Response To Infection

Question 1

What is cell recognition

Answer 1

The ability of the body to distinguish between its own cells and foreign cells

Question 2

How does the body recognise a self or foreign cell

Answer 2

Cells have protein molecules on their surface membrane
These proteins include glycoproteins which are proteins with a carbohydrate component.

Question 3

What are antigens

Answer 3

Non self glycoproteins that are recognised by white blood cells during the specific immune response

Question 4

What is non specific response

Answer 4

Response to infection triggered by body cells breaking down and releasing chemicals, and by pathogens that have been labelled by the specific immune system e.g. inflammation, fevers and phagocytosis

Question 5

Inflammation

Answer 5

-Generally occurs when an infection is relatively localised e.g. when you cut yourself.
-Mast cells are found in the connective tissue as well as basophils, which release chemicals when damaged. -These chemicals are known as histamines which cause blood vessels to dilate causing local heat and redness.
-The higher temperature reduces effectiveness of pathogens in the area.
-Plasma containing leukocytes and antibodies is forced out of the capillaries causing swelling and pain.
-Antibodies disable the pathogens which are then destroyed by phagocytosis.

Question 6

Fevers

Answer 6

-When a pathogen infects the body it causes the hypothalamus to reset to a higher body temperature
-A raised temperature is above the optimum for pathogens to reproduce therefore reduced the ability for pathogens to reproduce effectively
-The specific immune response works better at a higher temperature so will be more effective
-If the body’s temperature gets too high it can be fatal as the enzymes in our body will denature therefore necessary reactions can’t proceed

Question 7

Phagocytosis (macrophages + neutrophils capacity)

Answer 7

-Neutrophils and granulocytes make up 70% of leucocytes in the blood.
-Each neutrophil can only digest a few pathogens before it dies (they can’t renew their lysosomes so once the enzymes are used up they can’t break down any more pathogens)
-Macrophages make up 4% of the leucocytes in the blood, but there are large numbers of macrophages in the tissues.
-Macrophages have a huge capacity for ingesting pathogens as they can renew their lysosomes.

Question 8

Phagocytosis (process)

Answer 8

-Phagocyte engulf the pathogens and enclose it in a vesicle called a phagosome
-Phagosome then fuses with a lysosome
-Enzymes in the lysosome break down the pathogen
-When phagocytes engulf a pathogen it produces cytokines in the surrounding tissue (these are cell signalling molecules that stimulate other phagocytes to the site of infection, they also raise body temperature and stimulate the specific immune response)

Question 9

What are the two main types of white blood cell involved in the specific immune system?

Answer 9

Lymphocytes and macrophages

Question 10

What are the two main types of lymphocyte?

Answer 10

B cells and T cells

Question 11

B cells

Answer 11

-Produced in bone marrow and once matured found in lymph glands and free in the body
-Have membrane bound globular receptor proteins that are identical to antibodies they will later produce
-Antibodies are known as immunoglobulins

Question 12

What are the three types of B cell produced when a B cell binds to an antigen?

Answer 12

B effector cell - divide to form plasma cell clones
Plasma cells - produce antibodies to particular antigens at a rate of around 2000 antibodies per second
B memory cells - provide immunological memory to a specific antigens allowing the body to respond rapidly if the antigen reoccurs

Question 13

T cells

Answer 13

-Produced in bone marrow but once mature become active in the thymus gland
-Each T cell has thousands of of identical T cell receptors on its surface which bind to antigens on infected cells

Question 14

What are the 3 types of T cell?

Answer 14

T killer cell - produce chemicals to destroy infected body cells
T helper cells - activate plasma to produce antibodies against a pathogens antigens and secretes opsonins to ‘label’ the pathogen
T memory cells - divide rapidly when they meet a pathogens antigens for the second time to form a large clone of T killer cells which quickly destroy the pathogen

Question 15

What does MHC do?

Answer 15

Proteins that display antigens on the cell surface membrane for other white blood cells to recognise

Question 16

What is the humoral response?

Answer 16

Immune system reacting to antigens outside the body cells resulting in the production of antibodies which aren’t attached to cells me are carried around in the blood and tissue fluid

Question 17

What are the two main stages of the humoral response?

Answer 17

T helper activation
The effector stage

Question 18

What is T helper activation?

Answer 18

-Neutrophils and macrophages destroy pathogens but macrophages take longer.
-Macrophage separates antigen from digested pathogen and combines it with MHC to display the antigen on the cell surface (this macrophage is now an antigen presenting cell (APC)
-T cell receptors bind to the antigen on the MHC resulting in the T cell reproducing a clone of cells
-Most of these cells become T helper cells and some become inactive T memory cells

Question 19

What is the effector stage?

Answer 19

-B cells engulf the pathogen by endocytosis
-Macrophage forms a phagolysosome to break down pathogens and leave behind fragments of the antigen
-These fragments attach to an MHC molecule and are presented on the cell surface
-T helper cell clone produced recognises this antigen and binds to it triggering the release of cytokines stimulating the B cells to divide and produce clones (clonal selection)
-Thus produces B effector cells and B memory cells, but B effector cells differentiate to form plasma cells (plasma cell clones)

Question 20

What are the 3 ways an antibody causes destruction and what are they?

Answer 20

Agglutination - antibodies binding to antigens on pathogens causing them to clump together preventing them from spreading and making them easier to be engulfed by phagocytes
Opsonisation - antibody acts as an opsonin with makes pathogens easier recognises by phagocytes
Neutralisation - antibodies neutralise the effects of bacterial toxins by binding to them

Question 21

What is the cell mediated response and when is it used?

Answer 21

-Used when pathogen is inside the host cell so humoral response is not effective
-Involves T killer cells which respond to specific antigens
-When a body cell is infected by a virus it becomes an APC similarly to macrophages but is still infected by the pathogen
-T killer cells bind to the MHC complex in this body cell
-If the T cells are exposed to cytokines from an active T helper cell, they undergo a rapid series of cell divisions to produce a clone of active T killer cells which can all bind to infected body cells
-T killer cells make pores in the membrane of infected cells letting water and ions in causing the cells to lyse (burst) — perforins

Question 22

Difference between primary and secondary immune response?

Answer 22

Primary = very effective but time consuming, making us feel ill before the pathogens are fought off
Secondary = quicker and longer lasting as we already have our long lived B memory cells

Question 23

What is natural active immunity?

Answer 23

When the immune system makes antibodies against a foreign antigen and the pathogen is destroyed

Question 24

What is natural passive immunity?

Answer 24

Preformed antibodies passed from the mother to fetus during pregnancy and through colostrum, providing the baby with temporary immunity until its own system becomes active

Question 25

What is immunisation

Answer 25

The process of protecting people from infection by giving them passive or active artificial immunity

Question 26

What is artificial passive immunity

Answer 26

When antibodies are formed in one individual and are extracted and injected into another individual

Question 27

What is artificial active immunity

Answer 27

Small amounts of antigen are used to produce immunity in a person

Question 28

What is herd immunity

Answer 28

It occurs when a significant proportion of the population is vaccinated against a disease. It is importantly for disease eradication, elimination or control

Question 29

Pros of vaccination

Answer 29

-Child is always protected against diseases that could otherwise kill or disable it
-Society benefits as the potential pool of infection is reduced through herd immunity protecting people without vaccination as well
-The cost of treating serious diseases is reduced as less people get it

Question 30

Cons of vaccination

Answer 30

-People can be allergic to vaccines
-Some children become severely ill after a vaccination with an extreme immune response
-Mass vaccination programmes have shown to cause asthma and allergies in kids
-Some vaccines such as rubella are given more for the benefit of society than the child itself