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Immunology Definition

“The study of the immune system, the cell-mediated and humoral aspects of immunity and immune responses.”

Immunology is a branch of biology involved with the study of the immune system, components of the immune system, its biological processes, the physiological functioning of the immune system, types, its disorders and a lot more.

The immune system acts as a body’s defence system by protecting our body cells, tissues and organs from invading infections through various lines of defence. Overall, the immune system functions by recognising and destroying foreign antigens including harmful microorganisms and other disease-causing microbes.

Under certain conditions, when our immune system is weak or stops functioning, this results in various infectious diseases, such as fever and flu,  and may also lead to dreadful diseases like cancer AIDS, etc.

Also Read: Immunity

Let us have a detailed look at Immunology to learn about the immune system, its different parts, functions and other significance of Immunology.

Immune System

Immune system consists of different types of cells and organs which protect our body against pathogens. Pathogens are defined as microorganisms that cause infections in the body such as bacteria, fungi, viruses and protozoans. Antigens are molecules that elicit antibody generation. They can be everything that does not belong to our body, from parasites to fungi, bacteria, viruses, and haptens. Haptens are molecules that can elicit an immune response when combined with a carrier molecule. All the cells and molecules of the immune system are distributed in all the tissues of the body as well as lymphoid organs which eliminate microbial infectious diseases, decrease the growth of tumours and starts the repairing process of damaged tissues.

The tissues and organs of the immune system act as security forces where cells act as the security guards while molecules act as the guns & bullets and use the communication system to protect you.

Types of Immune System

We, humans, have two types of Immune system and are classified based on whether they are present at the time of birth or not.

  1. Innate Immune System.
  2. Adaptive Immune System.

Innate Immune System

Immune System fights against microbes and prevent their entry inside the body.

Innate Immune System is composed of cells and proteins that are always present and are ready to fight against microbes in the infection area. Innate Immune System is present from the time of our birth.

Main elements of the innate immune system are –

  • Dendritic cells.
  • Phagocytic leukocytes.
  • Natural killer (NK) cell.
  • Physical epithelial barriers.
  • Circulating plasma proteins.

Adaptive Immune System

The adaptive immune system is required to fight against pathogens that cannot be controlled by innate immune defences. It is also referred to as the acquired immune system because it is acquired during the course of life. They are specific to the type of pathogen invading the body.

All the components of the adaptive immune system are generally inactive however when activated these components adjust to the presence of all the infectious agents by proliferating and developing a potent mechanism for eliminating the microbes.

Two Types of adaptive responses are – humoral immunity moderated by antibodies which are developed by B lymphocytes and cell-mediated immunity, moderated by T Lymphocytes.

Immunology and Diseases

Immunological diseases are caused by defects in immune system. The immune system may be hyperactivated to release antibodies and other chemicals. This results in allergy and anaphylaxis. Sometimes the immune system fails to differentiate self cells from no-self cells, resulting in autoimmune diseases. In this situation, the immune system is challenged and evoke responses that damage cells and tissues rather than protecting. All the immunodeficiency diseases increase the risk of tumours and infections and are caused by malnutrition, immune suppresents, gene mutations, and viruses such as HIV.

Also Refer: Antigens and Immunology

Symptoms of Immune Dysfunction

  • Bowel disorders.
  • Parasite infections.
  • Candida overgrowth.
  • Allergies and Asthma.
  • Frequent colds and flu.
  • Autoimmune disorders.
  • Painful joints and muscles.
  • Herpes (cold sore) outbreak.
  • HPV and abnormal PAP smears.
  • Rhinitis or a constant runny nose.
  • Psoriasis, eczema, hives or rashes.

Immunology Techniques

This is an experimental method used for studying the structure and functions of the immune system. There are different techniques, which includes:

  • ELISA.
  • Immune cell isolation.
  • Immuno-histo-chemistry.
  • Generation of Antibodies.
  • Immuno-blotting and precipitation.
  • Isolation and Purification of Antibodies.

Applications of Immunology

Immunology is widely used in numerous disciplines, including medicine, in the fields of organ transplantation, bacteriology, oncology, virology, parasitology, rheumatic diseases, psychiatric disorders, and dermatology. The Immunology of transplantation mainly deals with the process of transplantation from a donor to the recipient, so that the recipient’s body does not reject the organ.

This was a brief introduction to Immunology, for more information on Immunology, immune system, its techniques, notes for Immunology Class 12, visit us at BYJU’S Biology.

Frequently Asked Questions on Immunology


What is ELISA?

Enzyme-Linked ImmunoSorbent Assay is known as ELISA. It uses antibodies to detect the presence of certain proteins in the sample. ELISA is used as a diagnostic tool.


What is hay fever?

Hay fever is the allergic response to certain allergens from the environment such as pollens, dust mites and fur.


What is graft rejection?

Graft rejection is the immune response happening in the recipient’s body, that attack and destroys the donated organ.


What is histocompatibility?

Histocompatibility is the property of having similar alleles in the Major Histocompatibility Complex [MHC]. It is required for organ transplantation.


Is thymus present in adults?

The thymus is active till puberty and after that, it slowly degenerates and is replaced by fat tissues.

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