Natural antimicrobials in pregnancy
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Date
2008Author
Stock, Sarah J.E.
Metadata
Abstract
Natural antimicrobials are peptides that are essential components of the innate
immune system, providing broad-spectrum protection against bacteria, yeasts and
some viruses. In addition to their innate immune activity, they exhibit properties
suggesting they interact with the adaptive immune system. These functions imply
they may be of particular importance in pregnancy. Intrauterine infection is
responsible for approximately one third of cases of preterm labour, and normal
labour is considered an inflammatory process, associated with leukocyte invasion of
the uterine tissues and increased cytokine production. Little is known, however,
about natural antimicrobial expression in pregnant reproductive tract. The aim of this
thesis was thus to characterize natural antimicrobial production in pregnancy. The
study focused on two main areas - the lower genital tract, comprised of the vagina
and cervix; and the innermost fetal membrane, the amnion.
In the lower genital tract, levels of natural antimicrobials were determined in samples
of cervicovaginal secretions collected from pregnant women, using enzyme linked
immunosorbance assay (ELISA). In addition Taqman quantitative PCR and ELISAs
were used to investigate natural antimicrobial production by cell lines derived from
endocervical, ectocervical and vaginal epithelium. It was found that elafin and
secretory leucocyte protease inhibitor (SLPI) were found at high concentrations in
cervicovaginal secretions, but levels were diminished in women with the common
vaginal infection bacterial vaginosis (p<0.05). Cells derived from the vaginal
epithelium expressed greater amounts of elafin than cervically derived cells.
However, elafin and SLPI production could be stimulated in endocervical cells by
the bacterial product lipopolysaccharide, a response that was not seen in the vaginal
cell line.
Natural antimicrobial production in the amnion was examined in tissue explants and
primary cultured amnion cells, using a combination of Taqman PCR and ELISAs. In
addition, cDNA microarray was carried out to investigate factors controlling
amniotic antimicrobial production, and the involvement of signalling pathways was studied using specific pathway inhibitors. It was shown that the amnion expressed
five antimicrobials: human beta defensins (HBD) 1, 2 and 3, SLPI and elafin.
Expression of HBD2 was significantly upregulated following normal labour
(p<0.05), with production in primary amnion epithelial cells dramatically increased
by IL-1ß. The pattern of HBD2 expression in response to IL-1ß was biphasic, which
suggested involvement of a secondary gene product. Several putative influential
factors were identified by cDNA micorarray, including the NF-kappaB cofactor NFkappaBinhibitorζ.
Its relationship to HBD2 was explored. The involvement of both
NF-kappaB and mitogen activated protein (MAP) kinase p38 signalling appeared
crucial in the response.
This work has shown that natural antimicrobials are expressed by both the lower
genital tract, where infections that are associated with preterm labour originate, and
in the amnion, which is the fetus last line of defence to infection. They may have an
important role in the prevention of infection associated preterm labour. Further
characterization of these responses may increase understanding of the physiology,
and pathophysiology of labour, and lead to strategies for the prevention of premature
delivery.