The immune system is very complex and nutritionally it is a nightmare to understand. Vitamins and minerals are important components of many of the chemical messengers produced by immune cells. Basically there are two parts of the immune system one is called the humoral immune system the other is called the cellular immune system. The humoral part is responsible for the production of antibodies and memory (acquired immunity), and the cellular part (natural immunity) protects without prior exposure to foreign substances. By convention, immunology is the study of acquired immunity and "immune response" refers to responses that are induced by antigens or foreign substances.
The other side, the natural or innate system includes, skin, mucous membranes, complement, phagocytes, and macrophage-derived cytokines (chemicals from cells). The Phagocytes make up the second major cell population of the immune system. The macrophage is a principle form of phagocyte. In the 1970's it was observed that macrophages infiltrate tumors and speculated that this infiltration was the first line of defense against metastatic spread (Birbeck and Carter 1972, VanLoveren and DenOtter 1973, Mansell et al. 1975). Tumor associated macrophages have been identified in several species and there is little doubt that the macrophage plays an important role in the host-tumor relationship. Since macrophages infiltrate tumors it is likely that they are the first line of defense against the spread of tumors. These cells take up other particles and foreign invaders such as microbes and represent the clearest example of cells that are critical for natural immunity (they also play a role in acquired immunity). Macrophages are one of the principal cell types involved in natural immunity, they swallow-up foreign particles and destroy or process them. These cells release enzymes, and other substances that kill microbes, and tumor cells and control the spread of infection. Often the release of these chemicals can damage normal tissues in the immediate area, leading to inflammation. Macrophages produce chemicals that signal other immune cells to the site of infection and produce such effects as fever. Macrophages also produce growth factors for cells that repair injured tissues. These cells do play various important roles in the progression of acquired immune responses as well. However, explanation of acquired antibody responses is also beyond the scope of this writing, here we will focus on cellular or natural immunity, and the macrophage.
Bacteria are capable of growing outside of cells, in circulation, in connective tissue, and in spaces and airways in the human body. These microorganisms can cause disease in two basic ways. First, they induce inflammation that damages surrounding tissue. Second, bacteria produce toxins with differing effects. Such toxins may be endotoxins, which are parts of the broken bacterial cell wall, or exotoxins, which the bacteria make and release. One type of endotoxin, a polysaccharide (similar to beta glucan) called lipopolysaccharide or LPS is a potent stimulator of immune cells. Immune cells respond to LPS in an effort to eliminate the bacteria producing it. Because bacteria, and tumor cells are rapidly killed by macrophages and the resistance of bacterial and tumor cells to phagocytosis is an important factor in how successful they are. Both cell types succeed by multiplying rapidly and overwhelming the immune system. For bacteria, toxins such as LPS are released as old bacteria die, and these stimulate the production of chemicals by macrophages that end up destroying the bacteria that released the toxin.
Both nutrient and non-nutrient compounds that have been shown to affect the immune system. Beta glucan polysaccharides are capable of stimulating macrophages (and other immune cells) and are capable of acting as dietary immunological response modifiers. Beta glucan carries a rating from the FDA, Generally Regarded As Safe (GRAS), which means that there is no known toxicity for an oral dose of the purified form. There is much evidence in scientific literature over the past 70 years indicating that beta glucan stimulates the macrophage to engulf foreign particles more efficiently, fight the growth and spread of tumors and is effective as a preventive treatment in promoting health.