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!!!!