What is Immunity? The Definitive Guide to Tea and Immunity
This article explores what immunity actually means, the different types of immunity, how immunity works, what mechanisms our body employs as part of its defense systems.
Immunity, or our immune system, is the complex group of defense mechanisms that our body employs to repel disease-causing organisms or pathogens. The body’s immunity system is typically capable of discriminating among body’s own cells and foreign entities. As soon as the foreign particle is identified, the collective and coordinated response of specific cells and mediators against strange substances constitutes the body’s immune response.
SECTION I. HOW IMMUNITY WORKS
These mechanisms can be further classified into two broad categories: 1) innate, non-specific immunity mechanisms; and 2) acquired, specific immunity mechanisms. Both of these work synergistically to prevent organisms, including micro-organisms, from entering and multiplying within our bodies. While our innate immunity works to repel all micro-organisms equally, our specific immunity mechanisms focus on targeting specific types of organisms. In many cases, these immunity mechanisms go further than repelling pathogens; they help eliminate abnormal or foreign or potentially harmful cells of the body that may develop into serious complications later.
- Innate, Non-Specific Immunity Mechanisms
Our body immediately repels most micro-organisms it encounters on a daily basis before they can cause any potential problem or initiate the onset of any disease. These pathogens are of various kinds: bacteria, viruses, fungi, worms, etc. Therefore, our body has developed a non-specific, i.e., widely effective defense system against all types of varied microorganisms. This system protects the body through various forms and mechanisms, such as:
- physical barriers such as the skin and mucous membranes: The skin for example serves as a physical barrier to infection, and also skin glands produce oily substances that can kill or break down the outer wall of many bacteria. The mucus, on the other hand, traps harmful particles and prevents them from getting attached to our body’s cells.
- chemical barriers such as anti-microbial proteins: These proteins include chemicals that incidentally also serve to protect the body, chemicals whose principal or primary function is to harm or destroy infectious organisms (such as complement and interferon), and chemicals produced by naturally occurring bacteria in organs such as our stomach or gut.
- cellular defenses: Our bodies have scavenger cells (such as leukocytes or white blood cells and macrophages) and natural killer (NK) cells that attack foreign bodies as well as any body cells that may be harboring such infectious cells. NK cells are unique in that they do not attack harmful micro-organisms directly but instead destroy the body’s own cells that have either become harmful or been infected with a virus.
- non-specific responses to infection such as acute-phase response and the inflammation response which can also help eliminate infectious cells or at the very least control their growth until the body has had time to develop specific, acquired immune responses.
- Specific, Acquired Immunity or Adaptive Immunity Mechanisms
The concept of specific, acquired immunity might already be obvious or familiar to most of us, even if the term is not. For centuries, it has been common knowledge that those who contract certain illnesses and survive do not generally catch or suffer from them again. They are said to have built or acquired immunity against that specific disease. However, specific immunity also implies that you have not developed immunity against all diseases, even if they are related or similar. For example, if you have developed immunity against measles, it does not necessarily mean you will not get chicken pox, or vice versa.
Building up specific, acquired immunity is primarily dependent on specialized white blood cells known as lymphocytes. Lymphocytes are the cells responsible for the body’s ability to differentiate between and fight all foreign organisms. They usually lie dormant in the body, until the need for them to act arises. As the name might suggest, they largely reside in our body’s lymphatic system (made up of the bone marrow, spleen, tonsils, etc.), specifically within the network of lymph capillaries.
Lymphocytes are further divided into two categories: T cells and B cells. T cells are those lymphocytes that, despite originating from stem cells in the bone marrow, travel to the thymus. It is in the thymus that these cells multiply and form T lymphocytes or T cells (Thymus-derived Cells). These T cells may then leave the thymus, enter the bloodstream, and circulate within the lymphatic system.
On the other hand, some of the lymphocytes originating in the bone marrow remain in the bone marrow, where they multiply before they circulate to and within the lymphatic system. These are called B cells.
T cells and B cells – though both working towards the same objective - also differ in other significant ways. While both are effective in identifying and eliminating foreign pathogens, they do so in different ways. While B cells secrete anti-bodies (proteins that bind themselves to the antigens), T cells do not produce anti-bodies but directly attack the foreign organisms. T cells therefore also focus on destroying antigens that have entered the body’s cells, while B cells focus on using the anti-bodies they produce to attack harmful pathogens that remain outside the body’s cells. Therefore, foreign pathogens that have been ingested by the body’s cells or microorganisms such as viruses that penetrate cells and multiply within the cells are out of reach of antibodies, but can be eliminated by T cells. At the same time, however, it must be noted that T cells also help regulate and support the function of the B cells.
In the case of the recent COVID-19 coronovirus, it is therefore the body’s T cells and B cells that are critical in helping us build up specific, acquired immunity towards this particular strain. The above also explains why people who do have the anti-bodies when tested have a certain level of immunity towards this strain of the virus. In other words, their B cells have produced enough anti-bodies to overcome the virus that was circulating in their body but had not necessarily entered the cells.
At the same time, therefore, as we think of building up our immunity, we should focus on having foods and beverages that will help boost our lymphocytes, and specifically our T cells and B cells. Notably, green tea and black tea have both been found to help boost our specific, acquired immunity.
SECTION II. HOW TEA HELPS BOOST IMMUNITY
In this section, we systematically and scientifically cover the actual mechanisms by which tea can help boost our immunity. The various types of teas – black teas, green teas, oolong teas, and white teas – affect and boost our immunity slightly differently, and we cover each individually.
The main active ingredient in green tea, epigallocatechin-3-gallate (EGCG), has been shown consistently to promote the healthy functioning of several systems within our body. In the immune system specifically, studies have accumulated evidence that reveals that green tea/EGCG have an immune-modulating effect, that is to say, it helps activate the body’s immune system.
Green Tea/ EGCG has been shown to positively activate several types of immune cells in both the innate, non-specific systems and the specific, acquired, adaptive immune systems. Chief amongst them is the significant effect that green tea, through EGCG, has on T cell functions, including T cell activation, proliferation, differentiation, and production of cytokines.
When our T Cells are not functioning well, i.e., they start to become dysfunctional, it often leads to the development of auto-immune diseases that also cause inflammation. Auto-immune diseases, as you may know, are diseases that are triggered by immune system over-activity incidentally. Under such conditions, the immune system may begin producing anti-bodies that instead of fighting infections, start to actually attack the body’s own cells. When you have an autoimmune disorder, your immune system does not distinguish between healthy tissue and potentially harmful antigens. Specifically, for example, upon stimulation by certain antigens, certain Helper T cells (naiive CD4(+) T cells) proliferate and differentiate, when they shouldn’t, into Th1 and Th17 cells that are responsible for inducing auto-immunity.
As a result, the body sets off a reaction that destroys normal tissues. Examples of auto-immune diseases include rheumatoid arthritis, lupus, inflammatory bowel disease, type 1 diabetes, and others.
Green Tea (EGCG) helps contain and often reverse that dysfunction of the specific T cells, and thus favorably regulates your body’s immunity response. How does EGCG do that? Studies have observed that EGCG helped suppress the proliferation of autoreactive T cells, reduced production of pro-inflammatory cytokines, decreased Th1 and Th17 cells, and increased Treg populations in lymphoid tissues and central nervous system.
In addition to boosting immunity through the above mechanisms, EGCG has been widely studied and reported for its in vitro and in vivo chemo-preventive, anti-angiogenic, anti-invasive, anti-proliferative, anti-inflammatory, and anti-oxidant effects. 
Incidentally, Kangra Green Tea has been found to contain the highest EGCG content, of all the green teas produced in India. A study analyzed green tea catechins (GTCs), namely, EGCG and ECG, in 25 prominent Indian tea cultivars cultivated in North, South and North-east states of India. This study found that Kangra Green Tea grown in Himachal Pradesh showed the highest content of EGCG (6.88%), followed by TRI-2026 (6.83%) grown in Coonoor (South India) and lowest content were recorded in P-126 (1.2%) grown in Darjeeling. Therefore, for those looking at the nutritional and immunity-boosting value of green tea should consider Kangra Green Tea.
Black Tea, like green tea, is rich in polyphenols, but of a different kind due to the fermentation or oxidation process that is undergone in the manufacturing of black tea. Unlike green tea which is rich in catechins such as EGCG, black tea is rich in theaflavins and thearubigins. A study on the polyphenols present in black tea concluded that:
“Theaflavin may influence activation of transcription factors such as NFnB or AP-1 that ultimately hinder the formation of nitric oxide expression gene. Likewise, black tea contains a unique amino acid theanine acts as neurotransmitter owing to its ability to cross the blood-brain barrier. Moreover, it boasts immunity by enhancing the disease-fighting ability of gamma delta T cells. Theaflavin & thearubigins act as safeguard against oxidative stress thereby effective in the cardiac functioning. The mechanistic approach of these antioxidants is likely to be associated with inhibition of redox sensitive transcription factors & pro-oxidant enzymes such as xanthine oxidase or nitric oxide synthase. However, their involvement in antioxidative enzyme induction as in glutathione-S-transferases is also well documented. They act as curative agent against numerous pathological disorders by disrupting the electron chain thus inhibiting the progression of certain ailments.”
TEA AND COVID-19
As we write this, the world is in the grips of a global pandemic – COVID-19 – of a scale not seen in decades. The world’s entire scientific and medical communities are currently working hard towards finding a cure, or a vaccination, that could prevent higher fatalities amongst humans globally.
While the scientific community focuses on developing, testing and producing vaccines and targeted therapies for the treatment of COVID-19, some researchers are focusing on known natural molecules with the same objective in mind.
Some researchers are interested in a compound from green tea with antiviral and anti-inflammatory properties. Chemists looking at computer models of the virus (SARS-CoV-2) that causes COVID-19 believe epigallocatechin gallate (EGCG) from green tea will have high binding affinity for SARS-CoV-2, as they explain in a preliminary report.
It’s important to state that COVID-19 has no known universally accepted treatment or cure at the time of publication. There is no clinical evidence that EGCG can prevent, treat, or cure COVID-19. That said, tea and immunity have a big role to play in this situation too.
 What are Auto-Immune Disorders?, A to Z Guides. Accessed online at https://www.webmd.com/a-to-z-guides/autoimmune-diseases on August 11, 2020
 Pae M, Wu D. Immunomodulating effects of epigallocatechin-3-gallate from green tea: mechanisms and applications. Food Funct. 2013;4(9):1287-1303. Accessed online at https://pubmed.ncbi.nlm.nih.gov/23835657/ on August 11, 2020.
 Wu D, Wang J, Pae M, Meydani SN. Green tea EGCG, T cells, and T cell-mediated autoimmune diseases. Mol Aspects Med. 2012;33(1):107-118. Accessed online at https://pubmed.ncbi.nlm.nih.gov/22020144/ on August 11, 2020.
 Singh BN, Shankar S, Srivastava RK. Green tea catechin, epigallocatechin-3-gallate (EGCG): mechanisms, perspectives and clinical applications. Biochem Pharmacol. 2011;82(12):1807-1821. Accessed online at: https://pubmed.ncbi.nlm.nih.gov/21827739/ on August 11, 2020.
 Jantan I, Ahmad W, Bukhari SN. Plant-derived immunomodulators: an insight on their preclinical evaluation and clinical trials [published correction appears in Front Plant Sci. 2018 Aug 13;9:1178]. Front Plant Sci. 2015;6:655. Accessed online at:
 Longo, G., Karan, M., Sharma, P. D., Rakesh, D. D., Vyas, S. and Vasisht, K., Quantitative Analysis of Green Tea Polyphenols in Indian Cultivars. Accessed online at https://pdfs.semanticscholar.org/40e1/20182db93d3addd0abf272edd40e92d82ded.pdf on August 11, 2020.
 Butt MS, Imran A, Sharif MK, et al. Black tea polyphenols: a mechanistic treatise. Crit Rev Food Sci Nutr. 2014;54(8):1002-1011. Accessed online at: https://pubmed.ncbi.nlm.nih.gov/24499118/ on Aug 11, 2020.