2. Basic immunology Definitions
Immune system
cells, tissues, and molecules that mediate resistance to infections
Immunology
study of structure and function of the immune system
Immunity
resistance of a host to pathogens and their toxic effects
Many body cells and tissues are involved in the implementation
of immunity (Not just lymphocytes and other immune cells)
Immune response
collective and coordinated response to the introduction of
foreign substances in an individual mediated by the cells and
molecules of the immune system
3. Role of the immune system
Defense against microbes
Defense against the growth of tumor cells
kills the growth of tumor cells
Homeostasis
destruction of abnormal or dead cells
(e.g. dead red or white blood cells, antigen-
antibody complex)
5. Innate immunity (we are born with this capability)
First line of immune response
Based on genetic make-up
Relies on already formed components
Rapid response: within minutes of infection
Not specific
same molecules / cells respond to a range of
pathogens
Has no memory
same response after repeated exposure
6. Innate immunity
Type of innate
immunity
Explanation Examples
Species
immunity
Innate immunity towards a
microbe exhibited by all
members of a given species
frogs are resistant to
Bacillus anthracis; while
toads are susceptible.
Racial innate immunity confined to a
particular race; may be absent
in other communities
Negroes of America are
more susceptible to
tuberculosis than the
whites.
Individual
immunity
Antimicrobial defense
mechanisms that are confined
to a particular individual; may
not be exhibited by others.
One exception is
identical twins
Innate immunity is constitutive and can be considered at
Species, Racial and Individual level.
7. Innate - Nonspecific Defenses
1st line of defense
Physical barriers: Skin and mucosal barriers - keep hazardous materials outside the body
2nd line of defense
Phagocytes: neutrophils and macrophages: engulf pathogens and cell debris
Immunological Surveillance: natural killer cells (NK cells) destroy abnormal cells.
Interferons: Chemical messengers that coordinate the defenses against
viral infections. Antiviral proteins do not kill viruses but block
replication in cell
Complement: Complement action of antibodies to destroy pathogens
Inflammation: Triggers a complex inflammatory response limiting the spread
of infection
Fever: A high body temperature which increases body metabolism, and
accelerates body defenses
8. Protective barriers of the body. The barriers of the body represent the
first line of defense and prevent or retard the entry cells and molecules
into the body
9. Barriers of the innate immune system
Types Function
Physical/
anatomical
barriers
Tight junctions In the epidermal skin layer: water-
proof and blocks UV
Subcutaneous glands
In the dermis: contain fatty acids
maintaining a pH of 3-5
Mucous membranes Traps microbes
Mechanical
removal
Mucus
In the respiratory tract: microorganism
trapping and attachment prevention by
the mucus
Cilia Cilia propels the mucus and trapped
microbes towards the sites of removal
Cough and sneeze reflex Respiratory tract: removal of
microorganisms from the body
Vomiting and diarrhea GI tract: removal of toxins and
pathogens from the GI tract
Flushing of body fluids
Systemic: fluids such as tears, urine,
saliva and sweat also flush microbes
from the body
10. Types Function
Physiological
barriers
Temperature
Normal body temperature slows
down the growth of
some pathogens
pH Stomach, skin and vaginal pH
inhibit microbial growth
Chemical
barriers
Lysozymes Bactericidal enzyme secreted by
the cells, found in tears & at the
mucosal surfaces
Lactoperoxidase Mucosal secretion that stimulates
cells to produce toxic radicals
Cryptidins and α-defensins Base of crypt cells in the small
intestine: damage cell membranes
β-defensins
Produced within the skin,
respiratory tract: damage cell
membranes
Surfactant proteins A and D
Present in lungs: function as
opsonins, enhancing the
phagocytic activity of cells.
Barriers of the innate immune system
11. Innate immune response
Pathogens surviving their transit into the tissues
below the epithelial layers
are then targeted by the innate immune system’s second line
of defense,
an array of cells expressing membrane receptors that
recognize microbial components and activate a variety of
cellular defense mechanisms against the invaders
Some white blood cell types are activated to rapidly
engulf and destroy extracellular microbes through the
process of phagocytosis.
12. Innate immune response
Other receptors induce the production of
proteins and other substances that have a
variety of beneficial effects
including direct antimicrobial activity, as well as the
recruitment of fluid, cells, and molecules to sites of
infection.
This influx causes swelling and other
physiological changes that collectively are
called Inflammation.
13. Cellular Innate Response Receptors and
Signaling
Several families of cellular pattern recognition receptors (PRRs) have
essential roles in
Detecting the presence of a pathogen and activating innate immune
responses that combat the infection.
PRRs are capable of distinguishing between self tissues and a specific
class of microbes by recognizing highly conserved PAMPs.
PRRs identify two classes of molecules:
Pathogen-associated molecular patterns (PAMPs), which are associated
with microbial pathogens, and
Damage-associated molecular patterns (DAMPs), which are associated
with components of host's cells that are released during cell damage or
death.
The PRRs are divided into four families:
Toll-like receptors (TLR)
Nucleotide-binding oligomerization domain-like receptors (NLR)
C-type lectin receptors (CLR)
RIG-1 like receptors (RLR)
15. Cellular Innate Response Receptors
and Signaling
Many cell types in the body
express PRRs, including all types
of myeloid white blood cells
and subsets of three types of
lymphocytes (B cells, T cells,
and NK cells).
PRRs are also expressed by
some other cell types,
especially those commonly
exposed to infectious agents;
examples include epithelial cells
of the skin and mucosal and
glandular tissues, vascular
endothelial cells that line the
blood vessels, and fibroblasts
and other stromal support cells
in various tissues.
16. Toll-like receptors (TLRs) were the first family of PRRs
TLRs are membrane proteins that share a common structural element
in their extracellular region called leucine-rich repeats (LRRs);
multiple LRRs make up the horseshoe shaped extracellular ligand-
binding domain of the TLR polypeptide chain
When TLRs bind their PAMP or DAMP ligands via their extracellular
LRR domains, they are induced to dimerize, either as a homodimer
(e.g., TLR3/3) or as a heterodimer (e.g., TLR2/1)
TLR signaling results in change in the transcription factors that
regulate a multitude of genes, including those encoding important
proinflammatory cytokines.
17. Toll like receptors(TLRs) - classical examples of pattern recognition
receptors.
There are 13 types of Toll like receptors (TLR 1 to 13). Important ones
are-
TLR-2 binds to bacterial peptidoglycan
TLR-3 binds to dsRNA of viruses
TLR-4 binds to LPS of Gram negative bacteria
TLR-5 binds to flagella of bacteria
TLR-7 & 8 bind to ssRNA of viruses
TLR-9 binds to bacterial DNA
TLR2, TLR3 and TLR7 binds to Coronavirus
When triggered by binding to a PAMP on an infectious organism, TLRs
mediate the generation of defensive responses
that include transcriptional activation, synthesis, and secretion of
cytokines (immune chemicals secreted by immune cells) to promote
inflammation,
and the attraction of macrophages, neutrophils, natural killer
(NK) cells, and dendritic cells to the site of infection.
18. Endosomal TLR signaling through the MyD88 and TRIF
adaptors
Plasma membrane TLR
signaling through the
MyD88 adaptor.
19. Phagocytes express membrane-bound PRRs on their
cell surface,
which often function in concert with the secreted PRRs.
When these cell surface PRRs bind PAMPs,
they initiate phagocytosis, release of toxic oxidants, and
delivery of pathogens to lysosomes filled with microbicidal
products.
In macrophages, pathogen-derived proteins are also
processed into peptides
and presented by major-histocompatibility-complex
molecules on the cell surface to engage and instruct
antigen-specific T lymphocytes.
PRRs linked to phagocytosis
20. - Inflammatory factors –
released by mast cells,
etc.
- Vasodilation –
capillaries become
permeable
- Margination – WBCs
slow down & align on the
vessel wall
-Diapedesis – blood cells
leave vessels & enter
the CT
-Chemotaxis – blood
cells follow a chemical
gradient (move toward
the source ie., bacteria)
How do phagocytes invade the area of infection or injury?
21. Phagocytes: engulf bacteria
Originally WBCs –
they migrate into
connective tissue
The “clean-up crew”:
phagocytose debris
and digest via
lysosomes
Neutrophils enter first
then macrophages
(derived from
monocytes)
Eosinophils involved
with parasitic
infections and
antigen-antibody
complexes
22.
23.
24. Cellular components of Innate
immunity
NK cells:
Class of lymphocytes that kill virus infected cells and tumor cells.
Mast cells:
Present lining the respiratory and other mucosa.
Activated by microbial products binding to toll like receptors or by IgE antibody
dependent mechanism.
They release abundant cytoplasmic granules rich in histamine, prostaglandins &
cytokines
that initiate inflammation and proteolytic enzymes that can kill bacteria
Dendritic cells:
Respond to microbes by producing numerous cytokines that initiate inflammation.
Serve as vehicle in transporting the antigen(s) from the skin and mucosal site to
lymph nodes where
they present the antigen(s) to T cells - bridge between innate and acquired
immunity.
27. Innate lymphoid cells
Most recently discovered family of innate immune cells,
derived from common lymphoid progenitors (CLPs).
ILCs are primarily tissue resident cells,
found in both lymphoid (immune associated), and non-
lymphoid tissues, and rarely in the peripheral blood.
In response to pathogenic tissue damage, ILCs
contribute to immunity
via the secretion of signalling molecules, and the
regulation of both innate and adaptive immune cells.
28. Innate lymphoid cells
They are particularly abundant at mucosal surfaces,
playing a key role in mucosal immunity and homeostasis.
Based on the difference in developmental pathways,
phenotype, and signaling molecules produced,
In 2013, ILCs were divided into three groups: 1, 2 and 3,
however, after further investigation, now appreciate five
distinct subsets within these groups:
NK cells,
ILC1s,
ILC2s,
ILC3s,
Lymphoid Tissue inducer (Lti)cells.
29. Classification of ILCs into three groups on the basis of their
functional characteristics.
Transcription factors:
• GATA-binding
protein 3 (GATA3)
• Retinoic acid
receptor-related
orphan receptor-
α (RORα)
• Aryl hydrocarbon
receptor (AHR)
• Eomesodermin
(EOMES)
• T bet
30. Complement pathways
In the innate immune system, complement can be activated in two
ways:
via the alternative pathway
via the mannose -binding lectin (MBL) pathway
Alternate complement pathway is activated in response to bacterial
endotoxin.
Mannose binding Lectin pathway is stimulated by mannose
carbohydrate residues on bacterial surface.
Biological function;
Lysis of the target microbes (by forming pores on the microbial
surfaces)
Stimulate inflammation (by secreting inflammatory mediators)
Promotion of phagocytosis (opsonization)
Clearance of immune complexes from circulation.
32. Alternative pathway
initiated by cell-surface
constituents that are
recognized as foreign to the
host, such as LPS
Various enzymes cleave C3 to
C3a and C3b
Unstable C3b fragment
readily attaches to receptors
on cell surfaces
C3b binds Factor B. Factor B in the complex is cleaved
by Factor D to produce an unstable C3 convertase.
C3bBb binds Factor P to produce stabilized C3 convertase,
C3bBbP.
Additional C3b fragments join the complex to make
C3bBbP3b, also known as C5 convertase.
C5 convertase cleaves C5 into C5a and C5b.
C5b inserts into the cell membrane and is the
necessary step leading to formation of the membrane
attack complex (MAC) and cell lysis.
33. Mannose -binding lectin pathway
Lectins are proteins that bind to specific
carbohydrates.
Activated by binding of mannose-binding
lectin (MBL) to mannose-containing residues
of glycoproteins on certain microbes (e.g.,
Listeria spp. , Salmonell spp. , Candida
albicans) .
MBL is an acute phase protein, one of a
series of serum proteins whose levels can rise
rapidly in response to infection, inflammation,
or other forms of stress.
MBL, once bound to appropriate mannose-
containing residues, can interact with MBL-
activated serine protease (MASP).
• Activation of MASP leads
to subsequent activation
of components C2, C4,
and C3
34. Innate Immunity: Inflammation
When the outer barriers of the innate immune system—skin
and other epithelial layers—are damaged,
the resulting innate responses to infection or tissue injury can
induce a complex cascade of events known as the inflammatory
response.
Inflammation may be :
Acute (short-term effects contributing to combating
infection, followed by healing)—for example, in response to
local tissue
Chronic (long term, not resolved), contributing to conditions
such as arthritis, inflammatory bowel disease, cardiovascular
disease, and type 2 diabetes
35. The innate immune system contributes to inflammation
by activating the alternative and lectin-binding complement
pathways, attracting and activating phagocytic cells
that secrete cytokines and chemokines, activating NK
cells, altering vascular permeability, and increasing body
temperature
37. Innate Immunity: Fever
Fever is a protective defense mechanism of body.
The thermoregulatory center in the hypothalamus is sensitive to microbes
and their products.
Increasing body temperature increases the circulation of blood and flushing
of tissue that help to eliminate toxin through urine and sweat.
• Events of fever
• Results from
• release of pyrogens such as interleukin 1, interferons
• toxins from infectious agents, drug reactions toxins, brain tumors
• Pyrogens released and circulate through the body
• target hypothalamus and cause release of prostaglandin E2
• raises temperature set point of hypothalamus
38.
39. Innate Immunity: Fever
• Benefits of fever
• Inhibits reproduction of bacteria and viruses
• Promotes interferon activity
• Increases activity of adaptive immunity
• Accelerates tissue repair
• Increases CAMs on endothelium of capillaries in lymph nodes
• additional immune cells migrating out of blood
• Risks of a high fever significant above 100 degrees F
• High fevers potentially dangerous above 1030 in children
• Changes in metabolic pathways and denaturation of proteins
• Possible seizures, irreversible brain damage at greater than 1060,
death above 1090
40. Factors influencing innate immunity
Age
Very old or very young more susceptible toinfectious
disease
Hormone
Endocrine disorders such asDiabetes Mellitus,
hypothyroidism and adrenal dysfunctions –enhanced
susceptibility to infection
Nutrition
Immune response is reduced in malnutrition patient
41. Defects in innate immune system
Cystic fibrosis- gene defect in ion-gated chloride channel, leading to
accumulation of abnormally thick secretion in air ways.
Congenital achlorhydria- inability of gastric mucosal cell to produce
HCl,
Chronic Granulomatous Disease- congenital defect in NADP
phagosome oxidase (NADP phox) production, leading to poor generation
of ROSs and RNS by phagocytes.
Congenital deficiency of C8 Compliment- Defective MAC formation
Factor I deficiency- uncontrolled complement activation, leading to
complement protein depletion.
42. Deficiency in Innate immunity
Toll-like Receptor (TLR) Deficiencies:
typical presentation of TLR deficiencies is susceptibility to
infection with either bacteria or viruses.
MyD88 Deficiency
MyD88 deficiency was initially described in nine children suffering from
recurrent and severe pus-forming or pyogenic bacterial infections.
These children were susceptible to invasive infections with S. pneumoniae,
S. aureus, and P. aeruginosa,
but had normal resistance to other common bacteria, viruses, fungi, and
parasites.
The defect in the children with this disorder displayed autosomal recessive
inheritance.
43. IRAK4 Deficiency
Patients with IRAK4 deficiency have recurrent
severe infections (cellulitis, arthritis, meningitis,
osteomyelitis, organ abscesses and sepsis)
mainly caused by S. aureus, S. pneumoniae
(pneumococcus) and Pseudomonas
aeruginosa.
No patients had severe viral, fungal or parasitic
infections
44. UNC93B1 Deficiency and TLR3 Mutations
Deficiency of UNC93B1 or TLR3 leads to susceptibility to encephalitis
caused by herpes simplex (HSV-1) (the virus that causes cold sores) due
to decreased production of interferons in the central nervous system.
mutations -severely disable innate responses that are critical to protection
against CNS infection by HSV
45. NEMO deficiency syndrome
NEMO deficiency syndrome is a complex disease caused by
genetic mutations in the X-linked NEMO gene
NEMO syndrome was originally described as an association
between ectodermal dysplasia (ED) and susceptibility to
infections.
Patients with ED have thickened skin, conical teeth, absence of
sweat glands, and thin, sparse hair
46. Human Natural Killer Cell Deficiencies
Human NK cell deficiencies have been divided into two
categories:
Quantitative defects: with decreased numbers of NK cells in the
peripheral blood
Qualitative defects: with normal numbers of NK cells with
abnormal function
Two genetic causes of NK cell deficiency have been identified
including
an autosomal recessive CD16 functional defect
autosomal dominant GATA2 mutation causing classic NK deficiency.
Defects in Interferon-γ (IFN-γ) and Interleukin-12 (IL-
12) Signaling
IFN-γ/IL-12 pathway deficiencies are rare genetic disorders
characterized
by susceptibility to mycobacteria and salmonella infections.
47. Excessive or chronic innate and inflammatory
responses results variety of conditions
Most dangerous of these conditions is sepsis,
a systemic response to infection that includes fever,
elevated heartbeat and breathing rate, low blood
pressure, and compromised organ function due to
circulatory defects.
Several hundred thousand cases of sepsis occur
annually in the United States, with mortality rates
ranging from 20% to 50%
but sepsis can lead to septic shock— circulatory and
respiratory collapse that has a 90% mortality rate.
48. The systemic inflammatory response
triggered by septicemia can
lead to circulatory and respiratory failure, resulting in
septic shock and death.
As high levels of circulating TNF-α and IL-1β
are highly correlated with morbidity,
considerable effort is being invested in
developing treatments that block the adverse
effects of these normally beneficial molecules.
49. Disease Therapy:
Use of INF-α in HCV infection treatment
Use of IL-13-PE (IL-13 immunotoxin) for
treatment of Pancreatic Adenocarcinoma
Use of aerosolized IL-2 for treatment of
pulmonary metastatic liver cancer
50. o Barriers – epithelium, secretions , fluid flow
o Cells: phagocytes (neutrophils, macrophages, eosinophils), NK
cells, Innate lymphoid cells
o Chemical signals – interferons, complement proteins,
inflammatory mediators, pyrogens for fever
Summary of Innate - Nonspecific
Processes