Gamma delta (γδ) T cells are enriched at barrier sites such as the gut, skin, and lung, where their roles in maintaining barrier integrity are well established. However, how these cells contribute to homeostasis at the gingiva, a key oral barrier and site of the common chronic inflammatory disease periodontitis, has not been explored.
Loss of oral barrier homeostasis leads to the development of periodontitis, the most common chronic inflammatory condition of mankind. Therefore, it is important to better understand the immune mediators acting at this unique barrier to safeguard tissue integrity.
Here, researchers at the University of Manchester demonstrate that the gingiva is policed by γδ T cells with a T cell receptor (TCR) repertoire that diversifies during development. Gingival γδ T cells accumulated rapidly after birth in response to barrier damage, and strikingly, their absence resulted in enhanced pathology in murine models of the oral inflammatory disease periodontitis.
The researchers performed 16S sequencing of γδ T cell-deficient mice and demonstrated that alterations in bacterial communities could not account for the increased disease severity seen in γδ T cell-deficient mice.
Next, they performed genome-wide RNA sequencing (RNA-Seq) of γδ T cells collected from various locations. They found significantly differentially expressed genes which resulted in substantial changes in gene expression in gingiva-specific γδ T cell compared with those from other locations. Further gene ontology analysis revealed overrepresentation of gene sets involved in responding to microbes, with specific antimicrobial peptides and bacterial response genes elevated, as well as multiple genes shown to promote tissue repair. Gene expression comparison between gingiva of control and γδ T cell-deficient mice revealed the expression of Areg gene was significantly decreased. The product of the Areg gene, amphiregulin, can promote reestablishment of tissue homeostasis after injury.
Next, they examined the periodontal pathology of control and Areg deficient mice and found increased bone loss compared with controls indicating amphiregulin is important for maintaining gingiva immune homeostasis. Indeed they found that the elevated disease pathology seen in γδ T cell-deficient mice could be completely rescued by amphiregulin administration.
Gingival γδ T cells produce Areg to limit oral pathology
(A and B) Volcano plots comparing gene expression of gingiva versus (A) spleen and (B) intestinal epithelium (intestinal intraepithelial lymphocytes; IEL) γδ T cells. (C) Gene expression signatures of gingival γδ T cells were examined using PANTHER to identify enriched gene ontology terms describing biological processes. Graph outlines terms enriched in gingiva γδ T cells. (D) Relative expression of Areg in gingival tissues of wild-type and tcrδ−/− mice. Expression in tcrδ-/− gingiva presented relative to that in wild-types, data from six to seven separate mice. (E) Representative FACS plots gated on gingival γδ T cells stained for Areg. Cells were restimulated with PMA, ionomycin, IL-6, IL-1β, and IL-23 with Brefeldin A. (Left) FACS plot is unstained for Areg. (Right) FACS plots shows representative staining for Areg. Graph shows percentage Areg+TCRγδ+ cells in unstained (FMO), spleen (SPL), and gingiva (GING) samples from four experiments. (F) CEJ–ABC distances in maxilla of aged wild-type (open circles) and Areg−/− mice (closed squares; n = 7–8 mice per group). (Left) CEJ–ABC distance was measured at six defined points across the molars. (Right) Graph shows total CEJ–ABC distance. (G and H) Experimental periodontitis was induced in control and tcrδ−/− mice, and mice received PBS or Areg i.v. every other day three times. (G) CEJ–ABC distance was measured at six defined points across the molars, and changes in bone heights determined in (Left) control mice and (Right) tcrδ−/− mice. (H) Graph shows total change in bone heights in ligated/periodontitis molars compared with unligated molars. Data representative of three experiments with two to five mice per group. *P < 0.05 as determined by unpaired Student’s t test. **P < 0.05; ***P < 0.0001, as determined by one-way ANOVA. Results are expressed as means ± SEM.
Thus, these researchers have identified in part through transcriptome profiling, a vital role for γδ T cells in constraining pathological inflammation at the oral barrier, as the absence of γδ T cells resulted in enhanced pathology during periodontitis. Additionally, they showed that oral barrier γδ T cells produce the reparative cytokine amphiregulin, administration of which rescued the elevated oral pathology of γδ T cell-deficient mice. Collectively, they identified a pathway controlling oral immunity mediated by barrier-resident γδ T cells, highlighting that these cells are crucial guards of oral barrier immune homeostasis.
- Krishnan S, Prise IE, Wemyss K, Schenck LP, Bridgeman HM, McClure FA, Zangerle-Murray T, O’Boyle C, Barbera TA, Mahmood F, Bowdish DME, Zaiss DMW, Grainger JR, Konkel JE. (2018) Amphiregulin-producing γδ T cells are vital for safeguarding oral barrier immune homeostasis. Proc Natl Acad Sci USA [Epub ahead of print].