The influence of pregnancy on CD8 cell subsets in women.

Adaptation of the maternal immune system to accommodate the semi-allogeneic
fetus is necessary for pregnancy success. Dysregulation of the maternal immune
adaptation is implicated in reproductive disorders such as infertility,
recurrent miscarriage, fetal growth restriction, and preeclampsia, which
together affect at least 25% of women seeking to reproduce.

The exact mechanisms being responsible for fetal tolerance are not known,
however T cells, natural killer (NK) cells, monocytes, and macrophages are all
regarded as important players in the adaptation of the maternal immune
response. Especially regulatory T cells (Treg) cells are thought to have an
important role in pregnancy. Treg cells are a subset of T cells with
immunosuppressive capacities, and are able to regulate immune responses and
regulate other immune cell subsets. Altered levels of Treg cells are associated
with adverse pregnancy outcomes, both in human and animal studies, and
furthermore, Treg based therapies improved pregnancy outcomes in animal studies.

Interestingly, incidences of immune related pregnancy disorders are higher in
first pregnancies, with lower rates of for example preeclampsia, in second and
third pregnancies. These epidemiologic findings could be explained by a priming
mechanism of the maternal immune system during pregnancy, which remains intact
after pregnancy. Which enables the maternal immune system to respond more
adequate to a possible following pregnancy .

Recently, both human and mouse studies have shown the effect of parity on the
maternal immune system. Depletion of Treg cells is known to cause fetal
resorptions in mice. A recent study shows lower rates of fetal resorptions in
second pregnancies compared to first pregnancies after depletion of Treg cells.
This study showed that in a second pregnancy T cells accumulate with
accelerated kinetics in lymph nodes compared with the first pregnancy. An
effect of previous pregnancies may also exist in women, as nulliparity was
associated with lower percentages of Treg cells in blood compared with parous
women.

The role of CD8 cytotoxic T cells in pregnancy is of recent interest, but
remains to be defined. CD8 cells are important in the cytotoxic immune
reaction. This immune reaction starts after a cell presents a foreign antigen.
Allogenic peptides derived from for example microbes are presented on cells by
specialised proteins called major histocompatibility complexes (MHC). In MHC
class I associated immunity MHC class I molecules express peptides derived from
intracellular antigens. The antigens are processed intracellularly, after which
they are presented on MHC class I molecules. CD8+ cells bind to the MHC class I
expressing cells, the CD8+ cytotoxic T cells become activated and kill the
antigen-expressing cells. This mechanism is very important for the immune
system in recognising foreign cells out of *own* cells. Interestingly, in human
pregnancy there is absence of classical MHC class I expression on trophoblasts
cells (the cells which invade the uterus), which causes partial prevention of
immune attack by maternal T cells. However, trophoblast cells do express HLA-C
and also the non-classical MHC molecules HLA-E and HLA-G, these molecules bind
to CD8 cells.

CD8 cells can be divided into subsets based on their function and phenotype;
naïve, effector, memory, and (recently) regulatory CD8+ cells. Till now there
is not a lot known about CD8 cell subsets in pregnancies, previous studies
found altered levels of activated CD8 cells in decidual tissue, but no
differences in peripheral CD8 cells between pregnant and non pregnant women.
These studies only analysed certain subsets of CD8 cells, and did not compare
former pregnant women with non pregnant women.

We hypothesise that pregnancy alters levels of CD8 subsets, not only during
pregnancy but also after pregnancy, preparing the maternal immune system for
any subsequent pregnancies.

Primary Objective: The main objective of this study is to analyse the effects
of pregnancy on levels and percentages of CD8 cell subsets in peripheral blood
both during and after pregnancy.

This study is an observational study. Levels of CD8 cell subsets will be
analyzed in peripheral blood in 3 subject groups. Namely, early gestational
pregnant women (n=15), former pregnant women (at least 6 months post partum)
(n=15), and non pregnant women (n=15) at a single moment. In the pregnant
group blood samples will be taken (10 ml) at weeks 11-13 of pregnancy during
routine blood sampling. In the former pregnant women blood will be taken at
least 6 months post partum. Blood samples will also be taken from non pregnant
healthy women without any pregnancies in their medical history. In whole blood
we will measure levels of CD8 cell subsets and monocytes using standard
techniques which are operational in our laboratory.

If possible blood samples will be taken by means of an extra blood sample taken
at a routine sampling moment or blood will be taken at an extra blood sample
moment at a suitable time point. This will not pose any risk on the
individuals. This study investigates the pregnancy related immune chances in
normal pregnancy, eventually these chances might not happen in immune related
disorders of pregnancy, and therefore could potentially lead to therapies.
Subjects have no direct benefits of this study..