STS-95 PAYLOADS - Human Research
Fighting Infection in Space: Immune System Function and Response

Spaceflight causes changes in the immune system that are not yet fully understood. Initial studies have identified two areas of change in the immune system: reactivation of latent (inactive) viruses and suppressed immune response. The mental stress and closed conditions associated with spaceflight often decrease the immune response to foreign organisms like viruses. In the human body, some viruses are present in a latent state or inactive state, until a condition like stress causes increased viral activity. This increased viral activity is a good indicator of how well the immune system is functioning during spaceflight.

A transmission electron micrograph of the Herpes Simplex Virus I shows its external envelope (or shell) and genetic material inside.

Two STS-95 investigations aim to better understand these immune system changes. Both studies use blood and urine samples collected during routine physicals taken before and after the flight. Any changes between pre- and postflight assessments may indicate altered immune response as a result of spaceflight. Data will be collected from all crewmembers before and after the flight. The first investigation, Cell Immunity and Reactivation of Latent Viral Infections, will determine if stress induces reactivation of the herpes virus in-flight. White blood cells, a type of cells that fight infection in the body, will also be assessed for structural and functional changes that occur as a result of spaceflight. This mission will add seven subjects to complement an existing database of 29 crewmembers from previous shuttle missions.

The second investigation, Space Flight and Immune Function, will determine the status of specific immune response elements, whose essential function may be altered during spaceflight. Changes to typical infection-fighting cells such as neutrophils, monocytes and cytotoxic cells will be assessed and then used to define the risk of developing an infectious disease during long spaceflights. This investigation is based on earlier spaceflight and ground-based studies.

A computer reconstruction reveals the complex protein units that make up the Herpes Simplex Virus I envelope (Chiu, Rixon and Zhou at University of Texas, Houston).

With preparations underway for establishing a continuously crewed space station, a healthy immune response becomes more important to mission success. Increased crew size and mission duration may influence the long-term immune response of crewmembers, as they are confined to the closed quarters of the space station for long periods of time. Decreased immune response is also found in a number of environments on Earth, where close confines create an environment similar to that found in a spacecraft. These environments include polar stations, submarines, hospitals and nursing homes. In particular, the elderly are susceptible to immune-related diseases and infection because of a decreased immune cell response that occurs with age. Research into immune system suppression and infection-fighting response during spaceflight will provide important insight into patients affected by immune suppression on Earth.

Nearly all of us come into contact with some form of infection every day but we rarely contract an illness because of our healthy immune response. The Epstein-Barr virus, for example, infects approximately 80-90 percent of the general population, but few people actually contract the disease because viral activity levels are low. Research into the regulation of the immune sytem during spaceflight will add to our understanding of the immune system in general and may reveal new avenues of research into immune disorders.