regnant women are more susceptible to the effects of
microbial products (i.e., endotoxins) and were the most
vulnerable subjects during the 1918 pandemic (influenza A
subtype H1N1), with a mortality rate that ranged between 50 and
75% (1). Exposure to the virus during pregnancy may also have
overt or subclinical effects that become apparent only over time.
Although substantial progress has been made in the understanding
of the immunology of pregnancy, many unanswered questions
remain, especially those associated with the susceptibility and severity
of infectious agents of mothers and unborn children (2), (3).
Epidemiological studies have demonstrated an association
between viral infections and preterm labor (4, 5) and fetal congenital
anomalies of the CNS and the cardiovascular system
(6–8). Although some viral infections during pregnancy may be
asymptomatic (9), approximately one-half of all preterm deliveries
are associated with histological evidence of inflammation of
the placenta, termed acute chorioamnionitis (10), or chronic chorioamnionitis
(10). Despite the high incidence of acute chorioamnionitis,
only a fraction of fetuses have demonstrable
infection (11). Most viral infections affecting the mother do
not cause congenital fetal infection, and only in a small number
of cases is the virus found in the fetuses (12–17), attesting to the
unique ability of the placenta to act as a potent barrier with an
immune-regulatory function that protects the fetus from systemic
infection (10, 12, 18, 19).
regnant women are more susceptible to the effects ofmicrobial products (i.e., endotoxins) and were the mostvulnerable subjects during the 1918 pandemic (influenza Asubtype H1N1), with a mortality rate that ranged between 50 and75% (1). Exposure to the virus during pregnancy may also haveovert or subclinical effects that become apparent only over time.Although substantial progress has been made in the understandingof the immunology of pregnancy, many unanswered questionsremain, especially those associated with the susceptibility and severityof infectious agents of mothers and unborn children (2), (3).Epidemiological studies have demonstrated an associationbetween viral infections and preterm labor (4, 5) and fetal congenitalanomalies of the CNS and the cardiovascular system(6–8). Although some viral infections during pregnancy may beasymptomatic (9), approximately one-half of all preterm deliveriesare associated with histological evidence of inflammation ofthe placenta, termed acute chorioamnionitis (10), or chronic chorioamnionitis(10). Despite the high incidence of acute chorioamnionitis,only a fraction of fetuses have demonstrableinfection (11). Most viral infections affecting the mother donot cause congenital fetal infection, and only in a small numberof cases is the virus found in the fetuses (12–17), attesting to theunique ability of the placenta to act as a potent barrier with animmune-regulatory function that protects the fetus from systemicinfection (10, 12, 18, 19).
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