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IMMUNITY
- By Ashwini PSaveetha Medical College
Definition – Immunity Active Immunity Passive Immunity Herd Immunity Agents causing Immunity
Resistance exhibited by the host towards injury caused by microorganisms and their products
Types ◦ Innate immunity◦ Acquired immunity
Immunity which an individual develops as a result of infection or by specific immunization
Can be acquired in three different ways◦ Following clinical infection
Chicken pox, rubella, measles
◦ Following subclinical infection Polio, diphtheria
◦ Following immunization
Primary Response
Determined by,◦ Dose and nature of antigen◦ Route of administration◦ Nutritional status of host
Immunological memory◦ Purpose of immunization
Secondary Response
Differs in a number of ways◦Shorter latent period◦Production of antibodies more rapidly◦Antibody more abundant◦Antibody response maintained at higher
levels for longer periods◦Antibody Greater capacity + Antigen
Immune response
Active immunity mainly depends on
Humoral immunity Cellular immunity Combination
B Cells Specific Ab’s (IgA, IgG, IgM,
IgE, IgD)
Antibodies are specific Acts directly by neutralizing the microbe or
its toxin Efficient phagocytosis
Proliferates
Secretes
Fundamental role in resistance to infection Mediated by T cells Initiates a chain of responses Responsible for immunity against many
diseases like Tb, Brucellosis
Joint functions of T and B lymphoid cells with some accessory cells constitute the complex events of immunity
Advantages of active immunity◦ Long lasting◦ Protective efficacy of active>passive◦ Less expensive
When antibodies produced in one body are transferred into another to induce protection against disease it is called passive immunity
Induced by Transfer of maternal antibodies across the placenta Administration of antibody containing preparation
Advantages – Immunity is rapidly established
Disadvantages – Temporary and no immunological memory
It’s the level of resistance of a community or a group of people against a particular disease
Epidemic wave declines – Herd immunity builds up
Elements contributing◦ Occurrence of clinical and subclinical infections in
the herd◦ Immunization of the herd◦ Herd structure
Vaccination Injection of a weakened form of the actual
antigen that causes the disease
Vaccines Live vaccines
BCG, Measles, Oral polio Preparation
More potent immunizing agents than killed vaccines
Live organisms
Tissue culture orChicken embryo
Lost capacity to induce full blown disease but retained their immunogenicity
BCG vaccine
Measles vaccine
Examples for live vaccines:
Polio vaccine
Administration of polio vaccine
Inactivated or killed vaccines Cholera, pertussis vaccine
Preparation
Safe but less efficient than live vaccines
Live organisms
Inactivated by head or chemicals
Stimulates active immunity
Examples of inactivated vaccines:
Cholera vaccine Pertussis vaccine
Toxoids Toxins produced by organisms are
detoxicated and used in the preparation of vaccines
Leads to production of antibodies The Abs produced neutralize the toxic
moiety produced during infection
Cellular fractions Vaccines are prepared from extracted
cellular fractions meningococcal vaccine, pneumococcal vaccine
Structure of immunoglobulins:
Normal human immunoglobulin ◦ Antibody rich fraction obtained from a pool of
1000 donors◦ WHO has laid down definite standards for its
preparation◦ Used to prevent measles aand HepatitisA
infection
Specific human immunoglobulin
◦Prepared form plasma of patients-recovered from an infection or from immunized
individuals◦Should contain atleast 5 times the antibody
potential of the standard preparation per unit volume
◦Used mainly for prophylaxis purposes
Materials prepared in animals Antitoxins prepared from non human
sources are still the mainstay of passive immunization◦ Eg. Antisera against tetanus and diphtheria
SUMMARY
Park's textbook of preventive and social medicine
Textbook of microbiology-Ananthanarayanan
Internet-google images
India no longer a polio-endemic countrysays WHO!
NO MORE POLIO
THANK YOU!!!!
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