 What is Vaccine? It is suspension of microorganism or fraction of
microorganism which is used to induce immunity. The vaccine mimics the role
of pathogen to the body. We might use a whole organism or part of it or
sometime genetically engineered antigenic part to be injected or taken orally
to produce immune response. As the microorganisms are virulent we need to
make them avirulent. Here comes the difference how we make that organism
avirulent which gives rise to different Types of Vaccines 1.Conventional Vaccines These contain whole living
pathogenic organisms. But those organisms are weakened; their pathogenic part
is attenuated or removed. So they cannot cause the infection rather they
mimic the actual infection to immune system. And body immune system produce
antibodies show humoral and cell mediated response against them and become
immune against that particular pathogenic organism. Preparation of this vaccine, a virulent form of wild organism is taken
usually a virus or bacteria, and placed in the differential media to subside
its pathogenecity and make it a virulent. This is done by serial passage in
foreign host like tissue embryonic egg or sometimes animals for multiple generations.
So in this way mutations are introduced in the new host. The pathogen which
is mutated now become different from the original virulent form and cannot
cause the infection in the host but rather can induce an immune response.
Sometimes high temperature conditions are also used to make microorganism
attenuated. Live attenuated vaccines are prepared from the strains
attenuated, which are completely devoid of pathogenecity but can induce
immune response. They multiply in the human body and reside there for longer
period of time. Characters: Induce both Humoral and cell mediated immune response local and systematic. These are heat unstable. It has of reverting back to pathogenic form but very rare. So potential harm to individuals with compromised immunity. It gives sufficient time for memory cells production. Applications: This technology is used to prepare vaccines for, Cholera
(caused by G.Negative bacteria), Vaccines against Salmonella species,
Tuberculosis BCG vaccines, Oral Polio Vaccine, Measles Vaccines, Leishmania
Species Vaccine, Influenza Virus vaccines, Mumps and Rubella Vaccines. b. Inactivated Killed
Vaccines (Killed microorganisms suspension) These
also contain the whole organisms i.e. whole bacteria or virus suspension, but
those are completely heat killed or inactivated. The organisms are pathogenic
when killed they cannot cause any infection, when injected the body immune
system recognize them as antigens and produce immune response against them.
Thus body becomes immune against that particular type of organisms. Characters: These do not stimulate local immunity. They produce shorter
response thus required a booster injection. They do not produce cytotoxic
T-cell response, as the pathogens are killed so safe in immune compromised
individual too. Usually it is heat stable. These do not converted back to
pathogenic or virulent form. Application: Tab Vaccine against enteric fever, Polio vaccine and
Influenza Vaccine, Typhoid Vaccine, cholera Vaccine, Also used against Rabies
in humans, Pneumonia Vaccines. 2. Genetically
Engineered Vaccines
These vaccines are prepared by genetic modification or just taken up
the antigenic genes and them amplify them and then make GMOs. a. Subunit/Recombinant
Vaccine These only
include the part of organism instead of using whole organism. The part is
antigenic, which induce the immune response and results in the production of
antibodies against that particular type of antigen used. The antigen part is protein,
usually 1-20 antigens used at a time which are taken directly or cultured in
the media taken from DNA of the Virus. These are also called recombinant DNA
subunit vaccines. Preparation: One
method is, a protein is isolated from virus and administered, but thus
protein may be weak and can be denatured and might associate with undesired
antibody. Second method is recombinant vaccine, in which a antigen gene from
Virus DNA is isolated and put into a vector which many be attenuated virus or
bacterium. The GM vector will express the antigen and is of no risk to host.
Bactria, viral, mammalian, yeast cells may be used for expression. Characters: these
may be single antigen or recombinant, Induce both humoral and cell mediated
response, usually stable, can also be given to the immune compromised
individuals; these are rather cheaper & simple to produce. Smaller
quantities are required for immune response. Applications: Influenza A and B vaccine, Recombinant Hepatitis B vaccine, Production
of hybrid Virus Vaccines, HBsAg, and Rabies. It also used to develop vaccines
for HIV and Ebola Virus. b. DNA Vaccine These are
the newest and most promising vaccines. Usually a piece of DNA of Bacterial
cell which is circular and small part. Experiments shows that plasmids with
naked DNA inserted into the muscle results in the production of protein
antigen (pathogen) encoded in the DNA. These proteins foreign to the host and
result in the immune response. There are different DNA vaccines depending
upon the host and vector being used. When the vectors used are highly
expression ones, then the immune response elicits by the vaccine would be the
best. Protein expression can be enhanced by optimizing the codons usage of
pathogenic mRNA for eukaryotic cell. Altering the genetic sequence of
immunogen to reflect the codon. Preparation: First of all the vectors and the genes are cut with
restriction enzymes at known sites, trimming of the open vectors and gene for
gene ligation, the spliced gene is put in the vector and ends of the vectors
joined with sliced gene. Now inserted into bacteria to get many copies of
this recombinant gene. Now purify the altered vectors from the bacteria. Can
be done by rupturing the bacterial cell and free vectors are obtained, now fill
up the syringe with the altered DNA vectors and billions of the vectors
inserted in the body and only 1% will work. Once the expressed proteins by
these recombinant vectors leave the cell body will recognize them. Characters: These are safe with no side effects, inexpensive and easy
to prepare, development time is relatively shorter, gives long term antigenic
protein production thus require low boosters. It gives Cytotoxic T cell and
helper T-cell response. And also Humoral response. Extended expression gives
good long-term immunological memory. It is very stable DNA vaccine. It is not
possible to revert back. Applications: So far for humans there is still clinical trials are
going on for usefulness. In animals two DNA vaccines are approved one is for
horses protect them against West Neil Virus and other protects the salmon
from viral disease.
c. RNA Vaccine
It involves the use mRNA for the synthesis of antigenic proteins
instead of DNA genes. As the RNA is single stranded and different from DNA so
there will be no chromosomal integration of foreign genetic material. When
administered it will be translated to proteins and will trigger the immune
response. RNA vaccines include mRNA and self amplifying RNA replicon has the
ability to overcome limitation with DNA vaccine. RNA vaccines will be
translated directly into the host cytoplasm. Work is still underway for the
RNA vaccines to be available for Vaccination. These will work faster than DNA
vaccines. Preparation: mRNA can be synthesized invitro, which will be translated
into the antigenic protein directly. Characters: Economical and fast acting can induce Humoral and Cell
mediated response. Can be given to immuno-compromised individuals. Long
lasting and booster are required. Applications: Can work quit well and efficiently
where the DNA vaccines work. Still trial work undergo in cancer patients and
HBV and HIV patients. Soon will be available in the market. Mechanism
of Vaccines against Infectious Diseases Vaccines
mimic the pathogen and trigger the humoral and Cell mediated immune response
in the body. Vaccines contains the antigens whether the whole organism or
antigenic part. DNA or RNA vaccines synthesis the antigenic part into the
host. Thus these antigenic proteins detected by the immune system causes the
immune response which include following main steps. Antigens Sound The Alarm: The
molecule on the surface of microbes also called epitopes, taken as antigens.
Every microorganism has unique set of epitopes and it is central to develop
vaccines. Macrophages engulf the cells and carry the epitopes to the lymph
nodes. A molecule called MHC displays these antigens to other immune cells.
This presentation recognized by the T cells which trigger the B cells to
produce antibodies. Lymphocyte
Takeover: Now it’s
time for lymphocytes which are B cells and T cells. T cells which are
defensive, they secrete the chemicals to show defensive response. In this way
some other immune responses may become activated. Helper T cells work with
killer T cells and also help B cells. B cells are very important to make and
secrete antibodies. Except
there are Cytotoxic T cells.CD8+ T lymphocytes which limits the infection.
Also secrete antiviral Cytokines CD4+ T helper lymphocytes. These helper T cells
may produce chemicals or help the B cells. Moreover CD4+ T cells are needed
for the antibodies production. Antibodies in Action: Immune
system only gets hold of antigens of the helper T cells and antibodies kill
the organism at faster rate than their reproduction. And gradually the
antigens or the microorganisms disappeared. After the eliminating the
microbes or antigenic protein some of the T and B cells become the Memory
cells and they quickly divide to make more antibodies against specific
antigen for which they were given task. Memory T cells further grow and
divide to become army of the immune system. Now when ever these particular
type organisms will attack body this army will eliminate the infection. |
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