Innate and Adaptive
Immunity
Innate (Natural) Immunity:
 Inborn resistance.
 present the first time a pathogen is
encountered (does not require prior
exposure).
 Not specific.
 not modified by repeated exposure to
the pathogen.
Adaptive (Acquired) Immunity:
 weak or absent at the first
exposure.
 Specific.
 increases dramatically with
subsequent exposures to the same
pathogen (memory).
Components of innate immunity:
 Cell mediated immunity.
 Humoral (soluble) immunity.
Types of adaptive immunity
 Cell mediated immunity.
 Humoral (soluble)immunity.
Cells of Innate Immunity:
Phagocytes:
- Monocytes and macrophages: blood
stream and tissues.
- Dendritic cells: lung, skin and GIT mucosa.
Granular leukocytes:
- Neutrophils, and eosinophils.
- Basophils and mast cells.
Natural killer cells (NK).
Soluble Mediators of Innate
Immunity:
o Proteins and enzymes.
o Cytokines & type 1 interferons.
o Complement (C3b: opsonization).
o Proteins and Enzymes
A variety of proteins and enzymes (present in
human blood and tissue fluids) are considered
the first part of innate immunity.
Example: C reactive protein (CRP), lysozymes and
defensins.
Proteins and enzymes
Major microbial targets
Effects
Lysozyme and defensins
Bacterial wall and
membrane
digestion
CRP
Polysaccharides of
microbes
Opsonization
Mannose binding proteins
Mann glycoprotein
Opsonization
and complement activation
o Cytokines and Type I Interferons:
 Cytokines: IL-1, IL-6, IL-12, and TNFα
produced by activated phagocytes.

Type I interferons:
INFs are rapidly produced, within minutes by
infected cells (virus infection).
INFs activate phagocytosis and apoptosis of
infected cells.
•
•
IFN- α produced by dendritic cells.
IFN-β Produced by fibroblasts.
Cellular and Humoral Adaptive Immunity:
Immune cells:
- T lymphocytes
- B lymphocytes
- N.K cells.
Soluble mediators:
- Cytokines: IL-2, IL-3, IL-10,IL-13.
- Interferons: INF-γ (Gamma).
- Complement.
Soluble and cell-bounded proteins:
-The Immunoglobulins.
Complement
Cytokines: IL2, IL3, IL10
& IL13.
Interferons: IFγ
Immunoglobulins.
Cytokines: IL1, IL6, IL12
& TNFα.
Interferons: IFα and IFβ.
n
Phagocytes: monocytes,
macrophages & DC
Granular leukocytes
NK cell
T lymphocyte & B
lymphocytes
Antigens,
Immunogens ,
Epitopes and
Haptens
Antigen:
Is a molecule or part of a molecule that is
recognized by the immune system.
Immunogen:
Is an antigen that evokes a specific, positive
immune response.
Example: Injecting a laboratory animal by
human chromosome
anti-DNA
antibodies and anti-histons antibodies will be
produced.
Epitopes (The Antigenic determinants):
 The smallest part of an antigen or
immunogen that can be recognized by the B &
T cells receptors. So it is the basic recognition
element.
N
 A single antigen molecule may have several
different epitopes.
 Immunodominant epitope is an epitope that
can stimulate a greater antibody response than
others.
N
epitopes
Immunogenicity and Properties of
Immunogen:
Immunogenicity is the ability of
immunogen to activate immune response.
Properties of Immunogen:
o Foreignness.
o Size.
o Chemical nature
o Complexity.
Foreignness:
Immune system can discriminate between
foreign and self substance (self & non self).
Size:
Molecular weight of at least 10,000 Dalton
(10 kDa).
Chemical nature:
-Proteins (polypeptide) are good immunogens.
-Carbohydrates, steroids, and lipids are poor
immunogens.
Chemical complexity:
 As the chemical complexity increases; the
immunogenicity increases.
N
 Homopolymers are poor immunogens
regardless of size, while heteropolymers are
strong immunogens.
 Proteins are heteropolymers (different
amino acids).
N
Which of these antigens
is more immunogenic?
epitopes
Epitopes Recognition
B cell receptors can recognize epitopes
whether they are:
 Free soluble molecules.
 Surface-bound molecules.
 Degraded fragments.
T cell receptors can bind only to epitopes
which are surface-bound molecules.
Superantigen:
o Is a substance such as a bacterial
toxin that is capable of stimulating
multiple T lymphocytes, leading to
release of relatively large quantities
of cytokines.
o Phagocytosis process is not required
for this type of activation.
N
Hapten:
Small, usually non-biologic molecules that
bind to immune cells receptors but cannot by
themselves induce a specific immune
response.
(Land-Steiner’s experiment).
Injected a mice with:
hapten
carrier (protein)
Hapten + carrier
carrier
No immune response
anti carrier
anti-hapten +anti-
T-cell Dependent and T-cell
Independent Antigens:

Antigens are classified as either T-cell
dependent or T-cell independent.

T cell dependent antigen activates
immune system depending on Tlymphocytes.
T-cell dependent
antigen
T-cell independent
Antigen
Complex
Simple
Chemical nature
Proteins, glycoprotein,
and lipoproteins
Antibody - class
induced
IgG, IgM, IgA, IgD,
and
IgE
Polysaccharide;
bacterial
Lipopolysaccharide.
Only IgM
Immunological
Memory
yes
No
Present in most
Pathogens
yes
No
Structural properties