What is Immunity | Definition, Types, Example, Know A-Z

Hello friends, today we will talk about immunity, what is immunity? If you know about it well step by step, then let’s start.

What is Immunity definition?

Immunity is the ability of the organism to recognize the intrusion of foreign matter (cellular or non-cellular) in the body and to mobilize cells and cell products of the immune system for removing the foreign matter with the greatest speed and effectiveness and protect the body against infection.

All organisms have defense mechanisms that protect them from a foreign organism or their product. There are two main types of these mechanisms.

1. Natural or innate or nonspecific immunity.
2. Adaptive or acquired or specific immunity.

What is Innate or natural immunity?

In our native, immunity is the resistance to infection that an individual possesses by virtue of his genetic and consideration makeup. It is not acquired through previous contact with the pathogen.

Innate immunity may be nonspecific when resistance to infection is in general, or it may be specific when resistance is to a particular pathogen.

The nonspecific innate immunity against a variety of harmful substances present in the environment is due to the organism’s Anatomical biochemical and physiological features.

For example –

1. The skin protects the body against the invasion of microorganisms (primary defense).
2. Various harmless bacteria that live on the skin inhibit the growth and multiplication of other microorganisms that might be harmful (bacterial antagonism). 
3. The moist mucous membrane of the nose, mouth, and other parts that are open to the external environment traps invading microbes. The nucleus contains microbicidal substances.
4. The oil secreted by sebaceous glands contains fatty acids, which have an antibacterial effect.
5. Sweat contains Lactic acid, which has microbicidal properties.
6. The high acidity of gastric juice kills most microorganisms that enter the stomach.
7. Tears contain a hydrolytic enzyme muramidase (lysosome) which dissolves bacterial cell walls and kills them.
8. Body tissues contain lysozyme that dissolves bacterial cell walls. Blood contains beta lysin. It is active against aerobic bacilli.
9. Phagocytes engulf and digest microorganisms are foreign substances that happen to enter the body. These form the second line of Defense. These circulate freely in the body.

A nonspecific defense mechanism destroys pathogens and prevents the spread of infection before the acquired immune mechanism becomes active.

What is acquired or adaptive immunity?

Acquired immunity is also called specific immunity. It is the resistance to immunity an individual acquires due to following infection, and it is exhibited by producing antibodies against the pathogen. 

This depends on the body’s ability to recognize the substances as foreign or non-self and to produce an immune response to them. Such substances are called antigens. The body reacts to the antigens by producing antibodies.

Acquired immunity may develop as a result of contact with a digit and recovering from it. These leave long-lasting immunity for subsequent exposure to the same pathogen because the antibody which was formed remains in the body and provides Immunity to subsequent attacks of the same pathogen.

Acquired immunity can also be induced artificially in individuals by immunization or vaccination. In vaccination, attenuated or cleared microorganisms or some of the metabolic products are injected. The injection of the vaccine produces resistance against the disease for which vaccination is done.

 Acquired immunity is long-term immunity. Moreover, it takes several days to activate the specific immune response in the cells of the immune system. Acquired immunity involves two separate phenomena.

1. Antibody-mediated or humoral immunity
2. Cell-mediated or cellular immunity

What is Antibody-mediated or humoral immunity?

It involves the production of antibodies by the T or B-Lymphocytes to destroy the invading pathogen.

What is Cell-mediated or cellular immunity?

 In this case, specific Lymphocytes attack the inviting pathogen and devour it. 

Role of macrophages in body defense –

 Macrophages are polymorphic cells. There are mono-nuclear phagocytes. These are formed from circulating monocytes. These are widely distributed throughout the body.

They are two types –

1. Those wondering in tissues and body spaces.
2. Those fixed to the epithelium.  These move like amoebae By extending pseudopodia. Foreign bodies by engulfing them with the help of pseudopodia. They contain enzymes hydrolases And Peroxidase, which kill ingested microorganisms and digest them. Electrostatic forces are necessary for initial attachment. The firm attachment is facilitated by serum opsonins. Opsonins are antibodies that make microbes to be more easily interested.

 The Phagocytes macrophages form networks in different tissue such as Kupffer cells in the liver microglia In the brain Histiocytes in the areolar tissue and specialized cells in the Kidney lung and lymph nodes. These are non-wandering macrophages.

What are Passive and active immunity? Or

Difference between active and passive immunity?

Acquired immunity is of two types.

1. Active immunity
2. Passive immunity

What is active immunity?

Active Immunity is the specific resistance by the person to any microbial infection, It is developed in individuals as a result of activation of the cells of the immune system against pathogenic microorganisms or their product i.e. antigen. 

The immune system churns out antibodies specific to the antigen entered into the body. These antibodies remain in the body even after recovery and give long-term resistance.

The antigen also causes the formation of some memory cells. These remain dormant in the body and start producing Antibodies as soon as they are activated by antigens due to subsequent infections. 

For example – If a Child had measles or mumps once, he will never have Infections again throughout his life because of memory cells.

Active immunity develops after direct contact with the antigen, which may be the microorganism itself or its product.  The effective contact with the microbes may be either by infection or by injection of live attenuated or killer microorganism or their antigens or their toxins (Inactivated toxins). 

In all these cases, the host immune system produces antibodies that retain it in the blood and provide resistance or immunity for subsequent infections with the same antigen. This may be antibody-mediated immunity or humoral immunity and cell-mediated or cellular immunity.

What is passive immunity?

Passive immunity is developed by injecting a normal person with antibodies against some specific antigen or microorganism to provide immediate resistance against infection from the particular pathogen.

Passive immunity is also called borrowed immunity. Its effect lasts for a short period only. It boosts the body’s defense temporarily against a particular disease. An Individual is given antibodies actively produced by another organism.

The serum or Gamma globulin containing these antibodies can be obtained from animals or humans. Such injections of Gamma offer protection for only a few months because these injections do not induce memory cells in the body and the body cannot produce antibodies to the pathogen.

Once the injected antibodies wear out, the immunity disappears. Passive immunization is used against poliomyelitis and infectious hepatitis.

Pregnant women confer natural passive immunity upon their developing babies by manufacturing antibodies for them.

These maternal antibodies of the I_g G class pass through the placenta and provide the newborn infant with a defense system for about six months until its own immune system matures.

Differences between active immunity and passive immunity.

Sr. No.	Active Immunity	Passive Immunity
1	Produced by the host’s immune system.	Received by the host as antibodies. The host immune system does not participate.
2	Induced by infection or by contact with immunogens (vaccines or allergens etc.	Conferred by the introduction of antibodies produced in some other animal.
3	Immunity is more effective and long-lasting.	Immunity is less effective and short-lived.
4	It takes time for the generation of antibodies, so the immunity develops after a long period.	Antibodies are not formed by the host but received by injection, so immunity develops immediately.
5	Immunological memory develops after the first infection, which provides lifelong immunity.	Immunological memory does not develop.
6	Booster doses of vaccine enhance immunity.	Subsequent administration of antibodies is less effective due to immune elimination.
7	Active immunity fails to develop in the immunodeficient host.	Passive immunity develops even in immunodeficient hosts.

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