Antigens and Immunology

Periodically, humans are affected by different types of infectious agents. Among which few infections lead to disease, as our body is unable to attack these agent so-called antigens.

Antigens are large molecules of proteins, present on the surface of the pathogen- such as bacteria, fungi viruses, and other foreign particles. When these harmful or foreign agents enter the body, it induces an immune response in the body for the production of antibodies.

For example: When a common cold virus enters the body, it causes the body to produce antibodies to prevent from getting sick.

These antigens are classified into Hetero Antigens and Autoantigens.

How does the body protect itself from antigens?

The ability of the body to act against the disease-causing agents and antigens by the immune system is termed as immunity. This immunity may be either inborn or acquired from vaccinations.

Let us explore more about types of immunity followed by the principle of vaccination.

There are two types of immunity which include:

Innate Immunity

Innate immunity is a nonspecific defense mechanism against antigens. After the invasion of antigens, instantly or within an hour’s time, innate immunity fights against these antigens. It consists of four types of barriers that prevent the entry of foreign agents viz.

  1. Physical barrier – Skin, mucous coating, and urogenital tract.
  2. Physiological barrier – Stomach acid, saliva, and tears.
  3. Cellular barriers – Types of leukocytes like monocytes, macrophages etc.
  4. Cytokine barriers – Proteins which are secreted by antigen infected cells.

Example: Interferons.

Antibodies for Antigens

Acquired Immunity

In contrast to innate immunity, acquired immunity is specific for that particular antigen. As mentioned earlier, it is acquired after birth. It comprises of antibodies and specialized cells namely B-Cells and T-Cells that circulates in the body fluid and are involved in the acquired immunity are as follows:

  1. B – Lymphocytes – These cells are able to produce antibodies against a particular pathogen and destroy them. IgG, IgA, IgM, IgE, and IgD are the different types of antibodies and are also known as immunoglobulins which are secreted by B cells.
  2. T – Lymphocytes – These cells act as a mediator between antigen and B cells in order to stimulate the B cell activation and antibody generation. Humoral and cell-mediated immune responses are mediated by T – cells. Graft rejection is caused by the cell-mediated immune system.

Acquired immunity is categorized into two types based on how they are obtained.

  1. Active immunity– It is an artificially induced immunity. Body acquires immunity when the body is exposed to the antigen. Active immunity is the working principle of vaccination. Example: Immunity against chickenpox.
  2. Passive immunity– It is naturally induced immunity that is transferred from maternal antibodies into the fetus through the placenta. Passive immunity is also called as ready-made antibodies. Example: Antiserum.


Vaccination works on the principle of acquired active immunity. Vaccination is the administration of a vaccine (weak or killed antigen) to improve the individual’s immunity against the particular antigen. Vaccines are prepared from inactivated antigens or antigenic protein of pathogen which are used to generate B-cells, T – cells and memory response against a particular antigen.

Recombinant DNA technology plays a major role in the preparation of antigenic proteins of antigens and vaccines. Example: Cholera vaccines.

To know more about antigens and antibodies, visit BYJU’S.

Practise This Question

Regarding the assertion and reason, select the right option:

Assertion [A]: Vaccination exploits the fact that the immune system’s response to a second exposure to pathogens is much faster and more vigorous than it is the first time around.

Reason [R]: Vaccines mimic live pathogens.