CS, It traditionally means upping the production/count of T-Cells in the body. Most feel that the immune systems are usually fairly depleted in most folks, due to poor diet, environmental pollutants, constant exposure in crowds, constant stress, just today's life in general. Most folks are functioning in their daily lives feeling tired, and run down most all the time. Sure sign you will probably "catch" something, but less likely if your immune system is at least functioning at a "normal" level, better yet above normal for flu season. There used to be a book available "Scientific Validation Of Medicinal Herbs" by ? Mowbrey (sp) which gave a breakdown of the chemical properties of several herbs touted as very healing, and how those chemical properties worked in the human body, etc. Very technical and very well footnoted with "proper" scientific trials/studies.