Cell-mediated immunity is a
type of immunity where the entire cell is involved in the attack against
microorganisms. Unlike humoral immunity, which involves the release of
antibodies into fluids, cell-mediated immunity is carried out by T cells that
do not release antibodies.
The Role of Humoral Response
Humoral immunity, on the
other hand, involves the release of antibodies by B cells into blood plasma,
tissue fluid, and lymph. The attack on microorganisms occurs in the fluid,
hence the term "humoral" as "humor" refers to fluid. B cell
antibodies are responsible for attacking bacteria and some viruses.
The Immune System's Memory
The immune system has memory
cells, which are divided into two types: memory cells and effector cells (also
known as plasma cells). Effector cells, or plasma cells, secrete a large number
of antibody molecules into blood, tissue fluid, and lymph, but they have a
short lifespan of only a few days. On the other hand, memory cells survive for
longer periods of time and enable a rapid response to any future infection.
The Importance of Memory Cells
Memory cells play a crucial
role in providing immunity against subsequent infections. If a person is
exposed to the same antigen again, the memory cells stimulate the production of
a large quantity of antibodies, resulting in a rapid and heightened immune
response called the secondary response. The secondary response is greater and
faster than the primary response to the initial infection, as the population of
memory cells is larger than the original population of B cells. This phenomenon
is the basis of vaccination and booster doses, where each exposure to an
antigen leads to a more efficient immune response.
Types of Immunity: Active and Passive
Immunity can be classified
as either active or passive, and both can be acquired naturally or
artificially. Artificially providing immunity is known as immunization.
Natural active immunity is
acquired through exposure to an infection, where the body produces its own antibodies
against the infectious agent. Memory cells formed during the first exposure to
the antigen enable the production of a large quantity of antibodies upon
subsequent exposure, resulting in a highly effective and long-lasting immune
response that can persist for a lifetime.
Artificial
Active Immunity (Vaccination)
Artificial active immunity,
also known as vaccination, is achieved by injecting small amounts of antigen,
called a vaccine, into the body. This stimulates the body to produce antibodies
against the antigen. Booster injections may be given to enhance the production
of antibodies, resulting in long-lasting protection against the disease.
Different types of vaccines are available, including toxoids, killed organisms,
live attenuated organisms, and new vaccines developed using modern molecular
biology and genetic engineering techniques.
Passive
Immunity
Passive immunity involves
the transfer of antibodies from one individual to another, providing immediate
protection against infection. Unlike active immunity, which takes time to
develop, passive immunity provides immediate but temporary protection as the antibodies
are gradually broken down by the body's natural processes.
Natural
Passive Immunity
Natural passive immunity can
be acquired when antibodies from a mother cross the placenta and enter the
fetus, providing protection until the baby's immune system is fully functional.
Passive immunity can also be provided through colostrum, the first secretion of
the mammary glands, which contains antibodies that are absorbed by the baby
through its gut.
Artificial
Passive Immunity
Artificial passive immunity
involves the direct administration of pre-formed antibodies, also known as immunoglobulins,
from a donor to an individual in need of immediate protection against a
particular pathogen. These antibodies are typically harvested from human donors
or produced through recombinant DNA technology, and they can be purified and
concentrated for therapeutic use.
Artificial
passive immunity can be used in various situations, including:
Post-exposure prophylaxis:
When an individual has been exposed to a particular infectious disease, such as
rabies or hepatitis B, artificial passive immunity can be administered to
provide immediate protection while the individual's own immune system mounts a
response. This can be especially critical in cases where the disease has a
short incubation period and may progress rapidly.
Prevention
of certain diseases: Artificial passive immunity can also be used
for prophylaxis in situations where individuals are at high risk of exposure to
a particular pathogen, such as healthcare workers dealing with patients
infected with highly contagious diseases.
Treatment
of certain diseases: Some diseases, such as certain autoimmune
disorders, may be treated with artificial passive immunity to help modulate the
immune response and reduce disease severity.
It's important to note that
artificial passive immunity provides temporary protection, as the transferred
antibodies eventually break down and are eliminated from the body. It does not
confer long-term immunity, as is the case with active immunity achieved through
vaccination or natural infection. However, artificial passive immunity can be a
valuable tool in certain situations where immediate protection is needed or in
individuals who are unable to mount an effective immune response on their own.
New
Vaccines: Modern Approaches to Vaccine Design
Advancements in molecular
biology and genetic engineering have opened up new possibilities for vaccine
design. One alternative approach is to synthesize antigens artificially from
amino acids once their amino acid sequences are known. This allows for precise
control over the antigenic properties of the vaccine, leading to potentially
more effective and safer vaccines.
Passive
Immunity
Passive immunity involves
the transfer of antibodies from one individual to another, providing immediate
protection against infection. Unlike active immunity, which takes time to build
up, passive immunity provides rapid but temporary protection as the transferred
antibodies are broken down by the body's natural processes over time.
Natural
Passive Immunity
Passive immunity can occur
naturally, such as when antibodies from a mother cross the placenta and enter
her fetus, providing protection until the baby's own immune system is fully
functional. Colostrum, the first secretion of the mammary glands, can also
provide passive immunity as the baby absorbs antibodies through its gut.
Artificial
Passive Immunity
Artificial passive immunity
involves extracting antibodies from one individual and injecting them into the
blood of another individual, which may or may not be of the same species. This
can be used for immediate protection if a person has been or is likely to be
exposed to a particular disease. For example, specific antibodies used for
combating tetanus and diphtheria used to be cultured in horses and injected
into humans, but now only antibodies of human origin are used for humans.
Antibodies against rabies and some snake venoms are also available, as well as
antibodies against the human rhesus blood group antigen used for some rhesus.
Concluding all of the above,
the immune system is a complex network of cells and molecules that work
together to protect the body from harmful microorganisms. Cell-mediated
immunity involves T cells, which do not release antibodies but play a crucial
role in defending against intracellular pathogens. Humoral immunity, on the
other hand, involves B cells that release antibodies into the blood, tissue
fluid, and lymph, providing defense against extracellular pathogens. The immune
system also has a memory, with memory cells enabling a rapid and efficient
response to future infections. Immunity can be acquired naturally through
exposure to infections or artificially through vaccination. Passive immunity
provides immediate but temporary protection through the transfer of antibodies,
either naturally from mother to fetus or artificially through the injection of
antibodies. Advancements in vaccine design continue to improve the
effectiveness and safety of vaccines, offering promising prospects for the
prevention and control of infectious diseases.
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