|MadSci Network: Immunology|
When naïve B lymphocytes see antigen, they can undergo clonal amplification and differentiate into plasma cells, which are the antibody secreting cells. Some of the cells differentiate into memory B cells, which have a very long lifespan. The “secondary” immune response (the one that occurs the second time you get infected or immunized with the same antigen) is more vigorous than the primary immune response. There are several reasons for this. 1) The frequency of B cells specific for that antigen is increased as a result of the clonal expansion and memory cell generation that took place during the primary response. 2) The memory cells have often undergone a process called somatic hypermutation, which allows them to mutate their antigen receptors and the cells with highest affinity (better fit) for antigen are selected for survival and clonal expansion. 3) The memory cells often have undergone isotype switching so when stimulated by antigen they can differentiate into plasma cells making IgG or IgA antibodies, rather than IgM antibodies that dominate the primary immune response. Most of the above events in B cells require the help of T cells. Naïve T cells also respond to antigen, undergo clonal amplification and differentiation into either helper or killer T cells, and they also produce memory T cells during the primary response. “Opsonize” refers to coating of pathogens such as bacteria with antibodies, which makes them more readily eaten and destroyed by macrophages and other phagocytic cells. You can find out more about these topics at the website for the Kuby Immunology text: http://www.whfreeman.com /college/book.asp? disc=&id_product=2001003121&compType=PREV
Try the links in the MadSci Library for more information on Immunology.