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The Immune System:
Adaptive Body Defenses
Part B
Human Anatomy & Physiology, Sixth Edition
Elaine N. Marieb
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Adaptive (Specific) Defenses - know
The adaptive immune system:
 Recognizes specific foreign (nonself) substances
 Acts to immobilize, neutralize, or
destroy foreign substances
 Amplifies inflammatory response
and activates complement
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Adaptive Immune Defenses - know
 The adaptive immune system is
antigen-specific, systemic (entire
body), and has memory
 It has two separate but overlapping
arms
 Humoral, or antibody-mediated
immunity (B lymphocytes)
 Cellular, or cell-mediated
immunity (T lymphocytes)
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Antigens - know
 Substances that can mobilize the
immune system and provoke an
immune response
 The ultimate targets of all immune
responses are mostly large,
complex molecules not normally
found in the body (non-self)
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Complete Antigens have important functional
properties – know definitions, examples
 Immunogenicity – the ability to
stimulate proliferation of specific
lymphocytes and antibody
production
 Reactivity – the ability to react
with the products of the activated
lymphocytes and the antibodies
released in response to them
Complete antigens include foreign
protein, nucleic acid, some lipids,
and large polysaccharides
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Haptens (Incomplete Antigens) – know
differences from complete antigens, examples
 Small molecules, such as peptides,
nucleotides, and many hormones, that are
not immunogenic alone but are reactive
when attached to protein carriers
 If they link up with the body’s proteins,
the adaptive immune system may
recognize them as foreign and mount a
harmful attack (allergy, autoimmunity)
 Haptens are found in penicillin, poison
ivy, dander, some detergents, and
cosmetics
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Antigenic Determinants - know
Only certain parts of an entire antigen are
immunogenic
Antibodies and activated lymphocytes bind to
these antigenic determinants
Most naturally occurring antigens have many
antigenic determinants that:
 Mobilize several different lymphocyte
populations
 Form different kinds of antibodies against
it
Large, chemically simple molecules (e.g.,
plastics) have little or no immunogenicity
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Antigenic Determinants - illustration
Figure 21.6
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Self-Antigens: MHC Proteins - know
 Our cells are dotted with protein molecules
(self-antigens) that are not antigenic to us
but are strongly antigenic to others
 One type of these, MHC proteins (Major
Histocompatability complex), mark a cell as
“self”
 The two classes of MHC proteins are:
 Class I MHC proteins – found on virtually
all body cells bind to T cells
 Class II MHC proteins – found on certain
cells in the immune response (B cells,
macrophages, monocytes and dendritic
cells) or “antigen presenting cells”
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
MHC Proteins – know
 Are coded for by genes of the major
histocompatibility complex (MHC) and
are unique to an individual
 Each MHC molecule has a deep
groove that binds and “displays” a
peptide, which is a normal cellular
product of protein recycling
 In infected cells, MHC proteins bind to
fragments of foreign antigens, which
play a crucial role in mobilizing the
immune system
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Peptide antigen in MHC groove - understand
Top view
MHC molecule
Peptide
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Side view, MHC groove - illustration
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
MHC Restriction - know
Antigens (Ag) are recognized as a complex
of antigenic peptide and a specific MHC
molecule molecule
This co-recognition of peptide and MHC
molecule is known as MHC restriction
because the MHC molecule is said to
“restrict” the ability of the T cell to
recognize antigen
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
MHC Restriction – know concept
T cell recognition and activation requires
correct combination of antigen + MHC molecule
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Cells of the Adaptive Immune System - know
1. Two types of lymphocytes that respond to Ag

B lymphocytes – oversee humoral immunity

T lymphocytes – non-antibody-producing cells
that constitute the cell-mediated arm of
immunity
2. Antigen-presenting cells (APCs):

Do not respond to specific antigens

Degrade proteins, bind antigen fragments to
MHC molecules, “display” them to T and B cells

Needed to produce a response from a B and T
cell
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
B and T Lymphocytes - know
 Immature lymphocytes released from
bone marrow are essentially identical
 Whether a lymphocyte matures into a B
cell or a T cell depends on where in the
body it becomes “immunocompetent” or
“educated” to recognize self vs nonself
 B cells mature in the bone marrow
 T cells mature in the thymus
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Antigen-Presenting Cells (APCs) - know
 Major rolls in immunity are:
 To engulf and degrade particles
 To present fragments of antigens on their
own surfaces, to be recognized by T cells
 Major APCs are dendritic cells (DCs),
macrophages, and activated B cells
 The major initiators of adaptive immunity are
DCs, which actively migrate to the lymph
nodes and secondary lymphoid organs and
present antigens to T and B cells
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Macrophages and Dendritic Cells - understand
Secrete soluble proteins that activate T cells
Activated T cells in turn release chemicals
that:
 “Rev up” the maturation and mobilization
of DCs
 Cause “resting” macrophages to become
“activated” macrophages, which are
insatiable phagocytes that secrete
bactericidal chemicals
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Adaptive Immunity: Summary - understand
Defensive system that uses lymphocytes,
APCs, and specific molecules to identify and
destroy nonself particles
Its response depends upon the ability of its cells
to:
 Recognize foreign substances (antigens) by
binding to them
 Communicate with one another so that the
whole system mounts a response specific
to those antigens
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
PowerPoint® Lecture Slides prepared by Vince Austin, University of Kentucky
Components Of The
Immune System
Human Anatomy & Physiology, Sixth Edition
Elaine N. Marieb
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Cellular components of the immune system illustration
All develop
from the
pluripotent
hematopoietic
stem cell.
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Cellular components - know
The cellular components of the immune
system are:
1. Lymphocytes
2. Monocytes/Macrophages
3. Dendritic cells
4. Granulocytes
5. Mast cells
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Cellular components - know
1. Lymphocytes
- Constitute 20-40% of the white blood cells
and 99% of the lymph.
- Lymphocytes are divided into 3 subsets:
a. T lymphocytes ( 60-80% )
b. B Lymphocytes (10-20%)
c. Natural Killer (NK) cells (10%)
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
a. T Lymphocytes - understand
Generated from immature precursors in the
thymus (located in chest, over heart).
- Mature in the thymus, hence they are named
T lymphocytes (T = thymus derived).
- Also found in T-cell zones of the peripheral
lymphoid organs such as the spleen, tonsils
and lymph nodes.
- Lymphocytes can be distinguished by their
expression of surface CD (“cluster of
differentiation”) molecules.
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Lymphocyte
lymphocyte
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Major Histocompatibility Complex (MHC) understand
Collection of genes located on
chromosome 6 in humans.
Genes codes for 2 major classes of
molecules:
i. Class I MHC
ii. Class II MHC
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Subsets of T cells – know definitions
Based on the expression of surface
molecules, T-cells are divided into 2 subsets:
CD4 Cells (helper T cells, TH )
CD8 Cells (cytotoxic T cells, TC )
- CD4 molecules bind to MHC II during
antigen presentation.
- CD8 molecules bind to MHC I during
antigen presentation.
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
T-Cell Receptor Complex - illustration
CD4 T cells bind
CD8 T cells bind
Class II molecules
Class I molecules
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
How antigens appear on cell surfaces - know
Cells digest proteins into short 5-10
amino acid long peptide antigens
Antigens appear on cell surfaces as
combinations of the cell’s own MHC
molecules + the peptide
MHC = major histocompatibilty
complex molecules
There are two classes of MHC
molecules: class I and class II
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Processing and Presentation of Endogenous
and Viral antigens - illustration
MHC Class I
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Structure of Class I MHC - understand
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Processing and Presentation of Exogenous
Antigen - illustration
MHC Class II
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Structure of Class II MHC - understand
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
b. B Lymphocytes - understand
- Develop from immature precursors in the
bone marrow, hence the name B
lymphocyte.
- Also present in the peripheral lymphoid
organs, such as the spleen, lymph nodes,
tonsils and extra-lymphatic organs such as
gastrointestinal tract.
- Membrane bound Ig immunoglobulins
serve as B-cell receptors.
- Products of B cells are also secreted Ig
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Structure of an Immunoglobulin (Ig) molecule,
also called an antibody molecule - know
Varies,
antigenspecific
Same
for class
of Ig
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
c. Natural Killer (NK) cells - understand
- Cytoplasm contains a large number of
granules.
- Also referred to as Large Granular
Lymphocyte.
- Do not have receptors for antigen binding
on their cell surface.
- Can kill tumor cells, virus infected cells
without prior sensitization (exposure to
them).
- Destroy cells based on what they lack
instead of what they express
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings