5.4 B lymphocytes and humoral immunity

Question 1

Explain the role of B cells in humoral immunity.

Answer 1

1) the surface antigens of invading pathogen are taken up by B cell
2) B cell processes antigens and presents them on surface
3) Helper T cells attach to processed antigens on B cell, activating B cell
4) B cell divides by mitosis to give clone plasma cells
5) cloned plasma cell secretes specific antibody to pathogen
6) antibody attaches to antigens on pathogen and destroys them
7) Some B cells develop into memory cells, which respond to future infection by the same pathogen and divide rapidly

Question 2

What is antigenic variation?

Answer 2

• each different cell has many different proteins on its surface (each acting as an antigen)
• some pathogens produce toxins which also act as antigens

Question 3

how does to body respond to antigenic variation?

Answer 3

• Many different B cells make clones, each of which produces its own type of antibody.
• each clone produces separate antibodies (monoclonal antibodies)

Question 4

What is the role of plasma cells?

Answer 4

• Involved in the primary immune response
• short lifespan
• produce a large amount of antibodies which destroy antigen
• responsible for the immediate immune defense

Question 5

What is the role of memory cells?

Answer 5

• involved in secondary immune response
• much longer lifespan than plasma cells
• do not produce antibodies directly
• when they encounter the pathogen in the blood/ tissue fluid later they rapidly divide and develop into plasma cells which attack pathogen, and new memory cells to remember the pathogen in the future
• provide long term immunity against the pathogen