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We created this website to help you understand the science of the immune system

The immune system intersects with almost every aspect of human health and disease. Its functions, both when things are going well and when things go wrong, are immensely complicated. That’s why The American Association of Immunologists created Immunology Explained—to help you learn more about the immune system and understand research on specific topics so that you can be an advocate for yourself and your family!  

What is immunology

Exploring the complexities of the bodys immune system.

Immunology is the study of your immune system—the complex network of cells, organs, and tissues that work together to protect you from infectious diseases and other threats.1

The immune system consists of two main branches: innate immunity and adaptive immunity. 

But what do these terms mean?

image showing close up of skin (neck) depicting innate immunity


The body’s first line of defense, this includes physical barriers like the skin, mucous membranes, and immune cells that rapidly detect common features of pathogens—viruses, bacteria, and other microscopic organisms that cause disease—and kickstart the rest of the immune response.

close up of cells depicting adaptive immunity


This branch of the immune system involves cells called lymphocytes, specifically B and T cells, that recognize, eliminate, and “remember” specific features of pathogens.
  • B cells produce antibodies, which are proteins that stick to a pathogen to impair or prevent its ability to cause disease.
  • T cells can directly attack infected cells and regulate the immune response. This attack can prevent a pathogen from spreading to other cells.

How the immune system changes with age

As we get older, our immune system starts to become less effective in counteracting pathogens. Learn more about how your immune system changes with age and how vaccinations can give your body a significant advantage against common threats as you grow older.

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About Us

The American Association of Immunologists (AAI) created Immunology Explained to help you understand the core principles of the immune system and its role in health and diseases. We’re here to make immunology easier to comprehend and explain the basic science and evidence that underlies what we know about the body’s defense system.

AAI brings together a diverse community of passionate scientists who share a common goal: advancing our understanding of immunology and its related disciplines. Our mission is to support an ongoing exchange of ideas and knowledge to explore how we can integrate immunologic principles into clinical practice and beyond. To learn more, visit


  1. National Library of Medicine. The innate and adaptive immune systems. Accessed October 4, 2023.
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