Microbiology and Immunology

WORLD OF MICROBIOLOGY AND IMMUNOLOGY Immunity: active, passive, and delayed

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The type of immunity invoked by the active response

tends to be permanent. Once the antibody has been produced, an

individual will be protected against the presence of the target

antigen for a lifetime. The immune system has a capacity for

memory of the antigen. If presented with the antigen challenge

again, the immune machinery responsible for the formation of

the corresponding antibody is rapidly triggered into action.

An example of active immunity is the injection into

healthy individuals of the disabled toxins of bacteriasuch as

Corynebacterium diphtheriae, the agent causing diphtheria,

and Clostridium tetani, the agent that causes tetanus. This

rational was first proposed by Paul Ehrlich. In 1927, Gaston

Ramon attempted his suggestion. He separately injected inac-

tivated version of the bacterial toxins and was able to demon-

strate an immune response to both toxins. This rationale has

carried forward to the present day. A combination vaccine con-

taining both inactivated toxins is a routine inoculation in

childhood.

Another historical development associated with active

immunity involved Louis Pasteur. In 1884, Pasteur used

weakened cultures of Bacillus anthracis, the causative agent

of anthrax, and inactivated sample from the spinal cords of

rabbits infected with the rabiesvirus to produce immunity to

anthrax and rabies. Pasteur’s method spurred the development

of other active immune protective vaccines. Just one example

is the oral poliomyelitisvaccine developed by Albert Sabinin

the 1950s.

Passive immunity also results in the presence of anti-

body. However, the particular individual does not produce the

antibody. Rather, the antibody, which has been produced in

someone else, is introduced to the recipient. An example is

the transfer of antibodies from a mother to her unborn child

in the womb. Such antibodies confer some immune protection

to the child in the first six months following birth. Indeed, the

transient nature of the protection is a hallmark of passive

immunity. Protection fades over the course of weeks or a few

months following the introduction of the particular antibody.

For example, a newborn carries protective maternal antibod-

ies to several diseases, including measles, mumps and

rubella. But by the end of the individual’s first year of life,

vaccinationwith the MMR vaccine is necessary to maintain

the protection.

Another example of passive immunizationis the admin-

istration to humans of tetanus antitoxin that is produced in a

Vaccination against hepatitis.

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