CD4 and infection: In case of abnormalities in the number and function of T lymphocyte subsets in the presence of impaired immune function of the body, immune dysfunction will then be caused and infections or autoimmune diseases will be triggered.21 According to the findings of Fujisawa et al.22, helper T lymphocytes (CD4+) are predominantly increased in the pre-ulcer phase of the mouth, while cytotoxic T lymphocytes (CD8+) appear significantly increased in the ulcer phase, suggesting that the formation of ulcers is related to the change of T cell subsets.