2. INTRODUCTION
• A vaccine is a biological preparation
that improves the immunity to a
particular disease.
• It contains certain agent that not only
resembles a disease causing
microorganism but it also stimulate
body immune system recognize the
foreign agent.
3. IMMUNITY AND IMMUNE SYSTEM
• A condition of being able to resist a particular disease.
• The immune system is the body's defense against infections.
• The immune system attacks germs and helps to keep us healthy.
4. PARTS OF IMMUNE SYSTEM
• Many cells and organs work together to protect the body. White blood cells, also
called leukocytes, play an important role in the immune system.
• Some types of white blood cells, called phagocytes , chew up invading organisms.
Others, called lymphocytes, help the body remember the invaders and destroy
them.
• The two kinds of lymphocytes are B lymphocytes and T lymphocytes. Lymphocytes
start out in the bone marrow and either stay there and mature into B cells, or go to
the thymus gland to mature into T cells. B lymphocytes are like the body's military
intelligence system — they find their targets and send defenses to lock onto them. T
cells are like the soldiers — they destroy the invaders that the intelligence system
finds.
5. TYPES OF IMMUNITY
Humans have three types of immunity-
• Innate immunity: Everyone is born with innate (or natural) immunity, a type of
general protection. For example, the skin acts as a barrier to block germs from
entering the body. And the immune system recognizes when certain invaders are
foreign and could be dangerous.
• Adaptive immunity: Adaptive (or active) immunity develops throughout our lives.
We develop adaptive immunity when we're exposed to diseases or when we're
immunized against them with vaccines.
• Passive immunity: Passive immunity is "borrowed" from another source and it lasts
for a short time. For example, antibodies in a mother's breast milk give a baby
temporary immunity to diseases the mother has been exposed to.
6. HOW DOES THE IMMUNE SYSTEM
WORK?
• When the body senses foreign substances (called antigens), the immune system works to recognize
the antigens and get rid of them.
• B lymphocytes are triggered to make antibodies. These specialized proteins lock onto specific
antigens. The antibodies stay in a person's body. That way, if the immune system encounters that
antigen again, the antibodies are ready to do their job. That's why someone who gets sick with a
disease, like chickenpox, usually won't get sick from it again.
• This is also how immunizations (vaccines) prevent some diseases. An immunization introduces the
body to an antigen in a way that doesn't make someone sick. But it does let the body make
antibodies that will protect the person from future attack by the germ.
• Although antibodies can recognize an antigen and lock onto it, they can't destroy it without help.
That's the job of the T cells. They destroy antigens tagged by antibodies or cells that are infected or
somehow changed. (Some T cells are actually called "killer cells.") T cells also help signal other cells
(like phagocytes) to do their jobs.
9. HOW DO MACROPHAGES
RECOGNIZE THE MICROBES?
• All cells and microbes wear a “uniform” made up of molecules that cover their
surfaces. Each human cell displays unique marker molecules unique to you.
Microbes display different marker molecules unique to them.
• The macrophages and other cells of our immune system use these markers to
distinguish among the cells that are part of our body, harmless bacteria that reside
in our body, and harmful invading microbes that need to be destroyed.
• The molecules on a microbe that identify it as foreign and stimulate the immune
system to attack it are called “antigens.” Every microbe carries its own unique set of
antigens, which are central to creating vaccines
10. LYMPHOCYTES TAKE OVER
There are two major kinds of lymphocytes, T cells and B cells’
• T cells function either offensively or defensively.
• The offensive T cells don’t attack the microbe directly, they use chemical weapons to
eliminate the human cells that have already been infected.
• These cytotoxic T cells, also called killer T cells, can “sense” diseased cells that are
harboring the microbe.
• The killer T cells latch onto these cells and release chemicals that destroy the
infected cells and the microbes inside.
• B cells make and secrete antibodies.
• Antibodies usually work by first grabbing onto the microbe’s antigen, and then
sticking to and coating the microbe.
11. ANTIBODIES IN ACTION
• The antibodies secreted by B cells circulate throughout the human body and attack
the microbes that have not yet infected any cells but are lurking in the blood or the
spaces between cells.
• When antibodies gather on the surface of a microbe, it becomes unable to function.
• Antibodies signal macrophages and other defensive cells to come eat the microbe.
• Antibodies also work with other defensive molecules that circulate in the blood,
called complement proteins, to destroy microbes.
12. CLEARING THE INFECTION: MEMORY
CELLS AND NATURAL IMMUNITY
• When T cells and antibodies begin to eliminate the microbe faster than it can
reproduce, the immune system finally has the upper hand. Gradually, the virus
disappears from the body.
• After the body eliminates the disease, some microbe-fighting B cells and T cells are
converted into memory cells.
• Memory B cells can quickly divide into plasma cells and make more antibody if
needed.
• Memory T cells can divide and grow into a microbe-fighting army.
• If re-exposure to the infectious microbe occurs, the immune system will quickly
recognize how to stop the infection.
