Apparently Beta Glucan & Soluble fiber helps boost the way the immune system finds and deals with pathogens and illness. I heard it described like if the invading army (your immune system) had the key to the front door of the castle it was attacking. Basically it gives makes your immune system fight disease better than it normally does. It has been shown to lower cholesterol, but as well now being used in cancer treatments and along regular treatments. Foods that are high in B-Glucans are OATS, Medicinal Mushrooms, Barley, Algae and Yeast (foods).
ScienceDaily (Mar. 2, 2010) — A new University of Illinois study touts the benefits of soluble fiber — found in oats, apples, and nuts, for starters — saying that it reduces the inflammation associated with obesity-related diseases and strengthens the immune system.
PS: if you want to learn a lot about beta glucans and how they work read the following interview with a scientist who is on the front of B-Glucans. Really Good FAQ