Immunity is the body’s ability to resist a particular pathogen that causes disease. In this article, we have given a detailed about the immunity system.
According to Abamoff (1970):
Immunity is the body’s ability to destroy or remove substances outside of itself and to defend itself against pathogens.. The immunity of the body is called Immunity.
The ability of a host to fight pathogenic organisms, acquired by the immune system, is called Immunity.
Louis Pasteur is called the father of Immunology.
Although some others call Amil-von Behring the father of Immunology.
Immune system
Many organs form a system to maintain homeostasis in our body by resisting the side effects of all kinds of pathogenic organisms i.e. microbes and antigens, which is called immune system.
Edward Jenner is credited with discovering the Immune system.
Types of immunity
There are two types of immunity:
1. Innate immunity,
2. Acquired Immunity
1. Innate immunity
Innate or innate immunity is a type of specific immunity that is present at birth and is innate.
This immunity creates a variety of barriers against the entry of external disease factors into our body.
Innate immunity produces four types of resistance against external factors-
(A) Physical barrier
The skin and mucous membranes of the internal organs of our body first of all act as a barrier for the entry of microbes.
An enzyme called lysozyme is found in the fluid secreted from the sweat glands. It destroys the cell wall of many bacteria.
The keratin-rich dead cells of the skin keep separating from the body from time to time, due to which the germs keep getting separated from the body.
On the mucosa of the respiratory tract there is a mucous layer (mucus) and cilia. All these do not allow the dust particles and micro-organisms present in the air to enter the lungs.
(B) Physiological barrier
Acid in the stomach, lysozyme present in the saliva of the mouth, lysozyme present in the tears of the eyes, all inhibit the growth of the pathogen.
(C) Cellular barrier
Leukocytes (monocytes, neutrophils) present in the blood of our body and macrophage cells present in the tissues protect the body by eating microbes.
(D) Cytokine inhibition
Virus-infected cells secrete proteins called interferons that protect uninfected cells from further viral infection.
Interferon – It was discovered by Askas and Lindenmann in the year 1957. It is a type of antiviral protein molecule that is synthesized by the body’s cells after a viral infection.
Function of interferon – it inhibits the multiplication of virus. It binds to the surface of uninfected cells and induces the secretion of specific enzymes that inhibit viral protein synthesis by destroying viral mRNA. Interferons do not interfere with the metabolism of the cell. They also enhance the feeding activity of macrophages.
2. Acquired Immunity
Acquired immunity is the acquired immunity from the body’s antibodies to avoid infection by pathogens and antigens present in the environment.
When microbes overcome the innate immunity and cause infection, the acquired immunity works to fight the pathogens.
Major parts of acquired immune system in humans:
This system includes human lymphoid organs, lymphoid tissue, cells and antibodies.
Lymphocytes – These are the organs in which production, maturation and proliferation of lymphocytes take place.
There are two types of lymphatic organs:
1. Primary lymphatic organ – Here the formation and maturation of lymphocytes takes place. This includes the bone marrow, and the thymus.
2. Secondary lymphoid organs – These are the places where lymphocytes interact with microbes or antigens, resulting in their production in abundance to become the dominant cells. This includes the spleen, lymph glands, lymphoid tissue (mucous-associated lymphoid tissue MALT), tonsils, patches of small bowel perforation, appendix, etc.
The main cells of acquired immunity are lymphocytes.There are two types of lymphocytes:
1. B Lymphocytes,
2. T Lymphocytes
The lymphocytes that mature in the lymphoid tissue are called B-lymphocytes.
The lymphocytes that mature in the thymus gland are called T-lymphocytes.
Types of acquired immune response:-
It is of two types:
1. Cell-mediated immunity,
2. Antibody-mediated immunity.
1. Antibody-mediated immunity:
B-lymphocytes are responsible for immune mediated immunity.
In response to pathogens, B lymphocytes produce an army of proteins in our blood to fight pathogens. These proteins are called antibodies which are of two types –
A- Some lymphocytes become activated and differentiate into plasma cells. These antibodies reach the lymph and blood and destroy specific germs or their toxins. When they encounter pathogens for the first time, their response is called the primary response. This is usually a mild reaction.
B- Some B-lymphocytes get stored as memory cells in the lymphatic tissue. When the same infection occurs again in the body, these cells start producing antibodies rapidly by making millions of cells like themselves. This is called secondary response of high intensity. This is because our bodies hold the memory of the first encounter with pathogens.
Antibodies work in the following way:
Antibodies stick to the microbes and form a covering around them, so that the microbes do not stick to the plasma membrane of the somatic cells and are destroyed.
A single antibody binds to multiple pathogens (antigens) and aggregates them into clusters. These clusters are subsequently destroyed by macrophage cells (neutrophils, monocytes).
It binds with solute microbes and destroys them making them insoluble.
The antigen-antibody complex activates a series of non-specific immune system complement protein molecules, these proteins form stomata in the plasma membrane of the bacterial cell, causing the germ to swell, burst and die.
2. Cell-mediated immunity:
T-lymphocytes participate in cell-mediated immunity.
T-lymphocytes themselves do not secrete antibodies, but assist B-lymphocytes in the production of proteins.
Upon exposure to antigens produced by microbes, T-lymphocytes become activated and multiply by mitosis (meiosis) and convert into four types of T-lymphocytes –
A-killer T-lymphocytes: These cells directly attack and destroy the germ cells.
B-Suppressor T-lymphocytes: These cells inhibit the activity of the body’s immune system after the infection is over and teach the immune system to differentiate between its own cells and foreign cells.
This is the reason why the body rejects an organ transplant or the patient has to take immunosuppressant medication for life even after the organ transplant.
C-Helper T-lymphocytes – These cells secrete substances that increase the activity of killer T-lymphocytes and B-lymphocytes.
D-memory T-lymphocytes – Certain cells exposed to microbes, after being sensitized, accumulate in the lymphatic tissue and are activated immediately upon re-infection with the same germ.
Acquired immune response is also called active immunity. Its action is slow and it takes some time to show effective response. It works for a lifetime. For example, once smallpox has occurred, the body has its own resistance to smallpox.
Passive Immunity:
When antibodies made from outside are given directly to the body to protect the body, it is called passive immunity.
It acts instantly, but in some cases, the body has to face other difficulties as well. Its effect is only for a few days. For example, vaccination against whooping cough, tetanus, rabies, polio, etc., are examples of passive immunity to colostrum (rich in IgA) acquired by the mother to the newborn.
Conclusion
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