The ability of the human body to resistalmost all types of organisms and toxins that tend to damage the tissues and organs is called IMMUNITY.
Activities of the immune system
• Defending against invading pathogens• Removing worn out cells & tissues damaged by
trauma/disease• Identifying and destroying abnormal or mutant
cells that have originated in the body “ImmuneSurveillance”
• Mounting inappropriate immune responses thatlead either to allergies or autoimmune diseases
Immunity
Innate Immunity
Active orAcquired immunity
Passive immunity
• Humoral Immunity• Cell mediated immunity
Innate Immunity
▪ Also called natural/non specific immunity▪ It is the inborn capacity of the body
to resist the entry of microorganismsin the body
▪ It results from general processes, rather than from processes directed against specific disease organisms
Innate immunity includes:
➢ Phagocytosis 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 compoundsin blood
• Lysozyme
• Basic polypeptides
• Complement complex
• Natural killer lymphocytes
Acquired Immunity
It is extremely powerful specific immunity that develops against an individualinvading agent, after the body is first attacked by a bacterium, virus, toxin orforeign tissues from other animals.
Types of acquired immunity
❑ Humoral immunity or B-cell immunity
❑ Cell- mediated immunity or T-cell
immunity
The body develops circulating antibodies
or activated T lymphocytes
➢ Antibodies are globulins in the blood capable of attacking the invading agent .
➢ Large no of activated lymphocytes are formed that are specifically present inlymph nodes to destroy the foreign agent
Acquired immunity is initiated by ANTIGENS
Each toxin or organism contains one or
more specific chemical compounds in its
makeup that are different from all
other compounds
An antigen :
➢ protein or large polysaccharides
➢ High molecular weight, 8000 or greater
➢ Regularly recurring molecular groups
called epitopes
T and B lymphocytes
Lymphocytes are essential for survival
of human beings.
No lymphocytes No acquired immunity
On exposure to an antigen:
➢ B- lymphocytes form antibodies .. Humoral
immunity
➢ T- lymphocytes form activated T lymphocytes….
Cell mediated immunity
Preprocessing of lymphocytes
After being formed from pluripotent
hematopoietic stem cells, lymphocytes are
preprocessed before going to their
destination, the lymphoid tissue
Thymus gland preprocesses the T-lymphocyte
After origination in bone marrow, migrate
to Thymus gland, divide rapidly and
thousands of lymphocytes leave thymus
and spread by way of blood throughout the
body to lodge in lymphoid tissue everywhere.
What happens in the Thymus ?
▪ Attain extreme diversity for reacting against different antigens
▪ Thousands of lymphocytes develop reactivity against thousands of antigens
▪ Selection of lymphocytes to be released
in blood by mixing with “self antigens”
Preprocessing of B-lymphocytes
B-lymphocytes are preprocessed in the
liver in the mid fetal life and in the bone
marrow in the late fetal life and after
birth
❑ Instead of whole cells, secrete
antibodies that are reactive agents
❑ Greater diversity than T-lymphocytes
❑ Many millions of antibodies with different
specific reactivities
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.
Clone of lymphocytes
Once the specific lymphocyte is activated
by its antigen, it reproduces wildly forming
tremendous number of duplicate lymphocytes
All the lymphocytes that are capable of
forming one specificity of antibody or
T-cell are called a
CLONE OF LYMPHOCYTE
Origin of clones of lymphocytes
Several hundred to few thousand genes code for Millions of different types of antibodies & T lymphocytes
• Random mixing of gene segments during preprocessing
Mechanism of clone activation
On the surface of B –cells, about
100,000 antibody molecules are present
that can bind to specific antigen.
When specific antigen comes and bind,
activation process begins.
On the surface of T-cell, there are
T-cell receptor proteins or T-cell markers
that are highly specific for one specified
activating antigen.
Role of macrophages in activation process
▪ Macrophages lining the sinusoids of lymph nodes engulf the invading organismand liberate antigenic products into cytosol.
▪ These are passed to lymphocytes for activation of lymphocyte clones
▪ Release IL-1
Role of T-cells in activationHelper T-cells
▪ Most antigens activate both T and
B cell
▪ Helper T-cells secrete Lymphokines
that activate specific B – cells
▪ Quantity of antibodies formed by
B-lymphocytes is slight without help
of T-cells