Clonal Selection

ninja icon


•  B lymphocytes are activated by T lymphocytes in mammals

•  Activated B cells multiply to form clones of plasma cells and memory cells

When the body is challenged by a foreign pathogen it will respond with both a non-specific and a specific immune reaction

  • Non-specific immune cells called macrophages will engulf pathogens non-selectively and break them down internally
  • A proportion of macrophages (dendritic cells) will present the antigenic fragments of the pathogen to specific lymphocytes 

The body contains millions of different T lymphocytes and B lymphocytes that each recognise a single, specific antigen

  • Antigenic fragments are presented to specific helper T lymphocytes (TH cells) that, when activated, releases cytokines
  • The cytokines stimulate a specific B cell that produces antibodies to the antigen to divide and form clones (clonal selection)
  • Most of the clones will develop into short-lived plasma cells that produce large quantities of specific antibody
  • A small proportion of clones will differentiate into long-lived memory cells that function to provide long-term immunity

Pathogens typically contain multiple distinct antigenic fragments on their surface and hence a single pathogen is likely to stimulate several different T and B lymphocytes to produce a variety of specific antibodies (polyclonal activation)

Clonal Selection

clonal selection