7d- initiation of the third line of defence

Question 1

what is the third line of defence?

Answer 1

the third line of defence is known as the adaptive immune system or the specific immune response.

Question 2

how is the third line of defence initiated?

Answer 2

through the presentation of non-self antigens to specific immune cells of the adaptive immune system.

Question 3

what are the 2 ways the third line of defence differs from the second line of defence?

Answer 3

specificity and immunological memory

Question 4

what is specificity in the third line of defence?

Answer 4

the adaptive immune system responds to each distinct pathogen in a unique and tailored manner.

Question 5

what is immunological memory?

Answer 5

the adaptive immune system results in the production of cells that allow the body to respond to future re-infections by a previously encountered pathogen quickly and effectively.

Question 6

what is antigen presentation?

Answer 6

antigen presentation refers to a process involved in the initiation of the adaptive immune response, involving the selection of a type of T-lymphocyte called a T-helper cell.

Question 7

how do antigen presenting cells present foreign antigens on their surface?

Answer 7

After APC’s engulf and digest pathogens via phagocytosis, displaying pathogenic antigens on their MHC Class II markers, they travel via the lymphatic system to lymph nodes to present foreign antigens on their surface using MHC Class II proteins.

Question 8

how do antigen presenting cells facilitate the specificity of the adaptive immune system?

Answer 8

The APC’s interact with complementary T-cell receptors on the surface of T-helper cells. Each T helper cell has a unique set of T cell receptors for a single antigen on its surface, facilitating the specificity of the adaptive immune system.

Question 9

How do T helper cell become selected and activated?

Answer 9

When the interaction between APC and complementary T cell receptors occurs, the T helper cell becomes activated and is said to be ‘selected.’

Question 10

what can the activated T helper cell help initiate?

Answer 10

the activated T helper cell can then help initiate the adaptive immune response through either the humoral or cell - mediated immune response.

Question 11

what is humoral immunity?

Answer 11

humoral immunity involves the neutralisation and destruction of extracellular pathogens via the production and secretion of antibodies

Question 12

what are they key mediators of humoral immunity?

Answer 12

B-lymphocytes, a type of white blood cell.

Question 13

what is the surface of B-lymphocytes covered with?

Answer 13

B cell receptors, also known as antibodies.

Question 14

Where do B lymphocytes circulate?

Answer 14

In the blood stream

Question 15

in where do B lymphocytes reside in high numbers in?

Answer 15

they reside in high numbers within lymph nodes

Question 16

How does the activation of B lymphocytes occur?

Answer 16

occurs through their interaction with pathogenic antigens and T helper cells.

Question 17

what is step 1 of the humoral response?

Answer 17

a pathogen with an antigen that is complementary in shape to the antigen binding site on the receptor of a B-cell interacts with that B-cell. When this occurs, the B cell is said to have been ‘selected’

Question 18

what is step 2 of the humoral response?

Answer 18

Once a B cell has been selected, a T helper cell that also has been selected through antigen presentation, and has a complementary receptor to the antigen, will recognise the selected B-cell and secrete various cytokines. these cytokines cause the B cell to undergo clonal expansion, producing many copies of the selected B cell. This process of selecting specific T helper cells and B cells is termed clonal selection theory.

Question 19

step 3 of humoural immunity?

Answer 19

In addition to cloning, the T helper cell also stimulates the selected B cell via cytokines to undergo differentiation, producing 2 types of B cells: B memory cells and effector cells (plasma cells)

Question 20

what is step 4 of humoral immunity?

Answer 20

Plasma cells are differentiated clones of the selected B cell. After differentiating, they secrete antibodies into the blood to defend against the selected pathogen.

Question 21

what are antibodies and what structure are they?

Answer 21

antibodies released by plasma cells are proteins with a quaternary structure

Question 22

what kind of chains and shape is an antibody in?

Answer 22

two heavy chains and two light chains, arranged into a ‘Y’ shape.

Question 23

what are the 2 heavy chains joined by?

Answer 23

disulfide bond

Question 24

what are the 2 regions of antibodies and what are they called?

Answer 24

the stem of the antibody is known as the constant region. the tops of the arms are known as the variable region.