Structure and Function of Neutrophils: Topic 1

Question 1

what % of WBC are neutrophils?

Answer 1

60%

most abundant type of leukocyte!

Question 2

what part of the immune system are neutrophils part of?

Answer 2

innate immune system

Question 3

what is the primary function of neutrophils?

Answer 3

acute inflammation

large numbers of neutrophils are the first cells to invade a site of infection, so you can think of neutrophils as the “first responders” to infection

Question 4

what color do basophilic WBC stain?

Answer 4

dark blue

Question 5

what color do eosinophilic WBC stain?

Answer 5

pink

Question 6

what do the receptors on neutrophils recognize?

Answer 6

neutrophils have receptors on their plasma membranes that allow them to recognize bacteria, tissue debris, and foreign bodies, which these cells then phagocytose

Question 7

what do the granules of neutrophils do?

Answer 7

granules help to destroy phagocytosed particles

but these granules are not replenishable - once their supply of granules is depleted, neutrophils die

pus is mainly composed of dead neutrophils and tissue debris.

Question 8

what does a neutrophil nucleus look like?

Answer 8

3-5 lobes connected by thin chromatin strands

each lobe is made up of condensed DNA or chromatin. The number of nuclear lobes changes as the neutrophil matures, with fewer lobes seen in active infection (band formation)

Question 9

what does the nucleus of a neutrophil look like before it segments?

Answer 9

nucleus of a neutrophil takes on a “U” shape right before it segments

these neutrophils are called bands and are usually only present in bone marrow

Question 10

where are band neutrophils seen?

Answer 10

only in the bone marrow

however they are seen in the blood in infections, however, when the bone marrow releases all neutrophils available to fight the infection, even if the cells are not quite mature

Question 11

what are hypersegmented neutrophils?

Answer 11

> 5 nuclear lobes

Question 12

what are examples of hypersegmented neutrophils?

Answer 12

Hypersegmented neutrophils with > 5 nuclear lobes are seen in Vitamin B12 and folate deficiencies

DNA synthesis is impaired in vitamin B12 and folate deficiencies

Question 13

what are the functions of neutrophils?

Answer 13

phagocytosis of foreign bodies and destruction of bacteria

neutrophils destroy bacteria using either an oxygen-dependent or oxygen-independent mechanism

Question 14

where do most of the body’s neutrophils reside?

Answer 14

bone marrow

of the small percentage that live in the blood, half are “marginated,” which means they are stuck against the side of blood vessel walls

Question 15

why are neutrophils fast responders?

Answer 15

they are already hanging out struck against the side of blood vessel walls and waiting to go to work!

When we get stressed or sick, the marginated neutrophils release off the vessel walls and travel to where they’re needed

Question 16

what’s the lifespan of a neutrophil?

Answer 16

25 days

but they typically only spend a few hours in the blood before heading off to inspect for infection within the tissues

Question 17

how are neutrophils guided to the scene of injury?

Answer 17

chemotactic factors

Question 18

what are the two ways neutrophils destroy invading organisms?

Answer 18

they’re phagocytes

destroy organisms via oxygen-dependent or oxygen-independent mechanism

both mechanisms utilize neutrophil granules

Question 19

what are the two main types of granules in neutrophils?

Answer 19

azurophilic (primary) granules (20%)

specific (secondary) granules (80%)

Question 20

what do the azurophilic granules of neutrophils contain?

Answer 20

• myeloperoxidase
• serine proteases
• defensins

Question 21

what do the specific granules of neutrophils contain?

Answer 21

• alkaline phosphatase
• lysozyme
• lactoferrin
• NADPH oxidase

Question 22

what’s the third type of granule in neutrophils and what do they contain?

Answer 22

tertiary granules

• gelatinase
• cathepsins
• glycoproteins

all help break down invading organism’s cell membrane to help with phagocytosis

Question 23

how does O2-dependent killing of bacteria in neutrophils work?

Answer 23

neutrophils use the NADPH oxidase enzyme within the specific granules to convert oxygen to the superoxide ion (O2 -), which is a free radical

free radicals are then able to damage the invading organism’s DNA, leading to its death

myeloperoxidase enzyme contained in azurophilic granules can take hydrogen peroxide produced by neutrophil and convert it into hypochlorous acid (HOCl-), increasing the bactericidal capabilities of the neutrophil

Question 24

how does O2-independent killing of bacteria in neutrophils work?

Answer 24

neutrophils can release their granules into the extracellular space to fight infections without engulfing the bacteria

granule enzymes such as definsins, cathespins, and lactoferrin can be used to “dissolve” an invading organism’s cell membrane and neutralize it

Question 25

what organism can be resistant to a neutrophil’s bactericidal mechanisms?

Answer 25

mycobacterium tuberculosis

can survive the death threats and can live phagocytized inside neutrophils until finally neutralized by macrophage

Question 26

what is chronic granulomatous disease?

Answer 26

CGD

a condition in which NADPH oxidase is impaired, leading to poor O2-dependent killing

this leads to increased risk of infection by catalase-positive organisms such as Staphylococcus aureus.

Question 27

Which type of neutrophil granule contains NADPH oxidase, and which contains myeloperoxidase?

Answer 27

NADPH oxidase is found in specific (secondary) granules

myeloperoxidase is found in azurophilic (primary) granules