the specific immune response - lqc 5a

Question 1

state the 4 main characteristics of a specific immune response

Answer 1

1. It can distinguish between self and non-self. 2. It recognises and targets specific antigens (rather than a general targeting of non-self). 3. It is diverse as it can recognise and target over 10 million different antigens. 4. It has immunological memory.

Question 2

what is an antigen

Answer 2

A molecule (usually protein or polysaccharide) found on the surface of cells or particles. It is recognised by immune system cells as non-self and activates/initiates an immune response.

Question 3

When an organism encounters a specific antigen for the first time what type of specific immune response do they carry out?

Answer 3

a primary immune response

Question 4

One of the first processes that occurs in the specific immune response is T helper cell activation. Which process in the non-specific immune response initiates the activation of T helper cells?

Answer 4

phagocytosis

Question 5

at the end of phagocytosis what has a macrophage now become?

Answer 5

an antigen-presenting cell (APC)

Question 6

describe how a T helper cell is activated

Answer 6

1. A T helper cell with complementary CD4 receptors binds to the antigen/MHC complex on the macrophage APC. The T helper cell becomes activated.
2. The activated T helper cell divides/proliferates by mitosis to form clones of active T helper cells.
3. Active T helper cells also differentiate and divide to form T memory cells. These remain dormant until they are used in the secondary immune response when the antigen is encountered again.

Question 7

describe how a B cell is activated

Answer 7

1. An antigen on a bacterium binds to a complementary shaped receptor on the B cell.
2. The B cell engulfs the bacterium and carries out antigen processing and presentation. Antigen is bound to an MHC protein. The B cell has now become an antigen-presenting cell (APC).
3. An activated T helper cell binds with its CD4 receptors to the antigen/MHC complex on the B cell. The activated T helper cell releases cytokines, which activates the B cell and stimulates it to divide by mitosis. This is known as clonal selection.
4. Some active B cell clones differentiate and divide to form B memory cells. These remain dormant until they are used in the secondary immune response when the antigen is encountered again.
5. Other active B cell clones become B effector cells.
6. B effector cells differentiate into plasma cells.
7. Plasma cells produce and secrete antibodies. The binding region of the antibody is the same complementary shape as the receptor on the B cell which bound the original antigen

Question 8

what type of protein are antibodies

Answer 8

immunoglobulin, a form of globular protein

Question 9

describe the main role of antibodies

Answer 9

Antibodies bind to the complementary antigen on the surface of the pathogen. This is known as opsonisation. They cause pathogens to agglutinate (clump together) which helps prevent their spread throughout the body.

Question 10

describe how antibodies enhance the process of phagocytosis by macrophages

Answer 10

1. The constant region of the antibody binds to the antibody receptor on the surface of a macrophage.
2. The macrophage engulfs the antibodies and pathogens into a vacuole. An increased number of pathogens are engulfed in the same period of time – this enhances phagocytosis.
3. Lysosomes fuse with the vacuole, releasing their digestive enzymes that destroy the pathogen

Question 11

Within the specific primary immune response, what is the collective activation of T helper cells and B cells, followed by the production of antibodies known as?

Answer 11

the humoral response