There are two groups of microorganisms that attack us. The first group is viruses and tiny bacteria that live inside cells, yeast, and cancer. The second group is regular bacteria, parasites, toxins, and allergens. The virus or intracellular bacteria fools the body into thinking that the threat is coming from the second group. There is a lot of evidence that many CFS patients have this process going on inside them.
Patients tend to over react to the second group and under react to the first group.
The yeast begins to flourish and possibly, at some future date, cancer might come out. When this occurs, NK cells diminish in number. There is an increased antibody production. Antibodies to anything a CFS patient has ever been exposed to are usually elevated. The only defense against this is a substance called RNase L. RNase L cannot kill any of these things.