A study recently revealed that one of the reasons the avian flu may be so deadly is that it causes an immune system overreaction. Virus cells from the deadly H5N1 strain, older samples of H5N1 from 1997, and common H1N1 were injected into healthy human cell samples. In reaction to the H5N1, a large number of cytokines rushed to the site of injection. Fewer cytokines responded for the older H5N1, and fewer still for the H1N1.
Cytokines are a type of protein that help regulate the body's immune response, specifically inflammation. There are many types of cytokines, involved in various specific activities within the body. For example, tumor necrosis factor alpha (TNF-alpha) stops the overgrowth of tumor-causing cells. It also is involved in the superfluous inflammation that causes rhematoid arthritis (RA), and may also be involved in the skin disease hidradenitis suppurativa (HS).
In the example of RA, biologic drugs such as Remicade and Enbrel can be used to decrease the effects of TNF-alpha, but the body can develop antibodies to the drug after prolonged use. Interestingly, the research on H5N1 suggests that individuals with compromised immune systems, such as the elderly and children, would be less susceptible to the virus. This was the case with the 1918 H1N1 pandemic, when young adults were more severely affected among the 20-100 million killed. This begs the question of whether purposefully weakening the immune system in H5N1 victims may help them to survive, and of course researchers are going ahead and testing this - though safely on cell samples, not healthy (or sick) humans!