Humoral antibodies of the IgG class are able to cross the placenta from mother to fetus.
PASSIVE (ARTIFICIALLY ACQUIRED) IMMUNITY
Humoral antibodies of the IgG class are
able to cross the placenta from mother to fetus. These antibodies will provide
passive protection of the newborn against those diseases which involve humoral
immunity and to which the mother is immune. In this manner, most newborn infants
in the UK will have passive protection against tetanus, but not against
tuberculosis. Protection against the latter relies to a large extent on cell-mediated
immunity. Secreted (IgA) antibodies are also passed to the gut of newborn,
together with the first deliveries of breast milk (colostrum). Such antibodies
provide some passive protection against infections of the gastrointestinal
tract. Maternally acquired antibodies will react with antigens associated with an
infection but also with antigens introduced to the body as part of an
immunization programme. Premature immunization, i.e. before degradation of the
maternal antibodies, may reduce the potency of an administered vaccine. This
aspect of the timing of a course of vaccinations is discussed later.
Administration of preformed antibodies taken from animals, pooled human
serum, or human cell lines is often used to treat existing infections (e.g.
tetanus, diphtheria) or condition (e.g. venomous snake bite). Pooled serum may
also be administered prophylactically, within a slow-release vehicle, for
individuals travelling to parts of the world where diseases such as hepatitis A
are endemic. Such administrations confer no long-term immunity and may
interfere with concurrent vaccination procedures.
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