Once the infection is cleared, the majority of the expanded cells die off. The surviving 10 percent are maintained as memory cells. This death stage is very important because there are only so many cells that constitute the immune system. The precise regulation of the death phase after the expansion allows us to respond to many different pathogens without exhausting our immune system. Until very recently, researchers evaluating the nature and strength of an immune response focused on antibody production.
Antibodies are molecules generated by the immune system to help fight infection.
They are easy to detect and quantify. In the last five years, however, there has been a revolution in scientists' ability to identify, count and assess the function of antigen-specific T cells with high precision. Measuring these cells gives a much more accurate assessment of an immune response to either an infection or a vaccine. In the current studies, Harty and his colleagues used these measuring techniques and previous research to set about carefully measuring the levels of T cells during different stages of infection. Investigating the immune response in mice, genetically engineered to lack either or both molecules, the researchers elucidated the regulatory roles of perforin and interferon gamma.