Human Host Defense Mechanisms

Question 1

Two types of Host defenses

Answer 1

Inborn (Innate) and Acquired

Question 2

Characteristics of Inborn host defenses

Answer 2

Inborn defenses are: Natural, Non-specific and represent the first line of defense.

Question 3

Characteristics of Acquired Immunity

Answer 3

Specific, long term and memory, T and B cell mediated. Can be active or artificial (via vaccines)

Question 4

Examples of natural barriers

Answer 4

Skin, mucous membranes, respiratory tract, mouth, GI tract, genitourinary tract. (Combinations of mechanical barriers, chemical barriers, enzymes and flushing actions)

Question 5

Characteristics of Skin

Answer 5

1. Several outer levels of keratin (water development).
2. The dermis contains tightly woven CT.
3. Tough, dry, salty, oily, thick.
4. Sweat glands secrete salt/fatty acid mixture (antimicrobial)
5. Normal flora provides competitive inhibition to pathogens

Question 6

Characteristics Mucous membranes

Answer 6

Bathed in antimicrobial secretions of IgG and IgA that prevent attachment

Question 7

Mucociliary Escalator

Answer 7

Lining epithelium of mucous membranes contain cilia and mucus with IgA that propels organisms to be either sneezed or coughed. (Neutralized and eliminated out of the body)

Question 8

Natural barriers of Respiratory tract

Answer 8

1. Turbulant ariflow in nose forces particles and microbes onto mucous lining.
2. Mucociliary Escalator
3. Alveolar macrophages (Dust cells) can destroy pathogens that reach the alveoli.

Question 9

Natural barriers in GI tract

Answer 9

1. Acid pH of stomach
2. Pancreatic enzymes, bile and intestinal secretions
3. Peristalsis
4. Bowel flora

Question 10

Natural barriers of Genitourinary tract

Answer 10

1. Length of male urethra
2. Kidneys produce/excrete mucoproteins to bind and excrete bacteria
3. Acid pH of vagina due to lactobacillus
4. Constant outward flow of mucous of vagina

Question 11

Natural chemical barriers

Answer 11

1. Lysozymes in tears and saliva
2. Acidic pH of skin, stomach, vagina
3. Mucous secretions (IgG & IgA)
4. Sebacous secretions

Question 12

Function and location of: Lysozyme

Answer 12

Degrades peptidoglycans

Found in tears, saliva, blood and phagocytes

Question 13

Function and location of: Peroxidase

Answer 13

Breaks down hydrogen peroxide to produce ROS. Found in saliva, body tissues and phagocytes

Question 14

Function and location of: Lactoferrin

Answer 14

Sequesters iron from microorganisms (essential for growth).

Found in saliva, blood/tissue fluids and some phagocytes.

Question 15

Function and location of: Defensins

Answer 15

Antimicrobial peptides inserted into microbial membrane.

Found on mucous membranes and in phagocytes.

Question 16

Describe the lymphatic system

Answer 16

Drainage system of tissues that removes extracellular fluid or drain-off of an inflammatory response. Waste filled lymph (ECF) is shuttled through lymph capillaries to lymph vells and through lymph nodes back to the blood via the thoracic duct. Lymph always travels towards the heart.

Question 17

Function of the lymphatic system

Answer 17

Renders surveillance, recognition and protection against foreign material.

Question 18

Lymphatics and cancer

Answer 18

The lymphatic system carries cancer cells to other parts of the body. Called metastasis. Instead of processing and killing the cancer cells they remain in the lymph nodes and can further spread via lymphatics to other parts of the body.

Question 19

Cytokines

Answer 19

1. Bind to surface receptors on inflammatory cells.
2. Induces change in cell (growth, differentiation, movement or cell death)
3. Act locally, regionally or systemically

Question 20

5 types of cytokines

Answer 20

1. Interleukins
2. TNF-alpha
3. Chemokines
4. Colony Stimulating Factors
5. Interferons

Question 21

Macrophages and cytokines

Answer 21

Pivotal cells in directing tissue inflammatory responses via their production of cytokines

Question 22

IL-1 and TNF-alpha

Answer 22

1. Produced by macrophages and develop/amplify inflammation.
2. Activate endothelial cells to release more cytokines, chemokines and express adhesions of leukocytes.
3. Mediate fever, catabolism of muscle and hemodynamic effects associated with inflammatory states.

Question 23

Interferon-gamma

Answer 23

1. Produced by NK and a subset of T cells.
2. Potent stimulus for macrophage activation and cytokine production that helps in viral killing.
3. Amplify immune response in viral and bacterial infections.

Question 24

Chemokines

Answer 24

1. Chemotactic cytokines direct cell migration of inflammatory cells to injury/infection.

Question 25

2 types of chemokines

Answer 25

1. Inflammatory chemokines

2. Homing chemokines

Question 26

Inflammatory chemokines

Answer 26

Produced in response to bacterial toxins and inflammatory cytokines. Recruits leukocytes during host inflammatory responses.

Question 27

Homing chemokines

Answer 27

Expressed and upregulated during disease states. Functions to direct traffic and homing of lymphocytes to lymphoid tissues during an immune response.

Question 28

Colony-Stimulating Factor

Answer 28

Secreted glycoproteins that stimulates the production of blood cells by binding on surface of hematopoietic stem cells.

Question 29

3 major Colony-stimulating factors

Answer 29

1. CSF-1: macrophage colony-stimulating factor
2. CSF-2: granulocyte macrophage colony-stimulating factor (GM-CSF)
3. CSF-3: granulocyte colony-stimulating factor (G-CSF)

Question 30

Gram - Sepsis and Cytokines

Answer 30

1. LPS is a potent activator of macrophages, endothelial cells and neutrophils.
2. LPS binds to a serum LPS-binding protein
3. Stimulates production/release of TNF-alpha and Interleukins (1,6,8,12) which modulates endothelial cell-leukocyte adhesion, leukocyte recruitment and other immune functions.