The Immune System

THE Body’s Defense Systems

Nonspecific DefensesFirst Line of Defense

• Skin• Antimicrobial proteins• Mucous membranes• Cilia• Gastric juice• Symbiotic Bacteria• Temperature

Nonspecific DefensesSecond Line of Defense

• Inflammatory Response– Injury breaking the skin introducing pathogens• Histamine is released causing increase blood

flow to area–Causes redness, swelling, warmth, and pain

• Vasodilation (dilation of the blood vessels)–Caused by histamine

• Phagocytes pass through capillary walls into tissues to ingest and destroy pathogens

Nonspecific DefensesSecond Line of Defense

• Phagocytes destroy the pathogens and the injury begins to heal.–Neutrophil; Macrophage

• Natural killer cells–Attack pathogen-infected cells–Effective at killing cancer cells and virus-

infected cells

Nonspecific DefensesSecond Line of Defense

• Complement–A group of about twenty proteins that

“complement” defense reactions.–Help to destroy foreign or infected cell by

promoting cell lysis• Interferon–Molecules secreted by viral infected cells that

stimulate neighboring cells to produce proteins that help them defend against viruses

Specific DefensesThird Line of Defense

A response aimed specifically at the pathogen• Lymphocyte = white blood cell of the immune

system• React to antigens• Two types– B cells

• Made in the bone marrow• A part of the humoral immune response• Produce antibodies• Plasma cell- B cells that release specific antibodies• Memory cell- long-lived B cells that do not release their

antibodies, they circulate in the body and respond quickly to eliminate any subsequent invasion by the same antigen.

Specific DefensesThird Line of Defense

A response aimed specifically at the pathogen

– T cells• Made in the bone marrow, mature in the Thymus (T for

thymus)• A part of the cell-mediated response

– Destroy infected cells

• Cytotoxic T cells (killer T cells); Helper T cells; Suppressor T cells

Comparing Immune ResponsesType of cell Function

Macrophage Engulfs and kills pathogens

Neutrophil Engulfs and destroys pathogens

Natural killer cell Punctures infected cells

Helper T cell Activates cytotoxic T cells

Cytotoxic T cell Punctures labeled infected cells

B cell Labels invaders for destruction by macrophages

Plasma cell Releases antibodies

Memory cell Stores information about a pathogen