Chapter 37
Immunity
Sections 7-12
Albia Dugger • Miami Dade College
37.7 Overview of Adaptive Immunity
• Vertebrate adaptive immunity adapts to different antigens an
individual encounters during its lifetime
• Lymphocytes and phagocytes interact to effect four defining
characteristics: self/nonself recognition, specificity, diversity,
and memory
4 Characteristics
of Adaptive Immune Responses
1. Self/Nonself recognition is based on the ability of T cell
receptors to recognize self (MHC) markers; TCRs and other
antigen receptors recognize nonself, in the form of antigen
2. Specificity means the adaptive immune response can be
tailored to combat specific antigens
4 Characteristics
of Adaptive Immune Responses
3. Diversity refers to the billions of different antigen receptors
that a person’s B and T cells can make
4. Memory refers to the capacity of the adaptive immune
system to “remember” an antigen – the second time an
antigen shows up, the response is faster and stronger
Two Arms of Adaptive Immunity
• Antibody-mediated immune response
• B cells produce antibodies that bind to specific antigen
particles in blood or interstitial fluid
• Cell-mediated immune response
• Cytotoxic T cells and NK cells detect and destroy infected
or altered body cells
Antigen Processing
• Once a B or T cell recognizes and binds to a specific antigen,
it begins to divide by mitosis
• All descendent cells recognize the same antigen
• T cells do not recognize an antigen unless it is presented by
an antigen-presenting cell
• Macrophages, B cells, and dendritic cells digest particles and
display antigen-MHC complexes
Antigen Processing
1
7
2
6
lysosome
5
3
MHC molecule
4
Intercepting Antigen
• A dendritic cell or macrophage migrates to a lymph node,
where it presents antigen to T cells
• The T cell secretes cytokines, which signal other B or T cells
with the same antigen receptor to divide and differentiate
• Effector cells are differentiated B and T cells that act at once
to fight infection
• Memory cells are long-lived B and T cells reserved for future
encounters with the same antigen
Clearing Out Antigen
• Effector cells destroy most antigen-bearing agents
• Antibody–antigen complexes form large clumps that are
quickly cleared from the blood by the liver and spleen
• Complement proteins assist in the cleanup
memory cells
memory cells
B or
T cell
effector cells
effector cells
primary
secondary
immune response immune response
first
exposure
second
exposure
Figure 37-15 p661
Take-Home Message:
What is the adaptive immune system?
• Phagocytes and lymphocytes interact to bring about
vertebrate adaptive immunity, which has four defining
characteristics: self/nonself recognition, specificity, diversity,
and memory.
• The two arms of adaptive immunity work together. Antibodymediated responses target antigen in blood or interstitial fluid;
cell-mediated responses target altered body cells.
37.8 The Antibody-Mediated
Immune Response
• Antibody-mediated immune response
• Antigen activates naïve B cells and dendritic cells
• Naïve T cell binds to APC and differentiates into effector
and memory helper T cells
• Helper T cells bind antigen-MHC complexes on activated
B cell and secrete cytokines
• B cell differentiates into effector B cells, which produce
antibodies, and memory B cells
2
1
dendritic
cell
bacterium
naive
B cell
complement
antigenpresenting
dendritic
cell
naive
helper
T cell
4
B cell
cytokines
3
memory
helper T
cell
effector
helper T
cell
5
memory
B cell
effector
B cell
6
Stepped Art
Figure 37-16a p662
Antibody Action
• Circulating antibodies attach themselves to pathogens
• An antibody coating prevents bacteria from attaching to body
cells and brings them to the attention of phagocytic cells
• Antibodies also cause agglutination of foreign cells – clumps
are removed from the circulatory system by the spleen
• Antibodies also initiate a complement cascade in innate
immune responses
Lymphocyte Activity in a Lymph Node
Clonal Selection
• Only B and T cells with receptors that bind antigen divide
(clone) and differentiate into effector and memory cells
• Primary response produces memory B and T cells; secondary
response is stronger and faster
antigen
Antigen binds only to a
matching B cell receptor.
mitosis
clonal
population
of effector
B cells
Many effector B cells secrete many antibodies.
Figure 37-18 p663
Take-Home Message: What happens during an
antibody-mediated immune response?
• T cells, B cells, and antigen-presenting cells carry out an
antibody-mediated immune response.
• Effector B cells that form during an antibody-mediated
immune response make and secrete antibodies that
recognize and bind antigen-bearing particles in blood or
tissue fluids. Antibody binding can neutralize a pathogen or
toxin and facilitate its elimination from the body.
• Memory cells also form, and these are reserved for a potential
future encounter with the antigen.
37.9 The Cell-Mediated Response
• Cell-mediated immune response
• Dendritic cell ingests altered body cell, displays antigenMHC complexes, and migrates to lymph node
• Naïve helper T and cytotoxic T cells bind to APC
• Activated helper T divides and differentiates into memory
and effector cells; cytokines signal division of activated
cytotoxic T cells
• Cytotoxic T cells circulate and touch-kill altered body cells
dendritic
cell
1
naive
antigencytotoxic presenting
T cell
dendritic
cell
naive
helper
T cell
3
2
4
activated cytokines effector
helper
cytotoxic
T cell
T cell
memory
cytotoxic
T cell
effector
cytotoxic
T cell
memory
helper
T cell
5
Stepped Art
Figure 37-19a p664
APC and T Cell
TCR Binding
Antigen/TCR/ MHC Complex
Cytotoxic T Cells
• Cytotoxic T cells kill body cells displaying antigen-MHC
markers – including cancer cells that display altered body
proteins, and body cells infected with intracellular pathogens
• T cell releases protein-digesting enzymes and perforins
• Perforins assemble into complexes that insert themselves into
a plasma membrane as a transmembrane channel; enzymes
enter the cell and induce it to commit suicide
Natural Killer Cells
• Cytokines secreted by helper T cells also stimulate natural
killer (NK) cell division
• Unlike cytotoxic T cells, NK cells can kill infected cells that are
missing all or part of their MHC markers
Take-Home Message: What happens during a
cell-mediated immune response?
• T cells, NK cells, and antigen-presenting cells carry out a cellmediated immune response.
• Effector cytotoxic T cells and NK cells that form during a cellmediated immune response kill infected body cells or those
that have been altered by cancer.
• Memory cells also form, and these are reserved for a potential
future encounter with the antigen.
37.10 When Immunity Goes Wrong
• An allergy is an immune response to something that is
ordinarily harmless to most people
• Autoimmune disorders occur when an immune response is
misdirected against a person’s own healthy body cells
• In immunodeficiency, the immune response is insufficient to
protect a person from disease
Allergies
• Allergy
• An immune response to a typically harmless substance
(allergen)
• First exposure stimulates production of IgE, which
becomes anchored to mast cells and basophils
• Later exposure stimulates secretion of histamine and
cytokines that initiate inflammation
Allergies: Hives
Allergies: Hay Fever
Overly Vigorous Responses
• Acute illnesses arise when mechanisms that limit immune
responses fail
• Severe episodes of asthma or septic shock occur when too
many neutrophils degranulate at once
• Anaphylactic shock is a severe and potentially fatal allergic
reaction
Anaphylactic Shock
Autoimmune Disorders
• Sometimes lymphocytes and antibodies fail to discriminate
between self and nonself
• Autoimmune response is an immune response that is
misdirected against the person’s own tissues
• Autoimmune diseases include rheumatoid arthritis, Graves’
disease, and multiple sclerosis
Table 37-4 p667
Immunodeficiency
• In immunodeficiency, the immune response is insufficient to
protect a person from disease
• Primary immune deficiencies such as SCIDs and ADA are
present at birth
• Secondary immune deficiency such as AIDS results from
exposure to an outside agent, such as a virus
Take-Home Message: What happens when the
immune system does not function properly?
• Normally harmless substances may induce an immune
response in some people. Sensitivity to such allergens is
called an allergy.
• Misdirected or compromised immunity, which sometimes
occurs as a result of mutation or environmental factors, can
have severe or lethal outcomes.
37.11 HIV and AIDS
• Acquired immune deficiency syndrome (AIDS)
• A group of disorders resulting from a failure of the immune
system due to HIV infection
• Includes rare cancers and infections caused by normally
harmless microorganisms
• Human immunodeficiency virus (HIV)
• A retrovirus that attacks specific cells of the immune
system, including helper T cells
Table 37-5 p669
Symptoms
• Early symptoms include fever, enlarged lymph nodes, chronic
fatigue and weight loss, and drenching night sweats
• AIDS results in infections caused by normally harmless
microorganisms, and cancers such as Kaposi’s sarcoma
Transmission of HIV through Mother’s Milk
Kaposi’s Sarcoma
HIV Revisited
• HIV is a retrovirus with a lipid envelope consisting of a small
piece of the host’s plasma membrane
• Viral proteins enclose two RNA strands and reverse
transcriptase enzymes
• Reverse transcriptase copies viral RNA into DNA, which
becomes integrated into the host cell’s DNA
• The host then begins to produce viral proteins
Cellular Struggle
• HIV infects macrophages, dendritic cells, and helper T cells
• For years or decades, IgG antibodies keep the level of HIV in
the blood low, and cytotoxic T cells kill HIV-infected cells
• Eventually the immune system becomes less effective at
fighting the virus, and HIV demolishes the immune system
• Secondary infections and tumors kill the patient
Infected T Cell with Budding HIV Virus
Transmission and Testing
• Common modes of HIV transmission include unprotected sex,
mother to child, and shared syringes
• Most AIDS tests check blood, saliva, or urine for antibodies
that bind to HIV antigens
• One test can detect viral RNA at about eleven days after
exposure
• Home test kits are not reliable
Treatments
• Drugs
• There is no cure; protease inhibitors and reverse
transcriptase inhibitors can slow its progress
• Education
• The best option for preventing the spread of HIV is
teaching people how to avoid being infected
Take-Home Message:
What is AIDS?
• AIDS is a secondary immune deficiency caused by HIV
infection.
• HIV infects lymphocytes and so cripples the human immune
system.
Video : Vaccinating Against Cancer
37.12 Vaccines
• Immunization
• The administration of an antigen-bearing vaccine designed
to elicit immunity to a specific disease
• Vaccine (active immunization)
• A preparation containing an antigen that elicits a primary
immune response
• Passive immunization
• Administration of antibodies; no immune response
The First Vaccine
• Benjamin Jesty showed that people deliberately infected with
cow pox became immune to the more deadly smallpox
• In 1796, Edward Jenner used cowpox to created the first
vaccine against smallpox
• The vaccine has now eradicated smallpox
A Case of Smallpox
Table 37-6 p670
Progress on an HIV Vaccine
• HIV vaccines are notoriously ineffective because the HIV
virus has a very high mutation rate
• One promising strategy involves reverse engineering HIV
antibodies isolated from people with AIDS
• Genes encoding effective antibodies are also being inserted
into viral vectors for use in gene therapy
Take-Home Message:
How do vaccines work?
• Immunity to many diseases can be elicited by administering
antigen-bearing vaccines, a process called immunization
Video: Restarting the Immune System