Health Hygiene & Sanitation

Lesson 11 : Host Defences

Immunizing Agents

Immunizing agents are:-

1. Vaccines
2. Immunoglobulin
3. Antisera

1. Vaccines: Vaccine is an immune-biological substance designed to produce specific protection against a given disease. It stimulates the production of protective antibodies and other immune mechanisms. Vaccines may be produced from live modified organisms, inactivated or killed organism, extracted cellular fractions, toxoids or combination of these. Recent preparations are sub-unit vaccines and recombinant vaccines.

Live Vaccines: Live vaccines are prepared by passing live organisms repeatedly in the laboratory in tissue culture or chick embryo so that the organisms loose their capacity to induce full blown disease, but have retained their immunogenicity e.g. BCG, measles, polio. Live vaccines are more potent immunizing agents than killed vaccines, because –

1. live organisms multiply in the host hence antigenic dose is larger than injected
2. live vaccines have all major and minor antigenic components.

Live vaccine should not be introduced to persons with immunodeficiency disease.

Killed or inactivated Vaccine: Organisms killed by heat or chemicals will be injected into the body to stimulate active immunity. They are usually safe but less efficient than live vaccines.

Toxoids: Some organisms produce exo-toxins e, g. diphtheria and tetanus. The toxins produced by these organisms are detoxicated and used in the preparation of vaccines. The antibodies produced will neutralise the toxic compound produced during infection. Toxoid preparations are highly efficient and safe.

Polyvalent Vaccines: Vaccines which are produced from 2 or more strains of the same species. The term auto or autogenous vaccine is applied when the organism in the vaccine is obtained from same patient.

Combination: If more than one kind of immunizing agent is included in the vaccine it is called as mixed or combined vaccine.

2. Immunoglobulins:

The human immunoglobulin system is composed of 5 major classes. (IgG, IgM, IgA, IgD and IgE) and subclasses with them.

All antibodies are immunoglobulins. Whether all immunoglobulins are antibodies? It is a big question.

IgG: It is the major immunoglobulin of serum comprising about 85% of the total serum immunoglobulin.

1. It is the only immunoglobulin that can pass through the placenta,
2. it is largely extra-vascular.
3. It produces antibodies against gram positive bacteria.

Antiviral and antitoxic antibodies are found among IgG globulins.

IgM: It accounts for about 10 per cent of normal serum immunoglobulins. IgM is first to appear immediately after exposure to antigen. Its presence indicates fresh infection.

IgA: Constitutes about 15% of the total serum immunoglobulins. It is active against wide range of viral and bacterial antigens. IgA is found relatively in large quantities in body secretions like milk, saliva, tears, bronchial secretions, nasal mucosa, prostatic fluid, vaginal secretions and mucous secretions of the small intestine. It provides primary defence mechanisms at the mucous membrane against local infections.

IgD: It is present at the rate of 0.3 to 40 mg/100ml of total serum. Its main function is not yet determined.

IgE: It is present at the concentration of 10-130 microgram per 100ml. It is concentrated in sub mucous tissues. It is the major antibody responsible for allergic and anaphylactic reactions.

Immunoglobulin preparation:

There are 2 types

1. Normal Human Immunoglobulin: It is an antibody rich fraction obtained from a pool of at least 1000 donors. WHO has laid certain definite standards for the preparation of human immunoglobulin. Human immunoglobulin is used to


1. prevent measles,
2. to provide temporary protection against Hepatitis A infection for travelers to endemic areas
3. to control institutional and household outbreaks of hepatitis A infection.


2. Specific Human Immunoglobulin: It should contain at least 5 times the antibody potential of the standard preparation per unit volume. These preparations are made from the plasma of patients who have recently recovered from an infection or an individual who has been immunized against a specific infection.