Unit 3 KA6 - specific cellular defenses against pathogens

Question 1

what are lymphocytes?

Answer 1

the white blood cells involved in the specific immune response, made from tissue stem cells in bone marrow
they respond to specific antigens on invading pathogens

Question 2

how are t lymphocytes developed?

Answer 2

some lymphocytes move to and mature in the thymus gland and develop into T lymphocytes

Question 3

how are b lymphocytes formed?

Answer 3

lymphocytes that remain and mature in the bone marrow develop into B lymphocytes

Question 4

what are antigens?

Answer 4

molecules, often proteins, located on the surface of cells that trigger a specific immune response

Question 5

describe clonal selection theory

Answer 5

lymphocytes have a single type of membrane receptor which is specific for one antigen
when a specific lymphocyte is activated by a specific antigen, it is said to have been ‘selected’ by the antigen
this antigen binding leads to repeated lymphocyte division forming a clonal population of identical lymphocytes

Question 6

describe how b lymphocytes work

Answer 6

activated b lymphocytes produce a clone of B lymphocytes that secrete antibodies into the lymph and blood where they seek out and destroy their specific pathogen
each B lymphocyte clone produces specific antibody molecules that will recognise a specific antigen surface molecule on a pathogen or toxin

Question 7

what is an antibody?

Answer 7

antibodies are Y shaped proteins that have receptor binding sites specific to a particular antigen on a pathogen
they become bound to antigens, inactivating the pathogen
forming an antigen-antibody complex inactivates the pathogen and then allows it to be destroyed by phagocytosis

Question 8

what is an allergic reaction and what causes them?

Answer 8

it is a hypersensitive reaction and happens when B lymphocytes respond to antigens on substances that are harmless to the body

Question 9

describe how t lymphocytes work

Answer 9

t lymphocytes destroy infected body cells by recognising antigens of the pathogen on the cell membrane and inducing apoptosis
t lymphocytes attach to infected cells and release proteins
these proteins diffuses into the infected cells causing production of self destructive enzymes which cause cell death
the remains of the infected cell are then removed by phagocytosis

Question 10

what is meant by a person’s antigen signature?

Answer 10

each person’s body cells are unique to that person because they contain a combo of cell surface proteins that are specific to that person

Question 11

why is a person’s antigen signature important?

Answer 11

to ensure a person’s own lymphocytes do not try to destroy their own body cells surface proteins

Question 12

how do T lymphocytes distinguish between self and non-self antigens?

Answer 12

identifying self - a self marker (MHC) labels the body’s cells as a friend and are tolerated by the immune system
identifying non-self - an antigen is a molecule that the immune system recognises as foreign

Question 13

what is apoptosis?

Answer 13

programmed cell death

Question 14

what is meant by autoimmunity?

Answer 14

immune system regulation failure

Question 15

what causes autoimmunity?

Answer 15

when T lymphocytes launch an attack (immune response) on the body’s own cells (self-antigens)

Question 16

what is the cause of autoimmune diseases and give examples of them

Answer 16

autoimmunity

• rheumatoid arthiritis
• type 1 diabetes
• lupus

Question 17

describe the primary response in relation to immunological memory

Answer 17

when the body responds to being infected by a disease-causing organism by producing antibodies

Question 18

describe the secondary response in relation to immunological memory

Answer 18

when the disease is prevented if the person survives and is exposed to the same antigen at a later date

Question 19

why is disease prevented the second time a person is exposed to the same antigen?

Answer 19

• antibody production is more rapid
• concentration of antibodies reaches a higher level
• higher antibody concentration is maintained for a longer time

Question 20

what makes the secondary response possible?

Answer 20

the presence of memory cells

Question 21

what are memory cells and when are they produced?

Answer 21

B and T lymphocytes specific to the antigen, produced in response to the body’s first exposure

Question 22

what is HIV and how does it affect the immune system?

Answer 22

human immunodeficient virus

attacks and destroys t lymphocytes which results in a weaker ability of the immune system to destroy pathogens

Question 23

what is AIDS and how does it affect the immune system?

Answer 23

individuals with acquired immune deficiency syndrome have a weakened immune system and so are more vulnerable to opportunistic infections such as pneumonia and rare forms of cancer