5.1: Immunity and Host Defense -Overview of Immunity

Question 1

what are the two major branches of the immune system?

Answer 1

1. Innate (non-specific) immune response
2. Adaptive (acquired, specific) immune response

Question 2

describe the Innate (non-specific) immune response)

Answer 2

• always present and defends against all invaders equally (hence non-specific)
• does not have memory -responds the same way every time an intruder is encountered (think: its just innate doesn’t adapt to anything)
• includes physical and chemical barriers, special immune system cells, physiological processes and molecular defenses

Question 3

describe the adaptive (acquired, specific) immune response)

Answer 3

• acts against specific intruders
• acquired when a pathogen is encountered for the first time
• adaptive -Has memory and responds more vigorously the second time a particular pathogen is encountered
• divided into two branches: humoral (antibody mediated) immunity and cellular (cell mediated immunity)

Question 4

what are the two branches of the adaptive (acquired, specific) immune response?

Answer 4

• Humoral (antibody mediated) immunity
• cellular (cell mediated) immunity

Question 5

what are the physical and chemical barriers involved in innate resistance to infection? how do they protect you from microbes?

Answer 5

• skin
• Mucous membranes
• Stomach
• Small intestine
• large intestine
• Genitourinary tract

Question 6

how does your skin protect you against bacterial infection

Answer 6

-has protective protein keratin impenetrable by most microbes, ~pH 5, high [NaCl] -which can be inhibitory to some microbes

Question 7

how do your mucous membranes protect you from bacterial infections?

Answer 7

-Mucous traps microbes to be removed (like by ciliated cells) and contains antimicrobial secretions:
-lysozyme
-defensins -small peptides that poke holes in bacterial membranes

Question 8

how does your stomach protect you against bacterial infections?

Answer 8

-strong acidity (pH ~2) and contains proteolytic enzymes (to degrade protein in food and bacteria are more than 50% protein)

Question 9

how does your small intestine protect you against bacterial infections?

Answer 9

Rapid change in
pH, pancreatic enzymes, and bile
from the liver.

Question 10

how does your large intestine protect you against bacterial infections?

Answer 10

Contains a large portion of the normal microbiota:
* which do competitive exclusion-take up attachment sites and limit available nutrients to other invading bacteria
* normal microbiota also do microbial antagonism -produce antimicrobial compounds to kill invading bacteria and prevent them from taking over

Question 11

how does your Genitourinary tract protect you from bacterial infections?

Answer 11

Flushing action, normal microbiota and pH ~4.5
-vaginal epithelial cells produce glycogen (polymer of glucose)
-lactobacillus acidophilus ferments the glucose to lactic acid

Question 12

Leukocytes (white blood cells) circulate in the _, reside in the _, and migrate into _, in response to _.

Answer 12

Circulate in the blood and lymph, reside in the lymphoid tissues, and migrate into tissues in response to infection.

Question 13

what branches of the immune response are leukocytes involved in?

Answer 13

Both the innate and adaptive immune response.

Question 14

some leukocytes are

Answer 14

phagocytic, but some play other roles

Question 15

what do granulocytes (category of wbcs) contain in their cytoplasm?

Answer 15

• their cytoplasm contains granules filled with reactive chemical that can kill microbes and/or signal other components of immunity.

Question 16

what are the 4 types of granulocytes?

Answer 16

1. Basophils
2. mast cells
3. eosinophils
4. neutrophils

Question 17

describe basophiles and mast cells

Answer 17

• type of granolocyte
• Not strongly phagocytic. Release signalling molecules (ex: histamine that is involved in allergic responses)

Question 18

describe eosinophils

Answer 18

• type of granolocyte
• Typically non-phagocytic, attack large parasites (ex: protozoa and parasitic worms) by releasing enzymes and reactive oxygen intermediates (ex: O2-, H2O2, OH*)

Question 19

Describe neutrophils

Answer 19

• type of granolocyte
• strongly phagocytic. Granules contain digestive enzymes (ex: lysozyme and defensins). Considered a central component of the innate immune system.

(think neutro >neutral =central (component)

Question 20

Monocytes circulate in the _, and then migrate into _ and differentiate into _ and _

Answer 20

Circulate in the blood, and then migrate into tissues and differentiate into macrophages and dendritic cells, which are strongly phagocytic and involved in antigen presentation.

Question 21

describe macrophages

Answer 21

• type of monocyte
• migrate to infection
• strongly phagocytic, reside in tissues, and have specific surface molecules that recognize pathogens
  -Toll-like receptors recognize peptidoglycan, fungal cell walls etc.

Question 22

describe dendritic cells

Answer 22

• type of monocyte
• reside in the skin and mucous membranes (don’t go to site of infection) and sample their surroundings by phagocytosis
• if they grab an intruder they present the foreign antigens on their surface to B and T lymphocytes to trigger the specific (adaptive) immune response.

Question 23

describe lymphocytes

Answer 23

• Specialized leukocytes involved primarily in the adaptive immune response
• circulate through the blood and reside in lymphoid

Question 24

what are the 3 types of lymphocytes? describe them

Answer 24

1. B lymphocytes (B cells)
   -antibody producing cells
   -involved in the humoral branch of adaptive immunity
2. T lymphocytes (T cells)
   -involved in the cell mediated branch of adaptive immunity
3. Natural killer cells (NK cells)
   -destroy abnormal body cells:
   -cancer cells
   -cells infected by bacteria or viruses

Question 25

describe pathogen recognition

Answer 25

* the innate ability to destroy a pathogen that has never been encountered before (doesn't remember it) * Involves phagocytic leukocytes (neutrophils and macrophages) that **recognize pathogen-associated molecular patterns (PAMPs)**: -lipopolysaccharide -lipotechoic acid -flagellin

Question 26

what do phagocytes have that allows recognition of pathogen-associated molecular patterns (PAMPs)? what do they trigger?

Answer 26

Phagocytes have toll-like receptors (pattern recognition receptors or PRRs) -bind to a PAMP (on a pathogen) -trigger **phagocytosis**

Question 27

describe phagocytosis

Answer 27

Phagocytes engulf and destroy invading microbes * cell membrane invaginates around a foreign particle * engulfs it into a phagosome * Phagosome fuses with a lysosome to form a **phagolysosome**

Question 28

what are phagolysosomes filled with?

Answer 28

* lysozyme and defensins * proteases (degrade proteins) * lipases (degrade phospholipids) * nuclease (degrade nucleic acids)

Question 29

what part of phagocytosis is oxygen independent killing?

Answer 29

the enzymes that break down the microbe from the lysosome the phagosome fuses with (forming the phagolysosome)

Question 30

what part of phagocytosis is oxygen dependent killing?

Answer 30

* activated phagocytes produce reactive oxygen compounds: -H2O2, O2-,OH*, HOCl, NO * kill ingested microbes by oxidizing cell components

Question 31

what happens in phagocytosis after the invaders have been killed?

Answer 31

* **Neutrophils** perform exocytosis -fragments are expelled from the cell * **Macrophages** and **Dendritic** cells become antigen presenting cells -fragments of the intruder are presented on the cell surface to trigger an adaptive immune response. (connection between innate and adaptive immunity, macrophages and dendrite cells are innate recognizing bacteria, but after it destroys bacteria it is adaptive by presenting antigens on surface)

Question 32

what's inflammation

Answer 32

General, non-specific reaction to pathogens, toxins or tissue damage

Question 33

describe what happens in the process of inflammation

Answer 33

* blood vessels dilate, which brings more leukocytes to the area * blood vessel walls become more permeable so that leukocytes can squeeze into tissues -**extravasation** * **Temperature increase** may slow the growth of pathogens * blood leaking into tissue spaces can clot to prevent the spread of pathogens

Question 34

what's the pro and con of inflammation

Answer 34

* pro: a little bit of inflammation acts as a protective mechanism * con: a vigorous inflammatory response can cause further damage to tissue

Question 35

what happens when inflammation spreads through the entire body

Answer 35

septic shock

Question 36

what can cause inflammation to spread through the entire body and can lead to septic shock?

Answer 36

* if gram negative bacteria get into the blood it can be carried though entire body -LPS acts as a PAMP (bc it includes repeating molecule O-antigen to be recognized by toll like receptors/PRRs) -triggers phagocytes to release proinflammatory cytokines (turns up inflammation) -results in extreme fever -loss of blood pressure due to vasodilation (blood vessels dilating =Blood pressure goes down) -if blood pressure gets low enough: organ failure (which is why LPS gets other name: Endotoxin)