6.32 Innate Immunity

Question 1

Innate Immunity

Answer 1

The innate immune responses share two key characteristics:
* They are non-specific (i.e. they do not differentiate between different types of pathogens)
* They are non-adaptive (i.e. they produce the same response to every infection – there is no immunological memory)

Question 2

Lymphatic System

Answer 2

The lymphatic system is a secondary transport system that
protects the body by producing and filtering lymph
* Lymph is a clear fluid rich in white blood cells that arises
from the drainage of interstitial fluid from the tissues
* Lymph is filtered at lymph nodes, whereby pathogens are
removed and the fluid is returned to venous circulation

Question 3

Inflammation

Answer 3

Tissue damage causes mast cells to release histamine, which
triggers vasodilation and increased capillary permeability
* This improves the recruitment of white blood cells
An inflammatory response, while necessary, has side effects:
* Vasodilation = localised redness & heat (⇧ blood flow)
* Capillary permeability = swelling & tenderness (⇧ fluid)
Inflammation can be short-term (acute) or long-term (chronic)

Question 4

Phagocytosis

Answer 4

Macrophages and dendritic cells migrate via the blood to
sites of infection (damaged cells release chemotactic agents)
The pathogens are surrounded by extensions (pseudopodia)
and are then internalised within a vesicle (via phagocytosis)
The vesicle may fuse with a lysosome to digest the pathogen
* Fragments (antigens) are presented on the surface of the
cell in order to activate the third line of defense (adaptive)

Question 5

Fever

Answer 5

Fever is an abnormally high body temperature (due to infection)
* It increases metabolism and activates heat shock proteins
* It reduces the growth rate of infectious pathogens
Fever occurs when white blood cells release cytokines
* This causes the hypothalamus to produce prostaglandin
* Prostaglandin increases the temperature of the body
While a fever may initially strengthen an immune response,
beyond tolerable limits it will cause damage to the body

Question 6

Complement System

Answer 6

Inactive complement proteins are produced by white blood
cells and certain body cells (particularly the liver)
In response to immune activation, they trigger a cascade of
reactions that help protect the body from infection:
* Opsonisation (increase pathogen recognition by phagocytes)
* Chemotaxis (recruitment of phagocytes to the infection site)
* Membrane attack (forms a complex that ruptures cell walls)

Question 7

Natural Killer Cells

Answer 7

Natural killer cells are a class of non-specific lymphocytes
that can target and destroy infected body cells or tumor cells
* Infected cells release chemicals called interferons, which
function to promote the activation of natural killer cell
* Natural killer cells induce apoptosis in the infected cell
Natural killer cells are part of the innate immune response
because they do not rely on antigen recognition to function