Question

How does the humoral immune system of our body work?

Answer 1

The humoral (antibody-mediated) immune system is made up of B lymphocytes (B cells) and the antibodies they release into the blood plasma and lymph. It defends the body against bacteria and viruses that enter the body fluids.

1. When a B cell in the lymph node comes into contact with a specific antigen, the receptors on its membrane recognise the antigen.
2. The B cell is stimulated and divides repeatedly to give rise to a clone of plasma cells and memory cells (clonal selection).
3. All the plasma cells are genetically identical and produce numerous identical antibodies, which are released into the lymph and eventually enter the blood. A single plasma cell can produce about 2,000 antibody molecules per second; plasma cells live only for a few days.
4. The antibodies stick to the surface of the bacteria and speed up phagocytosis, or neutralise the toxins produced by them, by agglutination, opsonisation and neutralisation.
5. The memory cells remain in the lymph nodes for years and give a rapid secondary response on a second encounter with the same antigen.

Thus the humoral immune system works through B cells, which on recognising a specific antigen produce a clone of plasma cells that secrete specific antibodies into the blood and lymph to neutralise or destroy the pathogen.