5.4 - B lymphocytes and humoral immunity

Question 1

Are antibodies soluble?

Answer 1

• yes,
• they’re soluble in the blood and tissue fluid of the body

Question 2

How many types of B cells are there

Answer 2

• millions
• each one producing a specific antibody that responds to a specific antigen
• for every antigen on the surface of a pathogen, foreign cell, toxin, damaged or abnormal cell = there will be one B cell that has an antibody on its surface that is complementary to the antigen

Question 3

Describe the process of Humoral immunity

Answer 3

• Antigen on surface of pathogen, foreign cell, toxin, damaged/abnormal cell enters the blood or tissue fluid
• the antigen enters the B cell (with the complimentary antigen on its surface) by endocytosis and processes the them, then presents them on its surface
• T-helper cells bind to these processed antigens and stimulate this B cell to divide by mitosis
• forming clones of identical B cells, that produce the specific antibodies that work specifically for specific foreign antigens (clonal selection/expansion)
• antibodies attaches to antigens on the pathogen and destroys them
• Some B cells develop into memory cell. These can respond to future infections by the same pathogen by dividing rapidly into plasma cells

Question 4

What is the primary response in humoral immunity

Answer 4

• plasma cells
• secrete antibodies directly + then produce memory cells (in case infected again)
• they only survive a few days
• response is slow and person will get ill before pathogen is killed

Question 5

What is the secondary response in humoral immunity

Answer 5

• memory cells
• They circulate in blood + tissue fluid
• when they encounter the antigen from the primary response they divide rapidly
• response is rapid and person will not get ill

Question 6

What is the difference between Humoral and Cell-mediated immunity

Answer 6

• HI = B lymphocytes, CMI = T lymphocytes
• HI = produced and matured in bone marrow, CMI = produced in bone marrow, matures in thymus gland
• HI = produces antibodies, CMI = doesn’t
• HI = pathogens are identified by the antigens in the blood by binding to B cell receptors, CMI = pathogens are identified by the antigens on the surface of infected cells or phagocyte, a cancer cell or a transplant cell
• HI = pathogens are killed when antibodies attach to antigens, CMI = cytotoxic cells
• Hi = once stimulated, B cells divide into either plasma or memory cells, CMI = once stimulated, T cells divide by mitosis into specialist cells, e.g. T-helper cells or cytotoxic cells