Chapter 1

What is immune system?

The immune system is made up of different organs, cells, and proteins.  These work together to defend the body against infection caused by bacteria, viruses or parasites while protecting their own cells.

The immune system is amazingly complex. It can recognize and remember millions of different enemies. It can produce secretions and cells to match up with and wipe out each one of them.

There are 2 main parts of the immune system:

  • The innate immune system. You are born with this.
  • The adaptive immune system. You develop this when your body is exposed to microbes or chemicals released by microbes.

These 2 immune systems work together.

As per Encyclopaedia of Toxicology (Second edition), 2005, immunity can be defined as all of the physiological mechanisms that enable an individual’s body to recognize materials as foreign and to neutralise, eliminate, or metabolize them without injury to its own tissue.

The innate immunity system

The innate immune system is the body’s first line of defence against germs entering the body. It responds in the same way to all germs and foreign substances, which is why it is sometimes referred to as the “nonspecific” immune system. It acts very quickly: For instance, it makes sure that bacteria that have entered the skin through a small wound are detected and destroyed on the spot within a few hours. The innate immune system has only limited power to stop germs from spreading.

The innate immune system comprises of:

  • physical barrier like skin and mucous membranes
  • chemical barriers like lysozyme, bile salts, sebum, HCl acid, etc
  • the action of cells such as macrophages, dendritic cells (DCs), natural killer cells (NKs), neutrophils and molecules such as cytokines, interleukins (ILs), nitric oxide (NO) and superoxide anion (O2–).

Adaptive immune system

The adaptive immune system takes over if the innate immune system is not able to destroy the pathogens. It specifically targets the type of pathogens that is causing the infection. But to do that it first needs to identify the pathogen. This means that it is slower to respond than the innate immune system. However, it is more accurate when it responds. It also has the advantage of being able to “remember” pathogens, so the next time a known pathogen is encountered, the adaptive immune system can respond faster.

This memory is also the reason why there are some illnesses you can only get once in your life, because afterwards your body becomes “immune.”

The Adaptive immune response is made up of:

  • T lymphocytes in the tissue between the body’s cells
  • B lymphocytes, also found in the tissue between the body’s cells
  • Antibodies in the blood and other bodily fluids
Chapter 2

The Structure of the Immune System

The organs of the immune system are positioned throughout the body. They are called lymphoid organs because they are home to lymphocytes, small white blood cells that are the key players in the immune system.



Organs which are part of the immune system are:

Bone marrow– the soft tissue in the hollow centre of bones, is the ultimate source of all blood cells, including white blood cells destined to become immune cells.

The thymus is an organ that lies behind the breastbone; lymphocytes known as T lymphocytes, or just “T cells,” mature in the thymus.

Lymphocytes can travel throughout the body using the blood vessels. The cells can also travel through a system of lymphatic vessels that closely parallels the body’s veins and arteries. Cells and fluids are exchanged between blood and lymphatic vessels, enabling the lymphatic system to monitor the body for invading microbes. The lymphatic vessels carry lymph, a clear fluid that bathes the body’s tissues.

Small, bean-shaped lymph nodes are laced along the lymphatic vessels, with clusters in the neck, armpits, abdomen, and groin. Each lymph node contains specialized compartments where immune cells congregate, and where they can encounter antigens.

Immune cells and foreign particles enter the lymph nodes via incoming lymphatic vessels or the lymph nodes’ tiny blood vessels. All lymphocytes exit lymph nodes through outgoing lymphatic vessels. Once in the bloodstream, they are transported to tissues throughout the body. They patrol everywhere for foreign antigens, then gradually drift back into the lymphatic system, to begin the cycle all over again.

Spleen- Spleen is a flattened organ at the upper left of the abdomen. Like the lymph nodes, the spleen contains specialized compartments where immune cells gather and work, and serves as a meeting ground where immune defences confront antigens.

Clumps of lymphoid tissue are found in many parts of the body, especially in the linings of the digestive tract and the airways and lungs—territories that serve as gateways to the body. These tissues include the tonsils, adenoids, and appendix.

Immune cells and their products

All immune cells begin as immature stem cells in the bone marrow. They respond to different cytokines and other signals to grow into specific immune cell types, such as T cells, B cells, or phagocytes.

Lymphocytes B cells and T cells are the main types of lymphocytes.

B cells work chiefly by secreting substances called antibodies into the body’s fluids. Antibodies ambush antigens circulating in the bloodstream. They are powerless, however, to penetrate cells.

T Cells -Unlike B cells, T cells do not recognize free-floating antigens. Rather, their surfaces contain specialized antibody-like receptors that see fragments of antigens on the surfaces of infected or cancerous cells.

T cells contribute to immune defences in two major ways:

  • some direct and regulate immune responses;
  • others directly attack infected or cancerous cells.

Helper T cells, or Th cells, coordinate immune responses by communicating with other cells. Some stimulate nearby B cells to produce antibody, others call in microbe gobbling cells called phagocytes, still others activate other T cells.

 Killer T cells—also called cytotoxic T lymphocytes or CTLs—perform a different function. These cells directly attack other cells carrying certain foreign or abnormal molecules on their surfaces. CTLs are especially useful for attacking viruses because viruses often hide from other parts of the immune system while they grow inside infected cells. CTLs recognize small fragments of these viruses peeking out from the cell membrane and launch an attack to kill the cell.

Natural killer (NK) cells are another kind of lethal white cell, or lymphocyte. Like killer T cells, NK cells are armed with granules filled with potent chemicals.

Phagocytes and Their Relatives Phagocytes are large white cells that can swallow and digest microbes and other foreign particles. Monocytes are phagocytes that circulate in the blood. When monocytes migrate into tissues, they develop into macrophages. Specialized types of macrophages can be found in many organs, including lungs, kidneys, brain, and liver.

Granulocytes are another kind of immune cell. They contain granules filled with potent chemicals, which allow the granulocytes to destroy microorganisms. Some of these chemicals, such as histamine, also contribute to inflammation and allergy.

Cytokines Components of the immune system communicate with one another by exchanging chemical messengers called cytokines. These proteins are secreted by cells and act on other cells to coordinate an appropriate immune response. Cytokines include a diverse assortment of interleukins, interferons, and growth factors.

Complement The complement system is made up of about 25 proteins that work together to “complement” the action of antibodies in destroying bacteria. Complement also helps to rid the body of antibody-coated antigens (antigen-antibody complexes). Complement proteins, which cause blood vessels to become dilated and then leaky, contribute to the redness, warmth, swelling, pain, and loss of function that characterize an inflammatory response.

Chapter 3

Immunization and Disorders of the Immune System


Immunization is the process of becoming protected against a disease through a vaccination. Vaccination and immunization can be used interchangeably which means getting a vaccine to become protected against a disease.

By the WHO definition:

  • Immunization: The process of making you immune or resistant to an infectious disease, typically via vaccination.
  • Vaccination: The use of vaccines to stimulate your immune system to protect you against infection or disease

What happens to immune response after immunization?

Vaccines contain weakened or inactive parts of a particular organism (antigen) that triggers an immune response within the body. Newer vaccines contain the blueprint for producing antigens rather than the antigen itself. This weakened version will not cause the disease in the person receiving the vaccine, but it will prompt the immune system to respond. This response will be like the first response to the actual pathogen. This way the immune system remembers the pathogen. It will attack the pathogen if it ever invades again. This “memory” protects you against the disease that the pathogen causes. This is how immunization protects us from diseases. Thus, vaccines train your immune system to create antibodies, just as it does when it’s exposed to a disease. However, because vaccines contain only killed or weakened forms of germs like viruses or bacteria, they do not cause the disease or put you at risk of its complications.

Some disorders that physicians advise immunization from a reliable source:

A study estimated that since 1924 vaccines have prevented over 100 million cases caused by eight contagious diseases. Physicians advise immunization for both children and adults. Immunization which are essential for children are:

Some of these vaccinations are also given to adults.

Other vaccines protect against many different diseases, including:

  • Cervical Cancer
  • Cholera
  • COVID-19
  • Japanese encephalitis
  • Malaria
  • Meningitis
  • Pneumonia
  • Rabies
  • Typhoid
  • Yellow Fever

Disorders of the Immune System

Failures of host defence occur and causes disorders of the immune system. This falls into three broad categories: Allergic diseases or hypersensitivities, autoimmunity and immunodeficiencies.

Allergic Diseases – The most common types of allergic diseases occur when the immune system responds to a false alarm. In an allergic person, a normally harmless material such as grass pollen or house dust is mistaken for a threat and attacked. Allergies such as pollen allergy are related to the antibody known as IgE. Like other antibodies, each IgE antibody is specific; one acts against oak pollen, another against ragweed.

Autoimmune Diseases – Sometimes the immune system’s recognition apparatus breaks down. The body begins to manufacture T cells and antibodies directed against its own cells and organs. Misguided T cells and autoantibodies, as they are known, contribute to many diseases. For instance, T cells that attack pancreas cells contribute to diabetes. Autoantibody known as rheumatoid factor is common in people with rheumatoid arthritis.

No one knows exactly what causes an autoimmune disease, but multiple factors are likely to be involved. These include elements in the environment, such as viruses, certain drugs, and sunlight, all of which may damage or alter normal body cells. Hormones are suspected of playing a role, since most autoimmune diseases are far more common in women than in men. Heredity, too, seems to be important.

Immunodeficiency Disorders

AIDS is an immunodeficiency disorder caused by a virus (HIV) that infects immune cells. HIV can destroy or disable vital T cells, paving the way for a variety of immunologic shortcomings. HIV also can hide out for long periods in immune cells. As the immune defences falter, a person with AIDS falls prey to unusual, often life-threatening infections.

Chapter 4

How can I keep my immune system healthy?

Our immune health is always a work-in-progress. Immunity cannot be strengthened with any miracle ingredient or food. With the right kind of lifestyle, nutrition and exercise, immunity can be enhanced gradually.

Immune system healthy?

  • Eating healthy and nutritious food on a daily basis – Consuming a balanced diet with all the essential nutrients like protein, complex carbohydrates, good quality fats, fibre, vitamins and minerals, probiotics help boost immune system. Certain vitamins and minerals have antioxidant properties and when taken in appropriate quantities via food or supplement help boost immunity. These are Vitamin C, Vitamin E, Vitamin A and minerals like zinc, selenium, iron etc.







  • Restricting sugar intake – Consuming too much sugar affects the immune cells. Diets high in added sugar may increase the susceptibility to certain autoimmune diseases, including rheumatoid arthritis. Patients with uncontrolled diabetes are considered immunosuppressed due to the negative effects of elevated blood sugars on the immune system. Hyperglycemia impairs overall immunity through different mechanisms.


  • Managing stress level – While completely eliminating stress from life is unrealistic. It can always be worked upon by finding ways to relax your mind and rejuvenate. Something as simple as taking a walk can help. Other ways are listening to good music, meditation, connecting with a friend etc.


  • Support your gut health – 70% of our immune system is actually located in our gut. The immune system is particularly interconnected with gut bacteria. These gut bacteria influence the immune system. The gut and the immune system support one another to promote a healthy body. Consuming probiotic-rich foods like fermented foods, curd etc. on regular basis can enhance healthy bacteria in the gut. This in turn can boost immunity.


These few lifestyle changes and pointer can actually help boost and strengthen immunity in the long run.

Chapter 5

Best Foods to support Immune Health

The immune system is amazingly complex and influenced by a variety of factors, including diet, exercise, stress level, age, sleep and other medical conditions. There is no shortcut or single superfoods that can strengthen your immunity quickly. However, there are certain foods which when combined with well balanced diet, exercise and lifestyle changes help strengthen the immune system. Some of these foods are listed below:

Foods to Support Immune Health

Amla – In folk tales, amla is described as sarvadosha hara, the cure for all diseases. Amla (Emblica officinalis) or Indian goji berry is Vitamin C rich fruit. Vitamin C boosts the production of white blood cells (WBC) in the body that help in fighting several infections and diseases. Amla is rich in Vitamin C which is equivalent to four oranges or five glasses of lemon juice. Amla is also rich in iron, calcium and several other minerals. Research has shown immense benefits of the incorporation of amla into the diet.

Garlic – Garlic (Allium satium) can improve immunity and also cardiovascular health. Supplementation of 2.56g of aged garlic extract to otherwise healthy persons for 90days was associated with increases in natural killer cells and -T cells in serum (2-fold and 8-fold, respectively). This was associated with a significantly reduced risk of developing sickness and a lesser decrease in symptoms. A sulphur-containing compound called ‘allicin’ from garlic is responsible for its immune-boosting properties. This active compound is activated when garlic is crushed or chewed.

Eggs – Adequate protein intake is important to support immune response. Protein deficiency is linked to impaired immune system function. Egg protein is considered as a complete protein. Egg protein has the highest digestibility with an excellent amino acid profile. It has the highest protein digestibility corrected amino acid score (PDCAAS). PDCAAS is the measure of quality of protein. Eggs also contain nutrients like vitamin D, zinc, selenium, and vitamin E that the body needs for proper immune functioning.

Fatty fishes – Fatty fish (such as salmon and tuna) contain ample amounts of healthy omega-3 fatty acids, which may enhance immune function. Omega-3s may help to reduce inflammation, and could increase your body’s ability to ward off illnesses. Fatty fishes like salmon, tuna, mackerel, sardines etc. are rich source of protein and omega 3 fatty acids

Turmeric – One of the most common ingredients in the Indian kitchen is turmeric. Curcumin is the most active polyphenol in turmeric. It has antioxidant, anti-inflammatory, antibacterial and wound-healing effects. The curcumin in turmeric is better absorbed with piperine in black pepper. Therefore, it is advised to take turmeric with a pinch of black pepper. Studies have shown the inhibitory action of turmeric extract against several pathogenic microbes, such as gastric – ulcer causing Helicobacter pylori. As an antioxidant, curcumin doesn’t only block the free radicals: it also stimulates the antioxidant mechanism in our body. Because of its immune-boosting properties, turmeric has been used extensively by Indian population during the novel coronavirus pandemic as a booster to enhance immunity.

Citrus fruits – Several scientific studies have proposed that vitamin C fights against the cold virus. Vitamin C acts as an antioxidant, protecting cells from damage caused by free radicals. Vitamin C (also known as ascorbic acid) is a water-soluble nutrient found in leafy greens and citrus fruits. Popular citrus fruits include oranges, grapefruit, tangerines, lemons and limes. Oranges are an exceptional source of Vitamin C. The healing properties of oranges are due to variety of phytonutrient compounds. These phytonutrients include citrus flavanones. Lemons and limes contain flavonoid compounds that have antioxidant and anti-cancer properties.

Ginger Ginger has powerful anti-inflammatory and antioxidant benefits. A compound called ‘gingerol’ in ginger is the active compound. Ginger may help decrease inflammation, which can reduce a sore throat (swollen glands) and inflammatory illnesses.

Almonds – Almonds are packed with the fat-soluble vitamin and also have healthy fats. Almonds have vitamin E which are great immune booster. Almonds are also rich in antioxidants that regulate free radicals to prevent infections, with an anti-inflammatory effect, immune-boosting properties.

Sunflower seeds – Sunflower seeds are nutritionally dense. Sunflower seeds are sources of vitamins and minerals, including vitamin E. Vitamin E have strong anti-inflammatory properties. Sunflower seeds are also sources of phosphorus for development of bone health and selenium, an antioxidant that protects against cell damage. It also contains manganese having bone production capacity and copper which helps with heart health and immune function They also are rich in vitamin B6 for cognitive development and function and zinc for metabolism and immune function.

Yogurt – Yogurt is packed with nutrients and are a probiotic source. Probiotics are beneficial bacteria that regulate gut health and immunity. Probiotics from yogurt enhance the production of immune cells and strengthens the lining of the gut. It also blocks the growth of harmful bacteria in your digestive tract. In a study, yogurt intake was linked with lower levels of chronic inflammation.

Green leafy vegetables – Leafy greens like spinach, kale, fenugreek leaves etc. are packed with beta-carotene, a form of vitamin A that is also an antioxidant. They are also rich source of folic acid. Vitamin A is essential for normal immune functioning. Green leafy vegetables are also rich in dietary nitrate, an organic compound that has anti-inflammatory properties and can help regulate the immune system.

These nutritious and whole foods when taken in required quantities help enhance immunity when combined with the right kind of balanced diet, exercise and lifestyle changes.

Chapter 6

Immune system booster

As they say, “Rome was not built in a day”, same thing implies to our immunity as well. Our immunity cannot be made robust in a day with a superfood or any magical ingredient.

To strengthen our immunity, we need to make healthy lifestyle changes with balanced meals, sleep well, work on stress levels, do physical exercise consistently. When we pair this correct lifestyle with the right supplements that boost immunity, we will be able to build a strong immunity.

What is immune system boosting supplement?

Immune system boosting supplements are dietary supplements containing vitamins and minerals and/or phytonutrients that help enhance the function of the immune system. Certain vitamins and minerals have a specific role in enhancing the immunity.

Vitamins and minerals are micronutrients required by the body to carry out a range of normal functions and are essential for the body’s normal functioning. However, these micronutrients are not produced in our bodies and must be derived from the food we eat.

Sometimes, if diet quality is low, or digestion and absorption is compromised, we don’t get enough of a vitamin or mineral to meet our body’s needs. If this goes on long enough, we can develop a deficiency.


Nutrient rich food and immune boosting supplements can be taken to prevent such deficiencies. Immune boosting supplement that meets the recommended daily allowance (RDA) of the vitamins and minerals can be taken daily to boost up our immune system.

Some of the essential micronutrients for immune cell development and function are:

Vitamin D – Vitamin D is actually a group of prohormones (hormone precursors). Vitamin D helps with calcium absorption, immune system function, and regulating glucose tolerance. Various studies have shown that vitamin D in adults and children can reduce the risk of respiratory tract infection. It was observed that people with low vitamin D status had been associated with severity in covid-19 subjects.

Vitamin A – Vitamin A is essential for normal reproduction, bone development and function, and immune system function. Vitamin A helps protect against infections by keeping skin and tissues in the mouth, stomach, intestines and respiratory system healthy.

Vitamin C – Vitamin C is probably most famous for its role in supporting the immune system. Vitamin C is required for the normal functioning of T cells. It has antimicrobial, anti-inflammatory and antioxidant effects. Vitamin C has shown to reduce respiratory tract and lung infection risk.

Vitamin E – Vitamin E is the most important lipid-soluble antioxidant in the cell. It protects the integrity of cell membranes from damage caused by free radicals. Vitamin E is also required for the correct function of the humoral and innate immune functions.

Iron – Iron helps to form haemoglobin, red blood cells, and blood vessels. It’s essential for helping transport oxygen throughout the body. Dietary iron comes in two forms: heme iron (from animal foods) and non-heme (from plant foods). Consuming iron with vitamin C helps enhance absorption.

Zinc – Zinc is needed for wound healing and supports immune response. Zinc supports lymphocyte and cytokine functions, and innate immunity overall.

Copper – Copper is an antioxidant and is also involved in energy production, collagen formation, and protein synthesis.

Selenium – Selenium is an antioxidant, and also plays a role in thyroid hormone metabolism. Selenium along with Vitamin E can act together to alleviate oxidative stress in certain tissues.