IMMUNITY

By:

Dr Asma Jabeen

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 T-lymphocytes occur

shortly before birth and few months

after birth

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

THANK YOU