The Immune System Overview

Study Notes

The immune system protects the body from disease by recognizing and fighting off foreign invaders, such as bacteria, viruses, parasites, and fungi.
There are two main branches of the immune system:
- Innate immunity is the body's first line of defense against infection. It is non-specific, meaning it attacks any foreign invader. Innate immunity is present from birth and includes physical barriers like skin, chemical barriers like stomach acid, and cellular components like phagocytes.
- Adaptive immunity is a more specific response to foreign invaders. It develops over time, and remembers past infections, allowing for faster and more effective responses to repeat infections. Adaptive immunity relies on specialized cells like lymphocytes (T cells and B cells).

Different cells and molecules work together to make up the immune system.
Cells:
- Macrophages are large, white blood cells that engulf and destroy foreign invaders.
- Natural killer (NK) cells are lymphocytes that kill infected or cancerous cells.
- T cells are lymphocytes that directly kill infected cells or regulate the immune response.
- B cells are lymphocytes that produce antibodies, which bind to foreign invaders and mark them for destruction.
Molecules:
- Antibodies are proteins that bind to specific antigens (foreign molecules) on the surface of invaders.
- Complement is a group of proteins that help to destroy foreign invaders by forming a membrane attack complex.
- Cytokines are signaling molecules that help to coordinate the immune response.

The immune system responds to infection in a coordinated manner.
The innate immune response is the first to respond to an infection. It involves physical and chemical barriers as well as the activation of cells like macrophages and NK cells.
The adaptive immune response is slower to develop but is more specific and long-lasting.
This response involves the activation of lymphocytes to produce antibodies and kill infected cells.

The immune system is able to distinguish between "self" (the body's own cells) and "non-self" (foreign invaders).
This ability is essential for preventing autoimmune diseases, in which the immune system attacks the body's own tissues.
Tolerance refers to the ability of the immune system to recognize self-antigens as non-threatening and not trigger an immune response.
Immune cells and molecules have mechanisms for detecting and eliminating non-self cells and molecules.