Ask A Scientist:
What’s the Difference Between Human Monocytes and Macrophages?

ask a scientist

ask a scientistMonocytes and macrophages are very closely related cells with a few important distinctions and different use cases. Put simply, monocytes are macrophages in the blood; macrophages are monocytes in tissue.

Understanding the Difference

Monocytes are the largest type of white blood cells and play an important role in the adaptive immunity process. Monocytes typically circulate through the blood for 1–3 days before migrating into tissues, where they become macrophages or dendritic cells.

Macrophages are monocytes that have migrated from the bloodstream into any tissue in the body. Here they aid in phagocytosis to eliminate harmful materials such as foreign substances, cellular debris and cancer cells.

Macrophages take on various names depending on the tissue to which they migrated:

  • Kidney: Intraglomerular Mesangial Cells — Specialized pericytes that monitor glucose levels
  • Liver: Kupfer Cells — Phagocytic cells that express macrophage biomarkers
  • Lungs: Alveolar Macrophages — Found in the pulmonary alveolus and “clean” respiratory surfaces
  • Lymph Nodes: Sinus Histiocytes — Immobile macrophages found in the medullary sinuses
  • Placenta: Hofbauer Cells — Thought to prevent vertical transmission of pathogens from mother to fetus
  • Skin: Langerhans — Dendritic cells in the skin and mucosa associated with HIV, HPV and LCH
  • Several Others

These subpopulations of macrophages have functional differences due to environmental signals but are all part of the same macrophage family.

Use Cases for Monocytes

Our monocytes are purified from peripheral blood and are versatile enough to meet your exact needs. With monocytes, you can:

  1. Thaw and use in an assay the same day
  2. Culture dendritic cells
  3. Culture to make macrophages
  4. Produce a variety of cytokines and chemokines

For in vitro studies, most laboratories culture monocytes for five days in the presence of M-CSF, at which point they consider the cells to be macrophages. Monocytes can also be cultured with GM-CSF or IFNγ added to the medium. These cytokines push the cells toward a more inflammatory phenotype.

Use Cases for Macrophages

Because macrophages can have suppressive effects on tumors, they are used to study various infections and immunotherapies. You can use your macrophages to:

  • Study chemotaxis
  • Study effects of drugs on macrophage functions
  • Study their role in wound healing

6 thoughts on “Ask A Scientist:
What’s the Difference Between Human Monocytes and Macrophages?

    • Avatar
      Anne Lodge says:

      Pigment cells are called melanocytes. There are probably other cell types with pigment but those are the ones that first come to mind.

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    Andrew says:

    Hi Dr. Lodge. I am confused between these different cell types: lymphocytes, leukocytes, monocytes, white blood cells, and macrophages. They all seem to be extremely similar and I am having trouble with the hierarchy. Another question I had is regarding infiltrating macrophages in the brain. We use markers such as CD11b and CD45 (low and high), to stain for infiltrating macrophages and resting/activated microglia, but I am a bit confused on what the “low” and “high” really means, and what cell type t specifically targets. I apologize for such the loaded questions, and I would very much appreciate it if you take your time to give me some clarity. Thank you!

    • Avatar
      Anne Lodge says:

      Hi Andrew, thanks for your questions. It can be quite confusing and the nomenclature doesn’t help. Leukocytes and white blood cells are the same thing. Leukocyte is just the scientific term. Leuko means “white” and cyte means cell. Lymphocytes and monocytes are both white blood cells but they are different in many ways, including morphology, development and function. The post you’ve just commented on discusses the difference between monocytes and macrophages and it is again, more of a naming problem. Monocytes are found in blood, macrophages are found in solid tissue.
      When you are looking at cells infiltrating the brain you will find any white blood cell will be positive for CD45 and the macrophages will be CD11b positive. You may be trying to distinguish the microglia with the CD45 stain since they have a lower expression of CD45. It is hard to see the difference if you are staining tissue sections but if you stain with fluorescent antibodies and analyze by flow cytometry the difference is pretty obvious.

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    Nisha Kumari says:

    Can exogenous macrophages (isolated from one animal) cross the blood-brain barrier after the intravenous injection?

    • Avatar
      Anne Lodge says:

      I would predict that they would. I think that this has been shown in fact. Richard Ransohoff published some nice papers on trafficking through the brain back in the 90’s. You might take a look at that work.

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