The document provides an overview of innate immunity, detailing its role as the body's first line of defense against infections through physical and chemical barriers, as well as various cellular responses. It distinguishes between innate and adaptive immunity, explaining the mechanisms underlying responses like inflammation and fever. Furthermore, it introduces key components of the innate immune system, including pattern recognition receptors (PRRs), phagocytes, natural killer cells, and the complement system.

1. Innate
Immunity
Hari Sharan Makaju
M.Sc. Clinical Biochemistry

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)

4. Immune System
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Immune System
Adaptive immunity
Delayed response to
specific antigen
B-lymphocytes
(humoral immunity)
T-lymphocytes
(cell-mediated
immunity)
Plasma cells
(synthesize and
release antibodies)
Physiologic responses
(e.g., inflammation,
fever)
Chemicals
(e.g., interferon,
complement)
Cells
(e.g., macrophages,
NK cells)
Skin and mucosal
Membranes & barriers
(prevent entry)
Immediate response to wide
array of substances
Innate immunity
Nonspecific
internal defenses

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)

14. C-type lectin receptors (CLR ) Toll-like receptors (TLR)
Nucleotide-binding oligomerization domain-like receptors (NLR)
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

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.

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Venule
Eicosanoids
Histamine
Basophil
Arteriole
Basophil and mast cell: Proinflammatory chemical-secreting cells
Heparin
Vasodilation
Increases capillary
permeability Capillary
Anticoagulant
Increases inflamation
Basophils open up vessels & increase
blood flow

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Recognizes unhealthy cell (usually expressing abnormal proteins or viral
proteins – uses perforins (make a hole in the membrane) and granzymes
(initiate apoptosis – programmed cell death via gene expression
Apoptosis
Unhealthy or
unwanted cell
NK cell
Granzymes
enter
pore, causing
apoptosis of cell
Perforin forms a
transmembrane pore
Perforin and
granzyme
NK cell: Apoptosis-initiating cells
NK Cell

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.

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C
C
Elimination of
immune complexes
Antigen
Antibody
Complement
Erythrocyte
Complement (C)
cross-links
immune (antigen-
antibody)
complexes to
erythrocyte and
transports to liver
and spleen.
Complement
proteins create
MAC to lyse cell.
Complement activates and
attracts various cells of
innate immunity.
Complement
(C) binds to
pathogen; acts
as opsonin
Macrophage
Pathogen
Complement
Inflammation
Opsonization Cytolysis
Complement
MAC
protein
Pathogen
Inflammation
Macrophage
Neutrophil
Basophil
Mast cell
Complement have a number of functions (below) to defend against
pathogens
Complement pathways

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

36. 1 4
3
2
Formation of
exudate and “washing”
of infected area
Exudate
Increase in fluid
uptake by lymphatic
capillaries
Delivery of
plasma
proteins
Diapedesis
Chemotaxis
Chemical
gradient
Injured
tissue
Bacteria
Release of inflamatory
and chemotactic factors
Mast cells
Neutrophil
CAMs
Lymphatic capillary
Lymph
Basophil
Recruitment of
immune cells
• Margination
• Diapedesis
• Chemotaxis
Vascular changes
include
• Vasodilation of
arterioles
• Increase in capillary
permeability
• Display of CAMs
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Margination
Inflammation

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

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

51. Thank you