We are independent & ad-supported. We may earn a commission for purchases made through our links.
Advertiser Disclosure
Our website is an independent, advertising-supported platform. We provide our content free of charge to our readers, and to keep it that way, we rely on revenue generated through advertisements and affiliate partnerships. This means that when you click on certain links on our site and make a purchase, we may earn a commission. Learn more.
How We Make Money
We sustain our operations through affiliate commissions and advertising. If you click on an affiliate link and make a purchase, we may receive a commission from the merchant at no additional cost to you. We also display advertisements on our website, which help generate revenue to support our work and keep our content free for readers. Our editorial team operates independently of our advertising and affiliate partnerships to ensure that our content remains unbiased and focused on providing you with the best information and recommendations based on thorough research and honest evaluations. To remain transparent, we’ve provided a list of our current affiliate partners here.

What Is the Innate Immune System?

By Emma Lloyd
Updated Mar 03, 2024
Our promise to you
The Health Board is dedicated to creating trustworthy, high-quality content that always prioritizes transparency, integrity, and inclusivity above all else. Our ensure that our content creation and review process includes rigorous fact-checking, evidence-based, and continual updates to ensure accuracy and reliability.

Our Promise to you

Founded in 2002, our company has been a trusted resource for readers seeking informative and engaging content. Our dedication to quality remains unwavering—and will never change. We follow a strict editorial policy, ensuring that our content is authored by highly qualified professionals and edited by subject matter experts. This guarantees that everything we publish is objective, accurate, and trustworthy.

Over the years, we've refined our approach to cover a wide range of topics, providing readers with reliable and practical advice to enhance their knowledge and skills. That's why millions of readers turn to us each year. Join us in celebrating the joy of learning, guided by standards you can trust.

Editorial Standards

At The Health Board, we are committed to creating content that you can trust. Our editorial process is designed to ensure that every piece of content we publish is accurate, reliable, and informative.

Our team of experienced writers and editors follows a strict set of guidelines to ensure the highest quality content. We conduct thorough research, fact-check all information, and rely on credible sources to back up our claims. Our content is reviewed by subject-matter experts to ensure accuracy and clarity.

We believe in transparency and maintain editorial independence from our advertisers. Our team does not receive direct compensation from advertisers, allowing us to create unbiased content that prioritizes your interests.

The innate immune system is the body’s first line of defense against infection by microorganisms such as viruses, bacteria, and parasites. This branch of the immune system is referred to as innate because it is activated immediately upon infection to defend against all pathogens. In contrast, the acquired immune system, the body’s second line of defense, is a much more specific reaction that takes time to build. The innate immune system consists of a multi-pronged attack which includes physical barriers to infection, immune cells, and protein molecules called complement and cytokines.

Of the physical barriers to infection, the most important is the skin. When intact, the skin is impervious to most invading pathogens, and additional mechanisms such as sweating help to flush bacteria and viruses from the skin. Similarly tears, mucus, and saliva flush pathogens from the eyes and nasopharynx. The gastrointestinal tract is also part of the innate immune system. Defense mechanisms in this location include the acidity of the tract, enzymes that digest organic matter, and antibacterial proteins called defensins.

When an infectious agent is able to bypass or negate these physical barriers, the first reaction of the innate immune system is an inflammatory response. This response is stimulated by the release of inflammatory chemicals by cells that are injured or dying. Inflammation can be triggered not only by infection, but also by injury. When infection is present, however, additional defense mechanisms are triggered in conjunction with the inflammation. These include both cellular and chemical responses.

The presence of pathogens at a site of inflammation triggers the release of a large number of different chemicals, some of which simply promote inflammation and some of which have other roles. In response to the presence of bacterial proteins, a chemical cascade called the complement system is triggered. This is a chain of chemical reactions involving a large number of different proteins. The completion of the complement cascade helps kill invading bacteria, and also recruits more immune cells to the infection site.

Other substances, such as lactoferrin, transferrin, and lysozyme, are also produced at the infection site. Lactoferrin and transferrin bind available iron to limit its availability to bacteria, while lysozyme helps destroy bacteria by breaking down their cell walls. Immune system-specific chemicals called cytokines are produced as well. These include interferons, which help reduce the rate of viral replication, and interleukin-1, which increases the effectiveness of the complement reaction.

While these chemical responses are developing, the cells of the innate immune system, including neutrophils, macrophages, and natural killer cells, also have their own parts to play. These cells are recruited to the site of infection by cytokines and other inflammation-promoting proteins. All three cell types fight invading pathogens, but do so via different mechanisms. Neutrophils and macrophages kill by engulfing bacterial cells and digesting them, while natural kill cells destroy cells that have been infected by viruses. Macrophages are also involved in triggering acquired immunity, which develops in response to continued infection.

The Health Board is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Discussion Comments
The Health Board, in your inbox

Our latest articles, guides, and more, delivered daily.

The Health Board, in your inbox

Our latest articles, guides, and more, delivered daily.