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Short answer: CD11b (gene ITGAM, also called integrin αM, Mac-1 or complement receptor 3) is a cell-surface integrin subunit that pairs with CD18. It is found mainly on myeloid cells such as neutrophils and monocytes, and on some NK, B and T cells, so it marks a family of cells rather than a single lineage.
This page is general reference for researchers and laboratory staff. It does not cover antibody clones, reagent selection or individual panel design.
What CD11b is
CD11b is the αM subunit of a β2 integrin. It pairs with the common β2 subunit, CD18, to form the heterodimer CD11b/CD18 (Arnaout 2016). The same complex has several names, Mac-1 and complement receptor 3 (CR3), and the gene for the CD11b chain is ITGAM (Schittenhelm et al. 2017).
Arnaout describes it as the most promiscuous β2 integrin, with more than 40 reported ligands, including the complement fragment iC3b, ICAM-1 to ICAM-4 and fibrin(ogen). Reported functions include phagocyte adhesion to inflamed endothelium, phagocytosis of serum-opsonized particles, and phagocytosis-induced neutrophil apoptosis; CD11b-deficient mice are more susceptible to sepsis. For the complement side of this, see the classical pathway of complement.
What type of cells express CD11b?
CD11b predominates on myeloid cells and is the most abundant integrin on neutrophils. It is also reported on NK cells, fibrocytes, some mast cells, B cells, CD8+ T cells and γδ T cells (Arnaout 2016). The practical consequence for any marker panel is that CD11b positivity does not identify one cell type on its own.
Monocytes, macrophages and dendritic cells (human)
- Monocytes: CD11b is high; CD11c is present but lower than CD11a and CD11b.
- Macrophages: CD11b is lower than on monocytes, while CD11c is similar to monocytes.
- Dendritic cells: CD11b is on monocyte-derived DCs and conventional DCs, higher on cDC2 than cDC1, and not on plasmacytoid DCs.
All three points are from Schittenhelm et al. (2017). For how these cells relate, see monocyte-to-macrophage differentiation and dendritic cell function.
Can NK cells express CD11b?
Yes. NK cells are among the non-myeloid populations listed as expressing CD11b (Arnaout 2016). Because neutrophils, monocytes and NK cells can all be CD11b-positive, CD11b is normally read together with other markers rather than alone.
What is the difference between CD11b and CD11c?
Both are α chains of β2 integrins that share the CD18 partner, but they are different proteins with overlapping ligands and different cell distributions. The table summarises only what the two review articles state.
| Feature | CD11b | CD11c |
|---|---|---|
| Integrin chain and partner | αM; pairs with CD18 | αX; pairs with CD18 |
| Complex names | Mac-1, CR3 | CR4 (p150,95) |
| Ligands | iC3b, C4b (high affinity), ICAM-1 to ICAM-4, fibrinogen; more than 40 reported | iC3b, ICAM-1, ICAM-4, VCAM-1, fibrinogen |
| Human monocytes | High | Present, below CD11a and CD11b |
| Human macrophages | Lower than monocytes | Similar to monocytes |
| Human DCs | moDCs and cDCs; higher on cDC2; not pDCs | Mature DCs; higher on cDC2; absent from pDCs |
| Mouse DCs | Subset-specific; higher on CD8− than CD8+ splenic DCs; absent from pDCs | Mainly a DC marker, on cDCs and pDCs |
| Other cells | Neutrophils (most abundant integrin), NK cells, fibrocytes and others | In human also monocytes, macrophages, granulocytes, NK cells |
Sources: Arnaout (2016); Schittenhelm et al. (2017).
What is the CD11c marker for?
CD11c is used chiefly as a dendritic cell marker; it is most abundant on myeloid DCs and also predominates on macrophages (Arnaout 2016). The species caveat matters: in mouse it is mainly a DC marker (cDCs and pDCs), whereas human CD11c is also found on monocytes, macrophages, granulocytes and NK cells (Schittenhelm et al. 2017). Plasmacytoid DCs illustrate the difference: they are CD11c-negative in the human data above but included among CD11c-bearing DCs in mouse.
Checklist: what CD11b does and does not tell you
- Not lineage-exclusive. Neutrophils, monocytes, NK cells and some B and T cells can be positive.
- Level matters. Human monocytes are CD11b-high and macrophages lower, so intensity can carry information that a positive/negative call hides.
- Check the species. Schittenhelm et al. caution that animal and human findings must be compared carefully; mouse and human DC and CD11c patterns differ.
- pDCs are CD11b-negative in the sources for both human and mouse.
- Pair it with other markers in an assay such as flow cytometry, where design choices like antibody titration are separate questions from what the marker means.
Common misunderstandings
- “CD11b means macrophage.” Human macrophages have lower CD11b than monocytes, and neutrophils, NK cells and others are also positive.
- “CD11c means dendritic cell.” Reasonable as a rule of thumb in mouse; in human it is not DC-specific.
- “CD11b is only a marker.” It is a functional adhesion and complement-receptor molecule with a large ligand list.
- “CD11b marker” versus “CD11b.” The phrase describes using the protein’s presence on a cell as an identification tool; it is not a different molecule.
FAQ
What type of cells express CD11b?
Mainly myeloid cells, notably neutrophils and monocytes, plus NK cells and subsets of B, CD8+ T and γδ T cells, fibrocytes and some mast cells (Arnaout 2016).
What is the difference between CD11b and CD11c markers?
They are different chains (αM and αX) that both pair with CD18 and share some ligands. CD11b is high on monocytes and neutrophils; CD11c is characteristic of dendritic cells, especially in mouse, and also appears on other human leukocytes.
What is the CD11c marker for?
It is used mainly to identify dendritic cells, with the caveat that in humans it also appears on monocytes, macrophages, granulocytes and NK cells.
Can NK cells express CD11b?
Yes, NK cells are among the reported CD11b-expressing populations.
Sources
- Arnaout MA. Biology and structure of leukocyte β2 integrins and their role in inflammation. F1000Research 2016;5:F1000 Faculty Rev-2433. doi:10.12688/f1000research.9415.1. pmc.ncbi.nlm.nih.gov/articles/PMC5054827. Read 2026-11-07.
- Schittenhelm L, Hilkens CM, Morrison VL. β2 integrins as regulators of dendritic cell, monocyte, and macrophage function. Front Immunol 2017;8:1866. doi:10.3389/fimmu.2017.01866. frontiersin.org. Read 2026-11-07.
