The Townsend Letter for Patients and Doctors, Dec. 2006

A recent scientific study, completed at Drexel University and published in the November issue of the Journal Of Nutrition, has found that a hybridized mushroom extract, AHCC, increases survival and decreases the severity and recovery time following influenza infection. The reason for the impressive results stems from AHCC’s ability to increase the immune system response to the influenza infection. In particular, AHCC increased the number and activity of Natural Killer (NK) cells, thought by many immunologists to be the front line defense of the immune system. Considering that new strains of influenza such as the H5N1 bird flu are resistant to almost all antibiotics, this research shows that AHCC could be a vital weapon in this battle.

Possible Pandemic

Every year, flu and its consequences such as pneumonia typically kill around 36,000 Americans, and bring severe illness to many thousands more. And with recent outbreaks of a deadly strain of bird flu originating recently in Asia and having already spread now to Europe and North America, the World Health Organization (WHO), the CDC, and other public health authorities are warning that this year or some year soon we could again see the sudden emergence of a flu pandemic – an epidemic of an especially virulent flu, spreading rapidly across the globe, killing millions, and disrupting normal life as we know it.

Innate Immunity and NK Cells

In clearing a virus from the body as quickly as possible, the body’s natural killer (NK) cells are extremely important. NK cells are part of the innate immune system or innate immunity. When functioning well, innate immunity can deal effectively and quickly with health threats that the body has not previously experienced, such as a new virus or a type of bacterial infection not encountered by the body before.

When NK cells are active, the remainder of the immune system can remain at rest, further preparing for attack when needed. And if NK cells are extremely effective, such back-up help may not be needed at all. This can be very important, since these other components of the immune system, though helpful in some ways, can also overreact, leading to inflammation which can seriously damage healthy tissue.

Boosting Immune Response to Influenza

A standout immune system booster called active hexose-correlated compound (AHCC), extracted from Japanese mushrooms, has previously been shown very effective in boosting the immune system response against a variety of immune system challenges, including cancer and other serious diseases. Now, new research is showing that this compound is extraordinarily effective in protecting against the flu virus as well.

Most importantly, AHCC boosts immune response to flu virus by boosting the activity of natural killer (NK) cells. This is especially important for three groups: young children, who have not lived long enough to encounter many of the viruses adults have encountered and so have no adaptive immunity to flu; the elderly, whose immune system functions tend to decline with advancing age; and people of any age exposed to viruses they have not encountered before, such as new strains of a flu virus.

The new research, done at Drexel University in Philadelphia, shows that in animals exposed to the flu, AHCC:

• Lessens infection
• Improves survival
• Reduces the severity of flu symptoms
• Speeds recovery from flu, and
• Reduces the amount of damage caused to lung tissue.

Breakthrough Research from Drexel University

Before this study, much was known about NK cells, but not enough about how they work against flu viruses, since most previous work in flu had focused on other parts of the immune system, under the belief that those parts of the immune system – the adaptive branch – were more active against flu, an idea which turned out to be true, but misleading.

To study the preventive and treatment effects of flu in mammals in a scientifically meaningful way without exposing humans to increased risk of severe illness and possible death, a team of Drexel University scientists, let by Elizabeth Gardner, PhD, and PhD student, Barry Ritz, compared the severity of the flu symptoms, lung damage from it, and relative survival of two groups of mice exposed to flu virus. Both groups were exposed to equal doses of flu virus, but with only one group’s diet supplemented with AHCC.

For a week before exposure to the flu virus and for 10 days afterwards, one group of mice was given AHCC daily in their water. The other group got plain water only, with no AHCC.

Flu infection can cause the mice’s weight to drop rapidly because of the increased energy needed to fight the virus infection and the lessened appetite the disease also causes, so all the mice were weighed regularly before and during the study to learn if the AHCC supplementation was helping fight the disease. Mice that lose more than 30% bodyweight from the flu usually die from it.

Mice not given AHCC lost over three times as much weight during the study as those getting it, with those getting AHCC losing only 7% of their bodyweight, compared to the loss of 23% of bodyweight among the mice not getting AHCC.

Among the mice not getting AHCC, 25% died, but among those supplemented with AHCC, only 5% succumbed to their disease, which is an 80% reduction in deaths.

In mice not getting AHCC, lung tissue was badly damaged, but the lungs of AHCC mice showed much less damage, with the virus cleared from their lungs in seven days.

Examining study data to find why the AHCC mice had much milder symptoms, quicker recovery and better survival, the researchers found that both the number and the activity of their NK cells were increased.

The substantially less damage to lung tissue in the supplemented mice meant less activity of the adaptive immune system was needed in those mice. That is extremely important because as mentioned previously, the adaptive immune system cells, while beneficial in many ways, can also cause inflammation that damages lung tissue and increases severity of flu symptoms.

“NK cell activity was strong enough to actually allow clearance of the inflammation, but they did not over-react to the point of it actually being detrimental,” noted Ritz. “The mice that got AHCC had less damage to lung tissue because there were fewer macrophages, which cause inflammation, at the site of infection. We found that AHCC boosts NK cell activity in flu substantially, increasing survival, decreasing the severity of the disease and speeding recovery, and results in less ‘collateral damage’ to the lung,” said Ritz.

1. From information accompanying a letter to the public from President George W. Bush, available at:

2. From a page on the World Health Organization’s web site (quoted extensively below this note); that page available at

3. Barry Ritz MS, Drexel University, Philadelphia, PA interview October 4, 2006