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Your Immune
System

A remarkable defense system
for a healthier, longer life.

Your immune system protects you from harmful germs, keeps you healthy, and helps your body stay in balance. It is a complex and dynamic network of cells, tissues and molecules that works around the clock — from your first breath throughout your life.

Explore the Immune System   →

What is the
immune system?

The immune system is your body’s built-in defense network. It identifies and eliminates harmful invaders such as bacteria, viruses, fungi and parasites, while also removing damaged cells and keeping the body in balance.

It learns from past encounters, adapts to new threats, and works with many organs and systems to protect your health — every day, throughout your life.

How it works   →

The lymphatic system

— a vital part of your immune system

Conceptual educational illustration of the human lymphatic networkTonsilsThymusLymphatic
vesselsSpleenLymph nodesBone marrowLymphatic vessels
throughout the body

Two arms, one team

The innate and adaptive immune systems work together

Your immune system has two complementary arms. The innate immune system provides a rapid, first line of defense against a wide range of microbes. The adaptive immune system responds more slowly but is highly specific and builds long-lasting memory. Working together, they give you both immediate protection and long-term immunity.

Explore innate immunity   →Explore adaptive immunity   →

Innate immunity

Fast, broad, immediate protection

Adaptive immunity

Targeted, long-lasting protection

Working
together
for stronger
protection

Explore the key topics

Milestones in the history of immunology

From early observations to today’s cutting-edge research, discoveries in immunology have transformed
our understanding of health and disease — and continue to shape a healthier future.

Ancient times

Early evidence of immunity

Observations that surviving an infection could provide protection.

1796

First vaccination

Edward Jenner demonstrates that smallpox can be prevented by vaccination.

1880s

Germ theory

Louis Pasteur and Robert Koch identify microorganisms as the cause of infectious diseases.

1900s

Antibodies

Discovery of antibodies and antigen-antibody interactions.

Mid-1900s

Immune cells and mechanisms

Identification of key immune cells and the basis of adaptive immunity.

1970s

Cytokines

Discovery of cytokines and chemokines as immune messengers.

1980s–1990s

Immune memory

Understanding how the immune system remembers past infections and vaccination.

Today

New frontiers

From immunotherapy to immune aging, research continues to unlock new ways to prevent and treat disease.

Selected sources and references

Artwork illustrates the main mechanisms schematically; molecular sizes, colors and distances are not literal.