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Immunity tends to refer to the capacity of the body to ward off infections, and tends to be measured acutely by seeing the count or activity of immune cells that can help ward off sickness. Enhanced immunity results in less sickness.

Our evidence-based analysis on immunity features 28 unique references to scientific papers.

Research analysis led by Kamal Patel .
Reviewed by
Examine.com Team
Last Updated:

Summary of Immunity

Primary Information, Benefits, Effects, and Important Facts

Immunity refers to the body's innate ability to fight off diseases. The immune system does this by fighting off pathogens, which can range from molecules to parasites. In order to do this, there are two main levels to immunity.

The first level is called the the innate immune system. This provides a quick first line of defense, and acts against a wide range of pathogens. The innate immune system is comprised in part by physical barriers such as the skin, nonspecific chemical defenses such as lysozyme (an enzyme secreted in various secretions such as tears and saliva that breaks down bacterial cell walls), and the normal flora, which are nonpathogenic bacteria that compete for space and resources with pathogenic bacteria. If a pathogen circumvents these defenses, it will then face the inflammatory response which can attract immune cells to the site of infection and dilate blood vessels to help ferry them there. Interferons can also be released which help fight viruses and tumors, and the complement system can attack the cell membranes of pathogens either disrupting them or promoting their elimination by other components of the immune system. Finally, various cells of the innate immune system can be activated. Phagocytic cells can engulf invading pathogens and destroy them upon ingestion, while natural killer cells can kill cells infected with a virus and tumor cells, and eosinophils can produce and release substances that are effective against parasites.

The second main level of immunty is called the adaptive immune system. This level takes time before responding to a pathogenic invasion, but once mobilized, it evokes a response specific to a particular pathogen, as opposed to the innate immune system, whose response is nonspecific. The adaptive immune system is also capable of remembering a specific pathogen, so that it can mount a more rapid, effective response to a pathogen which it has encounterd before. This is the basis of how vaccines work. The adaptive immune system is comprised of two main cell types: T cells (named because they were found in the thymus, the organ which they mature) and B cells (named for the bone marrow, where they are initially produced). Both kinds of cells are antigen-specific and are activated when they recognize an antigen of a pathogen. The two major types of T cells are killer or cytotoxic T cells and helper T cells. The former kill cells that are infected with viruses or cancer cells. They are also called CD8+ cells, since they have a co-receptor on their surface called CD8 that helps them recognize specific antigens. The latter help mount an immune response to a specific antigen in a multitude of ways, including the release of cytokines which help regulate parts of the immune system, and can mature into memory cells (which help remember a specific antigen) and regulatory cells (sometimes called Tregs for short, which help downregulate the immune response). Helper T cells are also called CD4+ due the the CD4 co-receptor on their surface. B cells make antigen-specific antibodies which can attach to pathogens and activate the compliment system more specifically, help phagocytes engulf the pathogen, or neutralize the pathogen by coating it.

Things To Know & Note

Also Known As

Immune system

Frequently Asked Questions about Immunity

Which supplements can help against colds and the flu?
Vitamin C, vitamin D, zinc, and other supplements may provide an edge against colds and the flu, but they should only serve to complement your main defensive arsenal: good hygiene, proper hydration, healthy diet, restful sleep, stress control, and exercise.

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Human Effect Matrix

The Human Effect Matrix looks at human studies (it excludes animal and in vitro studies) to tell you what supplements affect immunity
Grade Level of Evidence
Robust research conducted with repeated double-blind clinical trials
Multiple studies where at least two are double-blind and placebo controlled
Single double-blind study or multiple cohort studies
Uncontrolled or observational studies only
Level of Evidence
? The amount of high quality evidence. The more evidence, the more we can trust the results.
Outcome Magnitude of effect
? The direction and size of the supplement's impact on each outcome. Some supplements can have an increasing effect, others have a decreasing effect, and others have no effect.
Consistency of research results
? Scientific research does not always agree. HIGH or VERY HIGH means that most of the scientific research agrees.
grade-b Minor Very High See all 6 studies
There appears to be an increase in T-cell mediated immunity in older subjects when supplementing low dose (50-200mg) vitamin E; this immunity enhancement does not appear to occur in youth due to it alleviating an age-related immune suppression.
grade-c Notable - See study
Appears to activate T-cells to a degree higher than the reference drug echinacea
grade-c Minor - See study
Increase in salivary IgA suggests an immune enhancing effect; no comparison to an active control.

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The evidence for each separate supplement is still freely available ​here.



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  2. Foxman EF, et al. Temperature-dependent innate defense against the common cold virus limits viral replication at warm temperature in mouse airway cells. Proc Natl Acad Sci U S A. (2015)
  3. Carr AC, Maggini S. Vitamin C and Immune Function. Nutrients. (2017)
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  6. Ran L, et al. Extra Dose of Vitamin C Based on a Daily Supplementation Shortens the Common Cold: A Meta-Analysis of 9 Randomized Controlled Trials. Biomed Res Int. (2018)
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  14. Hemilä H, Chalker E. The effectiveness of high dose zinc acetate lozenges on various common cold symptoms: a meta-analysis. BMC Fam Pract. (2015)
  15. Hemilä H. Zinc lozenges and the common cold: a meta-analysis comparing zinc acetate and zinc gluconate, and the role of zinc dosage. JRSM Open. (2017)
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  17. Shah SA, et al. Evaluation of echinacea for the prevention and treatment of the common cold: a meta-analysis. Lancet Infect Dis. (2007)
  18. Karsch-Völk M, et al. Echinacea for preventing and treating the common cold. Cochrane Database Syst Rev. (2014)
  19. Tiralongo E, Wee SS, Lea RA. Elderberry Supplementation Reduces Cold Duration and Symptoms in Air-Travellers: A Randomized, Double-Blind Placebo-Controlled Clinical Trial. Nutrients. (2016)
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  24. Meng H, et al. Consumption of Bifidobacterium animalis subsp. lactis BB-12 impacts upper respiratory tract infection and the function of NK and T cells in healthy adults. Mol Nutr Food Res. (2016)
  25. Braga VL, et al. What do Cochrane systematic reviews say about probiotics as preventive interventions?. Sao Paulo Med J. (2017)
  26. Wang Y, et al. Probiotics for prevention and treatment of respiratory tract infections in children: A systematic review and meta-analysis of randomized controlled trials. Medicine (Baltimore). (2016)
  27. Strasser B, et al. Probiotic Supplements Beneficially Affect Tryptophan-Kynurenine Metabolism and Reduce the Incidence of Upper Respiratory Tract Infections in Trained Athletes: A Randomized, Double-Blinded, Placebo-Controlled Trial. Nutrients. (2016)
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