What the study is
Gonzalez Lopez, Katsura, and colleagues, with senior authors including Krivanek (Masaryk University), Adameyko (Karolinska Institutet), and Sharpe (King’s College London), published this work in Nature Communications on 2026-07-17 (doi:10.1038/s41467-026-75576-7, open access). It is a mouse developmental-biology study that combines reanalysis of published single-cell RNA sequencing data, immunohistochemistry, microCT imaging, two genetic macrophage ablation models, a bone marrow transplantation rescue, and short-term clodronate depletion in adults. The question is narrow: what do macrophages, known immune cells, actually do in a developing and continuously growing tooth?
Where the macrophages sit
AIF1-positive macrophages appear in the condensed dental mesenchyme from embryonic day 12.5, the bud stage, and spread through the dental papilla and follicle as development proceeds. Their abundance rises sharply after birth: the mean AIF1-positive area of the dental papilla/pulp is 0.75 to 2% from E12.5 to postnatal day 0, then 9.5 to 13% at pre-eruptive stages P3 to P14 (n = 4 animals per timepoint). In the incisor they are maintained by local proliferation (AIF1/Ki67 co-staining) and sit next to blood vessels, odontoblasts, and the dental follicle, including the labial cervical loop where the epithelial stem cell niche lives. Ligand-receptor analysis of existing incisor single-cell data flagged a macrophage Lgals9 to epithelial CD44 communication axis, and the cells make direct physical contact with Fos-lineage-traced transient epithelial progenitors. All of this is observational until the depletion experiments.
Development without macrophages
In Wnt1Cre/Csf1fl/fl mice, which delete the Csf1 ligand in neural crest derivatives, AIF1-positive macrophages are nearly absent from both mesenchymal and epithelial tooth compartments, and microCT shows shortened, hook-shaped, asymmetrically growing incisors with enamel defects and pulp chambers filled with dentinous tissue; one mutant also developed a supernumerary tooth. Molars erupt late with shorter roots, and the alveolar bone is thicker, traced to stalled osteoclast differentiation. Global Csf1r knockout mice, which lack tooth macrophages entirely, show the same direction of defect: hook-like incisors, flattened molar cusps, and delayed eruption. Transplanting healthy GFP-positive bone marrow into P1 knockout pups partially rescues the phenotype: AIF1/GFP double-positive cells reached 52.15 plus or minus 4.13 per region of interest in the dental pulp, incisor length increased slightly, and first molar lengths increased significantly, though the rescue group was too small (n = 2) for statistical testing. The rescue is the strongest evidence that macrophages themselves, rather than some other effect of Csf1 signaling, carry part of the requirement.
Adult depletion is reversible
In wild-type adult mice, three consecutive days of clodronate liposomes cut the F4/80-positive pulp macrophage fraction from 15.23 plus or minus 0.25% to 4.97 plus or minus 1.46%, recovering to 17.5 plus or minus 4.81% one week after the last dose. The prolonged regimen left a transient dentin and enamel lesion in the continuously growing incisor, about 1.5 mm from the cervical loop, a position matching the roughly 1.61 mm weekly incisor growth rate reported previously. No TRAP-positive osteoclasts were found at the lesion site, arguing against a bone-resorption artifact. After withdrawal, tissue morphology fully restored, and single-cell sequencing of recovered teeth showed the macrophage pool shifting from a resting M0-like state toward an M2-like healing state (Stab1 and C1qa up, Cxcl2 and Ccl4 down). Vessel counts were not the readout here; this is about patterning and matrix formation, not density.
Boundary and what it changes
Everything is mouse, and mostly the mouse incisor, an organ humans do not have. The authors are explicit that tooth-intrinsic and surrounding-bone effects cannot be fully separated for several phenotypes, that dendritic cells were not deeply characterized, and that the molecular mechanism by which macrophages refine morphogenesis is still unknown. Their therapeutic language (eruption failure, pulp stones, boosting tertiary dentin after injury) is hypothesis level. For the bioengineered tooth germ program, the takeaway is a requirement: protocols that dissociate, reaggregate, or mature tooth germ cells currently say little about the immune compartment. An independent Journal of Dental Research study published weeks earlier (Wang et al., doi:10.1177/00220345261470395) reports from its abstract that macrophages support vascular maturation in developing tooth germs, which points the same direction. The next question for the field is whether an engineered germ without resident macrophages can be induced to pattern and vascularize normally after transplant.
Provenance: primary source read in full at PMC13379590 (Nature Communications, CC-BY, published 2026-07-17); every number above was checked against the article text. See /method/ for the site’s evidence standards.