Lasting Immunity
When antigens are first encountered, the primary immune responseoccurs caus-
ing an increase in the antibody titer. The antibody titeris the amount of anti-
bodies in serum of the infected organism. There are no or undetectable levels of
antibodies when the antigen first attacks the organism. Then the antibody titer
gradually increases and then declines as the antigen is destroyed or neutralized.
When antigens are encountered for the second time, the secondary immune
responseoccurs, causing memory cells to quickly transform into plasma cells
that produce antibodies. The secondary immune response is also known as the
anamnestic responseor memory response. Amemory cellis a B lymphocyte that
was generated in the primary immune response but did not became an antibody-
producing plasma cell at that time.Antibodies Used for Diagnosing Diseases
Antibodies are useful in diagnosing diseases since a particular antibody is pro-
duced only if a complimentary antigen is present in the organism. This is useful
in identifying an unknown disease-causing pathogen.
Antibodies can be produced in the laboratory by a clone of cultured cells that
make one type of antibody. These antibodies are called monoclonal antibodies.
Malignant cells of the immune system called myeloma cells are used because
they divide forever. This is why malignant cells (cancer cells) are so devastating
to our body. These myeloma cells are then mixed with lymphocytes that have
been designed to produce a specific antibody. When these cells are mixed to-
gether, they fuse to become one cell called a hybridoma. Hybridomas divide
indefinitely because they have the gene from the myeloma cell. They can produce
large amounts of antibodies because they have the gene from the lymphocyte.
Monoclonal antibodies are used to diagnose streptococcal bacteria and
chlamydial infections. Some over the counter pregnancy tests use monoclonal
antibodies to detect the hormones found in urine during pregnancy.Chemical Messengers
Cells in the immune system communicate with each other by using chemical
messengers sending signals to trigger activities. These chemical messengers are
known as cytokines. There are 60 known cytokines.(^218) CHAPTER 14 Immunity