Systemic Inflammatory and Th17-Related Immune Responses in Patients with Oral Candidiasis and Type 2 Diabetes Mellitus: A Case-Control Study from Iraq

Background: Oral candidiasis is common in type 2 diabetes mellitus (T2DM), and the host immune response may determine whether oral Candida colonization becomes disease. The systemic inflammatory and Th17-related cytokine profile of diabetic patients with oral candidiasis is unclear. Methods: In this case-control study in Iraq, 180 adults were enrolled in three groups of 60: T2DM with clinically diagnosed and mycologically confirmed oral candidiasis (Group I), T2DM without clinical candidiasis (Group II) and healthy controls (Group III). Serum IL-17A (primary outcome), IL-6, TNF-α and IL-10 were measured by sandwich ELISA, and HbA1c and local oral risk factors were recorded. Results: Median serum IL-17A was 37.4, 24.3 and 15.7 pg/mL in Groups I, II and III (Kruskal–Wallis p<0.001; Group I vs II, Bonferroni-adjusted p=0.008), but the Group I vs II difference was no longer significant after covariate adjustment (geometric mean ratio 1.33, 95% CI 0.97–1.82). Adjusted differences remained significant for IL-6 (1.48, 95% CI 1.06–2.07) and IL-10 (1.84, 95% CI 1.45–2.33). Each 1% increase in HbA1c was associated with 2.45-fold higher odds of oral candidiasis (95% CI 1.63–3.68). Conclusions: In this study, poor glycemic control was the main host factor linked to oral candidiasis in T2DM. IL-6 and IL-10 stayed higher in infected patients after adjustment, whereas the IL-17A difference between diabetic groups was largely explained by glycemic and local oral factors.