Major Concepts of Host Defense

Question 1

Why do warm-blooded, long lived animals require complex immune defenses?

Answer 1

Infectious agents (bacteria) can rapidly divide in warm-blooded creatures

• optimal temperature for bacterial growth!
• fever - attempt to inhibit bacteria by raising body temperature higher than optimal growth temperature

Question 2

Viruses

Answer 2

Small, non-living parasites that exhibit properties of live organisms when integrated with host
*intracellular function

Question 3

Parasites

Answer 3

Protozoans/worms (helminths)

Difficult to eradicate because they multiply faster than our cells proliferate

Question 4

Bacteria

Answer 4

Commensal (normal) microflora - provide molecular signals for development of immune system in each person

Pathogenic bacteria (only few pathogenic to humans)

Question 5

Germ-free animals

Answer 5

Have no commensal microflora

Therefore:

• mucosal immune system is underdeveloped
• spleen and lymph nodes are underdeveloped
• serum hypogammaglobinemia

Not all abnormalities can be reversed by colonizing adult germ-free animals with commensal bacteria

Question 6

Germ theory

Answer 6

Original thought: foul odors/evil spirits caused disease

Robert Koch and Louis Pasteur discovered that small organisms called germs cause disease

Koch: particular germ causes particular disease . (anthrax experiment)

Question 7

Koch’s postulates

Answer 7

1) Infected tissue must show presence of particular microorganism not found in healthy animals
2) Microorganism must be isolated and grown in pure culture
3) Microorganism, when injected into healthy animal, must cause associated disease
4) “Second generation” microorganism should then be isolated and shown to be identical to original organism found in 1.

Question 8

Gram stain

Answer 8

Gram-positive: thick peptidoglycan layer, stains purple with crystal violet (primary stain)

Gram-negative: thin peptidoglycan layer, stained pink with safranin (counter stain)

Question 9

Extracellular pathogens

Answer 9

Can grow and survive on extracellular nutrients (circulation, connective tissues, airway, GI tract)

No direct damage to host cells

Induce inflammation and produce toxins

• endotoxin: cell walls
• exotoxin: secreted

Question 10

Intracellular pathogens

Answer 10

Invade and replicate intracellularly to utilize host-cell energy sources

Shielded from Abs and eliminated only by cellular immune response

Tissue damage caused by host response

Question 11

Immunity

Answer 11

Set of cooperative defense mechanisms which provide protection from various infectious diseases

Foreign Ags - immune response

Self Ags - autoimmune response

Question 12

Fixed elements of immune system

Answer 12

Lymphoid organs

Primary: bone marrow and thymus

Secondary: Spleen, lymph nodes, mucosal tissue

Question 13

Mobile elements

Answer 13

Immune cells, Soluble (Abs, complement, acute phase proteins)