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Immunity and infection prevention

Monocytes and macrophages

This topic builds on the main article on monocytes and macrophages (“Monocytes and macrophages”) and answers a practical question: what do monocytes in a blood test tell you during leukaemia and its treatment, and how do macrophages protect the body?

Last updated: ~1 min read
The first large monocytes on an empty field.
Figure 1.After chemotherapy, monocytes often return first.

01Short answer

When the bone marrow recovers after chemotherapy, monocytes are often the first cells to reappear in the blood; neutrophils follow a few days later. So the return of monocytes can be an early sign of recovery. A raised monocyte count (monocytosis) can happen with infection, inflammation and recovery, while in some leukaemias (monocytic AML, chronic myelomonocytic leukaemia) the cancer cells look like monocytes. Tissue macrophages, especially in the lungs, are an important line of defence against fungal spores.

02Simple explanation

First sign of recovery: after chemotherapy, monocytes often return first.

Monocytosis is not always disease.

Macrophages protect the lungs against fungi.

03Scientific explanation

Differential: MedlinePlus explains that the differential shows the share of five types of white cell; monocytes are usually a small part.

Monocytic leukaemias: in some AML subtypes and CMML, cancer cells can spread into the gums and skin, which is taken into account at diagnosis.

04What happens in the body?

The recovery wave

Rising monocytes while neutrophils are still low often show the marrow is “waking up”. But neutrophils remain the main measure of protection.

Macrophages in tissues

Macrophages in the lungs, liver and spleen swallow microbes and signal to other cells. Their role matters especially during deep neutropenia.

A macrophage reaching for a spore in the lung.
Figure 2.A macrophage engulfs a fungal spore.

When leukaemia looks like monocytes

In monocytic AML or CMML, swollen gums and skin nodules can occur. Tell your doctor about these signs.

Cells gathering in gum tissue.
Figure 3.In monocytic leukaemia, gums can swell.

05Monocytes in a blood test

Four steps.

Test — The differential is done.1TestThe differential is done.
Recovery — Monocytes return.2RecoveryMonocytes return.
Protection — Macrophages stand guard.3ProtectionMacrophages stand guard.
Meaning — The doctor explains.4MeaningThe doctor explains.

06Monocytes: what might it mean?

SituationPossible explanation
Rise after chemotherapyBone marrow recovery
Rise during infectionImmune response
Persistently highThe doctor may investigate further
Very lowTreatment or marrow weakness

07Key terms

Monocyte
A large white cell in the blood.
Macrophage
A “swallowing” cell living in tissues.
Monocytosis
A raised monocyte count.
CMML
Chronic myelomonocytic leukaemia.
Differential
The share of each white cell type.

08Key points

  • Monocytes can be an early sign of recovery.
  • Monocytosis is not always disease.
  • Neutrophils are the main measure of protection.
  • Macrophages matter against fungi.
  • Report swollen gums to your doctor.
  • Interpret results with your doctor.

09Frequently asked questions

My monocytes are up but neutrophils are still low. Am I protected yet?

Not yet. Precautions continue until neutrophils recover.

Does monocytosis mean the leukaemia is back?

Usually not; it is more often linked to infection or recovery. Your doctor will investigate if needed.

Can macrophages be seen in a blood test?

Not in a routine blood test; they live in tissues.

10Questions for your doctor

Take these questions to your appointment. The ones you save are collected on the “My questions” page and stay on this device only.

  1. My monocytes are up but neutrophils are still low. Am I protected yet?

  2. Does monocytosis mean the leukaemia is back?

  3. Can macrophages be seen in a blood test?

My questions

12Sources

  1. MedlinePlus (U.S. National Library of Medicine). Blood Differential
  2. MedlinePlus (U.S. National Library of Medicine). White Blood Count (WBC)
  3. InformedHealth.org (IQWiG) via NCBI Bookshelf. How does the immune system work?
  4. National Cancer Institute (NCI). Infection and Neutropenia during Cancer Treatment
  5. National Cancer Institute (NCI). Chronic Lymphocytic Leukemia Treatment (PDQ®) — Patient Version
  6. National Cancer Institute (NCI). CAR T Cells: Engineering Patients’ Immune Cells to Treat Their Cancers
  7. NHS. Sepsis
  8. American Cancer Society. How Is Acute Myeloid Leukemia Classified?
  9. American Cancer Society. Typing of Acute Lymphocytic Leukemia (ALL)
  10. National Cancer Institute (NCI). Mouth and Throat Problems during Cancer Treatment
Medical disclaimerThis information is for educational purposes only and does not replace medical advice.
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