5.3 T Lymphocytes and Cell Mediated Immunity

Question 1

How do T-lymphocytes respond to an infection by a pathogen?
(2nd stage of immune response)

Answer 1

~Phagocyte engulfs pathogen that has entered the body
~The phagocyte presents the pathogens antigens on its cell surface membrane
~ The T-cell has receptor proteins on its surface that are complementary to the antigens on the phagocyte - so they can bind.
~ The binding causes the T cells to undergo mitosis and form a clone of genetically identical cells.
~ The cloned T cells differentiate into memory cells, activates T(c) cells, activates B cells to divide, and stimulates phagocytosis.

Question 2

How are B cells activated?
(3rd stage of IR)

Answer 2

~ T cells activate B cells which are covered in antibodies
~ when the antibody on the surface of the B-cell meets a complementary shaped antigen, they bind
~ This activates the B cell which then divides into plasma cells

Question 3

How do plasma cells/B cells destroy pathogens?
(4th stage of IR)

Answer 3

~plasma cells are clones of the B cell so they can secrete antibodies specific to the antigens (monoclonal antibodies)
~ the antibodies bind to the antigen on the surface of the pathogen to form antigen-antibody complexes
~the pathogens then agglutinate
~ the phagocytes bind to the antibodies and phagocytose many pathogens at once
~this leads to the destruction of pathogens ( which carry this antigen in the body)

Question 4

What is agglutination and how is it formed?

Answer 4

~ When the pathogens become clumped together so the phagocytes can find them easier and destroy them
~ An antibody has 2 binding sites so it can bind to 2 pathogens at once causing the pathogens to clump

Question 5

What are antibodies made up of?

Answer 5

~ chains of amino acids

Question 6

How do variable regions differ on each antibody

Answer 6

~specificity of an antibody depends on its antigen binding site which is made up of the variable region.
~each variable region on an antibody has a unique tertiary structure due to different amino acid sequences, which is complementary to a specific antigen.

Question 7

How do T(c) cells kill infected cells ?

Answer 7

~ T cells activate cytotoxic T cells (killer cells)
~ T(c) cells produce a protein called perforin which make holes in the cell surface membrane of abnormal body cells or cells infected by pathogens
~these holes cause the membrane to become freely permeable to all substances and the cell dies
~T cells are most effective on viruses as they replicate inside of cells