A short discussion on Antigen and Vaccine

Vaccine

A preparation of inactivated or attenuated microorganisms or toxoids to include artificially acquired active immunity.

Types of vaccine:
1. Live vaccine
2. killed vaccine
3. Toxoid vaccine
4. Bacterial cell component vaccine
5. Viral subunit vaccines
6. Vaccines produced by genetic manipulation and


Now let’s read details to know about the characteristics and other features of vaccines.

1. Live vaccine: A vaccine prepared from living attenuated organisms or from viruses that have been attenuated but can still replicate the cells of the host organism. They multiply in the human host and provide continuous antigenic stimulation of the host organism. For example: Small pox, Measles Mumps and Rubella vaccine.

However it is important to know about safety and other factors of these vaccines.

Here the common problems of this vaccine include are:
a. Under attenuation
b. Mutation leading to reversion to virulence
c. Preparation instability
d. Preparation instability
e. Contaminating viruses in cultured cells
f. Heat stability

Advantages of live vaccine:
1. Live vaccine can provide strong and long immune response as they are similar to natural germ.
2. Due to strong immune response triggered by live vaccines, fewer doses of the vaccines are not usually required.
3. Live vaccines are safe in the majority of healthy children and usually do not cause illness.

Disadvantages of live vaccine:
1. Live vaccines must be kept cold, which can make transport vaccines difficult; especially in remote communities
2. Live vaccines cannot be administered to immune-compromised people due to risk of serious illness.
3. Even though there is careful selection of viral and bacterial strains used in live vaccinations, there is still some risk of reversion to a more strong strain virulent of the germ.



a. Killed Vaccine: Killed vaccines are suspensions of bacteria or viruses by disinfectants such as phenol or formaldehyde.
A vaccine prepared from dead microorganisms, generally used to provide immunization from organisms that are too virulent to be used to provide in the living attenuated state. For example: Polio, Hepatitis A and B, Tetanus, Diphtheria vaccines etc.

Advantages of killed vaccine:
1. They cannot infect the body with the relevant diseases. As inactivated or killed vaccines do not contain live germs, they carry no risk of reversion.
2. They can be given to immune-compromised hosts. As inactivated vaccines can’t attack any part of the body they are safe for people with immunity issues.
3. They are easy to transport and store as they can be freeze dried and still remain effective.


Disadvantages of killed vaccine:
1. Some inactivated or killed vaccines are less effective in providing immune protection than the live version.
2. It can be costly to inactivate or kill some germ components.

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3.Toxoid vaccine:
Toxoid vaccines are preparation derived from the toxins that are secreted by certain species of bacteria.

In manufacture of this vaccines the toxoid is separated from the bacteria cross infection. The most faithful approach is through the training and education of patients and hospital staff, pharmaceutical staff, so that medicine is used in their intended purpose.
For example: Diphtheria and tetanus vaccines.
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4. Bacterial cell component vaccines: Several bacterial vaccines are now available that consists of whole bacterial cell, as in conventional “Whopping cough” vaccines but if selected components of bacterial cell.
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5. Viral subunit vaccine: Originally non-replicated vaccines are derived from crude preparation of virus from animal tissues. Viral subunit vaccines like influenza vaccine, consisting of the two subunits of influenza virus known as the Haemagglutin and Neuraminidase.

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6. Vaccine prepared by manipulation: The technique of genetic manipulation has been applied to vaccine manufacture in various ways. In the case of viral vaccine it has been possible to transfer the gene possible for the production of the Hepatitis B surface antigen, HBs Ag to yeast cell expression of the gene in amount sufficient for vaccine.
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Synthetic peptides:
Synthetic peptides are the vaccine which is modern time known as the new researched vaccine. Though the name of the vaccines is like a amino acid stucture but it also a good type of vaccine,
Synthetic peptides: These are potential vaccines now that the amino acid sequences and structure of some proteins immunogens have been resolved. For example: tetanus toxoid to increase their immunegenicity.

Advantages of synthetic dyes:
1. Production and Quality control is simpler.
2. No external protein, therefore less toxic.
3. Safer in cases where viruses are oncogenic or establish a persistent infection.
4. Feasible even if virus cannot be cultivated.

Disadvantages of synthetic peptides:
1. May be less immunogenic than the conventional inactivated whole virus vaccines.
2. Requires adjuvant.
3. Requires primary course if infections followed by boosters.


Antigen: 
An antigen is simply any substance foreign to the immune system that causes an immune response, such as specific antibody production, when it has been brought into close contact with the tissues of any animal that is sensitive to it, and can combine with the specific antibodies that is formed.

A good antigen shows the following features:
A. Inter-molecular areas of stable structure and complex bonding
B. Large stretches which are not composed of long repeating units.
C. A molecular weight of at least 8000 to 10000 Da.
D. Can undergo processing by the immune system.
E. Have regions that can be presented antibody-forming process to stimulate the immune system.
F. Has structural dissimilarity with the host.
G. Peptide antigens should contain Immune-genic response with at least 30% of amino acids such as lysine, glutamine, arginine, glutamic acid, aspargine, aspartic acid, called immunogenic amino acids, as well as sufficiently high numbers of hydrophilic acid or charges functional groups.
H. An antigen reacts with antibodies mainly in an observable way.
I. By chemical nature, pure Poly-saccharides and Lipo-poly-saccarides are good antigens.
J. Antigens must have foreignness character.  

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