The immune system is significantly complex in its physiology and functionality. Maintaining homeostasis involves an intricate interaction between the innate and adaptive immune systems and the cells, receptors, molecules and chemical substances that comprise these systems.[1-3]
This complexity also extends to the impact of many factors on immune function, including diet and nutritional status, lifestyle, age, medications, stress, microbiome composition, and physiological and genetic variability.[4-8]
Echinacea purpurea (echinacea)
E. purpurea is commonly used for the amelioration of upper respiratory tract infections (URTI), cold and flu symptoms and overall immune system support, and is perhaps the herb most commonly associated with improvement of immunity.
It has been used in traditional medicine for many health concerns including wound healing, throat and yeast infections and coughs,[10,11] and overall the clinical evidence indicates it is beneficial for the treatment of cold, flu and URTI symptoms as well as urinary tract infections via immune stimulation and modulation.[9-11] The primary active constituents isolated from the aerial parts and roots includes the caffeic acid derivative cichoric acid (2,3-odicaffeoyl-tartaric acid), alkamides, volatile oils, polysaccharides and melanins, and these constituents are responsible for the herb’s impact on immunity.[9-13]
E. purpurea influences both innate and adaptive immune activity via a number of mechanisms including promoting white blood cell (leukocyte, monocyte, lymphocyte) production, activation and mobility, stimulating phagocytic activity, and cytokine synthesis in granulocytes and macrophages (tumour necrosis factor alpha [TNF-alpha], interleukins 1, 6, 8 and 10, interferon),[9-11] as well as modulating regulatory T-cells number and function,[14,15] and dendritic cell differentiation and expression.[16,17]
Andrographis paniculata (andrographis)
The aerial parts of A. paniculata have been used extensively in traditional Ayurvedic and Chinese medicine systems for a range of conditions including URTI symptoms, sinusitis, bronchitis and tonsillitis, pneumonia, whooping cough and urinary tract infections.[19,20,22]
The active constituent that is considered to be the most biologically significant for its immune modulatory and anti-inflammatory activity is the diterpene lactone andrographolide.[19-22] Human clinical evidence demonstrates that A. paniculata is beneficial for the alleviation of URTI symptom severity and frequency.[20,23,24]
Animal and in vitro data has found that there are many underlying mechanisms that contribute to these therapeutic effects.
These include stimulation of innate immunity via macrophage phagocytosis and lymphocyte production and activity,[20-22] and adaptive immunity by induction of antibody synthesis and activity.[19,22] Other mechanisms include reduction of pro-inflammatory mediators (TNF-alpha, inteferon, IL-1, IL-6),[19,25,26] inhibition of gram-positive and gram-negative bacterial growth,[27-29] viral replication and pro-inflammatory cytokines.
Astragalus membranaceous (astragalus)
The root of A. membranaceous is an important therapeutic herb in the traditional Chinese medicine system for many health issues including immune support, the treatment of viral infections, debility and wound healing.[31,32]
The primary active constituents are considered to be the triterpene saponins (astrogalosides), flavonoids and polysaccharides,[11,31,33] and clinical data supports the traditional use of the herb for modulation of the immune system due to the effects of these constituents.[11,31,32]
The specific mechanisms contributing to the therapeutic effects of A. membranaceous include increasing monocyte, neutrophil and lymphocyte levels, stimulating macrophage maturation and T-cell activity[11,31,35,36] and antibody production[11,34] as well as modulating the synthesis of inflammatory mediators (NO, IL-2, IL-4, IL-10, IL-12, NF-kB).[31,34,37-39]
Inula helenium (elecampane)
The biologically active constituents that have been isolated include coumarins, flavonoids, polysaccharides, fatty acids and saponins.
Olea europaea (olive leaf)
The main active constituents of O. europaea, the secoiridoids like oleuropein, as well as flavonoids and phenolic compounds,[45,46] contribute to the immune associated antimicrobial, antibacterial, antiviral and anti-inflammatory effects of the herb.
The mechanisms of these constituents observed in preliminary data include stimulation of macrophage activation, inhibition of a wide range of bacterial and microbial pathogens (Escherichia coli, S. aureus, Salmonella typhyimurium and Bacillus subtilis, Campylobacter jejuni)[45,47,48] and preventing viral host cell entry. Anti-inflammatory mechanisms include inhibition of the classical complement system pathway and pro-inflammatory cytokine synthesis (NO, IL-17).[45,49]
Sambucus nigra (elder)
Both the fruit and flowers from S. nigra have been documented in traditional western medicine for use against the cold and as a diaphoretic in catarrhal complaints.
Several types of anthocyanins have been identified as the primary active constituents of S. nigra, with smaller quantities of carbohydrates, vitamins and minerals.
The specific effects of S. nigra on the immune system includes inhibiting H1N1 viral replication, propagation and host cell entry,[50,52,53] stimulation of macrophage activity, increased production of pro-inflammatory cytokines (TNF-alpha, IL-1, IL-6, IL-8, IFN-gamma)[50,54] and antimicrobial activity against gram-positive and gram-negative bacteria.
Thymus vulgaris (thyme)
The German Commission E Monographs approves the use of T. vulgaris for the symptoms of bronchitis, whooping cough and upper respiratory catarrh.
Animal and in vitro data has demonstrated that the mechanism of T. vulgaris and its constituents involves inhibition of PPAR-gamma-dependent COX-2 expression, NF-kB transcription and subsequent cytokine gene expression and secretion,[55-57] and inhibition of gram-positive and gram-negative bacteria growth and colonisation (Candida albicans, S. aureus, E. coli, Enterococcus).[55,58]
The physiological effects of Echinacea purpurea, Andrographis paniculata, Astragalus membranaceous, Inula helenium, Olea europaea, Sambucus nigra and Thymus vulgaris on innate and adaptive immunity are diverse. The variability of these mechanisms highlights the importance of utilising a combination of herbs therapeutically to support the complex immune system for clinically relevant outcomes.
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