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Iba1 is the common name for ionized calcium-binding adapter molecule 1, the protein encoded by the AIF1 gene (also called allograft inflammatory factor 1). In neuroscience it is used as a broad marker that labels microglia, but it does not by itself show whether microglia are activated, and it does not cleanly separate microglia from infiltrating macrophages.
This page is general reference for researchers and lab staff choosing or interpreting a microglial marker. It contains no staining protocols, dilutions or product recommendations.
Short answer
Iba1 (also written Iba-1) marks microglia across brain regions and developmental stages, which is why it is widely used for microglial staining. Its limits matter as much as its reach: in the cited work it cannot indicate the direction of microglial activation, and it makes microglia hard to tell apart from infiltrating macrophages in pathology. Studies that need that distinction pair it with other markers.
Definition and scope: one protein, several names
UniProt entry P55008 gives the recommended name as Allograft inflammatory factor 1 (AIF-1). Its alternative names include Ionized calcium-binding adapter molecule 1 (Iba1) and Protein G1, and the gene is AIF1 (synonyms G1, IBA1). UniProt describes the function as an actin-binding protein that enhances membrane ruffling and RAC activation, and records roles in promoting proliferation of vascular smooth muscle cells and T-lymphocytes, enhancing lymphocyte migration, and vascular inflammation. It is reported in T-lymphocytes and peripheral blood mononuclear cells.
Two practical points follow. First, literature and catalogue listings may use any of these names, so search with all of them. Second, Iba1 is a protein with a documented biological function outside the brain, not a gene that exists only to label microglia; its use as a microglial marker is an application of where it is expressed.
How Iba1 is used in practice
A 2026 study in Sovremennye Tekhnologii v Meditsine (Guselnikova et al., 18(1):34-42, doi 10.17691/stm2026.18.1.03) examined Iba-1 labelling in Wistar rats at 7 days, 14 days and 4-6 months, in spontaneously hypertensive (SHR) rats, and in human cortex. Iba-1 labelled microglia in every region and developmental stage studied, and the authors describe it as a reliable and universal microglial marker. In the human cortex the study reports microglia at most amyloid plaques, with amoeboid morphology.
The same authors note two limitations: Iba-1 cannot determine the direction of microglial activation, and it makes it difficult to tell microglia from infiltrating macrophages in pathology. They suggest a multi-marker approach.
What Iba1 can and cannot tell you
| Question you want to answer | What the sourced evidence supports |
|---|---|
| Are microglia present in this tissue? | Yes: Iba-1 labelled microglia in all brain regions and developmental stages examined (Guselnikova et al., 2026). |
| Is this microglial population activated, and in which direction? | No: the authors state Iba-1 cannot determine the direction of activation (Guselnikova et al., 2026). |
| Is a labelled cell a resident microglia or an infiltrating macrophage? | Not reliably: Iba-1 makes the distinction difficult in pathology (Guselnikova et al., 2026). A microglia-selective marker such as TMEM119 is the type of addition used for this (Bennett et al., 2016). |
| Is the protein only a microglia gene? | No: UniProt records actin-binding and lymphocyte-related functions and expression in T-lymphocytes and PBMCs. |
Related markers and how they pair with Iba1
Bennett et al. (PNAS, 2016, “New tools for studying microglia in the mouse and human CNS”) report that TMEM119 is highly expressed by, and limited to, microglia, and is a stable marker selective for microglia in injury models involving bone-marrow-derived cells. They note that earlier approaches relied on morphology, flow-cytometry marker expression or bone-marrow chimeras. In human cortex, TMEM119 localised to highly ramified Iba1-positive cells.
| Marker | What the cited source says |
|---|---|
| Iba1 (AIF1) | Labels microglia across regions and stages; does not give activation direction or separate microglia from infiltrating macrophages (Guselnikova et al., 2026). |
| TMEM119 | Highly expressed by and limited to microglia; selective in injury models with bone-marrow-derived cells (Bennett et al., 2016). |
For a macrophage and microglial lysosomal marker used in similar panels, see CASRAI’s guide to CD68; for the cell-lineage background, see monocyte to macrophage differentiation.
Where it matters for labs
The practical consequence for study design is about interpretation, not reagents. A result that reads “more Iba1-positive cells” supports a statement about labelled cells, not about activation state or cell origin. If a question depends on either, the cited authors recommend more than one marker. Other CASRAI guides cover complementary morphology and imaging approaches, such as Golgi staining for cell shape and two-photon microscopy for live tissue imaging.
Common misunderstandings
“Iba1 is specific to microglia.”
It labels microglia broadly, but UniProt records expression in T-lymphocytes and PBMCs, and the cited pathology work reports difficulty separating microglia from infiltrating macrophages.
“Iba1 staining shows microglia are activated.”
The authors cited here state it cannot determine the direction of activation. Presence of the marker is not a readout of activation state.
“Iba1 and AIF1 are different proteins.”
They are the same protein under different names (UniProt P55008).
FAQ
What does Iba1 stand for?
Ionized calcium-binding adapter molecule 1. The same protein is called allograft inflammatory factor 1 (AIF-1) and protein G1; the gene is AIF1 (UniProt P55008).
What does Iba1 stain?
Microglia in the brain regions and developmental stages examined in the cited 2026 study, in rat and human tissue.
Can Iba1 distinguish microglia from macrophages?
Not reliably in pathology according to the cited authors. TMEM119 is described by Bennett et al. as limited to microglia.
Sources
- UniProt, entry P55008 (AIF1, human), rest.uniprot.org/uniprotkb/P55008.txt, read 2026-11-07.
- Guselnikova et al., Sovremennye Tekhnologii v Meditsine 18(1):34-42, 2026, doi 10.17691/stm2026.18.1.03, read 2026-11-07.
- Bennett et al., “New tools for studying microglia in the mouse and human CNS,” PNAS 2016, PubMed 26884166, read 2026-11-07.
