Cell Recognition + the Immune System

Question 1

How does the body’s immune system identify each type of cell?

Answer 1

• each cell has specific molecules (usually proteins) on their surface, enabling them to be identified

Question 2

What do these diff surface molecules enable immune system to identify?

Answer 2

• pathogens (bacteria, fungi, viruses)
• cells from other organisms of same species (organ transplants)
• abnormal body cells (cancerous cells)
• toxins (some pathogens release toxins into blood)

Question 3

Define antigen.

Answer 3

• molecules, present on surface of cells, that generate an immune response by lymphocyte cells when detected in body

Question 4

Describe the effect of antigen variability on disease + disease prevention.

Answer 4

• pathogens DNA can mutate frequently, + if mutation occurs in gene coding for antigen, then shape of antigen will change
• meaning any previous immunity to pathogen is no longer effective, bc memory cells in blood can no longer bind + produce a secondary immune response

Question 5

What is an e.g. of a common pathogen that exhibits antigen variability?

Answer 5

• the influenza virus, which mutates + changes it’s antigen v quickly, + so a new vaccine has to be created each yr

Question 6

What are the 2 types of white blood cell?

Answer 6

• phagocytes
• lymphocytes

Question 7

What are phagocytes?

Answer 7

• macrophages (type of WBC) found in blood + tissues, that carry out phagocytosis (non-specific immune response)

Question 8

Describe phagocytosis.

Answer 8

• phagocytes move towards pathogen via chemotaxis (attracted by chemicals/debris released by pathogen or abnormal cells)
• receptors on surface of phagocyte attach to antigens on pathogen
• phagocyte engulfs pathogen via endocytosis forming a phagosome
• a lysosome within phagocyte fuses w phagosome + releases lysozymes which hydrolyse + digests pathogen
• phagocyte absorbs soluble products + displays antigens on cell membrane to become an APC

Question 9

What are lymphocytes?

Answer 9

• white blood cells involved in specific immune response

Question 10

What are the 2 types of lymphocytes?

Answer 10

• T-lymphocytes (T cells)
• B-lymphocytes (B cells)

Question 11

What are T lymphocytes (T cells)?

Answer 11

• WBCs, made in bone marrow + mature in thymus, that are involved in cell mediated response

Question 12

Describe the cell mediated (cellular) response.

Answer 12

• once a pathogen has been engulfed + destroyed by a phagocyte, antigens are presented on cell surface (APC)
• helper T-cells have receptors on their surface, specific to 1 antigen, that attach to complementary antigens on APC
• this activates helper T-cells to divide by mitosis, to replicate + make large NO°s of clones that differentiate into diff types of cell

Question 13

What are the diff types of cell that helper T cells differentiate into?

Answer 13

• cytotoxic T cells (killer T cells)
• memory cells
• some remain as helper T cells to activate B cells + stimulate phagocytes to perform more phagocytosis

Question 14

What are cytotoxic T cells?

Answer 14

• cells that destroy abnormal or infected cells by releasing perforin (a protein)
• this embeds in cell surface membrane, creating a pore that allows any substances to enter + leave cell, causing cell death

Question 15

What is an antigen-presenting cell?

Answer 15

• any cell presenting a non-self antigen on its cell surface membrane

Question 16

What are B-lymphocytes (B cells)?

Answer 16

• WBCs, made + mature in bone marrow, that are involved in humoral response

Question 17

Describe the humoral response.

Answer 17

• each B cell has a specific antibody (receptor) on their cell surface membrane that’s complementary to 1 antigen
• when an antigen in blood binds w a complementary B-cell receptor, B cell takes in antigen by endocytosis + presents it on its cell surface membrane (APC)
• when antigen presenting B cell binds to a complementary helper T cell, it activates B cell to rapidly divide by mitosis (clonal expansion)
• clones then differentiate into plasma cells, which produce monoclonal antibodies, or memory B cells (primary response)

Question 18

What are memory B cells?

Answer 18

• long-lived cells that rapidly divide into plasma cells if reinfected w same pathogen
• this rapidly produces lots of antibodies, so pathogen is destroyed before symptoms occur (secondary response)

Question 19

Define antibody.

Answer 19

• proteins produced by plasma cells, as a part of immune response, which binds to antigens

Question 20

Describe the structure of an antibody.

Answer 20

• quaternary structure protein (4 polypeptide chains)
• 2 long chains (heavy) bonded to 2 short chains (light) by disulphide bonds
• has a constant region + a variable region, where complementary antigens bind

Question 21

What is agglutination?

Answer 21

• antibodies are flexible + can bind to 2 complementary antigens on a pathogen, to form an antigen-antibody complex
• this clumps them together, making it easier for phagocytes to locate + destroy pathogens