Comentarios Dr. Alberto Romeu

RESUMEN ORIGINAL

Objective: To examine interleukin-12 (IL-12), IL-18, IFN-g, intracellular adhesion molecule-1 (ICAM-1), leukemia inhibitory factor (LIF), and migration inhibitory factor (MIF) levels in precisely-timed blood and endometrial tissue samples from women with idiopathic recurrent pregnancy loss (RPL).

Design: Case-control study.

Setting: University hospital.

Patient(s): Twenty-one women with RPL and 20 women with proven fertility (controls).

Intervention(s): Primary endometrial cells and blood samples during the midsecretory phase (days 19–23).

Main Outcome Measure(s): Detection of IL-12, IL-18, IFN-g, ICAM-1, LIF, and MIF via enzyme-linked immunosorbent assay in both blood and endometrial tissue samples.

Result(s): The blood and tissue levels of IL-12, IL-18, and IFN-g were statistically significantly higher, and the blood and tissue levels of LIF and MIF were statistically significantly lower in patients with RPL. Only the level of tissue ICAM-1 was higher in patients with RPL. There was a strong correlation between blood and tissue level measurements of IL-12, IL-18, LIF, and MIF.

Conclusion(s): Our findings support the hypothesis that inflammatory processes may contribute to pregnancy loss, possibly through their role in implantation. We found that blood and tissue levels of IL-18, LIF, and MIF, and tissue levels of IL-12, IFN-g, and ICAM-1 have statistically significant prognostic relevance.

TRADUCCIÓN Y COMENTARIOS

Introducción

Comienzan su introducción los autores recordando que la pérdida reiterada de gestación (PRG), el aborto de repetición, se define como la pérdida de dos o más gestaciones clínicas (que se definen como aquellas en que es observable el latido cardiaco del embrión en la ecografía, según la definición de la web del Instituto Bernabeu de Alicante), que este trastorno se observa en menos del 5 % de mujeres y que menos del 1 % presentan 3 o más pérdidas gestacionales.

Refiriéndose a una cita (1), enumeran las causas de PRG, aunque señalan que aproximadamente el 50 % de las mismas son de causa desconocida.

Los autores afirman que procesos inflamatorios pueden jugar un papel en la PRG, puesto que, a pesar del aparentemente privilegiado estatus inmunológico del feto, la implantación humana requiere mediadores inflamatorios para la implantación (2).

En este contexto, durante la ventana de implantación, se observa la expresión específica de moléculas de adhesión y citokinas (3).

Citokinas producidas por las células T son importantes mediadores de señales entre las células del sistema inmune y otras células y cambios en el patrón de producción de estas citokinas puede tener efectos sobre la tolerancia inmunológica.

Existen distintos tipos de células T-helper (TH): las células TH1 producen citokinas como interferon-γ (IFN-γ), que juega un papel en inmunidad celular, mientras que las células TH2 producen citokinas antiinflamatorias que lo hacen en inmunidad humoral (4).

Existen evidencias de que la inmunidad tipo TH1 puede tener un efecto adverso durante la gestación porque los mecanismos dependientes de las mismas están potencialmente implicados en el rechazo de aloinjertos ((5, 6). También existe un debate sobre la importancia de la inmunidad tipo TH2 durante la gestación porque mantiene la tolerancia de aloinjertos ((7, 8).

En resumen, se ha sugerido que el tipo de respuesta TH2 de las citokinas es vital para que una gestación se establezca, mientras que una respuesta TH1 puede suponer la pérdida de la gestación (9), lo que se conoce como el paradigma TH1/ TH2: el feto no es rechazado por el sistema inmunitario materno porque existe un predominio de los mediadores antiinflamatorios (inmunidad tipo TH2) que protege al feto (10).

La molécula de adhesión intercelular-1 (ICAM1) se expresa en epitelio y endotelio y se regula por citokinas, IFN-γ, entre otras. Su patrón de expresión se corresponde con las interacciones de distintos factores implicados en el proceso de implantación; ICAM1 es una citokina inducible relacionada con el ciclo menstrual (11).

Leukemia inhibitory factor (LIF) tiene un papel importante en la implantación (12); deficitaria producción de LIF por las células T se ha objetivado en pacientes con PRG. El factor inhibidor de la migración de los macrófagos (MIF) es una citokina proinflamatoria también implicada en la respuesta inmune (13)  con un papel en procesos reproductivos.

MATERIAL Y MÉTODOS

Pacientes, sangre y muestras endometriales

Muestras de sangre y biopsias endometriales fueron obtenidas de pacientes de la clínica de ginecología e infertilidad de la Escuela de Medicina de la Universidad de Estambul.

La PRG idiopática se diagnosticó por exclusión de factores autoinmunes, anatómicos, infecciosos, genéticos y endocrinos.

Los factores de inclusión para el grupo de estudio fueron 1) pérdida de 2 gestaciones clínicas consecutivas, 2) cariotipo de la mujer normal, 3) ultrasonografía pélvice normal, 4) HSG normal, 5) Despistaje de síndrome antifosfolípido normal, 6) Ausencia de coagulopatías, 7)Ausencia de enfermedades crónicas, 8) Perfil hormonal del día 3 normal, 9) Última pérdida gestacional al menos 6 meses antes y no nacidos previos vivos, y 10) Ausencia de patología uterina en la histeroscopia.

El grupo de control incluyó mujeres fértiles, con al menos 1 hijo y sin abortos.

Las mujeres de ambos grupos no habían tomados antibióticos ni hormonas esteroideas. Las fumadoras fueron excluidas.

Edad de las mujeres entre 20 y 40 años.

Las muestras de sangre y las biopsias de endometrio fueron tomadas por la mañana entre los días 19 y 23 (ventana de implantación), siendo negativa la determinación de βhCG; el nivel de P4 evidenció que habían ovulado.

La determinación de IL-12, IL-18, IFN-γ, ICAM, LIF y MIF se realizaron mediante ELISA.

Análisis estadístico mediante test de Student (variables numéricas), correlación de Pearson (valoración de la relación entre determinaciones en sangre y determinaciones tisulares), regresión logística (cuantificación del efecto de los parámetros estudiados sobre la gestación) y curva ROC (valoración de valor predictivo de los parámetros estudiados). SPSS versión 20.0.

Resultados

El estudio incluyó 21 pacientes con PRG y 20 controles normales; no hubo diferencias significativas al comparar edad, IMC y perfil hormonal entre los grupos. Paridad y tiempo en meses desde la última gestación fueron significativamente mayores en el grupo PRG.

Los niveles  en sangre y tejidos de IL-12, IL-18, e IFN-γ y los niveles tisulares de ICAM-1 fueron estadísticamente mayores en pacientes con PRG. Los niveles hemáticos y tisulares de LIF y MIF fueron estadísticamente menores en las pacientes con PRG. Los niveles circulantes de ICAM-1 fueron similares en ambos grupos.

Se observó una fuerte y significativa correlación estadística entre los niveles hemáticos y tisulares de IL-12, IL-18, LIF y MIF. No hubo correlaciones entre los niveles hemáticos y tisulares de IFN-γ e ICAM-1.

Análisis de regresión logística binaria fueron realizados para cada parámetro que se presumió asociado a la PRG. Se ajustó por edad, IMC y tiempo desde la última gestación. Los análisis ajustados mostraron niveles hemáticos y tisulares de IL-18, IFN-γ, LF y MIF con significación estadística y valor predictivo de PRG; del mismo modo, los niveles tisulares de IL-12 e ICAM-1 mostraron significación estadística y valor predictivo de PRG.

Trazamos curvas ROC para comparar el valor predictivo de los niveles hemáticos y tisulares de IL-18, IFN-γ, LIF y MIF así como de los niveles tisulares de IL-12 e ICAM-1 y para determinar el punto de corte que mejor discrimina entre mujeres con PRG y mujeres normales. Las cuvas ROC, el área bajo curva y el valor de los puntos de corte mostraron que el valor predictivo de los niveles hemáticos y tisulares de IL-18, LIF y MIF así como los niveles tisulares de IL-12, IFN-γ e ICAM-1 fueron estadísticamente significativos.

IL-12, IL-18 e IFN-γ

Los hallazgos relativos a estas citokinas concuerdan con las observaciones de estudios previos, tanto en lo concerniente a IL-12 e IL-18 como en lo concerniente a IFN-γ, habiéndose sugerido que un correcto equilibrio IL-12/IL-18 es vital para proteges el útero materno de potenciales agresiones  inmunológicas.

LIF

LIF parece tener un papel en la decidualización, habiéndose relacionado en estudios previos niveles disminuidos de LIF con la infertilidad idiopática y aborto iterativo, lo que se ha atribuido a retardo del desarrollo endometrial. En concordancia con estas observaciones se ha evidenciado en este estudio que los niveles hemáticos y tisulares están disminuidos en pacientes con PRG.

MIF

MIF ha sido descrito como una citokina proinflamatoria implicada en distintas respuestas inmunes e inflamatorias. Distintos estudios han señalado MIF como mediador de la receptividad uterina y de la placentación inicial, actuando en la interfase materno-fetal, lo que se corresponde con los hallazgos de este estudio, en el que los niveles de MIF se mostraron bajos en las mujeres con PRG.

ICAM-1

Se conoce mal el papel de ICAM-1 en la gestación inicial. Podría jugar un papel en la regulación de la inhibición del sistema inmune materno durante la gestación, actuando como inmunoregulador.

En el presente estudio los niveles de ICAM-1 se mostraron elevados lo que puede sugerir alteraciones inmunológicas. La elevación de ICAM-1 podría también ser debida a la elevación de IL-12 e IL-18 y al estado proinflamatorio que se observa en las mujeres con PRG.

Discusión

Ha sido demostrado en este estudio que los niveles hemáticos y tisulares de IL-12, IL-18 e IFN-γ fueron significativamente más elevados, así como que los niveles hemáticos y tisulares de LIF y MIF fueron significativamente menores en las pacientes con PRG.

Los niveles Tisulares de ICAM-1 fueron más altos solo en pacientes con PRG pero no en su sangre. También se ha presentado que hubo una fuerte correlación entre los niveles hemáticos y tisulares de IL-12, IL-18, LIF y MIF. Además, el valor predictivo de los niveles hemáticos y tosulares de IL-18, LIF y MIF y los niveles tisulares de IL-12, IFN-γ e ICAM-1 para la PRG fue estadísticamente significativo.

Si se conociera mejor los mecanismos que controlan la implantación embrionaria, la PRG podría ser manejada de forma más eficiente para prevenirla. La evaluación de los parámetros descritos en sangre o tejido endometrial puede ayudar a investigar el potencial de implantación. La importancia concedida a la inmunología reproductiva y al papel de las citokinas en la implantación y la gestación. Algunos estudios apoyan esta teoría aduciendo que un aumento de la inmunidad tipo TH1 está relacionado con el aborto (14). Sin embargo, también hay evidencias de abortos recurrentes  cuando la inmunidad TH2 es dominante (14). En el presente estudio, pacientes con PRG presentaron elevados niveles de citokina producidas por las células TH1. Además podría existir un desequilibrio crónico de TH1 /TH2 en las pacientes con PRG. Han sido recogidas pacientes con PRG, al menos 6 meses después  de su última gestación, con el fin de excluir un desequilibrio agudo. Los niveles de mediadores inflamatorios fueron significativamente distintos en pacientes con PRG, respecto del grupo de control.

Puntos fuertes de este estudio son: el elevado número de citokinas y moléculas de adhesión celular que han sido evaluados, los estrictos criterios de inclusión y exclusión de las pacientes con PRG y la toma de muestras durante la ventana de implantación.

Una limitación del estudio ha sido que pacientes y controles no fueron aparejadas respecto al tiempo transcurrido desde la última gestación; además, el diseño de este estudio  no permitió establecer una causalidad.

Implicaciones clínicas

Las implicaciones clínicas de este estudio no son evidentes en la actualidad y los tratamientos relacionados no se han mostrado eficaces (15).

Conclusiones

Los hallazgos de este estudio reafirman el papel de las citokinas y las moléculas de adhesión para el éxito de la implantación. Un claramente descrito objetivo como adecuada implantación o gestación, o ambos, pueden ser utilizados para valorar el valor pronóstico de las determinaciones de citokinas y moléculas de adhesión con el fin de identificar cuáles son relevantes. En este estudio se halló que los niveles hemáticos  de IL-18, LIF y MIF y los niveles tisulares de IL-12, IFN-γ e ICAM-1 presentaban una significativa relevancia pronóstica. En el futuro, la optimización de la receptividad endometrial en el tratamiento de la PRG y la potencial manipulación de la expresión de genes endometriales clave mediante futuras terapéuticas puedan mejorar las tasas de implantación y posibilitar que las pacientes lleven sus gestaciones a término.

REFERENCIAS CONSIDERADAS DE INTERÉS POR EL EDITOR Y TRESÚMENES DE LAS MISMAS

1. Li T, Tuckerman E, Laird S. Endometrial factors in recurrent miscarriage. Hum Reprod Update. 2002;8:43 - 52.

Recurrent pregnancy loss may be a consequence of an abnormal embryonic karyotype, or maternal factors affecting the endometrium resulting in defective implantation. In order to study the endometrial factors responsible for recurrent pregnancy loss, endometrial biopsy samples should be precisely timed according to the LH surge, and the investigation should be carried out in a non-conception cycle, prior to the next pregnancy. The various methods of studying the endometrium including morphological studies, morphometry, immunohistrochemistry, measurement of endometrial protein in plasma and uterine flushings, cytokine expression in endometrial cells, leukocyte populations in the endometrium and ultrasonographic and hysteroscopic studies, were reviewed. The clinical relevance of the observed abnormality depends on whether or not the abnormality is persistent in subsequent cycles, and if the observed abnormality is of significant prognostic value. Very little is known about the treatment of endometrial defect associated with recurrent pregnancy loss, but preliminary data suggest that the use of HMG may be of benefit.



2. Krieg S, Westphal L. Immune Function and Recurrent Pregnancy Loss. Semin Reprod Med. 2015;33:305 - 12.

Recurrent pregnancy loss (RPL), defined as two or more consecutive miscarriages, is attributable to multiple causes. However, in 50% of cases no known cause is found. Although endometritis is a known cause of miscarriage, other inflammatory processes may play a role in idiopathic, recurrent loss. The fetoplacental unit evades rejection by the maternal immune system by poorly understood mechanisms. Despite this seemingly immune-privileged state for the fetus, human implantation requires inflammatory mediators for attachment and implantation. This review describes how the immune system must simultaneously permit and restrict trophoblastic invasion for healthy implantation and maintenance of pregnancy. Included in this review is a detailed description of the immune milieu in the decidua and abnormalities that are associated with RPL. Finally, autoimmune states associated with RPL and their treatment in an obstetrical setting are reviewed.



3. Hoozemans D, Schats R, Lambalk C, Homburg R, Hompes P. Human embryo implantation: current knowledge and clinical implications in assisted reproductive technology. Reprod Biomed Online. 2004;9:692 - 715.

A pregnancy rate of approximately 15% per cycle renders the process of human reproduction inefficient. The cycle-dependent expression of molecules involved in the embryo-endometrial dialogue has lead to the identification of a 'window of implantation'. This is the unique temporal and spatial expression of factors that allows the embryo to implant (via signalling, appositioning, attachment and invasion) in a specific time frame of 48 h, 7-10 days after ovulation. Integrin molecules, L-selectin ligands, mucin-1, heparin-binding epidermal growth factor and pinopodes are involved in appositioning and attachment. The embryo produces cytokines and growth factors [interleukins, prostaglandins, vascular endothelial growth factor (VEGF)] and receptors for endometrial signals (leukaemia inhibitory factor receptor, colony stimulating factor receptor, insulin-like growth factors and heparin binding epidermal growth factor receptor). The immune system plays an important role. Immunomodulatory factors such as glycodelin, inhibin and interleukin prevent a graft-versus-host reaction. Angiogenesis controlled by VEGF and prostaglandins is needed for formation of a receptive endometrium and a placenta. Identification of these factors has led to their use as markers of implantation that may identify defects causing subfertility. An ideal marker of implantation is sensitive and specific, and easy to obtain without disturbing implantation. Glycodelin and leukaemia inhibitory factor (serum) and integrins and pinopodes (biopsies) are promising candidates.



4. Mosmann T, Cherwinski H, Bond M, Giedlin M, Coffman R. Two types of murine helper T cell clone. I. Definition according to profiles of lymphokine activities and secreted proteins. J Immunol. 1986;136:2348 - 57.

A panel of antigen-specific mouse helper T cell clones was characterized according to patterns of lymphokine activity production, and two types of T cell were distinguished. Type 1 T helper cells (TH1) produced IL 2, interferon-gamma, GM-CSF, and IL 3 in response to antigen + presenting cells or to Con A, whereas type 2 helper T cells (TH2) produced IL 3, BSF1, and two other activities unique to the TH2 subset, a mast cell growth factor distinct from IL 3 and a T cell growth factor distinct from IL 2. Clones representing each type of T cell were characterized, and the pattern of lymphokine activities was consistent within each set. The secreted proteins induced by Con A were analyzed by biosynthetic labeling and SDS gel electrophoresis, and significant differences were seen between the two groups of T cell line. Both types of T cell grew in response to alternating cycles of antigen stimulation, followed by growth in IL 2-containing medium. Examples of both types of T cell were also specific for or restricted by the I region of the MHC, and the surface marker phenotype of the majority of both types was Ly-1+, Lyt-2-, L3T4+, Both types of helper T cell could provide help for B cells, but the nature of the help differed. TH1 cells were found among examples of T cell clones specific for chicken RBC and mouse alloantigens. TH2 cells were found among clones specific for mouse alloantigens, fowl gamma-globulin, and KLH. The relationship between these two types of T cells and previously described subsets of T helper cells is discussed.

5. Burns W, Wang Y, Tang P, Ranjbaran H, Iakimov A, Kim J, et al. Recruitment of CXCR3+ and CCR5+ T cells and production of interferon-gamma-inducible chemokines in rejecting human arteries. Am J Transplant. 2005;5:1226 - 36.

Chemokine receptors preferentially expressed by Th1 cells and their IFN-gamma-inducible ligands predominate in experimental and clinical allograft rejection. Previous chemokine-related transplantation studies have focused on parenchymal and microvascular inflammation which are of importance in acute rejection, but are not necessarily relevant in immune-mediated injury of conduit arteries. We have recently described a model of progressive human T cell-mediated infiltration and injury of allogeneic coronary artery segments using immunodeficient mouse hosts. In the present study, we investigated if recruitment of allogeneic T cells to different vascular compartments correlated with the expression of chemokines and their receptors. Transcripts were quantified by laser capture microdissection/real-time RT-PCR and their distribution was correlated to the corresponding protein expression detected by immunohistochemistry. Infiltrating T cells, confined to the adventitia and intima, expressed CXCR3 and CCR5, but were not recruited into the media despite production by vascular smooth muscle cells of IP-10, Mig, I-TAC, RANTES and MIP-1beta. Chemokine mRNA was detected primarily in vascular cells, although chemokine protein largely localized to infiltrating leukocytes which uniquely expressed their cognate receptors. These data explain the recruitment of IFN-gamma-secreting T cells to the vessel wall, and reinforce the suggestion that the arterial media may be a site of immunological privilege.



6. Erdmann A, Jung U, Foley J, Toda Y, Fowler D. Co-stimulated/Tc2 cells abrogate murine marrow graft rejection. Biol Blood Marrow Transplant. 2004;10:604 - 13.

CD3/CD28 co-stimulation activates T-cell cytokine and cytolytic effector function and therefore represents an approach to modulate donor T cells before allogeneic bone marrow transplantation (BMT). We hypothesized that co-stimulation of donor T cells under T2 conditions would generate CD4+ T-helper type 2 (Th2) and CD8+ Tc2 cells capable of abrogating marrow graft rejection with reduced graft-versus-host disease (GVHD). Relative to control co-stimulated Th1/Tc1 (T1) cells, co-stimulated T2 cells secreted reduced interleukin (IL)-2 and interferon-gamma and increased IL-4 and IL-10, expressed reduced fas ligand, and had similar total cytolytic capacity. In an F1-into-parent sublethal irradiation model, T2 cells potently abrogated rejection; this veto effect was partially attenuated if T2 cell infusion was delayed for 24 hours after BMT. Cell-tracking studies determined that T2 cells were quantitatively reduced after BMT when administered to hosts capable of mounting a host-versus-graft rejection response; both donor and host cytotoxic T lymphocytes may therefore have been deleted during Th2/Tc2 cell facilitation of engraftment. Donor T2 cells also abrogated rejection in an F1-into-parent model that used lethal host irradiation and subsequent host T-cell addback. Further experiments in a P1-into-P2 transplantation model demonstrated that donor T2 cells abrogated rejection with reduced GVHD in a transplant setting involving full major histocompatibility complex disparity in both the host-versus-graft and graft-versus-host directions. The capacity of T2 cells to abrogate rejection with reduced GVHD was a function of both the number of T2 cells infused and the number of T cells present after host preparation. Co-stimulation under T2 polarizing conditions therefore rapidly generates donor Th2/Tc2 cells that potently abrogate murine marrow rejection with reduced GVHD.



7. Li X, Zand M, Li Y, Zheng X, Strom T. On histocompatibility barriers, Th1 to Th2 immune deviation, and the nature of the allograft responses. J Immunol. 1998;161:2241 - 7.

In the present study, we have sought to determine the basis for the frequent failure of Th1 to Th2 immune deviation to blunt the severity of allograft rejection, as such immune deviation has proven highly effective in the treatment of several T cell-dependent autoimmune states. Our study demonstrates that treating islet allograft recipient mice with anti-IL-12 mAb is highly effective in producing Th1 to Th2 immune deviation in several model systems (i.e., fully MHC, partially MHC, or multiple minor Ag barriers). Nevertheless, anti-IL-12 failed to prolong the engraftment of fully MHC-mismatched islet allografts. However, anti-IL-12-treated recipients carrying MHC-matched but multiple minor Ag-mismatched allografts experienced prolonged engraftment; allograft tolerance was frequently achieved in the DBA/2J (H-2d) to BALB/c (H-2d) strain combination. In another model, in which the host response was dominated by CD4+ T cells responding to donor allopeptides presented upon host APCs in the context of self MHC class II molecules, anti-IL-12 treatment proved to be extremely potent. Thus, Th1 to Th2 immune deviation produces prolonged engraftment as compared with recipients of MHC-mismatched allografts when rejection is dependent upon indirectly presented allogeneic peptides and a reduced mass of responding alloreactive T cells.

8. Nickerson P, Steurer W, Steiger J, Zheng X, Steele A, Strom T. Cytokines and the Th1/Th2 paradigm in transplantation. Curr Opin Immunol. 1994;6:757 - 64.

With studies elucidating the cytokine programs associated with T-cell activation, allograft rejection and tolerance induction, the Th1/Th2 paradigm has become a unifying model to explain the observed cytokine profiles. The proof that these cytokines mediate allograft tolerance, however, is at best indirect. More recent studies highlighting the redundant and pleiotropic nature of cytokine networks suggest that the Th1/Th2 paradigm may not be sufficient to explain fully the mechanisms underlying allograft tolerance.



9. Bates M, Quenby S, Takakuwa K, Johnson P, Vince G. Aberrant cytokine production by peripheral blood mononuclear cells in recurrent pregnancy loss? Hum Reprod. 2002;17:2439 - 44.

BACKGROUND: Successful pregnancy may depend on a Th2-type cytokine response, whilst, conversely, a poor pregnancy outcome may be associated with an increase in Th1 cytokines and a concomitant decrease in Th2 cytokines. This prospective study was designed to elucidate whether a failure of the cytokine shift pre-dated miscarriage and was therefore likely to be an aetiological factor in recurrent pregnancy loss (RPL).

METHODS: Cytokine production by stimulated peripheral blood mononuclear cells from 46 pregnant women who had previously suffered idiopathic RPL during early pregnancy was compared with 25 gestationally age-matched pregnant controls and 11 non-pregnant women.

RESULTS: Production of IFN-gamma was lower in pregnant than in non-pregnant women and even lower in RPL pregnant women (P = 0.0191). IL-10 was increased in pregnant women compared with non-pregnant controls, and further increased in RPL patients (P = 0.026). IL-4 was also increased in women with RPL (P = 0.0001). No differences in IFN-gamma, IL-10 or IL-4 secretion were observed in RPL patients who subsequently miscarried compared with those who successfully completed the pregnancy. RPL women with a successful reproductive outcome had similar concentrations of TNF-alpha to pregnant women, RPL women who subsequently miscarried had significantly lower levels than either pregnant women (P = 0.02) or non-pregnant controls (P = 0.0004).

CONCLUSIONS: Contrary to our hypothesis, the cytokine shift, which appears to characterize normal pregnancy, was accentuated rather than diminished in RPL pregnant women.



10. Dealtry G, O'Farrell M, Fernandez N. The Th2 cytokine environment of the placenta. Int Arch Allergy Immunol. 2000;123:107 - 19.

It is now accepted that local changes to the balance of Th1/Th2-type cytokines occur during pregnancy within the maternal uterus and fetoplacental unit. These changes in cytokine profiles contribute to implantation of the embryo, development of the placenta, and survival of the fetus to term. Overall within the placenta there is a bias in the ratio of Th1:Th2 cytokines towards the Th2-type cytokines. However, there are specific fluctuations in this balance at implantation and during the initiation of parturition. The predominant cytokines at each stage of gestation function both to limit maternal immune rejection of the semi-allogeneic embryo/fetus, especially at the maternofetal interface; and to facilitate the on-going physiological processes within the maternal reproductive tract. These two, at times conflicting, roles are discussed in this review, with key evidence concerning cytokine expression and function from mouse and humans.



11. Gaffuri B, Airoldi L, Di Blasio A, Viganò P, Miragoli A, Santorsola R, et al. Unexplained habitual abortion is associated with a reduced endometrial release of soluble intercellular adhesion molecule-1 in the luteal phase of the cycle. Eur J Endocrinol. 2000;142:477 - 80.

Although the mechanisms causing recurrent spontaneous abortion (RSA) remain frequently speculative, recent evidence indicates that a specific uterine immune-endocrine network plays a pivotal role in the continuation of pregnancy. We have recently demonstrated that an adhesion molecule of the immune system, named intercellular adhesion molecule (ICAM)-1, is markedly expressed at both protein and mRNA levels in endometrial stromal cells and is able to mediate their interaction with lymphoid cells. Moreover, we have shown that the soluble form of ICAM-1 (sICAM-1) can be released by the endometrium in a hormone-dependent manner. The present study was designed to determine whether surface and/or sICAM-1 expression by cultured endometrial stromal cells could be related to early pregnancy loss in patients with a history of unexplained RSA. Luteal-phase endometrial biopsies were obtained from eight patients who had experienced three or more consecutive unexplained RSAs in the first trimester and 12 control fertile women. Surface ICAM-1 was similarly expressed on luteal-phase endometrial cells obtained from women with and without a history of unexplained RSA. In contrast, the endometrial release of sICAM-1 was significantly lower in abortion-prone patients than in control women. sICAM-1 is a cytokine-inducible molecule able to interfere with several immunological responses and the reduced levels of the protein shed by the endometrium in patients who have suffered from unexplained RSAs may reflect the presence of an altered immunological environment during the early phases of pregnancy.



12. Stewart C, Kaspar P, Brunet L, Bhatt H, Gadi I, Köntgen F, et al. Blastocyst implantation depends on maternal expression of leukaemia inhibitory factor. Nature. 1992;359:76 - 9.

A critical point during mammalian pregnancy is the implantation of the blastocyst when the embryo attaches to the wall of the uterus. The autonomously developing preimplantation embryo then becomes dependent on the maternal environment for its continued development. Little is known about the regulation of implantation, except that a complex interaction between peptide and steroid hormones synchronizes the preparation of the uterus for implantation with the development of the embryo. Whether the implantation event is under maternal or embryonic control is also unclear (reviewed in refs 1, 2). We have previously shown that a cytokine, leukaemia inhibitory factor (LIF), is expressed in the uterine endometrial glands specifically on the fourth day of pregnancy. This burst of expression is under maternal control and always precedes implantation of the blastocyst. Here we report that transient expression of LIF in mice is essential for implantation. Females lacking a functional LIF gene are fertile, but their blastocysts fail to implant and do not develop. The blastocysts, however, are viable and, when transferred to wild-type pseudopregnant recipients, they can implant and develop to term.



13. Calandra T, Roger T. Macrophage migration inhibitory factor: a regulator of innate immunity. Nat Rev Immunol. 2003;3:791 - 800.



For more than a quarter of a century, macrophage migration inhibitory factor (MIF) has been a mysterious cytokine. In recent years, MIF has assumed an important role as a pivotal regulator of innate immunity. MIF is an integral component of the host antimicrobial alarm system and stress response that promotes the pro-inflammatory functions of immune cells. A rapidly increasing amount of literature indicates that MIF is implicated in the pathogenesis of sepsis, and inflammatory and autoimmune diseases, suggesting that MIF-directed therapies might offer new treatment opportunities for human diseases in the future.



14. Chaouat G, Lédée-Bataille N, Zourbas S, Ostojic S, Dubanchet S, Martal J, et al. Cytokines, implantation and early abortion: re-examining the Th1/Th2 paradigm leads to question the single pathway, single therapy concept. Am J Reprod Immunol. 2003;50:177 - 86.

PROBLEM: Human in vitro fertilization (IVF) embryo transfer is accompanied by a low implantation rate even after a very successful IVF, and there are a certain number of 'idiopathic sterilities' which are due to repeated implantation failures. In the very same vein, the question of improving implantation rates is of prime importance in agricultural research to improve the management of livestock. Preimplantation prenatal diagnosis cannot be accomplished in individuals who have a high rate of implantation failure, whether women undergoing IVF, or animals, during genetic cloning. Implantation cytokine networks need to be known in such a perspective.

METHODS: We review the evolution and theories in reproductive immunology, briefly deal with the complexity of implantation as a step by step developmental event, and then present some of our recent data in mice and human.

CONCLUSIONS: We conclude that the T helper cell type 1/2 (Th1/ Th2) paradigm, as useful as it has been to explain pregnancy, is no longer sufficient in view of the emerging complexity of the cytokine network at the materno-fetal interface. This is peculiarly true for implantation, which, as a step by step developmentally regulated process, involving inflammatory molecules, cannot fit into such a scheme.



15. Wong L, Porter T, Scott J. Immunotherapy for recurrent miscarriage. Cochrane Database Syst Rev. 2014;10:CD000112.

BACKGROUND: Because immunological aberrations might be the cause of miscarriage in some women, several immunotherapies have been used to treat women with otherwise unexplained recurrent pregnancy loss.

OBJECTIVES: The objective of this review was to assess the effects of any immunotherapy, including paternal leukocyte immunization and intravenous immunoglobulin on the live birth rate in women with previous unexplained recurrent miscarriages.

SEARCH METHODS: We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (11 February 2014) and reference lists of retrieved studies.

SELECTION CRITERIA: Randomized trials of immunotherapies used to treat women with three or more prior miscarriages and no more than one live birth after, in whom all recognized non-immunologic causes of recurrent miscarriage had been ruled out and no simultaneous treatment was given.

DATA COLLECTION AND ANALYSIS: The review author and the two co-authors independently extracted data and assessed study quality for all studies considered for this review.

MAIN RESULTS: Twenty trials of high quality were included. The various forms of immunotherapy did not show significant differences between treatment and control groups in terms of subsequent live births: paternal cell immunization (12 trials, 641 women), Peto odds ratio (Peto OR) 1.23, 95% confidence interval (CI) 0.89 to 1.70; third-party donor cell immunization (three trials, 156 women), Peto OR 1.39, 95% CI 0.68 to 2.82; trophoblast membrane infusion (one trial, 37 women), Peto OR 0.40, 95% CI 0.11 to 1.45; or intravenous immunoglobulin, (eight trials, 303 women), Peto OR 0.98, 95% CI 0.61 to 1.58.

AUTHORS' CONCLUSIONS: Paternal cell immunization, third-party donor leukocytes, trophoblast membranes, and intravenous immunoglobulin provide no significant beneficial effect over placebo in improving the live birth rate.



COMENTARIOS DEL EDITOR

Se trata de la publicación de un estudio que desarrolla una hipótesis atractiva sobre un problema interesante, con una metodología  muy adecuada.

Cierto que el aborto recurrente o iterativo idiopático no es un problema mayor en clínica humana ni un elemento de trascendencia en la etiología de la infertilidad, aunque sí una importante causa de sufrimiento para las mujeres que lo padecen que, una vez tras otra ven frustado su deseo de maternidad de forma clínicamente dolosa. Sin embargo, considerando que puede estar relacionado con el fallo de implantación en FIV, su importancia puede ser mucho mayor.

Cierto que los autores no llegan a conclusiones clínicamente importantes.

No obstante, el estudio incide sobre un tema, las relaciones embriomaternas y la fisiopatología de la interfase embrión-endometrio, de gran interés en la actualidad. Sin duda puede ser un punto de partida de nuevas investigaciones que, profundizando en el conocimiento de la implantación y sus mecanismos moleculares, permita mejorar los conocimientos y abrir a puerta a nuevos desarrollos de la fecundación in vitro y la transferencia embrionaria