), PerCP and tandem dye labeled anti-human CD 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 phycobiliproteins photobleach rapidly, they are not recommended for microscopy. For additional information on phycobiliprotein-labeled CD antibodies and availability of other clones click on any label in the table below.

Need assistance selecting the best fluorophore for your experiment, use our Fluorescence Spectrum Viewer: