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Immune System
(immunus = to be free)
•primary defense against diseasecausing organisms
An overview of the body's
defenses
Lymphatic System
(lympha = clear fluid (Latin)
•consists of lymphatic vessels and
lymph organs; lymph capillaries
take up excess tissue fluid and
return it to the bloodstream
•it works with the immune system
to help defend the body against
disease
The Human Lymphatic System
(pharyngeal
tonsils)
Once lymph fluid enters the
lymphatic vessels, it is called lymph.
The capillaries merge to form
lymphatic vessels that merge before
entering one or two ducts: the
thoracic duct or the right lymphatic
duct
First Line of Defense – External
Barriers
•Skin and Mucus Membranes
•Low pH of skin
•Saliva and tears contain
lysozyme.
Red bone marrow is the site of
origin for all types of blood cells,
including the five major types of white
blood cells:
Neutrophils (65%) Lymphocytes (25%) Monocytes
(6%) Eosinophils (3%) Basophils (1%)
Never Let Monkeys Eat Bananas!
In a child, most bones have red bone
marrow, but in adults it is present only
in bones of the skull, sternum, ribs,
clavicle, pelvis, and vertebral column.
Second Line of Defense (Non
specific Internal Defenses) involves
phagocytic white blood cells.
1) Neutrophils and monocytes, change
shape to squeeze through capillary
walls and enter tissue fluid.
2) As they leave the blood and enter
the tissues,monocytes differentiate into
macrophages.
Phagocytosis by a Macrophage
Macrophage
Bacteria
3) Eosinophils phagocytize and
contain a number of destructive
enzymes within the cytoplasm
and defend against large
parasites.
Antimicrobial Proteins
•Mast cells release histamine, which
causes the capillaries to dilate and
become permeable, which allows proteins to escape into the tissues
causing swelling
Histamine is stored
in mast cells in
connective tissues.
Histamine increases
permeability of
capillaries
The complement system, is a
number of plasma proteins, that
attracts (“complements”)
phagocytes to the scene; some bind
to the surface of pathogens
already coated with antibodies
Interferon is a protein produced
by virus-infected cells. It binds
to receptors of noninfected cells,
causing them to prepare for
possible attack by producing
substances that interfere with
viral replication; it is species
specific.
A simplified view of the
inflammatory response
Natural (NK) Killer Cells kill the
body’s infected cells. They have
no specificity and no memory.
Third Line of Defense (pathogenspecific recognition)
Immunity is primarily the result of
action of B lymphocytes and T
lymphocytes. B cells mature in the bone
marrow and T cells mature in the
thymus gland and move to the blood.
B cells produce antibodies whereas T
cells attack cells that produce nonself
proteins
The Development of Lymphocytes
Can become any
type of blood cell
Clonal Selection- primary immune response
A plasma cell is a mature B cell
that mass-produces antibodies
against a specific antigen.
The clonal selection theory states
that the antigen selects which
lymphocyte will undergo clonal
selection and produce more
lymphocytes bearing the same type
of antigen receptor.
Immunological Memory
Antibodies bind to specific areas of
antigens
The Structure of a Typical
Antibody Molecule
Characteristics of B Cells
• Antibody-mediated immunity against
bacteria
• Produced and mature in the bone
marrow
• Reside in spleen and lymph nodes;
circulate in blood and lymph
• Directly recognize antigen and then
undergo clonal selection
 Clonal expansion produces antibodysecreting plasma cells as well as
memory B cells
Characteristics of T Cells
• Cell-mediated immunity against
viruses and cancer cells
• Produced in bone marrow; mature
in thymus
• Antigen must be presented in
groove of a MHC molecule
• Cytotoxic T cells destroy nonself
protein-bearing cells
• Helper T cells secrete cytokines
that control the immune response
The interaction of T cells with
MHC molecules
Cell-mediated Immune Response
1) Cytotoxic T Cells can bring about
the destruction of antigen-bearing
cells, such as virus-infected cells
2) Helper T Cells regulate immunity
by secreting cytokines, which are
chemicals stimulating other immune
cells.
Effector Mechanisms of Humoral Immunity
Opsonization:
bound antibodies
enhance macrophage attachment
or phagocytosis
of microbes
How Antibodies Work:
•agglutination (clumping) – makes it
easier for phagocytes to eat
•neutralization – blocking sites on
an antigen
•precipitation – phagocytes ingest
•complement (proteins) – get
activated by antibodies
An Overview of Acquired Immune Response
Specialized Lymphocytes Attacking a
Cancer Cell
A Cytotoxic T Cell Has Lysed a Cancer Cell
Cytotoxic (Killer)
T Cell
An Overview of the Immune Responses
A T cell Infected with HIV (gray particles)
HIV on a Lymphocyte
Detail of HIV on Lymphocyte
Compare and contrast B cell
and T cell action.
Immune System:
Name one component of each of
the three lines of defense.
How are antigens related to
antibodies?
How do interferons protect the
body against viruses?
How is lymph returned to the
bloodstream?
Name two places where white
blood cells are highly
concentrated.