Humoral Immunity (the neutralisation and destruction of extracellular pathogens via the production and secretion of antibodies)

1. 
   

a pathogen with an antigen that is complementary in shape to the antigen-binding site on the receptor of a B lymphocyte, interacts with that B cell, meaning the B cell has been ‘selected’

2. 
   

once the B lymphocyte has been selected, a T helper cell selected through antigen presentation which has a complementary receptor to the antigen, will recognise the B cell and secrete cytokines

the cytokines cause the B cell to undergo clonal expansion (where many copies of a lymphocyte are generated)

3. 
   

the T helper cell also stimulates the selected B cell via cytokines to undergo differentiation, where the clones of the selected B cell are driven to differentiate into B memory cells and plasma cells (a type of effector cell)

4. 
   

the plasma cells secrete specific antibodies into the blood to defend against the selected pathogen

the B memory cells reside in the body for a prolonged period of time and are responsible for immunological memory

B lymphocytes (type of white blood cell)

key mediators of humoral immunity

• their surfaces are covered in B cell receptors (aka antibodies)

• they travel around the body in the bloodstream and reside in high numbers within lymph nodes

• the activation of B lymphocytes occurs through their interaction with pathogenic antigens and T helper cells