THE IMMUNE SYSTEM
I.
Nonspecific defenses against infection include the skin and
mucous membranes, phagocytic cells, and antimicrobial proteins
a. Nonspecific defense means that they don’t distinguish between
microbes
b. The skin is the first line of defense
c. The respiratory and digestive systems are open to the
environment; lined with mucus to prevent bacterias (microbes)
from entering
d. If microbes do enter the body cells or tissues then
i. Neutrophils and monocytes attack foreign body
1. Phagocytic cells
ii. MACROPHAGES  large monocytes that wander
actively through interstitial fluid
iii. NATURAL KILLER CELLS  attack cancer cells and
infected body cells
iv. INTERFERONS  proteins produced by virus-infected
cells that help other cells resist viruses
1. Virus infection activates the interferon gene; while
cell eventually dies it helps other cells avoid viral
infection for a short time
v. COMPLEMENT PROTEINS  antimicrobial proteins
that may coat surface of microbes making it easier for
macrophages to engulf the microbes; may cut lethal hole
in microbe membrane; also amplify the inflammatory
response
II.
The inflammatory response mobilizes nonspecific defense forces
a. INFLAMMATORY RESPONSE  major component of our
nonspecific defense system
i. Damaged cells release chemical alarm signals like
HISTAMINE
ii. Chemicals spark the mobilization of various defenses
1. HISTAMINE  dilates the blood vessels and
making them leakier
iii. The white blood cells gathered in the area engulf the
bacteria and the remains of any damaged or dead cells
b. Inflammatory response helps prevent spread of infection by
releasing clotting factors
c. Inflammatory response may be localized or widespread (ex.
Fever)
d. Widespread inflammation can be dangerous (ex. SEPTIC
SHOCK  bacterial infection that brings about overwhelming
inflammatory response)
III.
The lymphatic system becomes a crucial battleground during
infection
a. LYMPHATIC SYSTEM  consists of a branching network of
vessels, numerous lymph nodes (sac-like organs packed with
the white blood cells called lymphocytes), the tonsils and
adenoids, the appendix and the spleen
i. Also includes the bone marrow and thymus (sites where
white blood cells develop)
ii. 2 main functions
1. Return tissue fluid to the circulatory system
2. Fight infection
b. LYMPH  fluid carried in the lymphatic vessels; similar to
interstitial fluid but less oxygen and nutrients
c. *Swollen glands are the result of lymph nodes making extra
lymphocytes to fight infection
IV.
The immune response counters specific invaders
a. IMMUNE SYSTEM  recognizes and defends against
invading microbes and against cancer cells
b. ANTIGEN  a molecule that elicits an immune response
c. ANTIBODY  a protein found in blood plasma that attaches to
one particular kind of antigen and helps counter its effects
d. Immune system has a remarkable “memory”; once it encounters
an antigen it remembers it and can combat it very quickly
e. IMMUNITY  resistance to specific invaders
i. Can be acquired naturally or by VACCINATION
1. VACCINE  harmless variant of a diseasecausing microbe
a. Stimulates the immune system to mount
defenses against the variant
ii. ACTIVE IMMUNITY  body is stimulated to produce
its own antibodies
iii. PASSIVE IMMUNITY  body is given antibodies (not
permanent)
1. Fetus gets from mother, direct shot of antibodies
V.
Lymphocytes mount a dual defense
a. LYMPHOCYTES  white blood cells that spend most of their
time in the tissues and organs of the lymphatic system
b. B CELLS  arise from immature lymphocytes that develop in
the bone marrow
i. Gives rise to HUMORAL IMMUNITY  immunity
occurring in the body fluids
c. T CELLS  arise from immature lymphocytes that develop in
the thymus
i. Gives rise to CELL-MEDIATED IMMUNITY  attacks
infected cells
d. ANTIGEN RECEPTORS  molecules capable of binding are
specific type of antigen
VI.
Antigens have specific regions where antibodies bind to them
a. ANTIGENIC DETERMINANTS  localized regions on the
surface of an antigen recognized by antibodies
VII. Clonal selection musters defensive forces against specific antigens
a. CLONAL SELECTION  attachment of an antigen to a
specific lymphocytes causes multiplication of that lymphocyte
via mitosis
VIII. The initial immune response results in a type of “memory”
a. It takes to exposures to a antigen to mount the strongest
immune response
b. PRIMARY IMMUNE RESPONSE  occurs when
lymphocytes are first exposed to an antigen and form a clone of
effector cells
c. SECONDARY IMMUNE RESPONSE  after primary;
second exposure elicits faster, stronger response
d. MEMORY CELLS  made at same time as effector cells;
differ in structure and function; may last for decades
IX.
Overview: B cells are the main warriors of humoral immunity
a. PLASMA CELLS  another name for effector B cells, the
ones producing antibodies
X.
Antibodies are the weapons of humoral immunity
a. Antibody has 2 related functions
i. Recognize and bind to certain antigens
ii. Assist in neutralizing the antigen
b. ANTIGEN-BINDING SITE  region of the molecule
responsible for the antibody’s recognition-and-binding function
XI.
Antibodies mark antigens for elimination
a. Antibodies bind to form antibody-antigen complex which
allows for antigen destruction
XII. Monoclonal antibodies are powerful tools in the lab and clinic
a. MONOCLONAL ANTIBODIES  all the cells producing the
antibodies are descendants of a single cell and therefore are
identical
i. Great promise in medicine and research
XIII. T cells mount the cell-mediated defense and aid humoral immunity
a. 2 main kinds of T cells
i. CYTOTOXIC T CELLS  attack body cells that are
infected with pathogens
ii. HELPER T CELLS  help activate cytotoxic T cells and
macrophages, even help stimulate B cells to produce
antibodies
b. Cytotoxic T cells bind to antigen
i. When bound it causes the production of PERFORIN
1. PERFORIN  protein that cuts holes in
membrane
2. Allows other proteins to enter and cause death of
antigen
XIV. Cytotoxic T cells may help prevent cancer
a. Cytotoxic T cells monitor cells and destroy cancerous ones
b. Why it stops working is a mystery
XV. The immune system depends on our molecular fingerprints
a. MAJOR HISTOCOMPATIBILITY COMPLEX (MHCs) 
group of self-protein genes
i. Proteins found on own cells; mark them as “off-limits” to
immune systems
XVI. Malfunction or failure of the immune system causes disease
a. AUTOIMMUNE DISEASES  results when the immune
system goes awry and turns against the body’s own molecules
(ex. LUPUS)
b. IMMUNODEFICIENCY DISEASES  lack one or more
components of the immune system, and are susceptible to
infections ordinarily would not cause a problem (ex. Hodgkin’s;
AIDS)
XVII. Allergies are overreactions to certain environmental antigens
a. ALLERGIES  abnormal sensitivities to antigens in our
surroundings
b. ALLERGENS  antigens that cause allergies
c. MAST CELLS  normal body cells that produce histamine
and other chemicals that trigger the inflammatory response
d. ANTIHISTAMINES  drugs that interfere with histamine’s
action and give temporary relief from an allergy
e. ANAPHYLACTIC SHOCK  very severe (possibly fatal)
allergic reaction
i. Can be countered with an injection of epinephrine
XVIII. AIDS leaves the body defenseless
a. HIV destroys the helper T cells; turning off humoral and cell
mediated immune responses
b. Leaves the body defenseless and open to opportunistic
infections
c. AIDS doesn’t kill, opportunistic infections due