I) PASSIVE IMMUNITY
The immunity that non-immune individual acquires by receiving antibodies or sensitized white blood cells from another immune individual is known as passive immunity.
The immunity is caused by passive immunization is less effective and inferior than that caused by active immunization. The main advantage of passive immunization is that it is immediate in its action of producing immunization and so this method would be used when immediate immunity is needed.
Passive immunity is also two types namely Natural and artificial.
a) Natural Passive immunity:
The immunity transferred from the mother to the child passively is known as natural passive immunity.
In human beings, this natural passive immunity occurs mainly by the passage of antibodies from the mother to her unborn child through the placenta during the later part of pregnancy.
The antibodies that are transferred are entirely Ig.G as other immunoglobulin sub-types (A, D, E and M) do not pass the placental barrier.
In other primates and in most of the other mammals such as pig the transfer of antibodies from the mother to the young one occurs mainly orally through the colostrums (the first milk produced by the mother after the birth of the offspring).