How the System Works

White blood cells called neutrophils are the front line "attack soldiers" of the immune system.

Their function is to guard and protect against bacteria and fungi. Other white blood cells work in slower, more complicated ways.

One type of white blood ceil, a B-lymphocyte, produces antibodies, proteins that neutralize destroy harmful microbes.

B-lymphocytes are prompted to make antibodies by immune system cells called "helper" T-cells, and to turn off the production when a job is finished by "suppressor" T-cells.

"Memory" T-cells, another type of immune system cell, patrol the body, recognizing villains encountered in the past and mobilizing attack teams including ''natural killer" cells that attack and destroy viruses or tumor cells.

"Street-sweeper" cells, called the macrophages (literally "big eaters"), are the final part of the system. They arrive and clean up the debris.

All of these activities usually occur in a harmonious and balanced way, but sometimes the immune system seems to "forget" how to turn on or when to turn off.