What is Immunity? And Its Classification

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Immunity generally means protection. In biological terminology, immunity is the natural process that is responsible for fighting microorganisms, which enter our bodies to damage the cells. Basically, when our body detects a pathogen, our immune system gets activated. Pathogens are the microorganisms that are either bacteria or viruses, which are capable of causing a disease.


Humans are gifted with immunity, a natural process which keeps them safe from minor and major ailments. We all know that ailments are inevitable whatsoever but can we even guess the number of times our body escapes infections? How many times our body fights bacteria and viruses without even letting us know? Our immunity system is our Superman inside who saves us from diseases except when he’s hit by kryptonite thrown by the pathogens making us get sick till he resurrects and saves us.  


Immunity can be classified into two types:

  • Innate Immunity
  • Adaptive Immunity

Innate Immunity

Innate immunity activates as the first response from our body to a pathogen. Skin itself is a part of innate immunity. It is the primary defense of body that stops harmful organisms from entering the body. However, pathogens can still break into the body by means of air, food or water. The second defense of the body is in the form of mucus which attaches the pathogen to itself and kills it right there. It is destroyed by the complement system which involves a set of proteins.

Now let’s assume the pathogen is even more powerful and it escapes from skin and then mucus as well.  It further goes inside and confronts the cells called phagocytes and NK cells. Phagocytes are of three types:

  • Macrophages
  • Neutrophils
  • Dendric cells

All these cells detect the pathogen, attack and destroy it right there by a process called phagocytosis. The body sends a whole army of cells to fight the pathogen. NK stands for natural killer cells. These cells on the other hand fix the damage already caused to the host cells. It kills them so the pathogen is finally eradicated from the body.

If the pathogen still survives phagocytes and NK cells, then our body activates the secondary immunity which is the adaptive immunity.

Adaptive Immunity

Adaptive immunity is of two types:

  • Active
  • Passive

Adaptive immunity is relatively slower as compared to innate immunity. Our immune system produces Y-shaped proteins known as antibodies. They aim at neutralizing the pathogen. Passive immunity involves the antibodies which are acquired from another person for example from a blood transfusion.

The active immunity on the other hand works by means of two kinds of cells:

  • T-cells
  • B-cells

Dendritic cells activate the T-cells by bringing the remaining pieces of destroyed pathogen to T-cells. When the T-cells are activated they become helper T-cells and cytotoxic T-cells. These cells are responsible to destroy any cells which are still infected by the pathogen.

Helper T-cells simultaneously activate B-cells which form antibodies that we just talked about.  These antibodies detect antigens. An antigen is nothing but a part of a pathogen and it’s located inside the pathogen. Antibodies can only stop the production of antigen and stop a pathogen from invading the body. It means that they cannot destroy the pathogen which is the exclusive function of innate immunity and T-cells.

B-cells form plasma or memory cells which are reactivated once the pathogen tries to reenter the body. The second time when a pathogen is reintroduced, there’s no way it can escape the immune system because of the memory cells.

Some Key Facts and Statistics about Immunity and Immune System

  • Immune system’s each and every part has a distinctive function.
  • Vaccines stimulate the immune system to generate antibodies against a pathogen without infecting a person with a disease.
  • Stress affects the functions of the immune system.
  • A healthy and sound lifestyle can boost the immunity.
  • The destruction of the healthy tissues of the immune system by the system itself causes autoimmune diseases. There are more than 80 categories of autoimmune diseases like psoriasis, rheumatoid arthritis, Crohn’s disease and many more.
  • As per the US Centers for Disease and Prevention, around 8% of the US population is affected by the autoimmune diseases. About 80% of them are women.
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