T lymphocytes and cell-mediated immunity

Question 1

Antigens

Answer 1

Any part of an organism or substance that is recognised by the immune system and stimulates an immune response
They are usually part of the cell-surface membranes or cell walls of invading cells
The presence of an antigen triggers the production of an antibody.

Question 2

Lymphocytes features

Answer 2

+Specific response.
+Slower in action but long lasting.
+Depends on the type of lymphocyte

Question 3

Two types of Lymphocytes

Answer 3

B lymphocyte
+They mature in bone marrow.
+They are associated in immunity involving anti-bodies (humoral immunity) in the humour.

T lymphocytes
+They mature in the thymus gland
+ They are involved in immunity involving body cells.

Question 4

Cell-mediated immunity

Answer 4

+Lymphocytes respond to own cells infected by non-self material.
+Also respond to cells from other organisms.

Question 5

How does T lymphocytes distinguish invader cell from normal cells?

Answer 5

+Phagocytes that have engulfed and hydrolysed a pathogen present some of a pathogen’s antigens on their own cell-surface membrane.
+Body cells invaded by a virus present some of the viral antigens on their own cell-surface,
+Transplanted cells from individuals of the same species have different antigens on their cell surface membrane
+Cancer cells are different from normal body cells and present antigens on their cell-surface membranes
+ Cells that display foreign antigens on their surface= antigen presenting cells
-T L only responds to antigens on a body and not antigens in body fluid.= Cell mediated immunity/cellular response

Question 6

Stages in the response of T lymphocytes to infection by a infection

Answer 6

+ Pathogens invade body cells or taken in by phagocytosis
+The phagocyte places antigens from the pathogen on its membrane
+Receptors on a specific helper T cell fit exactly onto these antigens
+This attachment activates the T cell to divide rapidly by mitosis and form a clone of genetically identical cells
+The cloned T cells -
a- develop into memory cells that enable a rapid response to future infections by the same pathogen.
b- Stimulate phagocytes to engulf pathogens by phagocytosis
c- Stimulate B cells to divide and secrete their antibody.
d- Activate cytotoxic T cells.

Question 7

How cytotoxic T cells kill infected cells

Answer 7

+Kill abnormal cells and body cells that are infected by pathogens. by producing a protein called perforin.
+This protein makes holes in membrane.
+These holes make the cell membrane freely permeable to all the substances.