Immunity
Dr Asma Jabeen
Assistant Professor
Physiology
Learning Objectives
At the end of this session, the student should be able
to:
•Define immunity and contrast the difference between
its 2 types (innate & acquired).
• Describe some mechanisms for innate immunity
(interferon’s & complement should be included).
• Identify the major differences between the two types
(humoral& cell-mediated) of acquired immunity.
• Relate the knowledge acquired to some clinical
problems (e.g., AIDS)
The ability of the human body to resist almost
all types of organisms and toxins that tend to
damage the tissues and
organs is called IMMUNITY.
It of two types;
 Innate immunity
 Acquired immunity
Immune defenses can be classified into 2 types which
usually interacts:
Nonspecific immune
defenses
(Innate Immunity)
Specific immune
defenses
(Acquired Immunity)
 Protect against microbes or
 Protect against microbes to
F.B. (invaders) without having
which the body is previously
to
exposed (recognized before) either
recognize
their
specific
identity.
through
 The mechanisms used are
immunization.
not specific to any invader.
 The
infection
mechanisms
used
specific for each invader.
or
are
Innate Immunity
Acquired
Immunity
Specificity
Non-specific
Specific
i.e., Reacts to invaders from i.e., Reacts to a specific
different type
invader each time and can not
react to another.
Diversity
Limited
Very high
i.e., Although the cells are of
the same type, each group
shows totally different surface
molecules.
Memory
No
Yes
Remembers the invader on reexposure.
Non-reaction to self
Yes
Yes
Components
Cells
Phagocytes
killer cells
Molecules
Complement
&
natural Lymphocytes
Antibodies
Innate Immunity
 Also called natural/non specific immunity
 It is the inborn capacity of the body
to resist the entry of microorganisms
in the body
 It results from general processes,
rather than from processes directed
against specific disease organisms
Innate immunity includes:
 Phagosytosis of invaders by white blood cells
 Destruction of swallowed organisms by acid
secretions of stomach
 Resistance of skin to invading organisms
 Presence of certain chemical compounds
in blood :
• Lysozyme
• Basic polypeptides
• Complement complex
• Natural killer lymphocytes
Complement System
The Complement system is the system of
twenty proteins, present normally among the
plasma proteins many of which are enzyme
precursors. Main eleven proteins C1 to C9,
B and D
Complement
family of plasma proteins which is involved in:
1) killing of microbes without prior phagocytosis.
2) Opsonization: making phagocytosis easier.
3) Chemotaxis: Direction of phagocytes toward the source of
infection.
Opsonization
Effects of complement activation
 Opsonization and phagocytosis C3b
 Lysis (lytic complex)
 Agglutination
 Neutralization of viruses Chemotaxis C5a
 Activation of mast cells and basophils
(C3a,C4a,C5a)
 Inflammatory effects
Interferon
 One of the innate defense mechanism is the release of
interferon from virus infected cells.
 Interferon briefly provides non specific resistance to viral
infections by transiently interfering with replication of
the same or unrelated viruses in other host cells.
In fact, interferon was named for its ability to interfere
with viral replication
Interferon has following effects:
 Antiviral effects
 Anticancer effects
 Mechanism of action: It markedly enhances the
actions of natural killer cells and cytotoxic cells, which
attack and destroy both virus infected cells and cancer
cells.
 Interferon itself slows cell division and suppress tumor
growth
Interferons
are a family of cytokines that nonspecifically inhibit viral replication inside
host cells
Acquired Immunity
It is extremely powerful specific immunity that
develops against an individual invading agent, after
the body is first attacked by a bacterium, virus, toxin or
foreign tissues from other animals.
Types of acquired immunity

Humoral immunity or B-cell immunity
 Cell- mediated immunity or T-cell immunity
 Millions of different types of preformed
B- lymphocytes and T-lymphocytes,
capable of forming antibodies or T cells are
stored in lymph tissues.
 Each is capable of forming one type of
antibody or activated T-cell against one
specific type of antigen.
Humoral Immunity
After antigen presentation to specific B-lymphocyte, Bcell enlarge and become lymphoblast
Plasmablast
Divides once every ten hrs
For nine divisions
500 plasma cells
(in 4 days)
2000 molecules of antibodies/sec
for each plasma cell, enter into lymph
and blood
Subsequent exposure to the same
antigen causes much more rapid and much
more potent antibody response.
BECAUSE ! !
There are many more memory cells than
there were original B-lymphocytes of
the specific clone.
Classes of antibodies
Five classes of antibodies
 IgM
Most effective, primary response
 IgG 75% of total antibodies in body
Opsonization, cross placenta
 IgE Allergy
 IgA Secretions
 IgD Helps cytotoxic cells
Cell-Mediated Immunity
On stimulation by a proper antigen, presented by antigen
presenting cells,T-lymphocytes of a specific lymphocyte
Clone proliferate and release large number
of activated, specifically reacting T-cells into the lymph.
Formation of T-lymphocyte Memory cells

On activation of a clone of T-lymphocyte by an antigen,
many of the newly formed lymphocytes are preserved
in the lymphoid tissues to become additional
T-lymphocytes of that specific clone.
 On second exposure to that specific Antigen anywhere in
the body release of activated T cells is much rapid and
much more powerful.
Types of T-cells

Helper T cells
 Cytotoxic T cells
 Suppressor T cells OR regulatory T cells
Helper T cells
Most numerous
 Major regulator of virtually
all immune functions

 Form protein mediators called
lymphokines
Cytotoxic T cells

Also called “KILLER CELLS”
 Capable of killing micro-organisms and
at times even body’s own cells
 Secrete hole forming proteins called
“perforins”
 Cytotoxic cells are especially lethal to
tissue cells invaded by viruses
 Act against cancer cells, heart
transplant cells and other cells foreign
to the person’s own body
Direct destruction of an invading cell by
sensitized lymphocytes
Suppressor T cells

They are capable of suppressing the functions of both
cytotoxic and helper T Cells.
 Prevent excessive immune reactions
 Important role in immune tolerance
Humoral
Immunity
Cell mediated
immunity
Main cells
Maturation
B lymphocytes
Generated and
matured in bone
marrow
T lymphocytes
Originate in bone
marrow and complete
development in
thymus
Protect against
Extracellular
Intracellular microbes
microbes and their
1.viruses
toxins
2.parasites
1.toxin induced
(leishmania)
diseases
3.bacteria
2.infections (virulence (mycobacteria,
related to
listeria)
polysaccharide
4.kill tumor cells
capsule)
End result of activation
Differentiation of
B cells into
antibody
secreting cells
called plasma
cells
Hypersensitivity reactions I, II, III are
antibody
mediated
Secrete locally
acting proteins
called cytokines
IV is cell
mediated
Regulator of antibody
synthesis
No
Yes
Onset
Rapid
Delayed type
hypersensitivity
Antibodies
Evaluation
Formed
Not formed
From plasma
Skin test for
level of antibodies development of
delayed type of
hypersensitivity
Cells involved
Ab synthesis
requires 3 cells:
1.t lymphocytes
2.b lymphocytes
3.macrophage
1.macrophage
2.helper T cells
3.natural killer T
cells
4.cytotoxic T cells