Immunity

Question 1

Where do phagocytes (macrophages and neutrophils) have their origin?

Answer 1

Neutrophils and macrophages are produces from stem cells in the bone marrow. They are released into the blood.

Question 2

Describe the mode of action of phagocytes (macrophages and neutrophils)

Answer 2

1. Both types of phagocyte engulf pathogens and other foreign particles by endocytosis 2. Chemotaxis. The phagocytes are attracted towards bacteria by chemicals that they release and by proteins in blood plasma that are activated when pathogens enter the body. 3. Attachment. The phagocytes have cell surface receptors that bind to antigens on the pathogen. 4. Engulfing and fusion. Extensions of the cytoplasm surround the bacteria, membrane fusion engulfs bacteria in a phagocytic vacuole, known as a phagosome. 5. Killing. Lysosomes fuse with the vacuole membrane releasing toxic chemicals, such as hydrogen peroxide, free radicals and toxic peptides. 6. Digestion. Lysosomes also release the enzyme lysozyme to hydrolyse glycosidic bonds in bacterial cell walls; other hydrolytic enzymes are also released. Products of digestion are absorbed into the cytosol; some may be removed by exocytosis.

Question 3

Name and state what type of pathogen causes malaria

Answer 3

Protoctist - Plasmodium falciparum, Plasmodium malariae, Plasmodium ovale, Plasmodium vivax

Question 4

Name and state what type of pathogen causes cholera

Answer 4

Bacterium - Vibrio cholerae

Question 5

Name and state what type of pathogen causes tuberculosis

Answer 5

Bacterium - Mycobacterium tuberculosis and Mycobactrium bovis

Question 6

Name and state what type of pathogen causes HIV/AIDS

Answer 6

Virus - Human Immunodeficiency virus (HIV)

Question 7

Name and state what type of pathogen causes measles

Answer 7

Virus - Morbillivirus

Question 8

Name and state what type of pathogen causes smallpox

Answer 8

Virus - Variola

Question 9

What is an antigen?

Answer 9

Any macromolecule e.g. polysaccharide or protein that stimulates the production of antibodies

Question 10

What is an antibody?

Answer 10

Protein that is secreted by plasma cells (active B-cells) n response to the presence of an antigen

Question 11

What is the immune response?

Answer 11

A series of events that occur in the immune system in response to the presence of a non-self antigen in the body.

Question 12

What are two types of T-lymphocytes?

Answer 12

Helper T-lymphocytes and cytotoxic T-lymphocytes

Question 13

What are the functions of a helper T-lymphocyte?

Answer 13

Helper T-lymphocytes: - respond to non-self antigens presented on the surface of macrophages - secrete cytokines (cell signalling molecules) to stimulate B-cells, cytotoxic T-cells and macrophages - produce memory T-lymphocytes

Question 14

What are the functions of a cytotoxic T-lymphocyte?

Answer 14

Cytotoxic T-lymphocytes: - respond to non-self antigens on the surface of many body cells - attach to cells infected with intracellular pathogens and kill them - attach to cancer cells and cells in transplanted tissues and kill them - production of memory T-lymphocytes

Question 15

What is a B-lymphocyte?

Answer 15

A cell that has the potential to make and release antibody molecules

Question 16

What is a T-lymphocyte?

Answer 16

A cell that has the potential either to release molecules (cytokines) to coordinate immune responses or to kill infected cells. T-lymphocytes DO NOT release antibodies.

Question 17

What are pathogens, antigens and antibodies?

Answer 17

Pathogens are a bacterium, virus, or other microorganism that can cause disease. Antigens are macromolecules of various types and antibodies are proteins produced by plasma cells (activated B-cells) in response to antigens.

Question 18

What is a plasma cell?

Answer 18

A short-lives activated B-lymphocyte that makes and releases antibodies into the blood and lymph

Question 19

Describe the immune response in terms of clonal selection, clonal expansion and memory B-cells

Answer 19

The immune response involves the activation of clones of lymphocytes by the presentation of antigens. When a pathogen enters the body for the first time there are very few lymphocytes with the specific membrane receptors that have a complementary shape to the partcicular antigen on the surface of the pathogen.

Question 20

Study the attached picture. State what is happening at stage J and explain the role of the cell L at stage K in the immune response.

Answer 20

Stage J is phagocytosis. This is the process by which a cell engulfs solid particles or pathogens to form a vacuole called a phagosome. This takes place by endocytosis. The phagosome fuses with lysosomes containing digestive enzymes such as proteases. These digest and destroy the particle or pathogen.

Cell L is a cytotoxic T-lymphocyte, in stage K which is active immunity. When the T-lymphocyte is activated by the presentation of antigens, it is able to recognise body cells that have non-self antigens on them. These are known as antigen-presenting cells. They may include (a) cells that are infected with viruses (b) macrophages that have taken up virus particles by phagocytosis and broken them down, in doing so exposing molecules of the virus on ther surface (c) cancer cells that have mutations that resulted in tumours.

T cells target these different antigen presenting cells and destroy them.

There are several different types of T cell.