Transcript Immunology Overview

Immunology Overview
W. Robert Fleischmann, Ph.D.
Department of Urologic Surgery
University of Minnesota Medical School
[email protected]
(612) 626-5034
Objectives
• Provide an overview of immunological
principles
• Provide a framework for future lectures
• Introduce immunological terminology
Jill and Andrew Phelan are concerned about their 4month-old daughter, Jackie. They report that Jackie
appears to have another bacterial infection, as she has
a fever and green colored mucous has been draining
from her nose.
They report that Jackie has had almost continual
bacterial infections in her nose and throat for the past
month. The bacterial infections appear to clear up with
a week-long antibiotic treatment. However, as soon as
the antibiotics have been used up, Jackie comes down
with another bacterial infection. She also has frequent
nose-bleeds.
What might cause a patient to have repeated bacterial
infections?
Jackie is a rather slender baby with silvery blond hair
and a very fair complexion and very light-colored eyes.
A physical examination by the physician suggests that
Jackie has enlarged cervical lymph nodes and may
have a swollen liver and spleen.
What do these physical findings suggest?
What would you do next?
The physician requests a total WBC
count with differential.
Immune System Function
• Normal Immune System:
– Protects against non-self
– Defends against microbes, foreign antigens, and tumors
– Results in a state of well-being most of the time
• Deficient Immune System:
– Cannot protect against non-self
– Develop infections and tumors
– Results in immunodeficiency diseases
• Hyperactive Immune System:
– Over-reacts to stimulus
– Can be fatal, e.g. bee sting
– Results in allergic and asthmatic diseases
• Blind Immune System:
– Cannot distinguish self from non-self
– Results in autoimmune diseases
A Conundrum
• We live in a environment rife with
microorganisms that seek to grow on or in us.
If the microorganisms succeed, we will
become ill and might die.
• Because of mutations that arise, we are
constantly producing precancerous and
cancerous cells. If the cancerous cells grow,
we will die.
• Yet, most of us are in a state of well-being
most of the time.
• How is this possible? We have a well
developed immune system that protects us
from microorganisms and cancerous cells.
What Kinds of Microorganisms
Seek to Infect Us?
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Viruses
Bacteria
Fungi
Protozoan parasites
Helminth parasites
Why Don’t Most
Microorganisms Cause
Infections?
• The skin provides a protective physical
barrier to microorganisms.
• Mucous secretions help to protect the nose,
lungs, and other orifices by entrapment.
• Saliva (lysozyme) helps to protect the mouth.
• However, some breaks in these defenses
inevitably occur and we become infected.
Why Don’t We Die When
Infected by Microorganisms?
• Is it because of man-made interventions?
– Vaccinations
• Can prevent infections
• Available for the past several hundred years
– Antivirals
• Very few antivirals are available
– Antibiotics
• Can cure established infections or prevent infections
• Available for only the past 75 years or so
Why Don’t We Die When
Infected by Microorganisms?
• Is it because of Innate Immunity?
– Innate immunity stops most infections
before they can cause symptoms.
– Innate immunity reduces the number of
invading organisms. So, the dose of
microorganisms needed to cause
symptomatic infection may be hundreds or
thousands of microorganisms.
– Still, some microorganisms do evade our
innate immunity.
Why Don’t We Die When
Infected by Microorganisms?
• Is it because of Adaptive Immunity (aka
Acquired Immunity)?
– Adaptive immunity does not develop
immediately.
– Adaptive immunity primarily protects us
from re-exposure.
– When an infection overwhelms innate
immunity and persists for a long enough
period of time, adaptive immunity can
provide protection (Ex., Mycobacterium
tuberculosis).
Why Don’t We Die When
Infected by Microorganisms?
• Actually, it is a combination of the
following.
– Innate Immunity
– Adaptive Immunity
– Man-made interventions
Types of Immunity
• Innate Immunity
– Pre-existing defenses that are non-specific
– Pre-existing defenses that do not change
with repeated exposure
• Adaptive Immunity
– Reactive defenses that are specific
– Reactive defenses that have memory
Results of Jackie Phelan’s Blood Work
Total WBCs:
5,000/µl
(4,300-10,900/µl)
Differential WBCs:
Neutrophils (PMNs)
Band cells
Lymphocytes
Macrophages
Eosinophils
Basophils
10%
0%
90%
0%
0%
0%
(35-80%)
(0-10%)
(20-50%)
(2-12%)
(1-7%)
(0-2%)
CD4+ T cells:
1,200/µl
(1,200/µl)
T cell function tests: normal
Antibody tests: normal
Introduction to Innate
Immunity
Functions That Are Activated
When Innate Immunity Is
Stimulated
Three Major Features/Functions of
Activated Innate Immunity
• Complement Activation
• Inflammation
• Cell Activation
– Cytokine and lymphokine production
– Phagocytosis or other killing
How Is Innate Immunity
Stimulated?
Stimulation of Innate Immunity
• It is the recognition of patterns that are
present in or on microorganisms and
not in our cells that stimulates or
activates innate immunity.
– Because innate immunity relies on pattern
recognition, it is non-specific and does not
generate immunologic memory
– Pattern recognition stimulates complement
activation and activation of non-specific
cell-mediated immunity
Factors of Innate Immunity
Barrier defenses
Skin, mucous secretions
Inflammation
Low pH, low O2
Phagocytes and other cytotoxic
cells
Macrophages, PMNs, NK cells
Soluble mediators
Complement, IFNs, ILs, TNFs,
chemokines (leukotrienes,
prostaglandins
Antimicrobial peptides
-defensin, -defensin,
cathelicidins
Acute Phase Response proteins
C-reactive protein, mannosebinding lectin
What Kind of Patterns Are
Recognized by Innate
Immunity?
Molecules Recognized by
Pattern Recognition
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Polyanions
Lipoproteins
Lipoteichoic acid
Lipoarabinomannan
Other mannosecontaining
compounds
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Lipopolysaccharides
Formyl peptides
Muramyl peptides
Peptidoglycans
Phosphorylcholine
Effects of Pattern Recognition
• Non-cellular effects of pattern recognition
– Bind to C-reactive protein
– Mannose-binding lectins bind to mannosecontaining molecules, triggering complement
– LPS triggers complement activation by the
alternate pathway
• Cellular effects of pattern recognition
– Phagocytosis by macrophages and PMNs
– Production of reactive oxygen and reactive
nitrogen molecules
– Killing by NK cells
– Activation of immune cells
Non-Cellular (Soluble) Pattern
Recognition by Innate Immunity
Soluble mediators
Complement, IFNs, ILs, TNFs,
chemokines, leukotrienes,
prostaglandins
Antimicrobial peptides
-defensin, -defensin,
cathelicidins
Acute Phase Response proteins
C-reactive protein, mannosebinding lectin
Antimicrobial Peptides:
Defensins are cationic proteins 29-35 aa in length produced by
neutrophils, epithelial cells of kidney and pancreas, and by paneth cells
in the gut. They kill S. aureus, S. pneumoniae, E. coli, P. aeruginosa,
and H. influenzae. They disrupt microbial membrane, block DNA, RNA,
protein synthesis.
Cathelicidin, a single protein, has chemotactic activity for
neutrophils, monocytes, mast cells, and T cells; degranulates mast
cells; and, promotes wound healing.
Acute-Phase Response Proteins:
C-reactive proteins bind to polysaccharide on S. pneumoniae and
to phosphoryl choline on many microbial surfaces and act as opsonins.
High levels of C-reactive protein are associated with higher risk of
coronary heart disease.
Mannose-binding lectins recognize mannose-containing patterns
on microbes but not on host cells. They direct complement to attack
the microbes to which they bind.
Cellular (Cell-Associated) Pattern
Recognition by Innate Immunity
• Toll-Like Receptors (TLRs)
– 11 TLRs have been identified
– Responsible for recognition
and binding to patterns
present in/on viruses, bacteria,
parasites, and fungi
– Each TLR recognizes a
distinct repetoire of highly
conserved molecules on the
different pathogens
– Extracellular domain has
leucine-rich repeats (LRRs)
– Intracellular domain has three
conserved sequences
Ligands of Different TLRs
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Different TLRs are
found on different
cells. Most are found
on macrophages,
PMNs, and B cells.
TLRs can serve as
heterodimers (TLRs 1,
2, and 6), homodimers
(TLR4 and TLR5?), or
monomers (TLRs 3, 7,
8, and 9).
Some TLRs are
surface proteins,
others are internal
proteins.
Ligand binding to TLR
activates
phosphorylation of
second messengers,
activating NFB and
turning on
transcription.
TLR Signalling
Cellular Responses to TLR
Signaling
• Activation of the transcription factor NFB
causes
– Expression of pro-inflammatory genes
• Production of prostaglandins and leukotrienes
• Production of interleukins and other cytokines
– Increased phagocytosis and synthesis of reactive
oxygen and nitrogen molecules in macrophages
and neutrophils
– Increased efficiency of antigen presentation
Complement Activation
Three Pathways of
Complement Activation
• Classical pathway (adaptive immunity)
– C1q binds to Ag:Ab complex cleaves C4 and C2 to form C4b2a (C3
convertase) and C4b2b (C5 convertase) to initiate a cleavage cascade
C1qr2s2 - C4 - C2 - C3 - C5. C3b also cleaves C5 to C5b.
– C5b binds to a membrane and initiates formation of the membrane
attack complex (C6, C7, C8, C9).
– C9 binds to C6, C7, C8 to form a pore in the membrane.
• Lectin pathway (innate immunity)
– Mannose binding protein bound to bacterial carbohydrates (the protein is
called a lectin) mimics C1q, binds and activates serum proteases, and
activates C4 cleavage. This initiates the rest of the cascade.
• Alternate pathway (innate immunity)
– C3 is spontaneously cleaved or cleaved to C3b by a serum protease
activated by bacteria. Normally this C3b would turn over.
– C3b binds to bacterial cell walls (Gram + and Gram - [LPS]), yeast cell
walls, and viral envelopes and is stabilized by this binding.
– Bound C3b, in turn, binds to Factors B and D and properdin to become
activated as C3 convertase and cleaves more C3 to C3b which then
cleaves C5 to C5b, initiating the rest of the cascade.
Complement Pores Versus Perforin Pores
Important Products of
Complement Activation
• C3 cleaved to C3a and C3b
• C4 cleaved to C4a and C4b
• C5 cleaved to C5a and C5b
Activities of C3a, C4a, And C5a
• Chemotactic factors that increase directional migration of PMNs
and macrophages
• Activating factors that cause PMNs and macrophages to
degranulate
– Release of digestive enzymes (cauterization)
– Release of adhesion molecules
• Activating factors that cause respiratory burst in PMNs and
macrophages
• Anaphylactic factors that cause mast cells and basophils to
degranulate releasing large quantities of histamine (vascular
collapse and shock)
• Potency: C5a >>> C3a >>> C4a
Activity of C3b and C4b
• C3 and C4 are cleaved to highly reactive C3b and
C4b, respectively.
• C3b and C4b are deposited on any surface with an
exposed amine or hydroxyl, such as a bacterium.
– Act as opsonins
– Act in a feedback loop to continue cleaving C3
• C3b and C4b can be down-regulated
– When C3b and C4b bind to body cells they are inactivated
by membrane bound decay-accelerating factor (DAF).
– Soluble factors Factor H, Factor 1, and anaphylatoxin
inactivator can block or inactivate C3b and C4b.
Activity of C5b
• Binds to microorganisms or host body cells
• Acts as a focal point for the deposition of C6-C9
– C9 is the critical part of the membrane attack complex that
punches a hole in the cell wall or cell membrane killing
bacteria.
• C5b can be down-regulated
– Soluble S protein can bind to soluble C5b and prevent its
binding to a cell membrane.
– Body cells have protectin (CD59) and homogolous restriction
factor (HRF) on their surface that bind to C8, preventing C8
binding of C9 and preventing formation of the membrane
attack complex.
Genetic Deficiencies Occur For Each Complement
Component And Regulatory Factor
• Deficiencies in C1q, C1r, C1s, C4, and C2
– Predispose individuals to systemic lupus erythematosus,
glomerulonephritis, and vasculitis, due to a lack of C3b
generation and resulting in a lack of clearance of immune
complexes
– Increased incidence of Streptococcus and Staphylococcus
infections because of reduced opsonization
• Deficiencies in C3 are most severe, with increased
immune-complex disease and recurrent bacterial
infections.
• Deficiencies in C5 and the membrane attack complex
lead to recurrent Neisseria infections.
• Deficiency in C1 inhibitor (C1Inh) cause hereditary
angioedema, a disease with trauma-induced or
spontaneous edema. Airway obstruction can be fatal.
Jackie Phelan
• C-reactive protein level was elevated,
consistent with infection.
• Measurements of levels of complement
proteins were normal.
Inflammation
Hallmarks of Inflammation
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Influx of fluid (edema)
Increased temperature (hyperthermia)
Decreased oxygenation (local hypoxia)
Influx of white blood cells (extravasation)
Triggers of Inflammation
• Complement C5a stimulation of basophil and mast
cell degranulation and activation
– Histamine = increased vascular permeability
– Prostaglandin E2 = vasodilation, increased vascular
permeability
– Leukotriene D2 = neutrophil chemotaxis, increased vascular
permeability
– Leukotriene D4 = increased vascular permeability
• Macrophages
– TNF = can cause fever; stimulates expression of E-selectin
– IL-1 = endogenous pyrogen; stimulates expression of Eselectin
– IL-8 = chemotaxis
• NK cells
– IFN-g = activation of phagocytic cells and NK cells
Extravasation
of PMNs
Cell Activation
Cells of the
Innate Immune System
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Polymorphonuclear Neutrophils (PMNs)
Eosinophils
Basophils and Mast cells
Macrophages/Dendritic
Cells/Interdigitating Cells
• Natural Killer cells (NK cells)
Origin and Distribution of
Cells of the Immune System
Polymorphonuclear Leukocytes
• Called PMNs or
polymorphonuclear
leukocytes for their trilobed nuclei
• Also know as Polys,
neutrophils or granulocytes
• Contain granules that do
not stain with either acidic
or basic stains
• Mediators of innate
immunity
• Short-lived cells
PMN Functions
• Primary phagocytic cells in the blood
• First cells to migrate to a site of inflammation or
infection
– Effector cells of acute inflammation or infection
• Phagocytize bacteria, viruses, and antigens
• Phagosome fuses with granules forming a
phagolysosome
– Contain enzymes that digest bacteria
– Contain myeloperoxidases that make reactive oxygen
species and reactive nitrogen species
• Have receptors for Fc portion of antibodies, so can
also kill by antibody-dependent cellular cytotoxicity
Eosinophils
• Another subset of
polymorphonuclear
leukocytes
• Have a bi-lobed
nucleus
• Contain eosinophilic
granules
Eosinophil Functions
• Eosinophilic granules contain agents that are
anti-parasitic
• Release histaminase and aryl sulphatase that
inactivate histamine and leukotrienes to
reduce the inflammatory response and
reduce PMN recruitment
• Activated by complement C5a and C3a to
degranulate
• Mediators (with Th1 cells and basophils) of
the delayed reaction of the allergic response
Basophils
• Multilobed,
polymorphonuclear
leukocytes
• Express Fc
receptors for IgE
and, thus have IgE
on their surface
• Contain an
abundance of
basophilic granules
Basophil and Mast Cell Functions
• Basophils
– Found at low levels in the blood
– Mediators of the delayed reaction of the allergic response
• Mast cells
– Mononuclear cells with analogous function to basophils found in
tissues (skin, lungs)
– Also contain basophilic granules; IgE on their surface
– Mediators of the immediate reaction of the allergic response
• Both release proinflammatory cytokines
– Release preformed histamine when IgE on surface is cross-linked
by antigen
– Synthesize and release prostaglandins and leukotrienes
• Activated by complement C5a and C3a to degranulate
Monocytes
• Differentiate to form
macrophages in the
peripheral tissues where
they are the first line of
defense against microbial
invasion
– Kupfer cells in liver
– Microglial cells in brain
– Bronchial alveolar
macrophages in lung
• Contain a horse-shoe
shaped nucleus and
cytoplasmic granules
• Long-lived cells
Macrophage Functions
• Late migrators to sites of inflammation (effector cells
of chronic inflammation)
• Major producers of cytokines and lymphokines
– IFN-: antiviral properties
– IL-1, IL-6, and TNF-: mediators of fever
– CXCL8 (IL-8): chemotactic factor recruits PMNs, basophils,
and T cells
– IL-12: activation of NK cells and CD4 Th1 helper T cells
• Prodigious phagocytic cells: professional phagocytic
cells (the “big boys”) that can be highly activated by
IFNs to phagocytize and kill, using reactive oxygen
and nitrogen species.
• Also present antigen to the adaptive immune system
Natural Killer Cells
• Lymphocytes that
participate in innate
immunity
• Also known as large
granular lymphocytes
• Contain acentric and
slightly irregular
nucleus, with
granules visible in the
cytoplasm
Natural Killer Cell Functions
• NK cells recognize
damaged cells by their
deficiency in MHC
antigens (HLA in
humans)
– Virus-infected cells
– Tumor cells
• Exposure to IFNs
(especially IFN-g) highly
activates NK cell killing
function (20-100X)
• IL-12 and TNF- activate
NK cells to secrete
cytokines, principally
IFN-g
Jackie Phelan
• Examination of neutrophils under microscope
show many large slate gray to blue granules.
• Studies on neutrophil phagocytosis showed
impaired chemotaxis and impaired
phagocytosis of bacteria.
• Neutrophils plated on agar after phagocytosis
of bacteria gave bacterial colonies, indicating
a lack of bacterial killing by the neutrophils.
• Genetic testing showed a mutation in the
CHS1 gene.
Jackie Phelan
• Jackie has Chediak-Higashi syndrome.
– Causes defective microtubule function that
compromises neutrophil function, leading to
repeated bacterial infections.
– Can cause seizures
– Can cause reduction in brain size
– Nerve conduction testing can show slow nerve
signaling.
• Treatment involves bone marrow
transplantation.
– Can correct immune defect
– Unfortunately, cannot correct neural problems
Deficiencies of Innate Immunity
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Congenital neutropenia
– Lack of GM-CSF
– Frequent bacterial infections
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Glucose-6-phosphate dehydrogenase deficiency (G6PD)
– Unable to produce NADPH by pentose phosphate pathway, buildup of reduced
glutathione
– RBC denaturation and hemolysis
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Chronic granulomatous disease
– Inability to produce hydrogen peroxide and hypochlorous acid
– Inability to kill phagocytosed bacteria
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Leukocyte adhesion deficiency (LAD)
– Lack of integrin subunit, the common  chain
– Inability to recruit innate immune cells to site of inflammation
– Increased susceptibility to bacterial, fungal, and viral infections.
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Complement defects
– Increased susceptibility to bacterial infections
– Reduced ability to remove immunocomplexes
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Chediak-Higashi Syndrome
– Defect in gene LYST (CHS1), a lysosomal trafficking gene that affects lysosomes
and melanosomes
– Increased susceptibility to bacterial infections.
Major Virus Diseases
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SARS
West Nile encephalitis
Yellow fever
Hepatitis B
Chickenpox
Mononucleosis
Influenza
Measles
Mumps
Poliomyelitis
Jaundice
Smallpox
AIDS
Rabies
Common Cold
Diarrhea
Rubella
Coronavirus
Flavivirus
Flavivirus
Hepadnavirus
Herpesvirus
Herpesvirus
Orthomyxovirus
Paramyxovirus
Paramyxovirus
Picornavirus
Picornavirus
Poxvirus
Retrovirus
Rhabdovirus
Rhinovirus
Rotavirus
Togavirus
Major
Bacterial
Diseases
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Trachoma
Bacillary dysentery
Food poisoning
Plague
Tularemia
Typhoid fever
Gonorrhea
Meningococcal meningitis
Meningitis, pneumonia
Legionnaire’s disease
Whooping cough
Cholera
Anthrax
Diphtheria
Tetanus
Gastroenteritis
Boils, wound infection
Pneumonia, scarlet fever
Tonsilitis
Leprosy
Tuberculosis
Respiratory disease
Typhus
Lyme disease
Syphillis
Chlamydia trachomatis
Shigella flexneri
Salmonella enteritidis, typhimurium
Yersinia pestis
Pasteurella tulaensis
Salmonella typhi
Neisseria gonorrhoeae
Neisseria meningitidis
Haemophilus influenzae
Legionella pneumophila
Bordetella pertussis
Vibrio cholerae
Bacillus anthracis
Corynebacterium diphtheriae
Clostridium tetani
Clostridium difficile
Staphylococcus aureus
Streptococcus pneumoniae
Streptococcus pyogenes
Mycobacterium leprae
Mycobacterium tuberculosis
Mycoplasma pneumoniae
Richettsia prowazeckii
Borrelia burgdorferi
Treponema pallidum
Fungal, Protozoan, Helminth
Diseases
• Fungal
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Aspergillosis
Athlete’s foot
Candidiasis, thrush
Pneumonia
Aspergillus species
Tinea pedis
Candida albicans
Pneumocystis jirovecii
• Protozoan parasites
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Leishmaniasis
Malaria
Toxoplasmosis
Trypanosomiasis
Leishmania major
Plasmodium falciparum
Toxoplasma gondii
Trypanosoma brucei
• Helminth parasites
– Common roundworm
– Schistosomiasis
Ascaris lumbricoides
Schistosoma mansoni