IL2 and infection: This study intends to observe the immune typing of peripheral blood lymphocytes and differential changes in the levels of interleukin-2 (IL-2), IL-4, IL-6, IL-10, tumor necrosis factor-α (TNF-α), and interferon-γ (IFN-γ) in children with severe adenovirus infection to explore the infection mechanism of adenovirus from cytokine levels and whether it can help early diagnosis and prognosis prediction of severe adenovirus pneumonia.