The Immune System 529B. Tolerance to self-antigens occurs in prenatal development
by destruction of T lymphocytes in the thymus that have
specificity for the self-antigens.
- This is called clonal deletion.
- Clonal energy, or the suppression of lymphocytes, may
also occur and may be responsible for tolerance to
self-antigens by B lymphocytes. - When tolerance mechanisms are ineffective, the immune
system may attack self-antigens to cause autoimmune
diseases.
C. Passive immunity is provided by the transfer of antibodies
from an immune to a nonimmune organism. - Passive immunity occurs naturally in the transfer of
antibodies from mother to fetus. - Injections of antiserum provide passive immunity to
some pathogenic organisms and toxins.
D. Monoclonal antibodies are made by hybridomas, which
are formed artificially by the fusion of B lymphocytes and
multiple myeloma cells.
15.5 Tumor Immunology 519
A. Immunological surveillance against cancer is provided
mainly by killer T lymphocytes and natural killer cells.
- Cancerous cells dedifferentiate and may produce fetal
antigens. These or other antigens may be presented to
lymphocytes in association with abnormally produced
class-2 MHC antigens.
2. Natural killer cells are nonspecific, whereas T
lymphocytes are directed against specific antigens
on the cancer cell surface.
3. Immunological surveillance against cancer is weakened
by stress.15.6 Diseases Caused by the Immune
System 521
A. Autoimmune diseases may be caused by the production
of autoantibodies against self-antigens, or they may result
from the development of autoreactive
T lymphocytes.
B. Immune complex diseases are those caused by the
inflammation that results when free antigens are bound to
antibodies.
C. There are two types of allergic responses: immediate
hyper-sensitivity and delayed hypersensitivity.
1. Immediate hypersensitivity results when an
allergen provokes the production of antibodies in the
IgE class. These antibodies attach to tissue mast cells
and stimulate the release of chemicals from the
mast cells.
2. Mast cells secrete histamine, leukotrienes, and
prostaglandins, which are believed to produce the
symptoms of allergy.
3. Delayed hypersensitivity, as in contact dermatitis, is a
cell-mediated response of T lymphocytes.Test Your Knowledge
- Which of these offers a nonspecific defense against viral
infection?
a. Antibodies
b. Leukotrienes
c. Interferon
d. Histamine
Match the cell type with its secretion.
- Killer T cells a. Antibodies
- Mast cells b. Perforins
- Plasma cells c. Lysosomal enzymes
- Macrophages d. Histamine
- Which of these statements about the F ab portion of antibodies
is true?
a. It binds to antigens.
b. Its amino acid sequences are variable.
c. It consists of both H and L chains.
d. All of these are true. - Which of these statements about complement proteins C3 a
and C5 a is false?
a. They are released during the complement fixation process.
b. They stimulate chemotaxis of phagocytic cells.
REVIEW ACTIVITIES
c. They promote the activity of phagocytic cells.
d. They produce pores in the victim cell membrane.- Mast cell secretion during an immediate hypersensitivity
reaction is stimulated when antigens combine with
a. IgG antibodies.
b. IgE antibodies.
c. IgM antibodies.
d. IgA antibodies. - During a secondary immune response,
a. antibodies are made quickly and in great amounts.
b. antibody production lasts longer than in a primary response.
c. antibodies of the IgG class are produced.
d. lymphocyte clones are believed to develop.
e. all of these apply. - Which of these cell types aids the activation of T
lymphocytes by antigens?
a. Macrophages
b. Neutrophils
c. Mast cells
d. Natural killer cells