12.6 : The Specific Immune System

Question 1

Describe the structure of antibodies

Answer 1

Made of two identical polypeptide chains called heavy chains, and two shorter identical chains called light chains.

Variable regions form the antigen bonding sites

Shape of variable region is complementary to a particular antigen. Gives it its specificity.

Hinge region allows flexibility.

Constant regions allow binding to receptors on immune system cells.

Disulfide bridges hold the polypeptide chains of the protein together.

Question 2

Describe how antibodies defend the body

Answer 2

Antibody of antigen-antibody complex acts as opsonin so complex is easily engulfed and digested by phagocytes.

Most pathogens can’t invade host cells once part of antigen-antibody complex.

Antibodies act as agglutinins causing pathogens carrying a-a complexes to clump together. Prevents spreading and easier for lots of pathogens to be engulfed at the same time.

Act as anti - toxins, binding to toxins produced by pathogens and making them harmless.

Question 3

Where are the two types of lymphocytes made?

Answer 3

B lymphocytes in Bone marrow

T lymphocytes in Thymus gland

Question 4

What are the main types of T lymphocytes?

Answer 4

T helper cells
T killer cells
T memory cells
T regulator cells

Question 5

What do T helper cells do?

Answer 5

Produce interleukins ( type of cytokine ) which stimulate activity of B cells.

This increases antibody production and stimulates production of T memory cells.

Question 6

What do T killer cells do?

Answer 6

Kill infected cells.

Produce perforin which kills the pathogen by making holes in the cell membrane so it is freely permeable.

Produce T memory cells.

Question 7

What do T memory cells do?

Answer 7

Long life span.

Part of the immunological memory. If they meet an antigen a second time, they divide rapidly to form lots of clones of T killer cells that destroy the pathogen.

Question 8

What do T regulator cells do?

Answer 8

Suppress the immune system, acting to control and regulate it.

Stop the immune system once a pathogen has been eliminated, and make sure the body recognises self antigens and does not set up an autoimmune response.

Question 9

What are the types of B lymphocytes?

Answer 9

Plasma cells
B effector cells
B memory cells

Question 10

What do plasma cells do?

Answer 10

Produce antibodies to a particular antigen and release them.

Question 11

What do B effector cells do?

Answer 11

Divide to form the plasma cell clones

Question 12

What do B memory cells do?

Answer 12

Long life span.

Provide immunological memory.

Programmed to remember a specific antigen and enable the body to make a very rapid response when a pathogen carrying that antigen is encountered again.

Question 13

What is cell mediated immunity?

Answer 13

T lymphocytes respond to the cells of an organism that have been changed in some way ( e.g. virus infection or mutation )

Question 14

Describe the stages of cell mediated immunity

Answer 14

Macrophages engulf and digest pathogens in phagocytosis. They from antigen presenting cells.

Receptors on T helper cells fit the antigens. These T helper cells become activated and produce interleukins, which stimulate more T cells to divide and form clones of identical activated helper cells.

These cloned T cells can :

develop into memory cells ( explain what these do)

produce interleukins that stimulate phagocytosis

produce interleukins that stimulate B cells to divide

stimulate the development of a clone of T killer cells that are specific for the presented antigen and then destroy infected cells

Question 15

What is humoral immunity?

Answer 15

The body responds to antigens found outside the cells e.g. bacteria and fungi, and to APCs.

Question 16

Describe the stages of humoral immunity

Answer 16

Activated T helper cells bind to the B cell APC. This is clonal selection.

Interleukins produced by the activated T helper cells activate the B cells.

Activated B cells divide to give clones of plasma cells and B memory cells. This is clonal expansion.

Cloned plasma cells produce antibodies that fit the antigens on the surface of the pathogen, bind to the antigens and disable them, or act as opsonins or agglutinins. This is the primary immune response.

Some cloned B cells develop into B memory cells. If body infected by same pathogen again, B memory cells divide rapidly to form plasma cell clones. They produce the right antibody and wipe out pathogen very quickly, before it can cause symptoms. This is the secondary response.