immunology of pregnancy Flashcards
which systems adapt during pregnancy?
endocrine respiratory cardiovascular gastrointestinal renal function and fluid homeostasis reproductive immune system metabolic
why is pregnancy an immune paradox?
the fetus is 50% foreign BUT its worth maternal investment to ensure genetic material passed on, there is maternal tolerance of fetal semi-allograft
what gene expression occurs at implantation?
increase in growth factors, proteolytic enzymes and inflammatory mediators = facilitates implantation
change in expression of proteins needed for immune response preventing blastocyst rejection and inappropriate blastocyst invasion
how does a blastocyst implant?
endometrium develops transient receptivity for an embryo = WOI
may span cycle day 20-24
implantation will not happen if outside this time frame
human blastocyst undergoes interstitial implantation = decider permits invasion, primary decimal reaction = uterine stromal cell enlargement, uterine NK cells prominent
hypoxic conditions (2-5%) facilitates cut-trophoblast differentiation, maternal decidua = permissive function
what do cytotrophoblast cells differentiate into?
extra-villus trophoblast (EVT)
syncytiotrophoblast (ScTB)
why is the blastocyst not rejected?
Syncytiotrophoblast cells have no self:non-self markers so unlikely to stimulate the maternal immune system
extra-villus trophoblast cells have modified self:non-self markers = modified maternal immune response
what immune markers are present on maternal immune cells?
HLA-A
HLA-B
HLA-C
MHC-II
what immune markers are present on EVT?
HLA-G
HLA-C
HLA-E
what is the role of uterine natural killer cells?
70% of decimal immune cells, CD56 + and CD 16-
express killer cell Ig-like receptors high bind to MHC-I
they are less cytotoxic
they synthesis cytokines and chemokine - close interaction with EVTB o facilitate invasion,
uNK cell has HLA-G receptor which causes inflammation and immunomodulates IL8,10 VEGF, PGF
uNK cells have HLA-C receptor which can determine implantation outcome
HLA_-E receptor inhibits NK cell cytotoxicity, and prevents EVTB death
how does placentation occur?
first interaction = loose adherence, apposition
interstitial invasion = EVT migrate from cell columns, anchoring villi invade decimal glands. invasion is limited by decide basalis
spiral arteries are = small bore, high resistance, facilitates hypoxia. EVTs plug spiral arteries which may exacerbate hypoxia
serial artery re-modelled = wide bore and low resistance
endovascular invasion = driven by EVT and uNK cells, taps into maternal blood supply, is completed by 10-12 weeks
how far do EVT cells invade into the myometrium?
inner third
what happens if EVT endovascular invasion fails?
invasion localised to decidua, reduced acquisition of maternal blood supply causes various pathologies
what diseases are caused by failed endovascular invasion?
premature birth fetal growth restriction recurrent miscarriage placental abruption pre-eclampsia
what happens in invasion in placenta creta?
absence of decidua causes chorionic villi invasion, usually at site of Caesarean section,
how far is the invasion in acreta, increta and percreta?
acreta = superficial myometrium just past the decidua basalis increta = deeper myometrium percreta = penetrates uterine serosa, invades into surrounding organs - bladder, bowel etc
what are the risks of placenta acreta?
poor placental separation
significant post-partum bleeding
how does a T-helper cell become Th1 and Th2?
Th-1 = IL-12 and INF gamma Th2 = IL-4
what kind of immunity does Th1 cells produce?
NK cells
T-cells
macrophages
= cell-mediated immunity
what kind of immunity does Th2 cells produce?
B-cells
antibodies
= humeral immunity
what happens to T-helper cells during pregnancy?
progesterone causes inhibition of Th1 cells so cell mediated immunity is suppressed, cytokine balance favours Th2, meaning maternal humeral immunity active so can still fight infection and the fetus is protected therefore immune response is modified
what happens if Th2 cell bias does not occur?
INF gamma increases, exaggerated inflammatory response => maybe pre-eclampsia, re-current miscarriage, IUGR
what antibodies are present in pregnancy?
IgA - secreted in breast milk
IgD - B-cell membranes, no known effector function as serum protein
IgE - mast cells = anaphylaxis
IgG - only Ig to cross the placenta
IgM - pentameric structure early antibody
how does the mother prevent a harmful immune response to paternal HLA antigens?
IgG cross resting with paternal HLAs are removed to stop response. (the paternal HLAs are present on placental macrophages, chorionic villus) immune complexes then removed by macrophages
how does haemolytic disease of the new born occur?
maternal Ig raised against paternal antigens on fetal red blood cells, IgG against paternal HLA antigen are not removed and then cause lysis of fetal RBCs
how do you treat rhesus disease?
anti D prophylaxis - this destroys anti Rh +ve IgG therefore fetal RBCs not attacked
how does rhesus disease occur?
1st preg = sensitisation
- fetal blood mixes at term/post natally
- maternal immune response to Rh +ve antigens on fetal RBC, usually IgM subtype and IgM cannot cross the placenta, creates a memory B-cell to fetal Rh+ve antigen
subsequent preg = rapid immune response to fetal Rh+ve antigens on RBCs, IgG subtype made due to memory Bcell, only IgG crosses placenta. causes fetal demise due to lysis of fetal RBCs if no intervention
