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Most immune enhancers are natural products derived from microbes. Carbohydrates found in the cell walls of bacteria, viruses or fungal spores represent the largest group of immune enhancers, but other substances such as bacterial or viral DNA and RNA are also potent modulators. They are taken up by macrophages and dendritic cells, which are found in high concentration in the mucosal membranes of the respiratory tract, nasal passages, gut, skin and urogenital tract. These phagocytic cells represent the first line of defence against possible infection. Of course, the mucosal membranes and particularly those of the respiratory tract is a major route of entry for microorganisms.
Consequently, these sentinel phagocytes have evolved to become highly effective at recognizing, or “seeing” a potential danger very early on after which they become activated and produce warning signals, called cytokines, which activate the effector cells of the immune system to prepare itself to fight a potential infection.
One of the key cytokines produced by phagocytes when stimulated by microbial products is IL-12. One of the primary effects of IL-12 is to cause the differentiation of T helper lymphocytes (Th cells) into the Th1 variety. There are two major types of Th cells: Th1 cells which promote a strong protective response to fight off infections and Th2 cells which are important for fighting parasites, but not for fighting off bacterial infections. The Th cells are generally regarded as the principle control cells of the immune system. They determine the kind of immune response that will be produced and are also essential for the generation of immunological memory and the production of antibodies against foreign antigens to neutralise microbes if there is any future infection.
There is a constant balancing act between the two populations of helper T cells. Generally, a healthy immune system is dominated by a robust Th1 response to foreign antigens and infectious organisms and the production of IgG neutralising antibodies.
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