Memory cellsare also produced when a B cell is stimulated by an antigen. A
memory cell provides the organism with long-term immunity to the antigen.
B cells react to one kind of antigen that is referred to as its complementary
antigenand are able to identify that antigen because antigen receptors bind to
one specific antigen. Here’s how it works: Once the antigen binds to the antigen
receptor, the B cell replicates into a clonal selection. Aclonalselection is a large
cluster of clone cells.
An antibody attaches to an antigen at an antigen-binding site to form an
antigen-antibody complex. This complex is very specific. However, when there
are large quantities of antigens, the antigens attach to antibodies where they do
not exactly fit. This makes for less-than-perfect matches for the antigen-anti-
body complex. These antibodies are said to have less affinity to the antigen.
B cells under go apoptosis if the B cell does not come in contact with an anti-
gen. Apoptosisis a programmed death of the B cell that causes phagocytes to
remove the cell from the organism.
STRATEGIES FOR COMBATING ANTIGENS
The formation of antigen-antibody complexes is useful in the response to in-
fectious organisms or foreign substances because they remove the infectious
agent from the body. Protective methodology of binding antibodies to antigens
is accomplished by agglutination, opsonization, neutralization, antibody-depend-
ent cell-mediated cytotoxicity, and the activation of complement.
- Agglutinationgenerates antibodies that clump together antigens, making
them easy to ingest by phagocytes. - Opsonizationcoats the antigen with antibodies to make it easy for phago-
cytic cells to ingest and for lysis. - Neutralizationblocks antigens from attaching to targeted cells, thereby
neutralizing the antigen. - Antibody-dependent cell-mediated cytotoxicitycoats the foreign cell with
antibodies. Nonspecific immune cells then destroy the foreign cell from
the outside. This is used for organisms that are too large for phagocytic cells
to ingest. - Theactivation of complementis used when infectious agents are coated with
reactive proteins that cause IgG and IgM antibodies to attach to the agent,
causing lysisof the cell membrane and resulting in ingestion by phagocytes.
CHAPTER 14 Immunity^217