Staphylococcus epidermidis - virulence factors and innate ... - Munin

1.2.6 Antibodies in neonates
Antibodies are produced by B-lymphocytes, cells in the adaptive immune system, as an adaptive
response to an infection. The adaptive immune system is not generally covered in this thesis.
However, as antibodies interact with the innate immune system, I will give a short description of
their function in neonates. The fetus produce very little antibodies themselves due to immaturity
in the adaptive immune system, poor signaling between the innate and the adaptive immune
system and fetal life in a sterile environment (192). However, IgG antibodies (not IgM, IgA, IgE
and IgD) are actively transported across the placenta in the last trimester of the pregnancy (192).
Despite this active transfer, of antibodies, the total IgG level is lower in neonates (cord blood)
than in adults (255). Furthermore, differences in transport kinetics between the IgG subclasses
may cause quantitative differences in titers of IgG subclasses (191, 256), e.g. IgG1, IgG3 and
IgG4 are fairly efficiently transported across placenta whereas transport of IgG2 is less efficient
(256, 257). Titers of maternal IgG antibody decrease gradually during the first months after
birth.
Preterm infants are often born before the active placental transfer of antibodies has occurred, and
very low antibody titers in preterm neonates increase the risk for infections (258-260).
Consequently, several clinical trials have investigated the effect of pooled intravenous
immunoglobulin (IVIG) administration for prevention or treatment of neonatal sepsis (261-264).
Many of these trials were small and of poor quality. It has therefore for a long time been difficult
to make a clear recommendation whether immunoglobulins should be a part of sepsis treatment
in neonates or not. In September 2011 the results of a large randomized controlled trial (INIS
trial) including more than 3000 infants was published.(265) This study showed that therapy with
IVIG had no effects on the outcome of suspected or proven sepsis (265).
26