June 2009 KUWAIT MEDICAL JOURNAL 93

Review Article

The Immune System in : Friend or Foe?

Raj Raghupathy Department of Microbiology, Faculty of Medicine, Kuwait University, Kuwait

Kuwait Medical Journal 2009; 41 (2): 93-102 ABSTRACT

Pregnancy is an intriguing immunological paradox; how in the field of immunology of pregnancy has opened up the does an allogeneic survive despite a potentially possibility of cellular immune effectors that might underlie antagonistic maternal immune system, while tissue allografts these pregnancy complications. Particularly interesting are succumb to rapid immunological rejection? While several the effects that pro-inflammatory and anti-inflammatory hypothetical models have been proposed in the last five cytokines have on the conceptus and thus on the success and decades to explain the immunological success of pregnancy, failure of pregnancy. This review focuses on the association the model that has survived the test of experimentation between some cytokines and successful pregnancy on the is the one that proposes a state of immunomodulation one hand, and between other cytokines and complications of during pregnancy. Several factors appear to prevent the pregnancy as also the possible pathways of effector function rejection of the fetus. Yet, pregnancy can be compromised of cytokines in pregnancy loss. This review proceeds to by a variety of complications such as recurrent spontaneous discuss the therapeutic redirection of cytokine profiles , preeclampsia and preterm delivery. Research towards one that is favorable to the success of pregnancy.

KEY WORDS: allogeneic fetus, cellular immune effectors, immunomodulation in pregnancy

INTRODUCTION rejection; one of these was that pregnancy induces a One of the basic tenets of immunology is that state of immunosuppression in the mother because the host immune system recognizes anything that is of which rejection reactions are either not induced foreign or “non-self”, mounts an immune response or are not effective[1]. Subsequent experimentation against it and then eliminates it. Thus, pathogens, has demonstrated the lack of a generalized, toxins and foreign antigens in general are recognized systemic state of immunosuppression, though a and eliminated. This holds true for foreign cells and sort of immunomodulation, or manipulation of tissues as well, which is why tissues from other maternal immunity towards a less harmful and individuals are recognized as foreign and then more conducive status seems to be in effect. In fact, rejected. How then is the fetus not rejected? The some immune system factors actually act as positive fetus is derived from both paternal and maternal growth factors for the placenta, as we shall see later; genes, thus the fetus expresses both paternal and thus, the maternal immune system may actually maternal antigens. Paternal antigens, such as the contribute to nurturing the conceptus and to the strongly antigenic human leukocyte antigens (HLA) success of pregnancy. could well be foreign to the maternal host and could stimulate maternal immune responses which could The Maternal Immune System during Normal potentially lead to the immunological rejection of Pregnancy the fetus. The fact that pregnancy does succeed has Evidence from animal experiments and clinical long been considered an immunological paradox, evidence from humans indicate that humoral a puzzle of sorts, which prompted the British responses are enhanced during pregnancy[2]. On the immunologist Peter Medawar more than 55 years other hand, cell-mediated immune reactions such as ago to ask “How does the mother contrive to nourish delayed-type hypersensitivity, natural killer (NK) within herself an antigenically foreign fetus?” activity, cellular responses to intracellular infections Medawar went on to propose several mechanisms and the course of cell-mediated autoimmune for the protection of the fetus from maternal immune disorders are downregulated. These observations

Address Correspondence to: Dr Raj Raghupathy, PhD, FRCPath, Department of Microbiology, Faculty of Medicine, Kuwait University, P.O. Box 24923, Safat 13110, Kuwait. Tel: 25319602, Fax: 25332719, E-mail: [email protected] 94 The Immune System in Pregnancy: Friend or Foe? June 2009 suggest that there is a downregulation of membranes, cytotrophoblast and both maternal Th1-type immunity and upregulation of Th2- and fetal endothelial cells[10]. type immunity during pregnancy[2]. Th1-type IL-13, an anti-inflammatory Th2 cytokine has immunity is primarily mediated by Th1 cells and the capacity to limit inflammatory reactions that Th2-type immunity is induced by Th2 cells. Th1 may arise locally at the site of implantation and and Th2 cells are the two major subsets of CD4+ within the placenta during pregnancy. Dealtry T helper cells; these two subsets have different et al[11] demonstrated the expression of IL-13 by patterns of cytokine production and different human trophoblast cells and suggested that IL- roles in immune responses. Each subset induces 13 may play important roles in this dialogue that immune responses that are effective at handling aids in the establishment and maintenance of the certain types of pathogens, but can be ineffective, placenta. There are reports of significantly higher or even pathological if made in response to other IL-10 production by mitogen-activated PBMC in types of pathogens[3,4]. Th1 cells secrete the pro- pregnant women as compared with non-pregnant inflammatorycytokinesinterferon-γ (IFN-γ), tumor women[12]. Using a sensitive on-line quantitative necrosis factor-β (TNFβ), interleukin (IL)-2 and RT-PCR Kruse et al[13] reported significantly reduced TNFα; these Th1 cytokines activate macrophages expression of Th1 cytokine mRNA during normal and cell-mediated reactions important in resistance human pregnancy. Th1/Th2 ratios revealed a to infection with intracellular pathogens, and shift to a pronounced Th2 status. Significantly in cytotoxic and delayed-type hypersensitivity increased IL-4-producing CD4+ and CD8+ T cells (DTH) reactions. Th2 cells secrete IL-4, IL-5, IL-6, were demonstrated in normal pregnant women IL-10 and IL-13; these Th2-type cytokines induce as compared to non-pregnant women. In contrast, strong antibody production and are therefore Th1 cytokine-producing T cells were significantly commonly found in association with strong reduced in pregnancy, which is suggestive of a Th2 antibody responses that are important in combating shift in pregnancy[14]. Th2-type cytokine production infections with extracellular organisms. Which reportedly predominates in the second and third type of reactivity, Th1 or Th2, is activated first may trimesters of pregnancy[15,16] leading to a hypothesis influence the subsequent outcome; if a particular that successful pregnancy is correlated with and T cell subset is activated first or preferentially in perhaps depends on the preferential stimulation of a response, it can suppress the development of Th2 cytokine-producing T cells. the other subset. The overall effect is that certain Besides an anti-inflammatory effects mediated responses are dominated by either humoral (Th2) by Th2 cytokines, several other non-Th2 cytokines or cell-mediated (Th1) immunity[3,4]. Furthermore, have positive influences on the conceptus; Th1 cytokines such as IL-2, TNF-α and IFN-γ cytokines such as IL-3, granulocyte-macrophage generally tend to provoke inflammatory cellular colony-stimulating factor (GM-CSF) and colony- immune reactions and are thus also referred to as stimulating factor-1 (CSF-1) have been shown to act pro-inflammatory cytokines, while Th2 cytokines as growth factors for the placenta[2]. such as IL-10, IL-13 and IL-4 are considered Thus, we can view normal, successful pregnancy anti-inflammatory cytokines as they tend to as a situation in which the maternal immune system downregulate inflammatory reactions. acts in a “friendly” manner, either not generating What is the Th1/Th2 status during normal strong rejection reactions or keeping such reactions pregnancy? Pregnancy seems to bring about a under check. We can view this as a sort of a shift towards Th2 bias. Th2 cytokines have been “friendly”, protective role of the immune system in detected in post-partum human placental tissue[5], nurturing the conceptus and ensuring the success amniotic fluid[6], endometrium and decidua of of pregnancy. early pregnancy[7], and in supernatants from cultures of endometrial cells, decidual stroma[7], Maintenance of a Protective Th2 Status during cytotrophoblast[5] and epithelial cells. Pregnancy Piccinni et al[8] demonstrated significantly If pregnancy brings about a protective Th2-bias, higher levels of IL-4- and IL-10-producing T cell how is this bias maintained? Cytokines, hormones clones from the decidua of women with normal and other molecules appear to play critical roles in pregnancy than from women with unexplained directing the immune reactivity towards a Th2 bias recurrent spontaneous miscarriage (RSM). Some and then maintaining it that way. The Th2-inducing Th2 cytokines have been shown to be expressed effect of IL-4 predominates over other cytokines, in the human placenta; IL-10 is synthesized by the so that if IL-4 levels reach a given threshold, decidua, and amnion cells of the placenta[9], differentiation of Th cells into the Th2 phenotype IL-4 is expressed by the decidua, amniochorionic occurs. June 2009 KUWAIT MEDICAL JOURNAL 95

One of the most vital cytokines that helps in the presence of lower levels of the Th1 cytokines maintain a Th2 bias, once initiated, is IL-10; this IL-2 and IFNγ and higher levels of the Th2 cytokines anti-inflammatory, immunosuppressive cytokine IL-4 and IL-10, an environment that has been shown interferes with antigen presentation, downregulates to favor the development of Th2 cells[20]. The high cytokine production by Th1 cells and directly or levels of progesterone secreted at the beginning of indirectly inhibits NK responses[3,4]. Trophoblast pregnancy may well be necessary for the orientation cells produce IL-10 in a gestational age-dependent of the maternal immune response against the manner[12]. Chaouat and colleagues[17] have reported conceptus towards a Th2-like pattern; these Th2 high expression of IL-10 on murine and human cytokines downregulate the potentially antagonistic trophoblast and describe the placenta as a “strong Th1 response, thus preventing fetal rejection. Th2 cytokine shield”. Evidence for possibly crucial It is likely that prostaglandin E (PGE) plays roles for IL-10 came from the studies of Chaouat et useful roles in this immunomodulation given its al[18] in which the administration of IL-10 to - ability to inhibit IL-2 production, to inactivate Th1 prone mice was shown to reverse the high rate of cells and to inhibit cytotoxic activity of NK cells[29]; in these mice. Likewise, Rivera’s PGE may serve as one of the factors that skew the group showed that the increased uterine TNFα, balance in favor of Th2 responses. Glucocorticoids release of nitric oxide and apoptosis of uterine enhance Th2 activity, and synergize with IL-4[30]; epithelia that followed administration of LPS were thus the steroid alterations that occur in pregnancy all normalized upon injection of IL-10[19]. may influence decidual lymphocytes in favor of a Hormones have been shown to have important Th2 response. roles in promoting the differentiation of Th cells or in favoring the shifting of already differentiated CYTOKINES AND PREGNANCY COMPLICATIONS Th cells from one cytokine profile to another. We have seen how some cytokine patterns (i.e., Progesterone at concentrations comparable to anti-inflammatory Th2 cytokines) are conducive those present at the maternofetal interface, favors to successful pregnancy; evidence accruing from the development of human T cells producing experiments on animal models and humans Th2-type cytokines[20]. Thus, Piccinni proposes supports the contention that some cytokines are that the high levels of progesterone present at detrimental to the success of the conceptus. The the maternofetal interface during may activation of some forms of maternal cellular contribute, at least in part, to the development of a immunity is potentially hazardous for fetal prevalent Th2-type profile which allows successful development[31]. Cellular immunity mediated by pregnancy[21]. Progesterone may therefore be effector cells and/or cytokines released by them responsible at least in part for a Th1→Th2 switch have been shown to have significant deleterious at the maternal-fetal interface. Hill’s laboratory[22] effects on the conceptus[32,33]. The pro-inflammatory, and our laboratory[23,24] have demonstrated that Th1 cytokines TNFα, IFNγ and IL-2 contribute the production of Th1 cytokines by trophoblast adversely to the survival of the conceptus. The antigen-activated peripheral blood mononuclear injection of TNFα, IFNγ and IL-2 into pregnant mice cells (PBMC) cultures was significantly inhibited causes while the injection of antibodies by co-culture with progesterone. to TNFα results in a reduction in abortion rates Besides bringing about a skew towards Th2 in a murine model of natural, immunologically- reactivity, progesterone has an indirect and very mediated abortion[34]. TNFα and IFNγ inhibit the interesting mediatory role in influencing the outgrowth of human trophoblast cells in vitro[35] Th1/Th2 balance; Szekeres-Bartho et al have and synergistically stimulate the programmed lymphocytes from pregnant females, when exposed death of human primary villous trophoblast to progesterone, produce an immunomodulatory cells[36]. factor, the progesterone-induced blocking factor Gradually, substantial evidence was obtained (PIBF). This protein suppresses various cell-mediated to demonstrate an interesting connection between immune reactions[25,26]. In mice[27] and in humans[28] Th1 cytokines and pregnancy loss[33,37,38] just as PIBF upregulates Th2 cytokine production and researchers observed interesting connections thus brings about a shift in the Th1 to Th2 cytokine between successful pregnancy and Th2 immunity. bias. PIBF is proposed to play an important role in How are cytokines associated with clinical pregnancy by helping the conceptus escape immune complications of pregnancy? Most laypersons surveillance. Thus, priming and maturation of T cells may think of pregnancy as a very successful in pregnancy would seem to occur in an environment phenomenon, but it is not nearly as successful as that is gradually progesterone-enriched. This would one might think; the actual rate of early pregnancy result in T cell priming, activation and differentiation loss after implantation may be as high as 31%[39]. 96 The Immune System in Pregnancy: Friend or Foe? June 2009

About 15-20% of fertilized are lost within and may play a role in reproductive failure while the first 2 weeks of fertilization and another 10- Th2 immunity may be the natural response to the 15% are lost during the next 12 weeks of gestation. trophoblast, in contributing to normal, successful A variety of conditions threaten the success of pregnancy[42]. the fetus; these include spontaneous miscarriage, We have published convincing evidence for a pre-term delivery, pre- and premature clear Th1 cytokine bias in RSM. Peripheral blood rupture of membranes. For these conditions, not all lymphocytes from normal pregnant women at the cases can be attributed to the so called “known” or end of the first trimester and at delivery, and from “explained” causes such as chromosomal anomalies, recurrent aborters at the time of abortion, were endocrinologic abnormalities, infections, anatomic stimulated with a mitogen and the supernatants problems and humoral factors. For example, as tested for Th1 and Th2 cytokines. Levels of several many as 60% of the cases of RSM are consigned Th2 cytokines were higher at the end of the first to “unknown” or “unexplained” etiology[40]. The trimester and at delivery in normal pregnancy than existence of such a large proportion of cases with in RSM, while the levels of pro-inflammatory Th1 unidentified etiologies has inspired interest in the cytokines were uniformly higher in RSM than in investigation of possible immunologic etiologies of normal pregnancy[43,44]. This was substantiated by pregnancy failure. studies on specific maternal immunity to placental antigens assessed by co-culturing maternal Cytokine Patterns in Recurrent Spontaneous lymphocytes with autologous placental cells and Miscarriage exposing maternal lymphocytes to a trophoblast RSM is one of the most common and challenging antigen preparation[45]. Since the absolute complications of pregnancy faced by obstetricians. concentrations of secreted cytokines may not reveal Spontaneous miscarriage is defined as a clinically a Th1- or Th2-bias per se, we analysed the ratios of detectable pregnancy loss prior to 20 weeks of Th1 to Th2 cytokines in the various permutations. gestation; one of every four pregnant women In every combination of Th1 to Th2 cytokines, the suffers from one or more pregnancy losses. Only ratios were higher in the RSM group as compared about 40-50% of RSM, defined as the occurrence to the normal pregnancy group, indicating a greater of three or more pregnancy losses before the 20th Th1-bias in RSM and a greater Th2-bias in normal week of gestation, is attributable to the so called pregnancy. “known” causes such as chromosomal anomalies, Decreased production of Th2 cytokines and endocrinologic abnormalities, infections, anatomic increased production of Th1 cytokines by antigen- problems and humoral factors, with as much as stimulated lymphocytes were demonstrated 60% relegated to “unknown” or “unexplained” in women with RSM as opposed to those from etiology[40]. Thus, the causes of RSM remain normal pregnancy[46]. Piccinni et al demonstrated “unexplained” in the majority of women. significantly higher levels of Th2 cytokine- Extensive research into immunologic etiologies producing T cell clones from the decidua of women and pathogenesis of RSM has shown that the with normal pregnancy than from women with conceptus appears to be fairly impervious to unexplained RSM[8]. Most reports thus support the attack by humoral immunity except for anti- contention that women with recurrent miscarriage phospholipid antibodies[41]. This then raised the exhibit a predominantly Th1 cytokine pattern, possibility of cell-mediated immune effectors as whereas healthy women exhibited decreased Th1 possible etiologic agents for RSM. This includes cytokines and increased Th2 cytokines; there is thus cellular immunity mediated by effector cells and/ an increased pro-inflammatory cytokine bias in or cytokines released by them, and these have been recurrent miscarriage[42-48]. shown to have significant deleterious effects on the How might Th1 cytokines bring about conceptus. spontaneous miscarriage? Several mechanisms Most studies to date suggest that women with involving natural killer (NK) cells, activated RSM have a greater Th1-type or pro-inflammatory macrophages and direct apoptosis have been cytokine bias as compared to normal pregnant suggested as being responsible for Th1 cytokine women. Hill and colleagues have shown that PBMC mediated effects. Increased NK activity in the blood of women with a history of RSM when stimulated and has been linked to miscarriage; in fact, with a human trophoblast antigen extract produce elevated NK levels in the blood has been shown to higher levels of the Th1 cytokines and embryotoxic be predictive of RSM[49]. While direct cell-mediated activity as compared to normal pregnancy[38]. lysis of trophoblast cells by NK cells has not been They concluded that Th1 immunity to trophoblast demonstrated, it has been proposed that NK cells, antigens is associated with recurrent miscarriage like activated Th1 cells, could release inflammatory June 2009 KUWAIT MEDICAL JOURNAL 97 cytokines that are harmful to the trophoblast. Hill in cervicovaginal fluid, IL-1, TNFα and IL-6 in and Choi speculate that cells in the decidua respond placental cells and IL-1β, IL-6 and IL-8 in amniotic to trophoblast invasion by generating a Th1- and chorionic-decidual tissues and in cervical dominated response which could be detrimental secretions[57] are found in PTD as compared to normal to early placental growth and may be toxic to the term delivery. Indeed Romero et al propose that development of the [50]. Alternatively Th1 preterm labor in the setting of infection results from cytokines may convert NK cells to lymphokine- the actions of pro-inflammatory cytokines secreted activated killer (LAK) cells that have been shown as part of the fetal and/or maternal host response to lyse trophoblast cells; levels of LAK cells in the to microbial invasions and suggest that a fetal pro- blood correlate with high miscarriage rates[51]. inflammatory cytokine response is followed by the Decidual NK cells are not cytolytic, but produce IFNγ onset of spontaneous preterm parturition[58]. Dudley which activates decidual macrophages which then suggests that pre-term labor associated with sub- secrete toxic levels of nitric oxide[51]. For their part, clinical infection may trigger a dysregulation of a activated macrophages may bring about damage to local inflammatory response leading to a so called the conceptus not by direct lysis of trophoblast cells, “intra-uterine inflammatory response syndrome” but via the production of nitric oxide and TNFα[52]. leading to pre-term labor and delivery[59]. Even in The role of Th1 cytokines in this scenario would be the absence of intrauterine infection, pre-term labor to activate such cellular effectors and to also cause has been shown to be associated with enhanced apoptotic damage to the placenta. placental cytokine production; elevated levels of Th1 cytokines, such as TNFα and IFNγ, may IL-1, IL-6 and IL-8 have been demonstrated in directly damage the conceptus by apoptosis of premature parturition with no signs of infection[60]. trophoblast cells[37] and by inhibiting the secretion We have demonstrated that higher levels of of the growth-stimulating GM-CSF from the uterine the Th1 cytokines IL-2 and IFNγ are produced epithelium[36]. Clark et al propose that maternal by women with unexplained PTD, while greater “rejection” of the implanted conceptus may be concentrations of the Th2 cytokines IL-4, IL-5 due to the process of what they term “cytokine- and IL-10 are produced by mitogen-stimulated triggered vascular autoamputation” which involves peripheral blood lymphocytes from women with the activation of coagulation mechanisms, leading normal pregnancy[61]. Furthermore, the ratios of to vasculitis affecting maternal blood supply to the Th1 to Th2 cytokines in PTD versus normal term implanted embryo[53]. delivery are indicative of a bias toward stronger pro-inflammatory cytokine reactivity in PTD. These Cytokine Patterns in Preterm Delivery observations support the existence of a so-called Preterm delivery (PTD) is an important cause of intrauterine cytokine-based inflammatory response perinatal morbidity and mortality and a condition syndrome which may account for preterm labor for which there is a dearth of treatment modalities[54]. with both infectious and non-infectious etiologies, It occurs at a rate of 12.5%. Preterm labor is believed suggesting that the production of inflammatory to be initiated by inappropriately early activation cytokines may form the pathophysiologic basis for of elements that initiate normal parturition at this association. term. Factors that predispose to preterm labor and Thus, we can view the positive and negative preterm delivery include premature rupture of fetal influences of the immune system on pregnancy as membranes, pregnancy-induced hypertension, a sort of balancing act that needs to be performed to amniotic fluid infection, faulty placentation, serious ensure the success of pregnancy (Fig. 1). maternal disease and genetic factors. Several factors Based on these observations, therapies that such as changes in the levels of progesterone, down-regulate Th1 cytokine reactivity may well be oxytocin, relaxin, prostaglandins, cortisol, and valuable in the clinical management of recurrent corticosteroids have been studied in relation to the miscarriage and premature labour and delivery with onset of PTD; however, the etiology of many cases a predominant Th1 cytokine bias. Various strategies of PTD is unexplained[55]. are worth pursuing; these include the down- There is strong evidence available to suggest regulation of Th1 cytokines, the neutralization of Th1 that pro-inflammatory cytokines are involved in cytokines and the upregulation of Th2 cytokines. the sequence of events leading to preterm labour and delivery associated with intrauterine infection. MODULATION OF CYTOKINE RESPONSES Increased levels of the pro-inflammatory cytokines TOWARDS A PREGNANCY-FRIENDLY PATTERN IL-1, TNFα, IL-6 and IL-8 have been found in The demonstration of an association between the amniotic fluid of women with infection- conditions such as RSM and PTD and maternal Th1 associated preterm labor[56]. Higher levels of IFNγ cytokine bias on the other, has led to research on 98 The Immune System in Pregnancy: Friend or Foe? June 2009

presence of dydrogesterone or progesterone. Thus, the levels of Th1 cytokines decreased significantly while levels of Th2 cytokines increased significantly when cells were exposed to dydrogesterone or progesterone[23]. We found a marked reduction in the ratios of Th1 to Th2 cytokines indicating a decrease in Th1 cytokine bias in lymphocytes from both women with RSM[23] and with PTD[24]. In order to ascertain whether dydrogesterone and progesterone mediate their cytokine-modulating effects via the progesterone receptor, we tested the influence of the progesterone-receptor antagonist, RU486 on cytokine modulation by dydrogesterone and progesterone. Since RU486 competes with progesterone (and dydrogesterone) for the progesterone-receptor, if the addition of RU486 reverses the effects of these substances, it would Fig. 1: The possible influences of maternal Th1 and Th2 immune indicate that dydrogesterone and progesterone have reactivity on pregnancy. Th1-type cytokines acting directly and to interact with the progesterone-receptor in order via effector cells such as activated macrophages, activated natural to affect cytokine production. When PBMC from (NK) cells and lymphokine-activated killer (LAK) cells may lead to subjects with unexplained RSM were cultured with pregnancy complications and pregnancy loss. On the other hand, Th2 cytokines, progesterone, progesterone-induced blocking dydrogesterone or progesterone in the presence or factor (PIBF), cytokines such as IL-3, GM-CSF and CSF-1 that have absence of RU486, we observed increased levels of placental growth-promoting properties help prevent Th1-mediated IFN-γ and TNF-α which are otherwise suppressed deleterious effects on the conceptus. by dydrogesterone and progesterone, and decreased levels of IL-4 and IL-6 which are otherwise manipulating the cytokine balance so as to down- upregulated by dydrogesterone and progesterone. regulate pro-inflammatory cytokines such as IFNγ Thus RU486 reverses the effects of dydrogesterone and TNFα; this is expected to create an environment indicating that the effect of dydrogesterone and that is more conducive to the success of pregnancy. progesterone is mediated via the progesterone One approach would be to use a hormone such receptor[23]. as progesterone, which has been shown to have Our data based on laboratory studies indicate anti-inflammatory and immunosuppressive that significantly lower levels of the Th1-type properties[62]. Piccinni and colleagues demonstrated cytokines IFN-γ and TNF-α are produced by that progesterone induces the development of lymphocytes exposed to dydrogesterone. These human T cells producing Th2 cytokines[20]. They two cytokines have been shown to deter embryo propose that as the Th1 cytokines IFNγ and TNFα development, implantation events and proliferation may compromise pregnancy, the production of Th1- of the trophoblast[54] and to have apoptotic effects inibitory Th2-type cytokines may allow allograft on human trophoblast cells[36]. In animals, these tolerance and fetus survival and that progesterone- cytokines bring about fetal demise when injected mediated immunosuppression is needed for the during gestation[34]. Furthermore, IFN-γ and TNF-α “natural” maintenance of normal gestation. may mediate placental / fetal damage via activation These observations inspired us to investigate of NK activity and macrophages[52], both of which dydrogesterone (6-dehydro-9β, 10α-progesterone) in their activated states have been shown to have for potential immunomodulatory properties. deleterious effects on the embryo. Thus, studies Dydrogesterone is a potent orally-administered demonstrating an association between high levels progestogen, similar to endogenous progesterone in of these Th1 cytokines and unexplained RSM its molecular structure and pharmacological effects, indicate a potential benefit in down-regulating their with a high affinity for the progesterone receptor. production. We exposed lymphocytes from women with RSM or We found that IL-4 and IL-6, both Th2 cytokines, are with PTD to the progestogens, dydrogesterone and upregulated in the presence of dydrogesterone[23,24]. progesterone, and observed that dydrogesterone Increased production of IL-4 has been shown to favor brings about a significantly reduced secretion further Th2 bias which would affect the eventual of the Th1 cytokines IFN-γ and TNF-α, as does outcome of Th1/Th2 dichotomy[3,4]. It is relevant to progesterone. On the contrary, levels of IL-4 and IL-6, note that progesterone has been shown to promote both Th2 cytokines, are significantly elevated in the the differentiation of T cells into Th2 effectors and is June 2009 KUWAIT MEDICAL JOURNAL 99 proposed to be responsible for a Th2 switch at the to inhibit the oxytocin effect of prostaglandin maternal-fetal interface during normal, successful and stimulation of alpha-adrenergic receptors gestation[20]. In our studies, progesterone was may explain its ability to prevent preterm labor tested at a concentration (10-5 mol/l) that is similar and delivery; our studies described here suggest to that achieved at maternal-fetal tissues. Thus a possible additional, non-mutually-exclusive the increased production of the Th2 cytokine IL-4 mechanism to elucidate the protective effect and the decreased production of the Th1 cytokines of progestogens in preterm delivery. Based on IFN-γ and TNF-α together could well result in a evidence that indicates an inflammatory bias in substantial swing in Th1/Th2 reactivity towards preterm labour and delivery, shifting the cytokine the pregnancy-conducive Th2 profile and away production profile away from an inflammatory from the potentially harmful Th1 profile. bias in the uterus may well lead to the prevention In summary, considering that inflammatory of preterm labour and delivery. cytokines such as IFN-γ and TNF-α may have effects Hill et al propose that potentially immuno- that are detrimental to pregnancy and may lead to suppressive doses of progesterone which has miscarriage, a shift in cytokine production patterns been termed “nature’s immunosuppressant” may away from a predominance of these cytokines may benefit individuals in whom the etiology of RSM well lead to the prevention of pregnancy loss due to related to maternal Th1 cytokine predominance[22]. miscarriage. However, progesterone administered orally is As far as PTD is concerned, a number of recent poorly absorbed, is subject to first-pass mechanism, publications by several investigators supports the has a short biologic half life[66], loses much of its idea that progesterone should be considered for bioactivity[67] and is rapidly cleared[68]. Therefore the preventive therapy in women with a history of orally-active progestogen dydrogesterone is quite spontaneous preterm delivery. Several promising attractive from this perspective. clinical studies have been reported on the use of 17 α- Our data indicates that dydrogesterone, a progestogen hydroxyprogesterone caproate (17P), a progestogen currently indicated for progesterone-related pregnancy that is structurally related to progesterone and disorders, has an immunomodulatory capability – in vitro dydrogesterone and that has been used for recurrent it appears to be able to induce a maternal cytokine shift miscarriage and various menstrual disorders in from Th1 cytokine dominance towards a Th2 bias, which women presenting with a history of spontaneous has been described as being conducive to successful PTD. Administration of 17P in a clinical trial resulted pregnancy[23,24,69]. Our observations are based on in vitro in a significantly lower occurrence of PTD as well studies; if clinical trials confirm the immunomodulatory, as a reduction in the risk of low birth weight[63]. cytokine-redirecting capability of dydrogesterone, A recent double-blind, placebo-controlled trial in then this molecule may well serve as an effective, safe women with a history of spontaneous PTD showed and orally-administered therapeutic intervention in that weekly injections of 17P led to a substantial unexplained RSM and PTD. decrease in the rate of recurrent PTD as well as a In summary, it appears that there are very strong reduction in the likelihood of perinatal mortality interactions between the immune system and the and very low birth weight infants[63]. Further reproductive system; cross-talk between these two analysis of this data revealed that the use of 17P not systems seem to be both positive and negative. The only reduces the overall risk of preterm delivery maternal immune system seems to contribute to but also reduces the risk of in women the success of pregnancy, by stimulating responses with a history of PTD[64]. that protect, rather than harm, the fetus. However, A recent meta-analysis of randomized controlled inappropriate maternal immune responses seem trials concluded that patients treated with 17P to be capable of compromising pregnancy. Much had lower rates of PTD. Administration of 17P or of this cross-talk between the immune system and progesterone suppositories in a clinical trial led to the conceptus is done by cytokines, with the Th2 a significant protective effect against PTD in six out type of cytokine pattern nurturing the conceptus of seven published clinical trials[65]. Taken together, and the Th1 type of pattern having deleterious these results suggest that patients who have had a effects on the conceptus. Future studies will no prior spontaneous preterm birth may benefit from doubt focus on the development of modalities for progesterone therapy. preventing and treating such cytokine-mediated Progesterone reduces intracellular calcium complications. levels and reducing uterine contractility, and promotes myometrial relaxation, thus sustaining ACKNOWLEDGEMENTS uterine quiescience. This relaxant effect of This study was supported by Kuwait University progesterone on the uterus in addition to its ability Research Administration Grant MI02/05. 100 The Immune System in Pregnancy: Friend or Foe? June 2009

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