Figure 1.

Changes in proportions of major cell types during ligature-induced periodontitis development in mice. (A) Mouse maxillary second molar (M2) has multi-roots and supported by alveolar bone (Bone), periodontal ligament (PDL) and gingiva connective tissue (gCT). The oral barrier immunity is not constitutively activated as evidenced by the lack of CD45+ immune cells. Picrosirius red (PSR) stained collagen fibers connected the root surface and alveolar bone in the PDL and organized as dense parallel bundles in gCT. (B) One day (Day 1) after a ligature (5.0 silk suture) was placed around M2, the cervical PDL and gCT demonstrated a localized connective tissue degradation (*), where CD45+ immune cells clustered (arrows). PSR-stained collagen architecture immediately under the ligature lost the thick collagen bundle structure (*). (C) Day 3 of ligature placement exhibited localized but increased CD45+ immune cell clustering adjacent to the collagen degradation area (*). (D) Day 7 of ligature placement, PDL and gCT tissue degradation increased with inflammatory vascularization (Vas). CD45+ myeloid cells (arrowheads) were observed near the alveolar bone surface and CD45+ lymphocytes (arrows) infiltrated the gCT area. PSR staining lost the typical collagen pattern in gCT and PDL, and a remnant of degraded PDL collagen fiber (white bracket) was attached to the tooth surface. (E) Single-cell RNA sequencing (scRNA-seq) t-distributed stochastic neighbor embedding (t-SNE) projection plots showing the major cell types present within gingival tissue during periodontitis development on Day 0, 1, 4, and 7. Colors indicate cell type, as follows: green, epithelial cells; blue, fibroblasts; pink, endothelial cells; yellow, B cells; red, T cells; and purple, myeloid cells. (F) Proportion plots showing the relative amounts of each major cell type on Days 0, 1, 4, and 7.