10.5 the humoral response

Question 1

what are B cells?

Answer 1

1. B cell recognise antigens through B cell receptor on their surface
2. produce antibodies that can bind to specific antigens
3. antibodies travel through the body in plasma
4. B cell receptors are Y-shaped. consists of 4 polypeptide chains bridged by disulphide bridges. each B receptor has two identical heavy chains and two identical light chains. all chains have a constant region and variable region. it is the same in every B cell receptor. variable regions form the antigen binding sites

Question 2

what is self-tolerance?

Answer 2

the ability of immune cell not to destroy self-cells. any B or T cells that carry a receptor that is complementary to a self antigen presented by MHC-I are destroyed

Question 3

what is clonal selection?

Answer 3

the process of selectively activating and cloning particular lymphocytes

Question 4

what happens to B cells in action?

Answer 4

1. unlike T cells, B cells interact directly with free pathogens in the lymph. when a naive B cell binds to a pathogen, B cell phagocytoses the pathogen.
2. antigens are then presented on the surface of the B cell. helper T cells interact with antigen presenting B cell. cytokines released by helper T cell to fully activate B cell.
3. activated B cells then undergo clonal expansion, producing plasma cells and memory B cells.

Question 5

what are plasma cells and antibodies?

Answer 5

1. plasma cells produce and secrete thousands of antibodies per second
2. antibodies (immunoglobulins) are glycoprotein molecules. they move through blood and lymph, and bind to any complementary antigens and pathogens.
3. 4 different functions:
   - neutralisation of toxins: antibodies can bind to a toxin molecule, preventing it from functioning
   - neutralisation of pathogens: antibodies bind to antigen on the surface of pathogens, preventing them from binding to host cells
   - precipitation: antibodies bind to soluble antigen molecules, causing them to come out of solution
   - agglutination: antibodies bind to multiple pathogens, clumping them together, preventing them from moving and making it easier for macrophages to find them.
4. antibody-antigen complexes also trigger the activation of macrophages and complement proteins

Question 6

what are memory B cells?

Answer 6

1. remaining cells produced by clonal selection
2. carry specific B cell receptors on their membrane surface. identical to those of the original B cell
3. remain the lymphatic system for a long time, they activate the humoral response in a secondary infection. when a familiar pathogen comes in contact with complementary mem B cells, mem B cells rapidly divide into plasma cells.