My daughter and I started AHCC with arabinogalactan from Douglas Labs at 1 cap twice a day months ago, and both of us have had increases in number of NK cells as well as notable lack of getting sick this past winter.
We have not tested NK cell function.
So as far as immune support goes, both of us feel it made a dramatic difference in avoiding getting sick. However, while there has been a definite benefit for my immune function, I have not noted any benefit to my CFS.