Immunomodulation is the modification of the immune response or functioning of the immune system by the action of an immunomodulator. Immunomodulators are biological or synthetic substances which can stimulate, suppress or modulate the immune system by influencing the innate or adaptive responses. In general immunomodulators can be classified into 3 categories such as immunoadjuvants, immunostimulants and immunosuppressants.
Immunoadjuvants are agents which can be used for enhancing the efficacy of certain vaccines e.g., Freund’s adjuvants.
Immunostimulants are agents (immunopotentiators) which are non-specific in nature and enhance body’s resistance against infections. They can act through innate or adaptive immune responses. Immunosuppressants are a structurally and functionally heterogeneous group of drugs which are often administered in organ transplant patients and for autoimmune diseases e.g., cyclosporine, cyclophosphamide, glucocorticoids, sirolimus, azathioprine etc.
Human immune system
Immune system is one of our most complex biological systems in the body. The term immunity refers to the specific resistance exhibited by human body towards infections by microorganisms or their products or against other foreign substances. The basic role of the immune system is to distinguish self from non-self. The non-self could be an infectious organism, a transplanted organ or an endogenous cell that can be mistaken as foreign. The immunity may be innate (natural) or acquired (adaptive). The innate immunity is present from birth (inborn immunity), which consists of many factors that are relatively non-specific. It may operate against any substance that threatens the body. The acquired immunity is acquired by contact with the invader and is more specialized. It supplements the protection provided by innate immunity. Both these responses have two components each viz., cellular and humoral. The basic functional units of the immune system are diverse cells belonging to the lymphoid and reticuloendothelial system.
Diet and nutrition can affect the functioning of various immune parameters. Immune modulation through dietary strategies maintains immune homeostasis in the healthy population. The functioning of immunoreactive cells (T-cell and B-cell subsets) and functions of innate immunity are strongly related to protein nutritional status. The dietary protein: carbohydrate ratio appears to be important in maintaining immune responsiveness. Immune function is the target for the development of functional foods. The functional foods that contain vitamins such as A, C, D and E, minerals as zinc and selenium and PUFAs such as docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) enhance immunity.
The natural immunomodulators act to strengthen weak immune systems and to moderate the immune systems that are overactive. The natural immunomodulators do not boost the immune response. Natural Immunomodulation is a normalizing process. Plant sterols and sterolins are natural immunomodulators found in some raw fruits and vegetables and in the alga spirullina. The other natural immunomodulators include herbs like Aloe vera, Plumbago indica, Aegle marmalos, ginseng root, chamomile tea, reishi mushroom extract, olive leaf extract, N.sativa oil, polysaccharides isolated from Juniferous scopolorum, Isodon serra extract, ficus carica leaf extract etc.
Cereal β – glucans
β – (1à3)-(1à6) glucans are non – starch polysaccharides having glucose polymers with the property of enhancing innate immunity by binding with the macrophages and NK cells. Beta glucans can be found in bacteria, yeasts, mushrooms, seaweed and cereals. Barley,oats and corn bran are considered to be major sources of cereal β glucans. Beta glucans are a major component of natural water soluble dietary fibres. Significant positive health effects have been attributed to oat β glucans including total cholesterol control, modulation of glucose and insulin responses, weight management and improved gastrointestinal function. The efficacy of oat and barley β glucans in reducing the risk of coronary heart disease (CHD) has been recognized by the U.S Food and Drug Administration (FDA). Βeta glucans significantly enhanced the immune response to bacterial infection through the stimulation of neutrophils.β – glucans appear to exert their immunomodulatory effects via activation of innate immune pathways.
Pro- and pre-biotics
Probiotics are, by definition, non-pathogenic microorganisms that when given in adequate amounts exert beneficial effects on the host whereas prebiotics are non-digestible food ingredients that selectively stimulate the growth and/or activities bacteria in the colon and thus improve host health. Lactobacillus (LGG) or Bifidobacterium lactis are the microorganisms endowed with the probiotic effect. Oat β glucans which are indigestible in the small intestine but fermented by bacteria in the colon are prebiotics. A number of health benefits have been claimed for pro- and pre-biotics including effectiveness against anti-biotic associated or traveller’s diarrhoea, improved stools as well as an array of immunity – related health claim of anti-allergic response.
Fungal immunomodulatory proteins (FIPs)
FIPs are 15kDa proteins of fungal origin. A number of FIPs have been found in Flammulina velutipes (golden needle mushroom), Volvarietta volvacea (paddy straw mushroom), Ganoderma lucidum and G.tsugae (Japanese lacquer mushroom). FIPs are stable in food processing conditions such as freezing, thawing, dehydration and acid/alkali conditions. They enhance and/ or activate macrophage immune responses leading to Immunomodulation.
The marine immunomodulators belong to cyclic depsipepetide, terpenes, polysaccharides (carbohydrates, uronic acids, sulphates), polyhydroxylated lactone, bioglycon, cyclic tripeptide, macrocyclic lactones etc. They are derived from Endarachne binghamiae, Gelloides fibrosa, Sargassum illicifolium, Phaeodactylum tricornutum etc. Marine algae (Spirullina, Chlorella, Aphanizomenon,Haematococcus) have been revealed to possess anti-coagulant, anti-viral, anti-oxidant, anti-allergic, anti-cancer, anti-inflammatory and anti-obesity activities (Lincoln et al 1991, El Gamal 2010). Chitosan, glucosamine,PUFA concentrates, and protomines are good examples of immunomodulators derived from marine resources.
Health benefits of Immunonutrition
Diet and nutrition can affect the functioning of various immune parameters. Immune modulation, for example via dietary strategies, may hold promise as well for maintaining immune homeostasis in the healthy population. Protein energy malnutrition (PEM), for instance, affects all aspects of immune function, with these effects being even more pronounced in the elderly. The dietary protein: carbohydrate ratio appears to be important in maintaining immune responsiveness. Immune function is the target for the development of functional foods. In particular, vitamins, such as A, C, D and E, and minerals as Zn and Se , PUFAs such as docosahexaenoic acid (22:6n-3; DHA) and eicosapentaenoic acid (20:5n-3; EPA) may have immunomodulatory properties.