ObjectivesTo explore the level of peripheral blood immune cells in patients with different stages and grades of periodontitis.Materials and methodsA total of 229 periodontitis patients and 36 periodontally healthy patients were included in this cross-sectional study. Individuals with systemic diseases were excluded. A periodontal examination and a complete blood cell examination were performed. The percentages of T and B cells and their subsets were analyzed via flow cytometry. Covariance and logistic regression analyses were conducted, and receiver operating characteristic curve analysis was used to assess the predictive ability of the indicators.ResultsThe white blood cell (WBC) count, absolute neutrophil count (ANC), neutrophil percentage (NEU%) and neutrophil-to-lymphocyte ratio (NLR) were greater, but the lymphocyte percentage (LYM%) was lower in the periodontitis group than in the healthy control group. Patients with severe periodontitis (Stage III and IV) presented higher WBC, ANC, NEU% and NLR than those with mild and moderate periodontitis (Stage I and II) did. Area under curve (AUC) of the ANC, NEU% and NLR for the prediction of Stage III/IV periodontitis were 0.750, 0.771, and 0.774, respectively. Compared with Grade A or B periodontitis patients, Grade C periodontitis patients had a significantly lower absolute lymphocyte count (ALC) and LYM% but higher NEU% and NLR in Grade C periodontitis. The AUC of the NLR, LYM% and NEU% for predicting Grade C periodontitis were 0.797, 0.799, and 0.793, respectively. In lymphocytes, the proportions of T and B cells were lower in Grade C periodontitis patients than in Grade A or B group. Similarly, immune regulatory cells, including B10 and Treg cells, also decreased. Conversely, the Th17/Treg ratio was greater. Moreover, the Th17/Treg ratio was most strongly correlated with Grade C periodontitis (r = 0.87), followed by Treg cells(r = -0.70) and B10 cells(r = -0.38).ConclusionsANC, NEU%, NLR and LYM% are closely correlated with periodontitis. ANC, NEU%, and NLR may serve as potential markers for Stage III/IV periodontitis. LYM%, NEU%, and NLR may serve as potential markers for Grade C periodontitis. An increase in the Th17/Treg ratio is a high-risk factor for Grade C periodontitis.Clinical relevancePeripheral immune cell levels vary with the stage and grade of periodontitis and can be used to distinguish the grade and stage of periodontitis.