NOTES:
CH 43, part 1
The Immune
System Nonspecific &
Specific
Defenses
(43.1-43.2)
The lymphatic system is closely associated
with the cardiovascular system.
LYMPHATIC PATHWAYS
Lymphatic capillaries
● microscopic, closed-end
tubes that extend
into intercellular spaces
● receive LYMPH through
their thin walls
(LYMPH = the fluid of the lymphatic
system)
● lymphatic capillary networks parallel blood
capillary networks
Functions of lymph:
1) returns to the bloodstream small proteins
that leaked out of blood capillaries
2) transports foreign particles, such as
bacteria or viruses, to lymph nodes
**if lymph movement is impaired, it may
accumulate within the intercellular
spaces and produce EDEMA, or
swelling
(example: after surgery, the lymphatic
vessels and lymph nodes around the
wound may be damaged, causing fluid to
accumulate around the surgery site and
lead to swelling)
Lymph Nodes:
Structure of a Lymph Node:
● lymph nodes are subdivided into nodules
● nodules contain
masses of
lymphocytes
and macrophages
Locations of Lymph Nodes:
● lymph nodes aggregate in groups or
chains along the paths of larger lymphatic
vessels
Functions of Lymph Nodes:
● filter potentially harmful foreign particles from
lymph
● are centers for the production of lymphocytes
(attack invading viruses, bacteria, parasites,
etc.)
● contain phagocytic cells
(engulf and destroy foreign
substances, damaged
cells, cellular debris)
THYMUS AND SPLEEN
Thymus:
● shrinks slowly after puberty
● contains large numbers of
LYMPHOCYTES which
mature into T CELLS (T
lymphocytes) – important in
providing immunity (more on
these later…)
Spleen:
● largest lymphatic organ
● resembles a large lymph node (divided
into lobules)
Spleen:
● spaces within splenic
lobules are filled with blood
● contains many macrophages,
which destroy/remove foreign
particles and damaged RBCs
from the blood
**the spleen filters blood as
the lymph nodes filter
lymph!**
So, how does the body
defend itself???
The body has nonspecific and
specific defenses against
infection / pathogens.
Why don’t
YOU have
mold on your
skin???
● PATHOGEN: a disease-causing agent;
causes infection
-pathogens include:
viruses
fungi
bacteria
protozoans
Nonspecific Defenses:
● general defense
● provide protection against
many different pathogens
● involve physical and
chemical barriers, fever,
inflammation, phagocytosis
Specific Defenses:
● very precise
● target certain pathogens
● also known as IMMUNITY
● involve specialized
lymphocytes (T cells and B
cells) that recognize and
respond to specific
pathogens
**nonspecific defenses are
quick to respond; specific
defenses are slower-torespond
NONSPECIFIC DEFENSES
1) Species Resistance
● each species is resistant to certain
diseases that may affect other species
● examples: measles, mumps,
gonorrhea, and syphilis infect
humans but not other animal species
● one species may be resistant to a disease that
affects another species because its tissues
somehow fail to provide a suitable environment for
the pathogen (temperature, chemical environment,
receptors, etc.)
2) Mechanical Barriers = FIRST
LINE OF DEFENSE
● mechanical barriers / physical barriers
include:
-skin (and associated hairs)
-mucous membranes
-fluid (sweat and mucus)
● as long as they remain intact, they can
keep out many pathogens
SKIN
MUCUS
SALIVA
**all other
“nonspecific
defenses” are
considered the
SECOND LINE
OF DEFENSE
3) Chemical Barriers
● gastric juice: contains
hydrochloric acid and
enzymes (e.g. pepsin) that are
lethal to pathogens
● tears: contain the enzyme
LYSOZYME
(which has antibacterial action)
● the salt in perspiration
accumulates on the skin and
kills bacteria on the skin
3) Chemical Barriers (cont.)
INTERFERONS:
chemicals released by
virus-infected cells;
they stimulate other
immune cells to:
-synthesize antiviral
proteins that stimulate
phagocytosis, block
virus replication
Interferons:
● most effective against cold and flu virus
● now mass-produced by recombinant DNA
technology to be potentially used as
treatment for viral infections and cancer!
3) Chemical Barriers (cont.)
COMPLEMENT
SYSTEM:
● group of 30 proteins;
● catalyze a series of
steps resulting in lysis
of invading microbes
and/or inflammatory
response
4) Fever
● higher body temperature increases the
rate of phagocytic cells
● also lowers iron levels in the blood
(bacteria and fungi require iron, so this
slows their growth)
5) Inflammation
● produces: localized
redness, swelling, heat
and pain
● HISTAMINE and
prostaglandins released
by damaged tissues
attract WBCs to the site
 the mass of WBCs,
bacterial cells, and
damaged tissue forms a
thick fluid called PUS
6) Phagocytosis – removes foreign
particles from the lymph and blood
● the most active
phagocytes in blood are
NEUTROPHILS and
MONOCYTES
● Monocytes give rise to
MACROPHAGES
● MACROPHAGES are found in the
linings of blood vessels in the:
-bone marrow
-liver
-spleen
-lungs
-lymph nodes
EOSINOPHILS:
● kill antibody-coated parasites
Specific Defenses / Immunity
Immune System…
● the body’s “third line of
defense”
● characterized by:
 specificity
 diversity
 self / non-self
recognition
 memory
ANTIGENS…
● ANTIGENS: specific foreign molecules
that trigger an immune response; usually
located on a cell’s surface
-antigens include:
proteins
glycoproteins
polysaccharides
glycolipids
ANTIGENS…
● before birth, body cells sort “self” proteins
and other large molecules
● lymphocytes develop receptors that allow
them to differentiate between nonself
(foreign) and self antigens
● nonself antigens combine with T cell and
B cell surface receptors and stimulate
these cells to cause an immune reaction
LYMPHOCYTES (T and B Cells)
● originate in the red bone
marrow
● some reach the THYMUS,
where they mature into
T CELLS
● others, the B CELLS, mature in
the RED BONE MARROW
● both T cells and B cells reside
in lymphatic tissues and organs
(lymph nodes, spleen, etc.)
LYMPHOCYTE FUNCTIONS
**a lymphocyte must be ACTIVATED
before it can respond to an antigen**
Antigen Presentation:
● Carried out by a group of approx. 20
glycoproteins that make up the
MAJOR
HISTOCOMPATIBILITY
COMPLEX (MHC)
Two main classes of MHC molecules:
● Class I MHC: located on all nucleated body cells
*cytotoxic T cells (TC) bind to fragments of
antigens displayed by class I MHC
● Class II MHC: found only on specialized cells
(macrophages, B cells, activated T cells)
*helper T cells (TH) bind to fragments of
antigens displayed by class II MHC
Antigen-Presenting Cells (APCs):
-cells that take up antigens (B cells,
macrophages);
-engulfed foreign matter binds to a class II
MHC molecule and is conveyed to the outside
of the APC;
-foreign antigen is recognized by a helper T
cells (TH);
-this interaction is enhanced by CD4, a
membrane protein on TH cells.
CD4
*CLONAL SELECTION:
 antigen-specific selection of a lymphocyte;
 activates lymphocytes to divide and
differentiate to produce CLONES of
effector cells & memory cells designed to
eliminate the antigen that provoked the
initial response
SPECIFICITY & MEMORY!
PRIMARY IMMUNE RESPONSE
● PRIMARY IMMUNE RESPONSE: the first
reaction / response to an antigen (first
exposure)
 during this response, antibodies are
produced for several weeks
 antibodies first show up within 5-10 days
 some B cells remain dormant as
MEMORY B CELLS
SECONDARY IMMUNE RESPONSE
● SECONDARY IMMUNE RESPONSE: the
second response (exposure) to an antigen
rapid response due to
memory cells produced
during the first exposure
 antibodies produced within a day or two