In the process of acute infection, when antigen is cleared or inflammation subside, effector CD8+ T lymphocytes (T cells) further differentiate into functional memory CD8+T cells, which produce interferon⁃γ (IFN⁃γ), tumor necrosis factor (TNF), interleukin-2 (IL-2), etc. When secondary infection occurs, effector CD8+ T cells can produce strong memory response quickly and efficiently, and carry out immune defense. The gene discussed is IFNG; the disease is infection.