An Overview about the Immune Response

The immune response is a process of the human immune system with which the body identifies and keeps external agents at bay. It's a complex mechanism but we'll explain in today's article.

Written and verified by the doctor Elisa Martin Cano.

Last update: 09 October, 2022

The immune response is an essential mechanism of the human body and we use it to defend ourselves from external agents that can be harmful to our health. Also, it’s made up of different processes and cells. Today we’ll tell you everything you should know about it.

Overview of the immune response

The immune response is the set of phenomena the body carries out to recognize and eliminate external agents it perceives as harmful. These phenomena are based on the recognition of these foreign substances, also known as antigens.

Antigens are usually found on the surface of viruses, bacteria, and fungi. Likewise, they’re in other inert substances such as chemicals; other different materials or toxins can also be antigens.

People have two different types of immunity. Today we’re going to tell you what each of them is about.

Innate immunity

Innate immunity isn’t specific. It’s present even before coming into contact with a given antigen and, as suggested by the name, all people are born with it. We can divide this type of immune response into two different mechanisms:

• Barriers can be physical, such as the skin that prevents the passage of the substance within the body, or chemical. There are many chemical barriers present in the human body. Runny nose, tears, saliva, or vaginal discharge, for example. These substances have characteristics that make it difficult for a virus or bacteria to survive. We can mention the pH of vaginal discharge as an example, most pathogens cannot survive in there.
• Cellular mechanisms comprised of the complement system, the inflammation mechanism, and phagocytes. The base of all three mechanisms are substances present in the blood and continuously circulating in the blood vessels. These systems become active in eliminating any foreign agent that makes its way into the body.

Specific types of immunity

This is the second type of immune response. Unlike the innate response, we’re not born with a developed specific immunity. It takes shape as the body comes into contact with various antigens. It becomes faster and more effective at eliminating pathogens.

The tissue responsible for this type of immunity is lymphoid tissue, made up of organs such as the spleen or thymus, and lymphatic vessels. This tissue houses the production of lymphocytes, which will be the cells in charge of carrying out this type of immune response.

Thus, specific parts of the antigens, called epitopes, recognize the newly invading antigens. Innate immunity activates faster when one of them enters the body, but it’s less effective. Similarly, the adaptive one is slower but much more effective.

A lymphocyte will recognize the epitope of an antigen. You may not know it but lymphocytes are responsible for producing substances called antibodies, which will be responsible for eliminating the pathogen. Additionally, this lymphocyte will activate more lymphocytes that’ll come to the site to help clear the antigen. This is the primary specific immune response.

Aside from the primary immune response, there’s also a production of memory lymphocytes. These memory lymphocytes will cause specific immunity when they come into contact with the same type of antigen. In fact, they activate faster to eliminate the harmful agent. This is known as a secondary immune response.

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Passive and active immunity

Active immunity is all about the complex we mentioned above. The human body does it naturally when it comes into contact with an antigen. The innate immune response will activate first, then the primary specific one, and finally, and in case of successive contacts, the secondary immune response.

Similarly, specific antibodies are already circulating in the body without having been in contact with antigens in passive immunity. This can only happen twice:

• In newborn babies, through antibodies that a mother passes down to her baby during her pregnancy
• In vaccinated people, because vaccines can be made up of antibodies or fragments of the pathogen that triggers the production of memory lymphocytes without actually causing the disease

The immune response is a defense system

Immunity is a natural body defense system and there are many ways to take care of it and maintain it. We must be up-to-date on vaccinations and also do all we can to keep our immune system in good shape.