[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Immunology](https://durgical.com/en/immunology/) › [Immune cells](https://durgical.com/en/immunology/#a-cells) › Monocyte and macrophage

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

# Monocyte and macrophage

- Cell

Monocytes circulate in blood and become macrophages in tissues: big eaters that clean up, kill germs, signal alarm and show antigens to T cells.

Updated 2026-11-01

## Key points

- Monocyte in blood, macrophage in tissue; marker CD14.
- Tissue names: Kupffer cells (liver), alveolar macrophages (lung), microglia (brain), histiocytes (connective tissue), splenic macrophages; osteoclasts belong to the same family.
- Macrophages release IL-1, IL-6 and TNF-α (fever and acute-phase response) and IL-12 (drives Th1 cells).
- Interferon-γ from Th1 cells activates macrophages to kill intracellular microbes.
- Granuloma: activated (epithelioid) macrophages and multinucleated giant cells; TNF-α keeps it intact, so anti-TNF drugs can reactivate latent tuberculosis.

## What it is

Monocytes are the largest white cells in blood, with a kidney- or horseshoe-shaped nucleus. When they enter tissues they mature into macrophages, long-lived phagocytes that remove microbes, dead cells and debris and release cytokines that drive inflammation. Activated by helper T cells, they wall off hard-to-kill microbes such as Mycobacterium tuberculosis inside granulomas.

## Key facts

- Origin: myeloid progenitor in the bone marrow; some tissue macrophages settle before birth and renew locally.
- Lifespan: monocytes circulate for a short time; tissue macrophages live much longer than neutrophils.
- They are professional antigen-presenting cells (MHC class II) but weaker than dendritic cells at starting new T-cell responses.

## Function

- Phagocytosis of microbes, dead cells and old red cells.
- Killing with reactive oxygen species and nitric oxide.
- Recognition of microbes through Toll-like receptors and cytokine release.
- Tissue repair and clean-up after inflammation.

## Markers

- CD14
- CD16 (some monocytes)
- CD68
- MHC class II
- CD80/CD86 when activated

## Clinical notes

- Monocytosis: tuberculosis, chronic inflammatory disease, some viral and parasitic infections and some leukemias.
- Tuberculosis, a public health priority in Colombia, is the classic granulomatous infection of macrophages.
- Defects in the IFN-γ and IL-12 pathway cause severe mycobacterial infections.
- Leishmania and Histoplasma also live inside macrophages.

## In the lab

- Absolute monocyte count in the differential.
- Tissue biopsy: granulomas with epithelioid macrophages and giant cells; stains for acid-fast bacilli.

## Memory aid

Monocyte in the bus, macrophage at the job: it boards the blood, gets off in a tissue and takes the local job title (Kupffer, alveolar, microglia).

## Test yourself

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

## What is a monocyte called once it settles in the liver, and in the brain?

A Kupffer cell in the liver and a microglial cell in the brain.

## Which cytokine from Th1 cells activates macrophages?

Interferon-γ.

## Why can anti-TNF drugs reactivate latent tuberculosis?

TNF-α is needed to keep granulomas intact; blocking it lets contained mycobacteria escape.

## Which three macrophage cytokines cause fever and the acute-phase response?

IL-1, IL-6 and TNF-α.

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## Related

- [Neutrophil](https://durgical.com/en/immunology/neutrophil/)
- [Dendritic cell (professional antigen-presenting cell)](https://durgical.com/en/immunology/dendritic-cell/)
- [Granulomatous inflammation](https://durgical.com/en/immunology/granulomatous-inflammation/)
- [Interferon-γ](https://durgical.com/en/immunology/interferon/)
- [TNF-α](https://durgical.com/en/immunology/tnf/)
- [Antigen processing and presentation](https://durgical.com/en/immunology/antigen-processing-and-presentation/)
- [CD markers: the table to know](https://durgical.com/en/immunology/cd-markers-the-table-to-know/)

## Related conditions

- [Tuberculosis](https://durgical.com/en/conditions/tuberculosis/)
- [Pulmonary tuberculosis](https://durgical.com/en/conditions/pulmonary-tuberculosis/)

## Microorganisms

- [Mycobacterium tuberculosis](https://durgical.com/en/microbiology/mycobacterium-tuberculosis/)

[← 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: [18.4 Leukocytes and Platelets](https://openstax.org/books/anatomy-and-physiology-2e/pages/18-4-leukocytes-and-platelets) (OpenStax, Rice University (Anatomy and Physiology 2e), 2022); [21.2 Barrier Defenses and the Innate Immune Response](https://openstax.org/books/anatomy-and-physiology-2e/pages/21-2-barrier-defenses-and-the-innate-immune-response) (OpenStax, Rice University (Anatomy and Physiology 2e), 2022); [Macrophages](https://www.immunology.org/public-information/bitesized-immunology/cells/macrophages) (British Society for Immunology, 2024); [Blood differential test](https://medlineplus.gov/ency/article/003657.htm) (MedlinePlus, U.S. National Library of Medicine, 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/monocyte-and-macrophage/