T and B lymphocytes

Question 1

What are antigens and what do they do?

Answer 1

Usually proteins that are recognised as foreign by the immune system + stimulates an immune response.
It triggers production of antibodies as part of body’s defence system

Question 2

Where are antigens found?

Answer 2

Part of the cell-surface membranes of invading cells e.g microorganisms or abnormal body cells e.g cancer cells

Question 3

What are lymphocytes produced by?

Answer 3

Stem cells in bone marrow

T cells mature in thymus gland + B cells mature in bone marrow

Question 4

What are the two types of lymphocytes?

Answer 4

T and B lymphocytes

Question 5

How can T lymphocytes distinguish invader cells from normal cells?

Answer 5

The invader cells e.g pathogens, virus, transplanted cells and cancer cells have different specific antigens on their cell-surface membranes

Question 6

What are antigen-presenting cells?

Answer 6

Cells that display foreign antigens (from other cells) on their surface

Question 7

What type of response are T lymphocytes involved in?

Answer 7

Cell-mediated immunity (cellular response)

Question 8

What do T cells have on their surface and what do they do?

Answer 8

They have receptor proteins on their surface that detect specific (complementary) antigens

Question 9

What are the two forms of T cell?

Answer 9

• Helper T cells

- Cytotoxic T cells

Question 10

Describe the cell-mediated immune response

Answer 10

• After the pathogen is engulfed, the phagocyte presents the pathogen’s antigens on its surface (becomes antigen-presenting cell)
• Receptors on specific helper T cells bind to antigens on antigen-presenting cells (fits perfectly - complementary)
• This activates the T cells

Activated T cells:

• Divide by mitosis to produce T helper cell clones (they continue to circulate in the blood)
• Releases cytokines to activate T cytotoxic cells
• Activate B cells
• Stimulate phagocytosis

Question 11

Describe what cytotoxic T cells do

Answer 11

• Produce perforin protein
• Makes holes in cell surface membrane
• Results in cell death

Question 12

What type of lymphocytes are involved in cell-mediated immunity?

Answer 12

T lymphocytes

Question 13

What type of lymphocytes are involved in humoral immunity?

Answer 13

B lymphocytes

Question 14

What do B lymphocytes have on their surface?

Answer 14

They have antibodies on their surface

Question 15

Describe the humoral immunity response

Answer 15

1. The B cells with complementary antibodies engulfs the pathogen
2. The antigens from the pathogen are presented on the B cell
3. The activated helper T cells bind to the presented antigen using its complementary receptor protein
4. B cells clone by mitosis - activated by T cells to divide
5. Plasma cell clone is made to secrete antibodies
   OR
6. Memory cells made, circulate in blood for future infections

Question 16

What do the antibodies secreted by plasma cell clones do?

Answer 16

The antibodies attach to antigens and:

• Agglutinate (stick together in large clumps to target)
• Stop pathogens invading body cells
• Bind to free toxin proteins

Question 17

What is the primary response (part of humoral immunity response)?

Answer 17

Antibodies are secreted

Question 18

What is the secondary response (part of humoral immunity response)?

Answer 18

Memory cells are made

Question 19

What do B cells produce?

Answer 19

Clones. Each clone produces one specific antibody - referred to as monoclonal antibodies