Immunity is a very common word that most of us use in our daily lives and during this COVID-19 pandemic situation, understanding and development of immunity in our body has become prime importance. So, what does this word immunity mean? In a simple way, immunity means the capacity of our body to fight against diseases. Our body has a natural defence mechanism that stops the entry of various types of pathogens. In this article, we will learn about what is meant by immunity, its types, the immune system of humans, and much more.

How Do You Define Immunity?

The word immunity is derived from the Latin word “immunis” which means “exempt ordom”. Immunity is defined as the ability of our body to fight against all types of foreign bodies or antigens like bacteria, virus, fungi, toxic substances, etc. which enters our body.

Immunity is also termed as disease resistance and lack of immunity is known as susceptibility. The branch of science that deals with the study of immunity and the immune system is called immunology.

What are the Types of Immunity?

Depending on the specificity to resist the antigens or the foreign bodies and the mode of development, immunity can be of two major types, i.e. innate or natural or non-specific immunity, and acquired or adaptive or specific immunity.

Innate Immunity

The type of immunity that is conferred or present at the time of birth is called innate immunity. It is inherited by the organism from the parents and protects it from birth throughout life. For e.g., humans have innate immunity against distemper, a fatal disease of dogs. The features of innate immunity are given below:

1. Innate immunity guards against the entry of microorganisms into the body hence form the first line of defence.
2. Innate immunity is also called non-specific immunity because these defence mechanisms do not distinguish one invader from another.
3. Innate immunity is also termed natural immunity as it is available since birth.
4. The aim of innate immunity is to stop the entry of a pathogen into the body and if the pathogen has broken the first barrier and entered the body, then to kill it directly or indirectly.
5. This immunity consists of the following four types of barriers:

Types of Barriers	Characteristics and examples
Physical barriers	1.  Form the first line of defence and guard against the entry of pathogens into the body. 2. Includes the skin and the mucous membranes lining the respiratory, gastrointestinal, and urogenital tracts that help in trapping the microbes.
Physiological barriers	1. Prevent the growth of pathogens and microorganisms in the body. 2. Includes the barriers like the rise in the body temperature (fever), acidic pH in the stomach, and various body secretions like lysozymes in saliva and tears.
Cellular barriers	1. Form the second line of defence and work when the pathogens have gained entry into the body. 2. Includes the wandering leucocytes or phagocytes or white blood cells (WBCs) that circulate in the body.
Cytokine barriers	1. Play a major role against the invading viruses 2. Virus-infected cells secrete interferons that protect the non-infected cells from further viral infections.

Important Fact!

1. Cytokine storm is an acute hyperinflammatory response that can be seen in the COVID- \(19\) patients who all are infected with SARS-CoV- \(2\) (Severe acute respiratory syndrome coronavirus-\(2\).
2. Patients suffering from COVID-19 have higher levels of interferon gamma-induced protein \(\left( {{\rm{I}}{{\rm{P}}_{{\rm{10}}}}} \right)\) and interleukin \(1\) beta \({\rm{(IL – I\beta )}}\) that leads to hyperinflammatory response affecting the respiratory tract, gastrointestinal tract, kidneys and even the cardiac tissue.
3. Interferons are antiviral proteins and are used as biological immune modifiers.

Acquired Immunity

The immunity that the body develops after birth by coming in contact with the pathogens is called acquired immunity or adaptive immunity. The characteristic features of acquired immunity are as follows:

1. Acquired immunity is also called specific immunity because it is pathogen-specific and has the ability to recognise and selectively eliminate specific microorganisms.
2. It supplements the protection provided by innate immunity.
3. It may take several days for this immunity to get activated after the foreign antigen has entered the body.
4. It can discriminate between the foreign molecules (non-self) and the molecules present within the body (self) of an organism.
5. It is mediated by antibodies or lymphocytes or both which make the antigen harmless.
6. It not only relieves the victim of the disease but also prevents its further attack in the future. The memory cells formed by B-cells and T-cells are the basis of acquired immunity.
7. Thus, this immunity consists of B and T- lymphocytes and antibodies.

Important Fact!

The cells of the immune system are derived from the pluripotent stem cells (cells that can differentiate into many different types of tissue cells) in the bone marrow.

The pluripotent stem cells can form the following two major kinds of stem cells which further give rise to different types of cells:

1. Myeloid stem cells: These cells give rise to monocytes, macrophages and granulocytes (neutrophils, eosinophils and basophils), RBCs, blood platelets.
2. Lymphoid stem cells: These cells form B-lymphocytes (B-cells), T-lymphocytes (T-cells) and Natural Killer cells (NK cells).

Types of Acquired Immunity

Depending on the mode of development of the acquired or adaptive immunity, it can be divided into two types, i.e. active immunity and passive immunity.

1. Active Immunity: When a host is exposed to antigens (living or dead microbes or their toxins), resulting in the development of antibodies in the host body itself the immunity is termed active immunity.
2. Passive Immunity: In this type of immunity, the organism’s own body does not produce the antibodies, instead ready-made antibodies from some other organisms are introduced to protect the body against the disease.

Know About Human Body And Its Movements

Differences between Active Immunity and Passive Immunity

Active immunity	Passive immunity
1. Immunity is said to be active when a person’s own cells produce antibodies in response to infection or vaccination.	1. Immunity is said to be passive when antibodies produced in other organisms are injected into a person to counteract antigens such as snake venom.
2. It takes time for the formation of antibodies.	2. It provides immediate relief.
3. Active immunity is slow but provides immunity for a longer duration.	3. Passive immunity is fast but provides immunity for a short duration.
4. It is relatively safe.	4. It may create problems. Foreign antibodies may cause a reaction and the body may destroy them by forming its own antibodies.

Components of Acquired Immunity

Based on mode of action, and the types of cells involved, acquired immunity has two important components, i.e. humoral immunity and cell-mediated immunity.

1. Humoral immunity or Antibody-Mediated Immune System (AMIS): It consists of B-lymphocytes that produce antibodies against pathogens or antigens present in the body fluids.
2. Cellular immunity or Cell-Mediated Immune System (CMIS): It consists of T-lymphocytes that destroy pathogens or antigens present on the cell surface.

Humoral Immunity and Cell-mediated Immunity

Humoral Immunity	Cell-mediated Immunity
It consists of B-lymphocytes which produce antibodies that circulate in the body fluids.	It consists of T-lymphocytes that normally produce four types of T-cells.
It defends the body against bacteria, viruses, and toxins.	It defends the body against all kinds of pathogens including protists and fungus.
It does not respond to transplants.	It reacts against transplants.
It does not provide immunity against cancer.	It reacts against transplants.

B–lymphocytes	T–lymphocytes
1. B-cells form a humoral or antibody-mediated immune system.	1. T-cells form a cell-mediated immune system.
2. They are processed in the bone marrow and, hence, are called B–cells.	2. They are formed in the thymus gland and, hence, called T –cells.
3. They defend against some viruses, encapsulated bacteria, and toxins that enter the blood.	3. They defend against some viruses, protists, fungi, and some bacteria which enter the cells.
4. They release the antibodies produced into the lymph which eventually enter the blood.	4. They do not release but hold on to the antibodies.
5. Antibodies produced to attack the antigens	5. The whole body directly attacks the antigens.
6. They defend the body against invading bacteria or viruses. They do not react against transplants and cancerous tissue.	6. They defend the body against pathogens but also attack the transplants and the cancerous cells.

Antibodies

Antibodies are also called immunoglobulins (Igs) or gammaglobulins or \({{\rm{H}}_{\rm{2}}}{{\rm{L}}_{\rm{2}}}\) are chemically glycoproteins that are produced in the body by B-Plasma cells in response to the antigen or foreign bodies. Antibodies are produced by mature plasma cells that are formed by the transformation of B-lymphocytes.

Types of Antibodies

Diagrammatic View of Antibody

Each antibody is made up of four polypeptide chains:

1. Two identical short polypeptides called light chains \(\left( {\rm{L}} \right)\), and
2. Two identical long polypeptides called heavy chains \(\left( {\rm{H}} \right)\).
3. Each of the light chains is bonded to one of the heavy chains.
4. The four polypeptide chains are held together by disulphide \({\rm{( – S – S – )}}\) bonds forming a \({\rm{Y – }}\) shaped molecule.
5. Each of the four chains has a constant \(\left( {\rm{C}} \right)\) region and a variable \(\left( {\rm{V}} \right)\) region.

Did you know?

1. IgG antibodies can pass through the placenta from the mother’s body to the foetus and help in developing natural passive immunity in the foetus.
2. IgG antibody is responsible for erythroblastosis foetalis. To learn more about erythroblastosis foetalis click here.
3. IgA antibody is transferred from mother to infants during lactation in an initial few milks called colostrum.

Role of Vaccines in Developing Immunity

Vaccination is a possible way to induce active acquired immunity against the germ of various diseases like polio, diphtheria, whooping cough, tetanus, and smallpox, etc. The process of immunization involves the introduction of weakened or attenuated bacteria into the body by vaccination. The immune system of the body recognizes these bacteria and starts developing antibodies and memory cells. The vaccines are generally given in multiple doses called primary dose and secondary dose.

1. Primary dose: The initial dose given to the patients which are usually of a small amount of attenuated pathogen and is capable of inducing a weak immune response is called as primary dose.
2. Secondary dose: The subsequent doses given to the patients which are usually of a large amount of attenuated pathogen and is capable of inducing a weak immune response is called a secondary dose. The doses given later are called booster doses.

Immune Response

The response given by the immune system varies drastically and can be broadly classified into primary immune response and secondary immune response, based on the immunity developed and the response given by the body.

Primary Immune Response

1. This immune response occurs as a result of the first contact with an antigen.
2. It takes a longer time to establish immunity.
3. This immune response declines rapidly.
4. B and T-lymphocytes play a major role in this immune response.
5. It leads to the development of memory cells which helps in developing secondary immune response.

Secondary Immune Response

1. This immune response occurs at the second and subsequent exposure of the same host to the same antigen.
2. It is a more rapid response.
3. It lasts for a longer period.
4. Memory cells play a major role in this immune response.
5. This immune response is also known as a booster response.

Human Immune System

The human immune system consists of lymphoid organs, tissue cells, and antibodies. The lymphoid organs are those organs where the maturation and proliferation of lymphocytes take place.

? Learn About Immune System

Significance of Immune System

The significance of the immune system are as follows:

1. It helps to protect our body from outside invaders like bacteria, viruses, fungi, and toxins.
2. It contains B-lymphocytes that produce antibodies to fight against any antigen or pathogen that may have entered the body.
3. It also contains NK cells that secrete perforins which attack the cancerous cells.
4. It has the ability to recognise and neutralise a vast variety of foreign molecules or antigens.
5. It also contains the memory cells which provide immediate protection when a person’s body is attacked by the same antigen or pathogen for the second time.

Disorders of Immune System

1. Allergies: It is an exaggerated response of the immune system. Many people are very sensitive to one or more substances. These substances are called allergens. The allergens are generally weak antigens. These may be pollen grains, dust, chemicals, drugs, fabrics, plants, cold, heat, sunlight, various types of foodstuff, etc. any person can become allergic to anything and at any time of his life. It produces symptoms of a wide variety. Allergens trigger the formation of antibodies (IgE) in the body which combines with the receptors of the body’s mast cells. Histamines are released which cause inflammatory responses. The most common symptoms of allergic reactions are inflammation of mucous membranes, frequent sneezing, skin rashes, watering of eyes and inability to breathe.

2. Autoimmunity: Sometimes, the immune system of the body goes off track and starts working against the body or self-body cells. This leads to a variety of autoimmune diseases. Such disease depends on which type of self-antigen is involved. For example, if the self-antigen is RBC, then it destroys its own RBC causing severe anaemia, if the self-antigen is a muscle cell, it destroys the muscle causing severe weakness (a condition called myasthenia gravis) and if the self-antigen is liver cells, it causes damage to its liver cells resulting into a chronic case of hepatitis. However, these are some of the degenerative diseases. Other examples are Hashimoto’s thyroiditis, systemic lupus erythematosus, and rheumatoid arthritis, SCID, juvenile diabetes type-I, etc. Autoimmunity is induced either by infection of pathogens particularly viruses or deficiency of certain proteins.

Summary

The human body has various mechanisms for protection from foreign agents and combatting infection. These protective mechanisms in the body form the immune system and provide immunity against invading pathogens. Now, during this COVID- \(19\) pandemic situation, we must keep our immunity strong so that the virus cannot attack and enter our bodies. So, we need to take some precautions like wearing a mask always, cleaning our hands frequently, maintaining a safe distance, and getting ourselves vaccinated as soon as possible.

FAQs

Q.1. Which minerals and nutrients are important in developing immunity?
Ans: Minerals like zinc and vitamins like vitamin C are very helpful in boosting immunity.  

Q.2. What are the two major kinds of immunity?
Ans: The two major kinds of immunity are: i) Innate immunity, and ii) Acquired Immunity.

Q.3. What is the body’s first line of defence?
Ans: The body’s first line of barriers includes i) Physical barriers (skin and mucous membranes), and ii) Physiological barriers (fever, acidic pH, secretion of saliva, and tears).

Q.4. How does the immune response to COVID-19 occur?
Ans: The immune response to COVID-19 occurs with the help of interferons combined with the production of antibodies.

Q.5. Can the use of alcohol affect the immune system?
Ans: Yes, the use of alcohol can affect the immune system because by consuming alcohol, the person’s immune system is affected making them more vulnerable to infectious diseases like COVID-19.

Q.6. How long does it take to develop an adequate immune response after receiving the COVID-19 vaccine?
Ans: After receiving the COVID-19 vaccine, the adequate immune response takes almost 2 – 3 weeks on completion of the entire vaccination schedule, i.e., after the second dose of the COVID-19 vaccine.

Q.7. Are interferons and antibodies the same?
Ans: No, interferons and antibodies are different. The difference between them is given below:

Interferons	Antibodies
1. Interferons are produced by any virus-infected cell.	1. Antibodies are produced by plasma B-cells only.
2. They leave the infected cell and enter a nearby healthy cell to dispose of the virus.	2. They pass into and circulate in blood and lymph to dispose of the antigens.
3. They induce the healthy cell to synthesize the antimicrobial proteins that check viral multiplication.	3. They selectively bind to the antigens that are immobilized for easy attack by phagocytes.
4. They are quick in action but give temporary protection.	4. They are slow in action but give long-lasting protection against antigens.
5. They act inside the cells.	5. The act outside cells.
6. They form the body’s second line of defence.	6. They form the body’s third line of defence.

Now that you have a detailed article on the immunity system, we hope you do not face issues. If you have any queries do let us know about it and we will get back to you soon.