The Immune System

Words To Know…• Pathogen – A disease-causing agent.• Histamine – a chemical which causes

an inflammatory response.• Vascular – Having to do with blood

vessels.• Antigen – a substance that causes an

immune response.• Antibody – A defensive protein

produced by the body towards a specific antigen.

The Immune System• The immune system is

a system of cells, structures and processes in an organism that protects against pathogens and diseases.

There are Two immune responses

• Non-Specific• No Target Enemy

• Specific• Specific Target Enemy

First Lines of Defense• SKIN

• Largest organ of body

• Protects against water loss, chemicals, pathogens

• Covered in Bacteria and yeasts

• MUCUS• Found inside

orifices (holes)• Protects against

chemicals, pathogens and debris

Non-Specific Response

• Second line of Defense•Inflammation•Temperature•Proteins•White Blood Cells

Second Lines of Defense - Inflammation• Inflammation

• A biological response by vascular tissues to harmful stimuli:• Pathogens• Damaged cells• Irritants/allergies

• 4 Cardinal Signs• Pain• Redness• Swelling• Heat

• What causes these 4 signs?

• Pain – excess blood in the area puts pressure on pain receptors

• Redness – oxygenated blood in area

• Swelling – excess blood/fluid in area

• Heat – carried in by blood

Second Lines of Defense - Fever• Temperature (Fever)

• The process of elevating core temperature in response to a pathogen

• An elevated tem can inhibit the growth of disease-causing bacteria

• Can also destroy good cell proteins

• Fever• Ave. temp: 98.6 F• Low-Grade:98.6 –

100.4 • High-Grade: over 103

F

Second Lines of Defense - Proteins• Membrane attack

complex (MAC)• Various proteins will

form a ring on pathogen surfaces, causing them to leak out and die

• Interferon• A protein released by

infected cells• Causes nearby cells

to produce an enzyme that prevents the virus from entering and reproducing.

Second Lines of Defense - WBCs• White Blood

Cells• Cells of the immune system

• Protect the body against pathogens and foreign bodies

White Blood Cells• Neutrophils

• Most abundant• Engulf bacteria, killing it and themselves

• Natural Killer Cells• Largest WBC• Best defense against cancer• Secretes a cytotoxin that disrupts infected cell

membrane• Macrophages

• Means “Big Eater”• Eats and kills pathogens and infected cells

White Blood Cells• Helper T Cells

• Activates Cytotoxic T and B cells• Cytotoxic T Cell

• Seeks out ‘labeled’ and infected body cells and destroys them

• B Cells• Labels invaders for future destruction

Specific Response• The specific line

of defense targets specific pathogens.

• Those pathogens who have survived the first two rounds now face the Immune Response!

• 4 Specific WBCs are central to the immune response:• Macrophages• Helper T Cells• Cytotoxic T

Cells• B Cells

Steps to Immune Response:• Step 1:

• Virus infects a cell; cell displays viral antigen (red flag)

• Step 2: • Macrophages ‘eat’ virus/cell; they now

display same viral antigen• Step 3

• Receptor proteins on Helper T Cells bind to those viral antigens

Steps to Immune Response:• Step 4

• Helper Ts don’t attack, but activate B and Cytotoxic T Cells

• Step 5• Activated B cells turn into plasma cells and

release lots of antibodies• Step 6

• Antibodies attach to viruses to mark them for destruction

Steps to Immune Response:• Step 7

• Antibodies cause viruses and antigens (red flags) to clump together, making it easy for macrophages to find and ‘eat’ them

• Step 8• Activated Cytotoxic T cells destroy infected

cells