What is immune system?

Immunisations train a child's immune system to make antibodies to protect him or her from harmful diseases.

The immune system protects a child’s body from outside invaders, such as bacteria, viruses, fungi, and toxins (chemicals produced by microbes). It is made up of different organs, cells, and proteins that work together.

The immune system has two main parts — the innate immune system, which you are born with; and the adaptive immune system, which you develop when your body is exposed to microbes or chemicals released by microbes.These two immune systems work together.

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Innate immune system is a child’s rapid response system. It patrols a child’s body and is the first to respond when it finds an invader. The innate immune system is inherited and is active from the moment a child is born. When this system recognises an invader, it goes into action immediately. The cells of this immune system surround and engulf the invader. The invader is killed inside the immune system cells — phagocytes.

The acquired immune system, with help from the innate system, produces cells (antibodies) to protect the body from a specific invader. These antibodies are developed by cells called B lymphocytes after the body has been exposed to the invader.

It can take several days for antibodies to develop. But after the first exposure, the immune system will recognise the invader and defend against it. The acquired immune system changes throughout a child’s life. Immunisations train a child’s immune system to make antibodies to protect him or her from harmful diseases.

Where cells of immune system are made?

Adenoids (two glands located at the back of the nasal passage).

Bone marrow (the soft, spongy tissue found in bone cavities).

Lymph nodes (organs which are located throughout the body and connect via the lymphatic vessels).

Lymphatic vessels (a network of channels throughout the body that carries lymphocytes to the lymphoid organs and bloodstream).

Peyer’s patches (lymphoid tissue in the small intestine).

Spleen (a fist-sized organ located in the abdominal cavity).

Thymus (two lobes that join in front of the trachea behind the breastbone).

Tonsils (two oval masses in the back of the throat).