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[Immunology](https://durgical.com/en/immunology/) · [Immune cells](https://durgical.com/en/immunology/#a-cells)

# CD markers: the table to know

- Topic

CD (cluster of differentiation) numbers name the surface molecules that identify each immune cell; a short list explains most exam questions.

Updated 2026-11-01

## Key points

- All T cells: CD3; helper: CD4 (MHC II); cytotoxic: CD8 (MHC I).
- B cells: CD19, CD20, CD21; plasma cells: CD138.
- NK cells: CD56 and CD16; monocytes and macrophages: CD14.
- Hematopoietic stem cells: CD34; all leukocytes: CD45.
- Treg: CD4, CD25, FOXP3; costimulation: CD28 on T cells binds CD80/CD86 on antigen-presenting cells.

## What it is

CD numbers are an international naming system for cell-surface molecules recognized by antibodies. Laboratories use them in flow cytometry to count and classify cells, and many are also the targets of drugs or the cause of disease when missing. A small set, shown below, covers what exams ask most.

## High-yield CD markers

| Marker | Main cells | What it does or means | Exam link |
| --- | --- | --- | --- |
| CD3 | All T cells | Signals for the T-cell receptor | Pan-T marker in flow cytometry |
| [CD4](https://durgical.com/en/conditions/hiv-infection-and-aids/) | Helper T cells (and some monocytes) | Binds MHC class II | HIV receptor; count used in HIV |
| CD8 | Cytotoxic T cells | Binds MHC class I | Viral and tumor killing |
| CD19, CD20 | B cells | B-cell co-receptor; CD20 lost in plasma cells | Anti-CD20 antibodies in B-cell lymphomas |
| CD21 | B cells | Complement receptor 2 | Receptor for Epstein-Barr virus |
| CD40 / CD40L (CD154) | B cells and APCs / activated CD4 T cells | T-cell help and class switching | CD40L defect: hyper-IgM syndrome |
| CD28 / CD80-CD86 (B7) | T cells / antigen-presenting cells | Second signal of T-cell activation | CTLA-4 competes for B7 (brake) |
| CD25 | Tregs, activated T cells | IL-2 receptor α chain | Treg marker with FOXP3 |
| CD56, CD16 | NK cells (CD16 also neutrophils, macrophages) | CD16 is an IgG Fc receptor | ADCC by NK cells |
| CD14 | Monocytes, macrophages | Binds bacterial lipopolysaccharide with TLR4 | Monocyte marker |
| CD15 | Neutrophils | Carbohydrate adhesion antigen | Also on Reed-Sternberg cells (Hodgkin, with CD30) |
| CD18 | All leukocytes (β2 integrin) | Firm adhesion to endothelium | Leukocyte adhesion deficiency type 1 |
| CD34 | Hematopoietic stem cells | Stem-cell marker | Counted when stem cells are collected for transplant |
| CD45 | All leukocytes | Common leukocyte antigen | Tells a blood-cell tumor from other tumors |
| CD117 (KIT) | Mast cells, stem cells | Stem cell factor receptor | KIT mutation in mastocytosis |
| [CD138](https://durgical.com/en/conditions/multiple-myeloma/) | Plasma cells | Plasma-cell marker | Multiple myeloma |
| CD1a | Langerhans cells | Presents lipid antigens | Langerhans cell histiocytosis |
| CD55, CD59 | Red cells and most cells | Protect cells from complement | Missing in paroxysmal nocturnal hemoglobinuria |

## In the lab

- Flow cytometry labels cells with fluorescent anti-CD antibodies and counts each population.
- Leukemia and lymphoma typing uses panels of CD markers on blood or marrow.
- The CD4 count in HIV is the best-known clinical use.

## Memory aid

B cells live on a short street of three houses in a row, numbers 19, 20 and 21; the stem cell lives at 34, and 45 is the address every white cell shares.

## Test yourself

Think of the answer, then tap the question to see it.

## Which CD marker is found on all T cells?

CD3, part of the T-cell receptor complex.

## Which CD marker does Epstein-Barr virus use to infect B cells?

CD21 (complement receptor 2).

## Which two markers identify NK cells?

CD56 and CD16.

## Which marker identifies hematopoietic stem cells?

CD34.

## Which missing molecule causes leukocyte adhesion deficiency type 1?

CD18, the β2 integrin subunit needed for firm adhesion to endothelium.

[Add to my cards (5)](https://durgical.app/estudiar/?add=/en/immunology/cd-markers-the-table-to-know/)

## Related

- [CD4⁺ helper T cell](https://durgical.com/en/immunology/cd4-helper-t-cell/)
- [CD8⁺ cytotoxic T cell](https://durgical.com/en/immunology/cd8-cytotoxic-t-cell/)
- [B cell and plasma cell](https://durgical.com/en/immunology/b-cell-and-plasma-cell/)
- [Natural killer cell](https://durgical.com/en/immunology/natural-killer-cell/)
- [Regulatory T cell (Treg, FOXP3)](https://durgical.com/en/immunology/regulatory-t-cell/)
- [Monocyte and macrophage](https://durgical.com/en/immunology/monocyte-and-macrophage/)
- [Neutrophil](https://durgical.com/en/immunology/neutrophil/)
- [Flow cytometry and the CD4 count](https://durgical.com/en/immunology/flow-cytometry-and-the-cd4-count/)

## Related conditions

- [HIV infection and AIDS](https://durgical.com/en/conditions/hiv-infection-and-aids/)

[← All of immunology](https://durgical.com/en/immunology/)

Educational content on the immune system; not a treatment or individual vaccination guide and no substitute for a health professional's advice. No doses are given.

Sources: [21.3 The Adaptive Immune Response: T lymphocytes and Their Functional Types](https://openstax.org/books/anatomy-and-physiology-2e/pages/21-3-the-adaptive-immune-response-t-lymphocytes-and-their-functional-types) (OpenStax, Rice University (Anatomy and Physiology 2e), 2022); [Dendritic Cells](https://www.immunology.org/public-information/bitesized-immunology/cells/dendritic-cells) (British Society for Immunology, 2024); [Regulatory T Cells (Tregs)](https://www.immunology.org/public-information/bitesized-immunology/cells/regulatory-t-cells-tregs) (British Society for Immunology, 2024); [Basophils](https://www.immunology.org/public-information/bitesized-immunology/cells/basophils) (British Society for Immunology, 2024).

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Representative model, for educational purposes only.

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/immunology/cd-markers-the-table-to-know/