Host Defenses

Question 1

Cells of the immune system

Answer 1

• Monocytes
• Granulocytes
• Lymphocytes

Question 2

Monocytes

Answer 2

• Circulate In blood stream
• Attracted to inflamed tissues
• Phagocytic
• Differentiate into macrophages & dendritic cells

Question 3

Granulocytes

Answer 3

• Cytoplams contains granules

Includes:
* eosinophils
* basophils
* neutrophils (phagocytic)
* mast cells (induce inflammation)

Question 4

Lmphocytes

Answer 4

• T cells: helper, cytotoxic
• B cells: antibodies

Question 5

Innate defenses

Answer 5

• Properties of the normal host
• Non specific

Question 6

Innate defenses of skin and mucous membrane

Answer 6

Skin:
* Thick layer of dead cells

Normal microbiome
* competes for attachment sites and nutrients
* secretes bacteriocin

Antimicrobial substances
* fatty acids
* Lysosymes
* antimicrobial peptides (AMPs)
* Antibodies

Mucous membrane
* Secretes mucous that traps bacteria

Question 7

Innate defenses of the airways

Answer 7

• Mucous membrane that traps bacteria
• Ciliated cells remove mucus and trapped bacteria

Question 8

Innate defenses of tissues and internal fluids

Answer 8

• Complement system
• Phagocytosis
• Inflammation

Question 9

Complement system

Answer 9

• Set of blood proteins
• Activation results in the formation membrane attach complex (MAC)
• Causes cell lysis of some Gram-negatives
• No effect on Gram positives

Question 10

Complement system activation pathways

Answer 10

• Classical: Antibodies
• Alternative: Microbial cell wall components

Question 11

Serum sensitivity

Answer 11

Test sensitivity to complement by exposing pathogens to serum

Question 12

Phagocytosis: Steps

Answer 12

1. Attachement of organism to the membrane of the phagocyte
2. Ingestion (organism becomes enclosed in a phagosome
3. Granules containing hydrolytic enwymes fuse zith the phagosome forming the phagolysosome
4. Oxidative burst (production of ROS)
5. Killing and digestion of the microorganism

Question 13

Phagocytes

Answer 13

• Neutrophils
• Macrophages

Question 14

Inflammation: Signs

Answer 14

• Redness
• Heat
• Swelling
• Pain

Question 15

Inflammation: Functions

Answer 15

• Recruitment of immune cells to thje site of infection
• Increased concentration of molecules

Question 16

Interleukin-1: Functions

Answer 16

• Increases movement of liquid from blood to tisses and causes inflammation
• Increases the concentration of immune cells at infection sites
• Increases the spacing between tissue cells to allow immune cells to enter tissues
• Activates phagocytes
• Acts on the thermoregulatory center of the brain and causes fever to limit the growth of pathogens

Question 17

Fever

Answer 17

1. macrophages sense the presence of endotoxins
2. Production of Il-1
3. Il-1 acts causes body temp to increas
4. High T reduces growth of some pathogens
5. Il-1 activates phagocytes and other cells of the immune system
6. Causes inflammation

Question 18

Adaptive defenses

Answer 18

• Induced by the infection
• Rely on the detection and response to foreing antigens
• Specific to pathogens

Question 19

Cells of the adaptive immune system

Answer 19

• T cells
• B cells
• Antigen-presenting cells (APCs)

Question 20

Antigen-presenting cells

Answer 20

Macrophages and dendritic cells

Question 21

Major histocompatibility complex (MHC)

Answer 21

• Antigen present molecular complex

MHC I:
* Antigens from inside the cell
* Present on all cells
* Recognised by cytotoxic T cells

MHC II:
* Antigens processed in phagolysosomes
* Present on APCs and B cells
* Recognised by T helper cells

Question 22

T cells types

Answer 22

T helper cells:
* Activate B cells and macrophages carrying the specific foreing antigens
* Useful against bacterial pathogens

Cytotoxic T cells:
* Rekease perforins/granzymes that kill host cells carrying the foreign antigen
* useful against infection by viruses/intracellular pathogens

Question 23

Interleukin-2

Answer 23

Produced by activated T cells
* Induces multiplication & differentiation into effector T cells and memory T cells

Question 24

Activated macrophages

Answer 24

• increased phagocytic activity
• produce much higher levels of
  hydrolytic enzymes

Question 25

B cells

Answer 25

Produce antibodies

Question 26

Activation of B cells

Answer 26

* The B cell displays its antibody on its surface * Pick up the foreign antigen it recognizes * Antigen is processed and displayed on its surface by MHC II. * A T cell specific for the antigen recognizes this complex and produces Il-4 * IL-4 activates the B cells which multiplies and differentiates into plasma cells and B memory cells

Question 27

Plasma cell

Answer 27

* Activated B cell * Produces antibodies

Question 28

Interleukin-4

Answer 28

* Produced by helper T cells * Activates B cells

Question 29

Antibodies

Answer 29

* Group of related proteins - immunoglobulins * Highly variable antigen binding site (Fab) * Constant region (FC) binds to receptor on macrophages

Question 30

Function of antibodies

Answer 30

* Activates complement * function as opsonins which increase phagocytosis efficiency * Bind to toxins which prevents binding of toxin to host cells * Bind to adhesins which prevents adhesion of microorganism to host cells

Question 31

Memory cells

Answer 31

Ensure that the immune response, following a second exposure to the same antigen, is faster and stronger

Question 32

Aquired active immunity

Answer 32

Involves the production of memory cells in response to antigenic stimulus * Natural: following infection * Artificial: vaccination

Question 33

Aquired passive immunity

Answer 33

Involves the acquisition of preformed antibodies * Natural: placental transfer or colostrum * Artificial: serum from an immune animal

Question 34

Natural immunity

Answer 34

Explained in part by the incompatibility of the virulence factor with the genetics of a species