Chapter 13 Flashcards
(84 cards)
1
Q
Adaptive immunity is initiated in secondary lymphoid tissues
A
- Lymph carries antigens and infected cells (DCs) to lymph node through afferent vessel.
- B and T cells in lymph node become activated upon encountering antigens.
- B and T cells mature into effector cells with specific functions, such as antibody production from B cells.
- Macrophages residing in lymph nodes filter out antigens and pathogens from lymph to protect blood.
- Lymph fluid and lymphocytes exit through efferent vessel
2
Q
Adaptive immunity: the third and final line of defense
A
• Adaptive immunity acquired only after an immunizing event such as an infection
• B and T lymphocytes undergo a selective process that prepares them for reacting only to one specific antigen or immunogen
• Immunocompetence: the ability of the body to react with countless foreign substances
3
Q
Immunocompetence
A
The ability of the body to react with countless foreign substances
4
Q
Antigen
A
Molecules that can be seen and indemnified by the immune system
5
Q
Antigens and immunogens
A
Antigens: molecules that can be seen and identified by the immune system
• If they provoke a response, they are called immunogens
• Protein or polysaccharide molecules on or inside cells and viruses
• Any exposed or released protein or polysaccharide is potentially an antigen, even those on our own cells:
• Our own antigens usually do not evoke a response from our own immune system
6
Q
Specificity
A
Antibodies are produced against the chickenpox virus and will not function against the measles virus
7
Q
Memory
A
Lymphocytes have been programmed to “recall” the first engagement with the invader and rush to the attack once again
8
Q
Stages of immunologic development and interaction
A
I. Lymphocyte development and clonal deletion
II. Presentation of antigen and clonal selection
- antigen presents and the selection for what reacts with that antigen is completed
III. Challenge of B and T lymphocytes by antigens
IV. T-lymphocyte response: cell-mediated immunity; and B-lymphocyte response: production and activities of antibodies
9
Q
Lymphocyte development
A
• All lymphocytes arise from the same basic stem cell type
• Both cell types migrate to separate areas of lymphoid organs -> dependent on where they are needed
• B and T cells constantly recirculate through the circulatory system and lymphatics, migrating into and out of the lymphoid organs
10
Q
Entrance and presentation of antigens and colonial selections
A
When pathogens carrying antigens cross the first line of defense:
• Resident phagocytes migrate to the site
• Tissue macrophages ingest the pathogen and initiate an inflammatory response
• Dendritic cells ingest the antigen and migrate to the nearest lymphoid organ, where they process and present antigen to T and B lymphocytes
• Gamma-delta cells can be activated by PAMPs
11
Q
Role of markers and receptors in presentation and activation
A
All cells have a variety of different markers on their surfaces for:
• Detection
• Recognition
• Cell communication
These markers play an important role in activating different components of immunity
12
Q
Role of markers and receptors in presentation and activation
MHC
HLA
A
Major histocompatibility complex (MHC): one set of genes that codes for human cell markers or receptors:
• Gives rise to a series of glycoproteins found on all cells except red blood cells
• Also called the human leukocyte antigen (HLA) system
• These markers play a vital role in recognition of self by the immune system and in rejection of foreign tissue
13
Q
Three classes of MHC genes
A
- Class I genes: code for markers that appear on all nucleated cells. They display unique characteristics of self and allow for the recognition of self molecules and the regulation of immune reactions. The system is rather complicated in its details, but in general, each human being inherits a particular combination of class I MHC (HLA) genes in a relatively predictable fashion
• Class II genes: also code for immune regulatory markers. These markers are found on macrophages, dendritic cells, and B cells and are involved in presenting antigens to T cells during cooperative immune reactions
• Class III genes: encode proteins involved with the complement system, among others
14
Q
CD molecules
A
CD: “cluster of differentiation”:
• Over 400 CD molecules have been named
• Many are involved in the immune response
Most important CDs:
• CD3
• CD4
• CD8
15
Q
Lymphocytes receptors
A
- major role is the “accept” or “grasp” antigens in some form:
- B cells have receptors that bind antigens
- T cells have receptors that bind antigens that have been processed and complexed with MHC molecules on the presenting surface
- there are potentially millions and even billions of unique types of antigens
16
Q
How to challenge B and T cells with antigens
A
- when challenges with antigens, both B and T cells proliferate and differentiate
- a clone, or a group of genetically identical cells, are created
- some clones are memory cells that will ensure the future reactiveness against a specific antigen
- B and T cell responses differ
17
Q
The three functions of T cells
A
Helper T cells
Regulatory T cells
Cytotoxic T cells
18
Q
Helper T cells
A
Activate macrophages, assist B-cell processes, and help activate cytotoxic T cells
19
Q
Regulatory T cells
A
Control the T-cell response by secreting anti-inflammatory cytokines or preventing proliferation
- the ability to do enough by not too much
- to kill but not stand out
20
Q
Cytotoxic T cells
A
Lead to the destruction of infected host cells and other “foreign” cells
21
Q
T cells secrete?
A
T cells secrete cytokines to help destroy pathogens, but they DO NOT produce antibodies
22
Q
How do B cells respond to antigens
A
- when activated, B cells divide and give rise to plasma cells
- plasma cells release antibodies into the tissue and the blood
- antibodies attach to the antigen for which they are specific, and the antigen is marked from destruction of neutralization
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Q
B cells
A
Site of maturation: Bone marrow
Specific surface markers: immunoglobulin
Circulation in blood: low numbers
Receptors for antigens: B-cell receptor (immunoglobulin)
Distribution in lymphatic organs: cortex (in follicles)
Does it require antigens presented with MHC: no
The product of antigenic stimulation: plasma cells and memory cells
General functions: production of antibodies to inactivate, neutralize, target antigens
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Q
T cells
A
Site of maturation: thymus
Specific surface markers: T-cell receptor -> several CD molecules
Circulation in the blood: high numbers
Receptors for antigens: t-cell receptor
Distribution in lymphatic organs: paracoritcal sites (interior to the follicles)
Does it require antigen presented with MHC: yes
Product of antigenic stimulation: several types of activated T cells and memory cells
General functions: cells activated to help other immune cells; suppress or kill abnormal cells; mediate hypersensitivity; synthesize cytokines
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What are some specifics events in T-cell development
• Maturation of T cells and development of their receptors is directed by the thymus gland and its hormones
• CD3 receptors: surround the T-cell receptor and assist in binding
• CD4 coreceptors: accessory receptor proteins that helps the T-cell receptor bind to MHC class II molecules
• CD8 coreceptors: found on cytotoxic T cells and helps bind MHC class I molecules
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What are some specifics events in B-cell development
• Develop in the bone marrow
• Naïve lymphocytes circulate in the blood, “homing” to specific sites in the lymph nodes, spleen, and other lymphoid tissue, where they adhere to specific binding molecules and come into contact with antigens throughout life
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How to build immunologic diversity
By the time B and T cells reach lymphoid tissues, each one is equipped to respond to a single unique antigen
Diversity is generated by rearrangement of gene segments that code for antigen receptors on T and B cells:
• Every possible recombination occurs, leading to a huge assortment of lymphocytes
• It is estimated that each human produces antibodies with 10 trillion different specificities
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immunoglobulin (Ig)
- large glycoprotein molecules that serve as the antigen receptors of B cells
- serve as antibodies when secreted
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what is the structure of immunoglobulin
- antigen binding sites
- variable (V) regions
- antigen binding sites -> pockets in the ends of the forks the molecules that can be highly variable in shape so that they can fit a wide range of antigens
- variable (V) regions -> areas of extreme versatility from one clone to another
- light chains, heavy chains, constant (c) regions: amino content does not vary greatly from one antibody to another
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T-cell receptors
belong to the same protein family as the B-cell receptors
similar to B cells:
- formed by genetic modification
- have variable and constant regions
- inserted into the membrane
- have an antigen binding site
relatively small and never secreted
31
clonal selection
- the mechanism by which the exactly correct B or T cell is activated by any incoming antigen
- lymphocyte specifically is preprogrammed, existing in the genetic makeup before an antigen has ever entered the tissues
- each genetically distinct lymphocyte expresses only a single specifically and can react to that chemical epitope
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clonal deletion
- one potentially problematic outcome of random genetic assortment is the development of clones of lymphocytes able to react to self:
- can lead to severe damage
Clonal deletion: process by which any such clones are destroyed during development
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clonal selection and deletion steps
Each genetically unique line of lymphocytes that arises from extensive recombination's of surface proteins is termed a clone. This stage of lymphocyte development does not require the actual presence of foreign antigens.
At the same time, any lymphocytes that develop a specificity for self molecules (and could be harmful) are eliminated from the pool of cells. This is called clonal deletion and leads to immune tolerance.
The specificity for a single epitope is programmed into the lymphocyte and is set for the life of a given cell. The end result is an enormous pool of mature but naive
lymphocytes that are ready to further differentiate under the influence of certain immune stimuli.
When any epitope enters the immune surveillance system, it encounters specific lymphocytes ready to recognize it. This stimulates activation of that clone,
leading to genetic changes that cause it to differentiate into an effector cell. Mitotic divisions then expand it into a larger population of lymphocytes, all bearing the same specificity. This is clonal expansion.
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Stage 2: presentation of antigens - entrance of antigens
to be perceived an an antigen or immunogen, a substance must meet certain requirements in foreignness, shape, size, and accessibility
examples of immunogens:
- whole microbes or their parts
- cells or substances that arise from other humans, animals, plants, and various molecules
- complex proteins and protein-containing molecules are more immunogenic than repetitious polymers composed of a single type of unit
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the antigen categories
most immunogens fall into the following chemical categories:
- proteins and polypeptides
- lipoproteins
- glycoproteins
- nucleoproteins
- polysaccharides
- lipopolysaccharides
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the six antigen categories
* Proteins and polypeptide: enzymes, cell surface structures, and exotoxins
* Lipoproteins: cell membranes
* Glycoproteins: blood cell markers
* Nucleoproteins: DNA complexed to proteins, but not pure DNA
* Polysaccharides (certain bacterial capsules)
* Lipopolysaccharides (Gram-negative)
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the "good" immunogens
Characteristics of good immunogens: (provoking a strong response) are a: their chemical composition; b: their context,
meaning what types of cytokines are present; and c: their size:
* In general, large antigens are better than small antigens,
but size alone is not sufficient for antigenicity:
* Glycogen, highly repetitious structure (molecular weight over
100,000 Daltons) is not immunogenic
* Insulin at 6,000 Daltons is immunogenic
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Superantigens
- bacterial toxins that are potent stimuli for T cells
- activate T cells at a rate 100 times greater than ordinary antigens
- the result can be an overwhelming release of cytokines and cell death
- toxic shock syndrome and certain autoimmune diseases are associated with superantigens
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Allergen
Antigens that evoke allergic reactions, characterized in chapter 14
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Antigen processing and presentation
In most immune reactions, the antigen must be formally presented to lymphocytes by antigen-presenting cells (APCs)
Examples of APCs:
• Macrophages
• B cells
• Dendritic cells
After processing is complete, the antigen is bound to the MHC receptor and moved to the surface of the APC so it will be readily accessible to T lymphocytes
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How antigens are presented to helper T cells
Antigen-presenting cells (APCs) engulf a microbe, take it into intracellular vesicles, and degrade it into smaller peptides or pieces. The antigen pieces are transported to the APC mem brane. They form a complex with MHC-II receptors. From this surface location the antigens are presented to a T helper cell, which is specific for the antigen being presented. (Note that in some cases the antigen is complexed with MHC-I receptors, not MHC-II.)
First, the MHC-II antigen on the APC binds to the T-cell receptor.
Next, a coreceptor on the T cell (typically CD4) hooks itself to a position on the MHC-II receptor. This double-binding ensures the simultaneous recognition of the antigen (nonself) and the MHC receptor (self). Once identification has occurred, the APC activates this T helper (TH) cell. The APC also secretes interleukin-1 (IL-1). The TH cell, in turn, produces IL-2, which is a growth factor for the T helper cells and cytotoxic T cells. These T helper cells can then help activate B cells.
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Antigen processing and presentation
Most antigens must be presented first to T cells, even though they will eventually activate both the T-cell and B-cell systems
T-cell-independent antigens: antigens that can trigger B cells directly without APCs or T helper cells:
• Carbohydrates with many repeating and invariable determinant groups:
• Lipopolysaccharide from the cell wall of Escherichia coli
• Polysaccharide from the capsule of Streptococcus pneumoniae
• Molecules from rabies and Epstein-Barr viru
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Which of the following is not an antigen-presenting cell?
Macrophage
Dendritic cell
T helper cell
B cell
T helper cell
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Stages 3 and 4: T-cell response
• T-cell reactions are the most complex and diverse in the immune system and involve several subsets of T cells
• Actions of T cells are dictated by the APCs that activate them
• Restricted: require some type of MHC (self) recognition before they can be activated
• All T cells produce cytokines with a spectrum of biological effects
• End result of T-cell stimulation is the mobilization of other T cells, B cells, and phagocytes
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T helper cell 1
Activates the cell-mediated immunity pathway; secretes tumor necrosis factor and interferon gamma; also
responsible for delayed hypersensitivity (allergy occurring several hours or days after contact); secretes IL-2
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T-helper cell 2
Can activate macrophages to expel helminths or protozoans, phagocytose extracellular antigens;
contributes to type 1 (allergic) hypersensitivity; can encourage tumor development
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T-helper cell 17
Promotes inflammation
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T follicular helper cell
Drives B-cell proliferation, and aids B cells in antibody class switching
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T regulatory cells
Controls adaptive immune response; prevents autoimmunity; CNA contribute to cancer progression
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T cytotoxic cell
Destroys a target foreign cell by lysis; important in destruction of complex microbes, cancer cells,
virus-infected cells; graft rejection; requires MHC-I for function
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Gamma-delta T cells
React in the innate and adaptive systems responsive to lipid antigens
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T helper (Th) cells
Many types of T helper cells all bear the CD4 marker and are critical in regulating immune reactions to antigens
Also involved in activating macrophages:
• Directly by receptor contact
• Indirectly by releasing cytokines such as interferon gamma (IFNγ)
Some secrete interleukin 2 (IL-2), which stimulates primary growth and activation of T cells, including cytotoxic T cells
Secrete IL-4, IL-5, and IL-6, which stimulate B cells Make up about 65% of the T-cell population
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Cytotoxic T (Tc) cells: cells that kill other cells
Target cells that TC cells can destroy include:
• Virally infected cells: recognize these because of telltale virus peptides expressed on their surface
• Cancer cells: TC constantly survey the tissues and immediately attack any abnormal cells they encounter
• Cells from other animals and humans: the most important factor in graft rejection
54
Gamma-delta T cells
Distinct from other T cells:
• Have T-cell receptors rearranged to recognize a wide range of antigens
• Frequently respond to certain kinds of PAMPs in the same way as nonspecific WBCs
• Respond more quickly and produce memory
• Particularly responsive to certain types of phospholipids and react to tumor cells
• Considered the bridge between innate and adaptive immune responses
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B-cell activation steps
1) binding of the antigen: a pre committed B cell binds the only epitope that its receptor fits. (APCs can also present antigens to naive B cells)
2) Antigen processing and presentation: The antigen is endocytosed by the B cell and degraded into smaller peptide determinants. The antigen is then bound to the MHC-II receptors on the surface of the B cell.
3) B cell/TH cell cooperation and recognition: For most B cells to become functional, they must interact with an already activated T helper cell that bears receptors for antigen from the same microbe. This T cell has also been activated by an APC. The two cells engage in linked recognition, in which the MHC-II receptor bearing antigen on the B cell binds to the T cell antigen receptor, the CD3 molecule, and the CD4 molecule on the T cell (inset).
4) B-cell activation: The combination of these stimuli on the membrane receptors causes a signal to be transmitted internally to the B-cell nucleus. These events trigger B-cell activation.
5) differentiation: the ordinal activated B cell now differentiates into here types of activated B cells: plasma cells, memory cells, and regulatory cells
6) Clonal expansion: Each of the three cells expands its population by undergoing numerous mitotic divisions. Plasma cells are short-lived factories for antibodies of the same specificity as the original B cell. Memory cells seed the lymphatic circulation, ready for encounters with the same antigen. Regulatory cells proliferate and secrete IL-10 to regulate the T-cell response.
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Antibody functions
Antibodies: Antibodies coat the surface of a bacterium, preventing its normal function and
reproduction in various ways
Opsonization: Antibodies called opsonins stimulate opsonization (ahp′′-son-uh-zaz′-shun), a process that makes microbes more readily recognized by phagocytes, so that they can dispose of them. Opsonization has been likened to putting handles on a slippery object to provide phagocytes a better grip.
Neutralization: in neutralization reactions, antibodies fill the surface receptors on a virus or the active site on a microbial enzyme to prevent it from attaching normally
Agglutination: The capacity for antibodies to aggregate, or agglutinate, antigens is the consequence of their cross-linking cells or particles into large clumps. Agglutination renders microbes immobile and enhances their phagocytosis. This is a principle behind certain immune tests discussed in chapter 15.
Lysing: the interaction of an antibody with complement can result in the specific nupturing of cells and some viruses
Antitoxin: an antitoxin is a special type of antibody that neutralizes bacterial endotoxins
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Adaptive immunity and vaccination
Natural immunity: any immunity that is acquired through the normal biological experiences of an individual
Artificial immunity: protection from infection obtained through medical procedures such as vaccines and immune serums
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Active immunity
- occurs when an individual receives immune stimulus that activates B and T cells to produce immune substances such as antibodies
- creates memory that renders the person ready for quick action upon reexposure to the same antigen
- requires several days to develop
- lasts for a relatively long time
0 can be stimulated by natural or artificial means
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Passive immunity
- Occurs when an individual receives antibodies form another human or animal
- recipient is protected for a short period off time, even though they have not had prior exposure to the antigen
- lack of memory for the original antigen
- lack of antibody for production against the disease
- immediate ————
-
-
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Antibody-antigen interactions and the function for the fab
Hypervariable region:
• The site on the antibody where the epitope binds
• Amino acid content of this region is extremely varied
• Specificity of antigen binding sites for antigens is very similar to enzymes and substrates
• Specificity on the two Fab sites is identical, so an Ig molecule can bind epitope on the same cell or on two separate cells, and link them
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Functions of the Fc fragment
Fc end can bind to receptors on the membranes of cells, such as macrophages, neutrophils, eosinophils, mast cells, basophils, and lymphocytes
Effect of Fc binding depends on the cell’s role:
• Opsonization: attachment of antibody to foreign cells and viruses is followed by binding of the Fc end to phagocytes
• Fc end of IgE binds to basophils and mast cells, causing release of allergic mediators such as histamine
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Classes of immunoglobulins
- forms of IgA
Isotypes: structural and functional classes of immunoglobulins
Two forms of IgA:
• Monomer that circulates in small amounts in the blood
• Dimer that is a significant component of mucous and serous secretions of the salivary glands, intestine, nasal membranes, breast, lung, and genitourinary tract
• Dimer is two monomers held together by a “J” chain and a secretory piece is added to facilitate transport of IgA across membranes
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What IgA does
• Coats the surface of mucous membranes
• Suspended in saliva, tears, colostrum, and mucus
• Provides adaptive immunity against enteric, respiratory, and genitourinary pathogens
• Colostrum: earliest secretion of breast milk; high in IgA that coats the gastrointestinal tract of a nursing infant
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Biological functions
IgG: monomer is produced by plasma cells in a primary response and by memory cells responding the second time to a given antigenic stimulus. It is the most prevalent antibody circulating throughout the tissue fluids and blood. It neutralizes toxins, opsonizes, fixes the complement
IgA: diner is secretory antibody on mucous membranes; monomer is in small quantities in blood
IgM: produced at first response to antigen. It can serve as B-cell receptor
IgD: the receptor on B cells and a triggering molecule for B-cell activation
IgE: antibody of allergy and of worm infection. It also mediates anaphylaxis, asthma, etc.
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Monitoring antibodies over time
Titer: levels of antibodies in the serum over time
Well-accepted principle is that memory B and T cells are only created from clones activated by a specific antigen:
• New research suggests that exposure to a particular antigen can result in memory cells that are chemically related to it, even if those antigens have not been seen by the host
• Activation of specific memory occurs via recognition of epitopes
• May lead to the use of nonpathogenic microbes in vaccines against more dangerous ones
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Primary and secondary response to antigens
Primary: the first exposure to an antigen the system undergoes
Secondary: when the immune system is exposed again to the same immunogenicity within weeks, months, or even years
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- COVID-19 immunotherapy
• In the spring of 2020, in the early days of the COVID-19
pandemic, the public became more aware of the option of
passive immunotherapy.
• It was widely called “convalescent serum,” referring to the
fact that it uses serum, containing antibodies, from people
who were ill with SARS-CoV-2, and had recovered
(thus “convalescent”).
• This approach is useful when there is no vaccine yet
availabl
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Immunization: a lively history
First recorded attempt at immunization occurred in sixth-
century China:
• Consisted of drying and grinding up smallpox scabs and
blowing them with a straw into the nostrils of vulnerable
family members
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Variolation in the 10th century
• Deliberate inoculation of dried pus from smallpox pustules
of one patient into the arm of a healthy person
• Used in parts of the Far East until it was brought to
England in 1721
• Unfortunately, many recipients and their contacts still died
of smallpox
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Edward Jenner, 1796
• Inspired by a dairymaid who had been infected by cowpox
and who was immune to smallpox
• Tested his theory by injecting a young boy with material
from human cowpox lesions, exposed him to smallpox 2
months later, and the boy proved immune to the disease
• Use of this vaccine was first regarded with fear and
skepticism, but later adopted when it proved successful
• Vaccination: any immunity obtained by inoculation with
selected antigens
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Define vaccination
Any immunity abstained by inoculation with selected antigens
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Passive immunization
- Gamma Globulin
First attempts involved the transfusion of horse serum
containing antitoxins to prevent tetanus and treat diphtheria
Antisera from animals has now been replaced with human
products
Gamma globulin:
• Immunoglobulin extracted from the pooled blood of many
human donors
• Processing concentrates antibodies to increase potency
and eliminate potential pathogens (such as hepatitis B and
HIV)
• Most useful in patients who have a diminished ability to
mount their own immune response
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Artificial active immunity: vaccination
Basic principles behind vaccination:
• Stimulate a primary response and a memory response
• Prime the immune system for future exposure to a virulent
pathogen
• If the pathogen enters the body, the response will be
immediate, powerful, and sustained
Vaccines have profoundly reduced the prevalence and
impact of many infectious diseases that were once common
and deadly
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Principles of vaccine preparation
In times of pandemics, such as the COVID-19 pandemic, vaccine
production can be sped up, but quality control is still maintained
Qualities of an ideal vaccine:
• Protect against exposure to natural, wild forms of the pathogen
• Have a low level of adverse side effects or toxicity, and not
cause harm
• Stimulate both antibody (B-cell) and cell-mediated (T-cell)
response
• Long-term, lasting effects (produce memory)
• Does not require numerous doses or boosters
• Inexpensive, have a relatively long shelf life, and be easy to
administer
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Vaccine preparations
Whole cell or virus vaccines:
• Live, attenuated cells or viruses
• Killed cells or inactivated viruses
Antigen molecules derived from bacterial cells or viruses
(subunits):
• Subunits derived from cultures of cells or viruses
• Subunits synthesized to mimic natural molecules found on
pathogens
• Subunits manufactured via genetic engineering
• Conjugated vaccines: subunits conjugated with proteins
(often from other microbes) to make them more
immunogenic
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Whole-cell vaccines
• Whole cells or viruses are very effective immunogens because they are so
large and complex. Depending on the vaccine, these are either killed or
attenuated.
• Killed vaccines (viruses are termed “inactivated” instead of “killed”) are
prepared by cultivating the desired strain or strains of a bacterium or virus and
treating them with chemicals, radiation, heat, or some other agent that does
not destroy antigenicity.
• The hepatitis A vaccine and three forms of the influenza vaccine contain
inactivated viruses. Because the microbe does not multiply inside the host,
killed vaccines often require a larger dose and more boosters to be effective.
• Live attenuated vaccines contain live microbes whose virulence has been
attenuated, or lessened/eliminated.
• This is usually achieved by modifying the growth conditions or manipulating
microbial genes in a way that eliminates virulence factors. Vaccines for
measles, mumps, polio (Sabin), and rubella contain live, nonvirulent
viruses.
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The advantages of live preparations of whole-cell vaccines
The advantages of live preparations are as follows:
• Viable microorganisms can multiply and produce infection
(but not disease) like the natural organism.
• They confer long-lasting protection.
• They usually require fewer doses and boosters than other
types of vaccines.
• They are particularly effective at inducing cell-mediated
immunity.
- Disadvantages of using live microbes in vaccines are that
they require special storage facilities and could conceivably
mutate back to become virulent again.
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Subunit vaccines
• If the exact epitopes that stimulate immunity are known, it is possible to
produce a vaccine based on a selected component of a microorganism.
• These vaccines for bacteria are called subunit vaccines.
• The antigens used in these vaccines may be taken from cultures of the
microbes, produced by genetic engineering or synthesized chemically.
• Examples of component antigens currently in use are the capsules of the
pneumococcus and meningococcus, the protein surface antigen of anthrax,
and the surface proteins of hepatitis B virus.
• A special type of vaccine is the toxoid, which consists of a purified bacterial
exotoxin that has been chemically denatured.
• These vaccines cause humans to produce antitoxins that can neutralize the
natural toxin.
• Toxoid vaccines provide protection against diseases such as diphtheria,
tetanus, and pertus
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Subunit vaccines: part of organisms
- antigens stimulate immunity without the whole pathogen being present
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DNA vaccines
• Microbial DNA is inserted into a plasmid vector and inoculated into a recipient
• Human cells will take up some of the plasmids and express the microbial DNA in the form of proteins
• These foreign proteins will be recognized during immune surve
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Route of administration of vaccines
Most vaccines are administered via the routes:
• Subcutaneous
• Intramuscular
• Intradermal
Nasal and oral vaccines:
• Available for only a few diseases
• Stimulates IgA protection on mucous membranes
• Easier to give than injections
• More readily accepted
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Adjuvants
Special binding substance required by some vaccines:
• Enhances immunogenicity
• Prolongs antigen retention at the injection site
• Precipitates the antigen and holds it in the tissues so that
it will be released gradually
• Facilitates contact with antigen-presenting cells and
lymphocytes
• Helps involve the innate immune system as well
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Vaccine side effects
Vaccines must go through years of trials in experimental animals
and human volunteers before they are licensed for general use
Still, some complications occur:
• Local reactions at the injection site
• Fever
• Allergies
• Other adverse outcomes
More serious reactions are extremely rare
People have attempted to link childhood vaccinations to later
development of diabetes, asthma, and autism:
• Original 1998 scientific paper that suggested that vaccines might be
responsible for autism was entirely discredited, and the principal
author’s medical license was revoked after authorities found the
research and its claims fraudulent
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Herd immunity
the majority of the population is immune, so chance of susceptible individuals contacting an infected individual is low
