Regulation of phenotypic maturation of intact and interleukin-2-activated NK and NKT cells by chorionic gonadotropin.
The explanation of mother immune system toler
ance to genetically allogenic fetus is a topical issue of
reproductive immunology, whose important branch is
the study of the role of hormones in immune system
control. In terms of maintaining normal pregnancy,
chorionic gonadotropin (CG) is the key hormone
having evident immunomodulatory properties [1, 2].
Natural killer cells (NK cells), together with the T
cells fulfilling the functions of natural killer cells
(NKT cells), play a significant part during pregnancy.
It is known that NK and NKT cells lyse not only target
cells infected with intracellular pathogens, but also
neoplasms, as well as cells of the trophoblast [3, 4].
Moreover, NKT cells actively produce cytokines
inducing type 2 immune response [5, 12].
Interleukin (IL2), increasing the NK and NKT
cell cytotoxic potentials [1] and trasforming NK cells
into lymphokineactivated killers (LAK cells) capable
of lysing trophoblasts [6], is one of essential activation
factors for NK and NKT cells. It is known that the
syncytioblast releases IL2 into the matricular–pla
centary compartment during pregnancy [7]. Thus,
mother immune system cells simultaneously contact
CG and IL2 in the hemochorial zone.
The aim of our research was to estimate the influ
ence of CG on the phenotypic maturation of intact
and IL2activated NK and NKT cells.
We obtained new facts proving that CG promotes
phenotypic maturation of intact NK and NKT cells.
IL2 significantly increases only the number of NK
cells, without affecting the level of NKT lymphocytes
with CD16 expression, which indicates phenotypic
maturation. Upon IL2 stimulation, CG at concen
trations normal for the first pregnancy trimester sup
presses the NKactivating IL2 effect. At the same
time, IL2activated NKT cells become more suscep
tible to the differentiation hormone activity.
A mononuclear leukocyte suspension from periph
eral blood of healthy nonpregnant women during the
follicular phase of the menstrual cycle (n = 5) was used
in our research. Mononuclear cells were fractioned by
density gradient centrifugation in ficollverografin
solution (1.077 g/cm3). After rinsing twice in Hanks’
solution, the final suspension (1 × 106 ctlls/ml) was
incubated in complete culture medium (199 medium
containing 10 mM HEPES, 2.5 mM Lglutamine,
100 μg/ml gentamicin, and 10% FCS) together with
the hormone for a day at 37°С and 5% СО2.
CG was injected into cultures at concentrations
specific for pregnancy trimesters I and III (100 and
10 IU/ml, respectively) [8]. Recombinant IL2
(Sigma, United States) was used at a concentration of
100 IU/ml, which is equivalent to its level during
immune response development [9]. After a day of
incubation in the presence of the hormone, IL2, or
CHIL2, we studied the lymphocytes' phenotype by
estimating the proportions of NK cells with the CD3–
CD16+CD56+(CD3FITC/CD16.56PE) phenotype
and NKT cells with the CD3+CD16+CD56+ (CD3
FITC/CD16.56PE) phenotype according to the
antibody producer protocol (Beckman Coulter,
United States). The measurements were made using
an EPICS XL flow cytofluorimeter (Beckman
Coulter, United States). Statistical data analysis was
performed using paired Student’s t test. In some cases,
Pearson’s correlation coefficient was calculated.
It is known that NK cells with the CD16+CD56+
phenotype are the most mature and possess a high
cytolytic activity [9, 10], because the molecule of
CD16 is a lowaffinity receptor for IgG1 and IgG3
(Fcγ RIII) Fc fragments and takes part in antibody
dependent cellular cytotoxicity response, as well as in
cytokine secretion induction [11].
It has been found that both CG and IL2 increased
the number of CD16+CD56+NK cells. Note that combined injection of the hormone and IL2 also retained
its stimulating effect on NK cells. However, together
with the IL2 stimulating effect, a high concentration
of CG (pregnancy semester I) statistically significantly
mitigate the cytokine activation impact (Fig. 1). A
close correlation (r = 0.76, p < 0.05) between an iso
lated CG effect (100 IU/ml) and the combined effect
of CG (100 IU/ml) and IL2 (r= –0.84, p <0.05) con
firms the conclusion that the mitigating effect is deter
mined by the hormone.
Therefore, CG enhances the NK cells phenotype
maturation and appears to suppress LAK transforma
tional cytokine action, which may be the mechanism
of hormonal control protecting the fetus against
mother immune attack during pregnancy.
It has been shown that, at the level of NKT cells,
CG increases the amount of CD16+CD56+NKT cells
irrespective of the concentration, while IL2 per se has
no influence on these cells. CG maintains its stimulat
ing effect during the combined action of cytokine and
CG (Fig. 2). Note that, in the case of combined stim
ulating effect of CG (10 IU/ml) and IL2 at low con
centrations, cytokine acts as the hormone’s costimu
lator, since the stimulating effect of the hormone
together with IL1 at this concentration is significantly
higher than the effect of CG itself (10 IU/ml). Thus,
the IL2 presence does not change the direction of CG
stimulating effect, and in the case of low CG concen
trations, IL2 enhances its NKTpotentiating activity.
Altogether, the data obtained evidence that CG
promotes maturation of NK and NKT cell phenotypes
associated with increase in their cytotoxicity and
cytokine producing activity. At the level of NK cells,
CG plays a part of IL2 antagonist eliminating the
LAKactivating cytokine activity. At the same time,
CG and IL2 are costimulator factors of NKT cell
phenotype maturation.
