2.4 Immune system

What is an antigen?

A foreign molecule that stimulates an immune response, leading to the production on an antibody

How are cells identified by the immune system?

Each type of cell has specific molecules on its surface that identify it

What type of cells can the immune system identify?

• Pathogens (viruses,bacteria)

• Cells from other organisms (organ transplants)

• Abnormal body cells (tumour, cancer)

• Toxins (poisons released by some bacteria)

What is the non-specific immune response?

Phagocytosis

What is the cellular response?

T lymphocytes forming clones which stimulate cytotoxic t cells, specific B cells and phagocytes

What is the humoral response?

B lymphocytes forming clones which differentiate into B plasma cells or B memory cells

Describe the process of phagocytosis/non-specific immune response

1. Phagocyte recognises foreign antigens on pathogen

2. Phagocyte engulfs pathogen by moving around it

3. Pathogen is contained in phagosome in cytoplasm of phagocyte

4. Lysosome fuses with phagosome and releases lysozymes

5. Lysozymes digest pathogen

6. Antigens presented on surface of phagocyte to stimulate an immune response

• Describe the process of the cellular response

1. T lymphocytes recognise antigens on surface of antugen presenting cells (infected cells, phagocytes, tumour cells, transplanted cells)

2. Specific T helper cells with complimentary receptors on the surface bind to antigens on antigen-presenting cell

3. This activates the T cell and causes it to divide by mitosis to form clones which stimulate cytotoxic T cells, specific B cells, phagocytes

What do cytotoxic T cells do?

Kill infected cells/tumour cells

Describe the process of the humoral response

Clonal selection -

1. Specific B lymphocyte with complimentary receptors on cell surface bind to antigen

2. This is stimulated by helper T cells

3. B lymphocyte divides rapidly by mitosis to form clones which differentiate into B plasma cells or B memory cells

What do B plasma cells do?

Secrete large amounts of antibodies

What do B memory cells do?

Remain in the blood for secondary immune response

What are antibodies?

Quaternary structure proteins secreted by B lymphocytes (eg plasma cells) in response to specific antigens

What do antibodies bind to and what does this form?

Antibodies bind to specific antigens, forming antigen-antibody complexes

Label the structure of an antibody

What is agglutination?

Antibodies bind to 2 pathogens at once causing them to clump together

How do antibodies lead to the destruction of pathogens?

1. Antibodies bind to antigens on pathogens, forming an antigen-antibody complex (specific tertiary structure so binding site/variable region binds to complementary antigen)

2. Each antibody binds to 2 pathogens at a time, causing agglutination (clumping) of pathogens

3. Antibodies attract phagocytes

4. Phagocytes bind to the antibodies and phagocytosis many pathogens are once