The Immune System

By Mikasa Modi and Anthony Chong

Innate immunity • Responses are active immediately upon infection and are the same

whether or not the pathogen was encountered previously• Found in all animals, but defenses differ in vertebrate and

invertebrates. – Barrier and internal defenses

• Responses are distinct for different pathogens

Invertebrate and Vertebrate Defenses

• Barrier• Cellular innate defenses• Antimicrobial Peptides • Inflammatory Response (Only found in

Vertebrates)• Natural Killer Cells (Only found in Vertebrates)

Acquired (Adaptive)Immunity• Adaptive immune responses are activated after innate immune

defenses take effect and develop more slowly• Lymphocytes are activated when put in contact with microbes

– B and T lymphocytes activated when they detect antigens on the microbes• The region detected is called the epitope

Antigen Presentation

Lymphocyte Development

• All lymphocytes are created in the bone marrow– B and T cells mature in different areas• Bone marrow and Thymus

– Tested for self-reactivity and self tolerance there

Clonal Selection

• Helper T Cells- secrete proteins that stimulate other lymphocytes

• Cytotoxic T Cells- secrete proteins that destory target cells

• B cells- anti-body secreting plasma cells

Active and Passive Immunity

• Active- develops naturally in response to an infection or artificially by immunization

• Passive- Immediate, short term protection that occurs naturally and artificially

Immune Rejection

• Certain antigens determine a person’s blood type– Incompatible blood leads to the destruction of

transfused cells• MHC molecules are responsible for the

rejection of organ transplants and tissue grafts• Lymphocytes in bone marrow cause problems

in bone marrow transplants