Immunology

Immunization Dr. Nada A HassoPh.D Immunology

Immunization

Immunization is the means of providing specific protection against most common and damaging pathogens.
Active immunity
Passive immunity

Active immunity

This refers to immunity produced by the body following exposure to antigens
Naturally acquired active immunityExposure to different pathogens leads to sub-clinical or clinical infections which result in a protective immune response against these pathogens.
Artificially acquired active immunityImmunization may be achieved by vaccination of the host using live or dead pathogens or their components.


Passive Immunity
Immunity can be acquired, without the immune system being challenged with an antigen.

Passive immunity

Naturally acquired passive immunityImmunity is transferred from mother to fetus through placental transfer of IgG or colostral transfer of IgA.

Artificially acquired passive immunity

Immunity is often artificially transferred by injection with gamma-globulins from other individuals or gamma-globulin from an immune animal.

Artificially acquired passive immunity

Passive transfer of immunity with immune globulins or gamma-globulins is practiced in numerous acute situations of infections (diphtheria, tetanus, measles, rabies, etc.)
and as a prophylactic measure (hypogammaglobulinemia).

Cont,

This form of immunization has the advantage of providing immediate protection, but is of short duration .
Passive transfer of cell-mediated immunity can also be accomplished in certain diseases (cancer, immunodeficiency diseases).

Primary and secondary immune response

Primary response
Is the first exposure of an individual to a particular antigen.
The 1st class of Ab appear is the IgM after 5-7 days.
The primary response has a characteristic lag phase, during which naive B cells proliferate and differentiate into plasma cells and memory cells. Following this, serum antibody level increases logarithmically, reaches the peak at about day 14, remains at a plateaus for some time, then begins to drop off as the plasma cells begin to die.
The memory cells remain in Go phase, and have a much longer life than plasma cells; some memory cells persist for the life of the individual.

Secondary immune response

Faster and more prolonged than primary immune response
Due to the immunological memory of sensitized memory B cells

The antibody level peaks in about 7 days, and the level of antibody is about 100 to 1,000­fold higher than that in the primary response.
Antibodies bind with greater affinity and blood levels remain high for weeks to months

Primary and secondary antibody response

Vaccination

Types of vaccines
1. Live attenuated vaccines
Live attenuated vaccines are made up of living virus or bacteria that have been modified through a process to weaken (attenuate) and reduce its virulence .
These wild viruses or bacteria are attenuated in a laboratory, usually by repeated culturing.

Live vaccines

Live vaccines are used against a number of viral infections (polio (Sabin vaccine), measles, mumps, rubella, chicken pox, hepatitis A, yellow fever, etc.).

The only example of live bacterial vaccine is one against tuberculosis, the BCG).

Live vaccines normally produce self-limiting non-clinical infections and lead to subsequent immunity, both humoral and cell-mediated, the latter being essential for intracellular pathogens.
However, they carry a serious risk of causing overt disease in immunocompromised individuals.
Since live vaccines are often attenuated, they can revert to their pathogenic form and cause serious illness.
It is for this reason, polio live (Sabin) vaccine, which was used for many years, has been replaced in many countries by the inactivated (Salk) vaccine.

2. Inactivated vaccineskilled vaccines

Inactivated vaccines do not contain live virus or bacteria.
The diseases҆ microbes have been killed by chemicals, heat or radiation.
They cannot replicate and cause disease.
Inactivated vaccines stimulate a weaker immune response than live vaccines.
Immunity can also diminish over time and a booster dose is required to maintain immunity.
Inactivated vaccines can be composed of either whole viruses or bacteria, or fractions of either.
e.g: viral vaccines include those for polio (Salk vaccine), influenza, rabies.
Most bacterial vaccines are killed organisms ( typhoid, cholera, plague)


3. Conjugate
These vaccines are very important especially in young infants.
Some bacteria that can cause disease have a polysaccharides capsule that hides them from the immune system (especially immature immune system of infants).
Conjugate vaccines link these capsules to an antigen or toxoid that an immature immune system can recognize, so it can respond and produce immunity.
The linkage helps the immature immune system react to polysaccharide coatings and defend against the disease-causing bacterium.

Cont, Conjugate

Examples of conjugate vaccines are Haemophilus influenzae type B (Hib)vaccine, pneumococcal vaccine and meningococcal vaccines in which a non toxic tetanus toxoid or non toxic diphtheria protein is used as the link to stimulate the immune system.

4. Toxoid vaccine

When the cause of an illness is the bacteria releasing a toxin that affects the body, a toxoid vaccine can provide protection.
A vaccine from just the deactivated toxin ( toxoid), rather than the whole bacteria.
A toxin can be inactivated by treating them with formalin.
Toxoids are safe for use in vaccines and the immune system produces antibodies that lock onto and block the toxin.
Vaccines against diphtheria and tetanus are examples of toxoid vaccines

5. Subunit vaccine

Subunit vaccines use only part of a target pathogen to provoke a response from the immune system.
This may be done by isolating a specific protein from a pathogen and presenting it as an antigen on its own.
Such as The acellular pertussis vaccine and the influenza vaccine.


5. Subunit vaccine
Subunit Vaccine may also be produced by genetic engineering technology.
Examples: Hepatitis B and Human papilloma virus (HPV) vaccine ( vaccine to protect against cervical cancer).
These vaccines do not use the entire microbe, but instead are made from only part of the microbe.
Scientists use the ‘part’ that best stimulates the immune system.
A gene coding for a vaccine protein is inserted into a suitable vector. When the vector reproduces, the vaccine protein is also created
E.g. : hepatitis B and Human papilloma virus vaccines

These vaccines are designed to reduce the problems of toxicity and risk of infection.

Viral peptide genes cloned into vectors such as vaccinia virus, when the modified virus is introduced into a person’s body, it transfect host cells and the immunogen is expressed and presented, generating an immune response against the immunogen—and, as a result, against the pathogen it originates from. and consequently produce a response similar to that produced against live-attenuated viruses.
Experimental recombinant vaccinia strains have been designed to deliver protection against influenza, rabies, and hepatitis B.
This type of vaccine is still experimental.
6. Recombinant vector vaccine