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Updated: Mar 2, 2026
Obtaining Human Microglia from Adult Human Brain Tissue
Published on: August 30, 2020
Pro-inflammatory activation of primary microglia and macrophages increases 18 kDa translocator protein expression in
David R Owen1, Nehal Narayan2, Lisa Wells3
11 Division of Brain Sciences, Department of Medicine Hammersmith Hospital, Imperial College London, London, UK.
Abstract:
The 18kDa Translocator Protein (TSPO) is the most commonly used tissue-specific marker of inflammation in positron emission tomography (PET) studies. It is expressed in myeloid cells such as microglia and macrophages, and in rodent myeloid cells expression increases with cellular activation. We assessed the effect of myeloid cell activation on TSPO gene expression in both primary human and rodent microglia and macrophages in vitro, and also measured TSPO radioligand binding with 3H-PBR28 in primary human macrophages. As observed previously, we found that TSPO expression increases (∼9-fold) in rodent-derived macrophages and microglia upon pro-inflammatory stimulation. However, TSPO expression does not increase with classical pro-inflammatory activation in primary human microglia (fold change 0.85 [95% CI 0.58-1.12], p = 0.47). In contrast, pro-inflammatory activation of human monocyte-derived macrophages is associated with a reduction of both TSPO gene expression (fold change 0.60 [95% CI 0.45-0.74], p = 0.02) and TSPO binding site abundance (fold change 0.61 [95% CI 0.49-0.73], p < 0.0001). These findings have important implications for understanding the biology of TSPO in activated macrophages and microglia in humans. They are also clinically relevant for the interpretation of PET studies using TSPO targeting radioligands, as they suggest changes in TSPO expression may reflect microglial and macrophage density rather than activation phenotype.
Insights
The 18kDa Translocator Protein (TSPO) is a marker for inflammation. Human myeloid cell activation decreases TSPO expression and binding, unlike in rodents, impacting PET imaging interpretation.
Area of Science:
- Neuroscience
- Immunology
- Radiochemistry
Background:
- The 18kDa Translocator Protein (TSPO) is a widely used biomarker for neuroinflammation in Positron Emission Tomography (PET) imaging.
- TSPO expression is known to increase in activated rodent myeloid cells (microglia and macrophages).
Purpose of the Study:
- To investigate the effect of pro-inflammatory activation on TSPO gene expression and radioligand binding in primary human and rodent myeloid cells.
- To clarify the role of TSPO as a marker of myeloid cell activation in humans for PET imaging.
Main Methods:
- Primary human and rodent microglia and macrophages were cultured and stimulated with pro-inflammatory agents in vitro.
- TSPO gene expression was quantified using RT-qPCR.
- TSPO radioligand binding was measured using 3H-PBR28 in human macrophages.
Main Results:
- Rodent microglia and macrophages showed a significant increase (approx. 9-fold) in TSPO expression upon pro-inflammatory stimulation.
- Human microglia did not show significant changes in TSPO expression after pro-inflammatory activation (fold change 0.85).
- Human monocyte-derived macrophages exhibited a significant decrease in both TSPO gene expression (fold change 0.60) and binding site abundance (fold change 0.61) upon pro-inflammatory activation.
Conclusions:
- TSPO expression and binding dynamics differ significantly between human and rodent myeloid cells during inflammation.
- The findings challenge the assumption that increased TSPO reflects myeloid cell activation in humans.
- PET imaging interpretation using TSPO radioligands in humans should consider myeloid cell density rather than solely activation status.
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