Passive Immunity

Passive immunization requires that antibodies be produced in a donor by active immunization and then these antibodies be given to susceptible animals in order to confer immediate protection. These antibodies may be raised in animals of any species and against a wide variety of pathogenic organisms. For example, they can be produced in humans against measles or hepatitis, in horses against tetanus, and in dogs against canine distemper.

·         One of the most important passive immunization procedures has been the protection of humans and other animals against tetanus by means of  antisera raised in horses.

·         The antibodies, known as immune globulins, are produced in young horses by a series of immunization injections.

·         Passive immunity is important for two major reasons:

1- It is essential for the protection of young animals during the first weeks or months of life from the dangerous micro-organism including viruses that are present in the environment into which animals are born. e.g. :Rota and Corona Viruses. and E.COLI

2- Maternally derived antibodies interfere with active immunization of the newborn and must therefore be taken into account when designing vaccination schedule.

·         Transfer of preformed antibodies or primed lymphocytes to a new recipient.  Usually, horse serum or pooled human sera are used.

·         Transfer can occur naturally, through placenta, milk or colostrum (e.g. diphtheria, tetanus, strep, rubella, mumps, polio)

·         Alternately, transfer can occur “manually”, via injection of antibodies into recipient

Passive immunization is performed in the following situations:

o   Recipient has congenital or acquired B cell defects

o   When exposure is likely, or when time doesn’t permit active immunization

o   When disease is already present (e.g. tetanus, spider/snake bites)

o   Risks include anti-isotype or anti-allotype responses in recipients