Ontogeny of the Immune Response

Ontogeny of the Immune Response

Ontogeny of the Immune Response

During development the human foetus receives antibodies from its mother through the placenta. These antibodies are all IgG, since only this class of immunoglobulins can cross the placenta. Most newly born animals cannot form specific antibodies, and would have been defenceless against infection had it not been for the antibodies acquired from the mother. Active synthesis of IgG is observed in infants after about six weeks after birth, although IgM and IgA synthesis begins earlier. Only after this period do the young ones become fully competent and respond to antigenic stimulus.

On being exposed to various microorganisms the infant begins to produce antibodies against them. This immunity may be comparatively short lived, e. g. about three years for smallpox, or may last several years, or even the entire lifetime, in the case of certain diseases. In any species the newborn animal also receives antibodies from the co strum of maternal milk, which contains high levels of IgG or IgA. This type of immunity is called passive or natural immunity. Passive immunity is due to the presence of preformed antibodies obtained from the mother. It can also be given to adults by injections of gamma globulin, e.g. in the case of tetanus and infectious hepatitis.

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