Cluster of Differentiation (CD)
Cluster of Differentiation (CD) Related Resources
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We offer a broad portfolio of products including recombinant proteins, native proteins, protein pre-coupled magnetic beads, cell and tissue lysates, chromatography reagents, GMP proteins and assay kits. These products can be used for various applications related to the study of clusters of differentiation (CD).
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About Cluster of Differentiation (CD)
Cluster of differentiation (CD) is a system used to classify cell surface molecules on immune cells. It is a nomenclature that assigns a unique number to each identified cell surface antigen or marker. The CD system was initially developed to help researchers categorize and characterize immune cells based on specific cell surface proteins.
The CD antigens are primarily identified using monoclonal antibodies, which are designed to bind specifically to these surface markers. These antibodies are labeled with fluorescent dyes or other markers, allowing for their detection and analysis using flow cytometry, immunohistochemistry, or other techniques.
The CD system has evolved over time, and currently, there are more than 370 different CD antigens identified. These antigens are expressed on various immune cells, such as T cells, B cells, natural killer (NK) cells, monocytes, macrophages, dendritic cells, and others. Each CD antigen has a specific function or is associated with a particular immune cell subset.
The CD nomenclature does not necessarily indicate the function of the antigen or its ligand but provides a standardized way to identify and classify immune cell populations. The assigned numbers are usually referred to as CD followed by a number (e.g., CD3, CD4, CD8).
The CD system has been instrumental in immunology research, enabling the identification and characterization of immune cell subsets, studying immune responses, and understanding the pathogenesis of various diseases. It has also facilitated the development of diagnostic and therapeutic approaches targeting specific immune cell populations.
It is important to note that the CD system is continuously evolving as new antigens and markers are discovered and characterized. Researchers and immunologists regularly update the CD nomenclature to incorporate new findings and advances in the field of immunology.
Expression Patterns of CD Molecules on Specific Cell Types
| Cell Type | Expression Patterns |
|---|---|
| T cells | CD3 is expressed on all mature T cells. It is involved in T cell receptor (TCR) signaling. CD4: Primarily expressed on helper T cells (CD4+ T cells) and some regulatory T cells (Tregs). CD8 is expressed on cytotoxic T cells (CD8+ T cells). |
| B cells | CD19 is expressed on B cells throughout their development, from early pro-B cells to mature B cells. CD20 is expressed on B cells, except for early pro-B cells and plasma cells. CD21 is expressed on mature B cells and follicular dendritic cells. |
| Monocytes/Macrophages | CD14 is expressed on monocytes, macrophages, and some dendritic cells. It is involved in the recognition of microbial components. CD16 is expressed on subsets of monocytes and macrophages. It is involved in antibody-dependent cellular cytotoxicity (ADCC). |
| Natural Killer (NK) cells | CD56 is expressed on NK cells and a subset of T cells known as natural killer T (NKT) cells. CD16 is expressed on NK cells and is involved in ADCC. |
| Dendritic cells (DCs) | CD11c is expressed on myeloid DCs and a subset of plasmacytoid DCs. CD123 expressed on plasmacytoid DCs. |
| Neutrophils | CD15 is expressed on neutrophils, eosinophils, and some monocytes. |
| Mast cells | CD117 is expressed on mast cells. It is a receptor for stem cell factor (SCF). |
These are just a few examples of CD molecules and their expression patterns on specific cell types. It's important to note that CD molecule expression can vary between individuals and can be influenced by factors such as activation, differentiation, and disease state. Additionally, cells may express a combination of CD molecules, providing a more specific signature for identification and characterization.
Fig.1 Surface antigens. (Julius M, et al., 2004)
Mechanism of Interaction Between CD Molecules and Immune Cells
The interaction between CD molecules and immune cells plays a crucial role in regulating immune responses and coordinating various immune functions. CD molecules are cell surface proteins expressed on different immune cell types. These molecules serve as markers for cell identification and are involved in cell-cell interactions, signaling, and immune modulation. Here is a general overview of the mechanisms of interaction between CD molecules and immune cells:
Cell-Cell Adhesion
CD molecules participate in cell-cell adhesion, allowing immune cells to interact and form stable contacts. For example, ICAM-1 (CD54) on endothelial cells interacts with LFA-1 (CD11a/CD18) on leukocytes, facilitating leukocyte extravasation from blood vessels into tissues during inflammation. This adhesion is essential for immune cell recruitment and migration to sites of infection or injury.
Co-stimulation and T-cell Activation
CD molecules on antigen-presenting cells (APCs) and T cells are critical for T-cell activation and co-stimulation. APCs express CD80 (B7-1) and CD86 (B7-2), which bind to CD28 on T cells, providing the necessary co-stimulatory signals for T-cell activation and proliferation. This interaction is crucial for initiating effective immune responses and maintaining immune tolerance.
Antigen Presentation
MHC class II molecules, represented by HLA-DR in humans, play a central role in antigen presentation to CD4+ T cells. These molecules bind antigens and present them to the T-cell receptor (TCR) on CD4+ T cells. The interaction between MHC class II molecules and the TCR initiates T-cell activation and subsequent immune responses.
Signal Transduction and Immune Modulation
Several CD molecules act as receptors on immune cells and transmit signals upon ligand binding, regulating immune cell functions. For example, CD3 complex, composed of CD3ε, CD3δ, CD3γ, and CD3ζ chains, is a critical component of the TCR complex. CD3 proteins transmit signals from the TCR to the intracellular signaling pathways, leading to T-cell activation and effector functions.
Immune Cell Regulation
CD molecules are also involved in immune cell regulation and tolerance. For instance, regulatory T cells (Tregs) express CD25 (IL-2 receptor α chain) and Foxp3, which are crucial for their immunosuppressive function. CD25 binds IL-2, promoting Treg survival and suppressive activity. Additionally, CD152 (CTLA-4) expressed on T cells interacts with CD80/CD86 on APCs, delivering inhibitory signals that dampen immune responses.
Cytotoxicity and Target Cell Recognition
Natural killer (NK) cells and cytotoxic T lymphocytes (CTLs) express CD16 (FcγRIII) and CD8, respectively, which are involved in target cell recognition and killing. CD16 on NK cells interacts with the Fc region of antibodies bound to target cells, facilitating antibody-dependent cell-mediated cytotoxicity (ADCC). CD8 on CTLs interacts with MHC class I molecules on target cells, mediating specific cytotoxicity against infected or abnormal cells.
These are just a few examples of the mechanisms of interaction between CD molecules and immune cells. The extensive repertoire of CD molecules and their interactions contribute to the complexity and versatility of immune responses, allowing precise regulation and coordination of immune cell functions in health and disease.
Progress and Future Directions of CD Molecular Research
CD molecular research has made significant progress over the years, leading to a better understanding of immune cell biology, immune responses, and disease mechanisms. Here are some key advances and future directions in CD molecular research:
- Identification of Novel CD Molecules: Advances in technologies such as genomics, proteomics, and high-throughput screening have facilitated the discovery of new CD molecules. Researchers continue to identify and characterize novel CD antigens, expanding our knowledge of immune cell subsets, their functions, and their roles in various diseases.
- Functional Characterization: Researchers are delving deeper into the functional characterization of CD molecules. This includes investigating their signaling pathways, downstream effects on immune cell activation, differentiation, and effector functions. Understanding the precise mechanisms by which CD molecules regulate immune responses provides insights into disease pathogenesis and potential therapeutic targets.
- Integration of Omics Approaches: Omics approaches, including genomics, transcriptomics, proteomics, and metabolomics, are being applied to CD molecular research. These approaches provide comprehensive profiling of immune cells, allowing the identification of CD molecules associated with specific immune cell subsets, disease states, and therapeutic responses. Integration of omics data can uncover novel biomarkers and therapeutic targets.
- Immunotherapy and Precision Medicine: CD molecules have become important targets for immunotherapy, including immune checkpoint inhibitors, CAR T-cell therapy, and therapeutic antibodies. Future research will focus on identifying and validating CD molecules as targets for precision medicine, tailoring therapies to individual patients based on their CD molecular profiles and disease characteristics.
- Functional Interplay and Networks: Research is uncovering the complex interplay and networks of CD molecules and their interactions with other immune receptors and signaling pathways. Understanding the crosstalk between CD molecules and their functional networks will provide a more comprehensive understanding of immune cell biology, immune responses, and disease processes.
- Therapeutic Development: The knowledge gained from CD molecular research is driving the development of novel therapeutics. This includes the design of specific agonists or antagonists targeting CD molecules to modulate immune responses, enhance immune cell functions, or restore immune homeostasis. Therapeutic strategies that utilize CD molecules are expected to expand, improving the treatment of immune-related disorders and cancers.
- Personalized Immunology: CD molecular research is contributing to the field of personalized immunology, wherein individual immune profiles can guide diagnosis, prognosis, and treatment decisions. Understanding the variations in CD molecule expression patterns among individuals and their impact on immune responses will pave the way for tailored immunotherapies and precision medicine approaches.
In summary, CD molecular research has made significant progress, and future directions are focused on identifying novel CD molecules, understanding their functional roles, integrating omics approaches, advancing immunotherapy and precision medicine, unraveling functional interplay and networks, and driving therapeutic development. These advancements hold great promise for improving our understanding of immune biology and developing targeted therapies for various diseases.
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Related References
- Julius M. Cruse, Robert E. Lewis, and Huan Wang. Cluster of Differentiation (CD) Antigens. Immunology Guidebook. 2004;47-124. doi:10.1016/B978-012198382-6/50027-3
- Engel P, Boumsell L, Balderas R, et al. CD Nomenclature 2015: Human Leukocyte Differentiation Antigen Workshops as a Driving Force in Immunology. J Immunol. 2015;195(10):4555-4563. doi:10.4049/jimmunol.1502033
- Mason D, André P, Bensussan A, et al. CD antigens 2002. Blood. 2002;99(10):3877-3880. doi:10.1182/blood.v99.10.3877
