The immunological agents are the agents
which produce active or passive immunity
and are used to prevent or to modify certain
infectious disease. Immunity can be
defined as the ability of the body to
neutralize and eliminate the pathogens and
their toxic products.
The immunity can be divided into two
sub-groups:
I. Active immunity:
Humoral immunity.
Cellular immunity.
Combination of these two.
II. Passive immunity:
Normal human Ig.
Specific human Ig.
Animal antitoxins or antisera.Active Immunity
Active immunity depends upon the
humoral and cellular responses of the host.
It is the immunity which an individual
develops as a result of infection and
production of antibodies or cells having a
specific action on the microorganisms
concerned with a particular infectious
disease or on its toxin.
The active immunity may be acquired
following clinical infection (chicken pox,
rubella, measles), following subclinical
infection (polio and diphtheria) and
following immunization with an antigen
which may be killed vaccine, live
attenuated vaccine or a toxoid.
When an antigen is administered for
the first time in human body, the antibodies
that is elicited first is entirely of the IgM
type. The IgM antibody titres rise steadily
during the next three to four days, reaches
a peak and then declines. Meanwhile if the
antigenic stimulus was sufficient, IgG
antibody appears in a few days, reaches a
peak in a week time and gradually falls over
a period of weeks or months, this is called
as primary response.
The secondary response is also known
as booster response. It differs from primary
response and has a shorter latent period,
production of antibodies is more rapid,
antibodies are more abundant, antibody
response is maintained at a higher level for
a longer period and antibodies elicited tend
to have a greater capacity to bind to the
antigen.(Mode of Action of Drugs)