CD28 and Epstein-Barr virus infection: In our study, the expression of PD-1 on CD3+, CD4+, and CD8+ T lymphocytes was significantly increased in children with EBV infection, whereas the expression levels of Tregs, as well as CD28 within CD3+ and CD8+ T lymphocytes, were markedly decreased, indicating a state of immune imbalance, consistent with the results reported by relevant (19).