Induction of Cytotoxic T-lymphocyte Antigen-2β, A Cysteine Protease Inhibitor in Decidua

Abstract

During early pregnancy, the steroid hormone progesterone induces differentiation of uterine stroma to decidual cells, which regulate embryo-uterine interactions. The progesterone-induced signaling molecules that participate in the formation and function of decidua remain poorly understood. We recently utilized high-density oligonucleotide microarrays to identify several genes whose expression is markedly altered in pregnant uterus in response to RU486, a well characterized antagonist of the progesterone receptor (PR). Our study revealed that the gene encoding cytotoxic T-lymphocyte antigen-2β (CTLA-2β), a cysteine protease inhibitor, is expressed during PR-induced decidualization. The spatio-temporal expression of CTLA-2β mRNA precisely overlapped with the decidual phase of pregnancy. Interestingly, administration of progesterone to estrogen-primed ovariectomized mice failed to induce CTLA-2β expression. A concomitant artificial decidual stimulation was necessary to trigger this expression. Uteri of PR knockout mice failed to express this mRNA, even after a combined administration of steroid hormones and artificial stimulation. The uterine expression of CTLA-2β was, therefore, dependent on PR as well as other unknown factor(s) associated with decidual response. To identify the molecular target(s) of CTLA-2β,we analyzed its interaction with proteins present in soluble extracts prepared from day 7 pregnant uteri containing implanted embryos. A protein affinity strategy employing recombinant CTLA-2β helped us to determine that cathepsin L, a cysteine protease, is one of its targets in the pregnant uterus. Consistent with this finding, expression of cathepsin L was detected in the giant trophoblast cells of the ectoplacental cone on day 7 of pregnancy. Collectively, our results support the hypothesis that expression of CTLA-2β in the decidua may regulate implantation of the embryo by neutralizing the activities of one or more proteases generated by the proliferating trophoblast. During early pregnancy, the steroid hormone progesterone induces differentiation of uterine stroma to decidual cells, which regulate embryo-uterine interactions. The progesterone-induced signaling molecules that participate in the formation and function of decidua remain poorly understood. We recently utilized high-density oligonucleotide microarrays to identify several genes whose expression is markedly altered in pregnant uterus in response to RU486, a well characterized antagonist of the progesterone receptor (PR). Our study revealed that the gene encoding cytotoxic T-lymphocyte antigen-2β (CTLA-2β), a cysteine protease inhibitor, is expressed during PR-induced decidualization. The spatio-temporal expression of CTLA-2β mRNA precisely overlapped with the decidual phase of pregnancy. Interestingly, administration of progesterone to estrogen-primed ovariectomized mice failed to induce CTLA-2β expression. A concomitant artificial decidual stimulation was necessary to trigger this expression. Uteri of PR knockout mice failed to express this mRNA, even after a combined administration of steroid hormones and artificial stimulation. The uterine expression of CTLA-2β was, therefore, dependent on PR as well as other unknown factor(s) associated with decidual response. To identify the molecular target(s) of CTLA-2β,we analyzed its interaction with proteins present in soluble extracts prepared from day 7 pregnant uteri containing implanted embryos. A protein affinity strategy employing recombinant CTLA-2β helped us to determine that cathepsin L, a cysteine protease, is one of its targets in the pregnant uterus. Consistent with this finding, expression of cathepsin L was detected in the giant trophoblast cells of the ectoplacental cone on day 7 of pregnancy. Collectively, our results support the hypothesis that expression of CTLA-2β in the decidua may regulate implantation of the embryo by neutralizing the activities of one or more proteases generated by the proliferating trophoblast. Progesterone plays a crucial role during early pregnancy by coordinating a complex series of interactions between the implanting blastocyst and the receptive uterus (1Psychoyos A. Greep R.O. Astwood E.G. Handbook of Physiology. American Physiological Society, Washington, D. C.1973: 187-215Google Scholar, 2Yoshinaga K. Ann. N. Y. Acad. Sci. 1988; 541: 424-431Crossref PubMed Scopus (127) Google Scholar, 3Parr M.B. Parr E.L. Wynn R.M. Jollie W.P. Biology of the Uterus. Plenum Press, New York1989: 233-277Crossref Google Scholar, 4Weitlauf H.M. Knobil E. Neill J.D. The Physiology of Reproduction. Raven Press, New York1994: 391-440Google Scholar, 5Carson D.D. Bagchi I. Dey S.K. Enders A.C. Fazleabas A.T. Lessey B.A. Yoshinaga K. Dev. Biol. 2000; 223: 217-237Crossref PubMed Scopus (659) Google Scholar). In mice, implantation is initiated 4 days after fertilization when the blastocyst reaches the uterus (1Psychoyos A. Greep R.O. Astwood E.G. Handbook of Physiology. American Physiological Society, Washington, D. C.1973: 187-215Google Scholar, 6Paria B.C. Huet-Hudson Y.M. Dey S.K. Proc. Natl. Acad. Sci. U. S. A. 1993; 90: 10159-10162Crossref PubMed Scopus (419) Google Scholar). The hormonal regimen necessary to prepare a non-receptive uterus to receive embryo and permit implantation involves 48 h of progesterone treatment followed by a dose of estrogen (1Psychoyos A. Greep R.O. Astwood E.G. Handbook of Physiology. American Physiological Society, Washington, D. C.1973: 187-215Google Scholar, 7Psychoyos A. J. Reprod. Fertil. Suppl. 1976; 25: 17-28PubMed Google Scholar, 8Psychoyos A. Ann. N. Y. Acad. Sci. 1986; 476: 36-42Crossref PubMed Scopus (331) Google Scholar, 9Yoshinaga K. Leroy F. Finn C.A. Psychoyos A. Hubinot P.O. Progress in Reproductive Biology 7. Karger, Basel1980: 189-199Google Scholar). Whereas the combined action of estrogen and progesterone is essential for acquisition of uterine receptivity, progesterone is the critical hormone for decidualization (1Psychoyos A. Greep R.O. Astwood E.G. Handbook of Physiology. American Physiological Society, Washington, D. C.1973: 187-215Google Scholar, 10Finn C.A. Wynn R.M. Biology of the Uterus. Plenum Press, New York1977: 246-308Google Scholar). Decidualization involves differentiation of the fibroblast cells of endometrial stroma into morphologically distinct cells, termed decidual cells, which show unique secretory and biosynthetic properties (10Finn C.A. Wynn R.M. Biology of the Uterus. Plenum Press, New York1977: 246-308Google Scholar, 11DeFeo V.J. Wynn R.M. Cellular Biology of the Uterus. North Holland Publishing Co., Amsterdam1967: 191-290Google Scholar). This differentiation, induced by progesterone following a brief priming by estrogen, is a prerequisite for successful implantation. Decidua is a transient tissue, which first develops at the time of blastocyst attachment on day 4 of pregnancy. During the next 3 days, the decidual cells proliferate and differentiate extensively, and eventually they undergo apoptosis. By the end of the invasive period (day 10.5), the decidua is regressed. A variety of functions have been attributed to the decidua (12Cross J.C. Werb Z. Fisher S.J. Science. 1994; 266: 1508-1518Crossref PubMed Scopus (1188) Google Scholar, 13Irwin J.C. Giudice D. Knobil E. Neill J.D. Encyclopedia of Reproduction. Academic Press, New York1999: 823-835Google Scholar, 14Gu Y. Gibori G. Knobil E. Neill J.D. Encyclopedia of Reproduction. Academic Press, New York1999: 836-842Google Scholar, 15Croy B.A. Chantakru S. Esadeg S. Ashkar A.A. Wei Q. J. Reprod. Immunol. 2002; 57: 151-168Crossref PubMed Scopus (122) Google Scholar). It facilitates nutrient transfer to the embryo and secretes hormones, growth factors, and cytokines that are critical for embryonic growth and development. Additionally, the two most widely accepted roles of decidua are regulation of trophoblast invasion and immunomodulation of fetal allograft during pregnancy (12Cross J.C. Werb Z. Fisher S.J. Science. 1994; 266: 1508-1518Crossref PubMed Scopus (1188) Google Scholar, 13Irwin J.C. Giudice D. Knobil E. Neill J.D. Encyclopedia of Reproduction. Academic Press, New York1999: 823-835Google Scholar, 14Gu Y. Gibori G. Knobil E. Neill J.D. Encyclopedia of Reproduction. Academic Press, New York1999: 836-842Google Scholar, 15Croy B.A. Chantakru S. Esadeg S. Ashkar A.A. Wei Q. J. Reprod. Immunol. 2002; 57: 151-168Crossref PubMed Scopus (122) Google Scholar). The progesterone-regulated factors that play critical roles during decidualization, leading to successful implantation and establishment of pregnancy, however, remain largely unknown. To understand how progesterone regulates implantation, it is essential to identify a broader spectrum of genes that are regulated by PR 1The abbreviations used are: PR, progesterone receptor; CTLA-2β, cytotoxic T-lymphocyte antigen-2β; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; DIG, digoxygenin. during this process. To achieve this goal, we employed RU486, a well characterized antagonist of PR function during pregnancy (16Baulieu E.E. Science. 1989; 245: 1351-1357Crossref PubMed Scopus (459) Google Scholar, 17Baulieu E.E. Trends Endocrinol. Metab. 1991; 2: 233-239Abstract Full Text PDF PubMed Scopus (62) Google Scholar). RU486 counteracts PR-dependent pathways by binding to the receptor and impairing its gene regulatory function (16Baulieu E.E. Science. 1989; 245: 1351-1357Crossref PubMed Scopus (459) Google Scholar, 17Baulieu E.E. Trends Endocrinol. Metab. 1991; 2: 233-239Abstract Full Text PDF PubMed Scopus (62) Google Scholar). We used oligonucleotide microarrays to identify the genes whose uterine expression is markedly altered at the time of implantation by RU486-complexed PR (18Cheon Y.P. Li Q. DeMayo F.J. Bagchi I.C. Bagchi M.K. Mol. Endocrinol. 2002; 16: 2853-2871Crossref PubMed Scopus (118) Google Scholar). Here we report the identification of a gene encoding cytotoxic T-lymphocyte antigen-2β (CTLA-2β) that is induced downstream of PR in the pregnant uterus. Denizot et al. (19Denizot F. Brunet J.-F. Roustan P. Harper K. Suzan M. Luciani F. Golstein P. Eur. J. Immunol. 1989; 19: 631-635Crossref PubMed Scopus (71) Google Scholar) first cloned CTLA-2β from a T lymphocyte-derived cDNA library and found it to be highly homologous to the proregion of cysteine proteases. Previous studies indicated that the proregion, purified from a given protease, can inhibit the activity of that protease in vitro (20Delaria K. Fiorentino L. Wallace L. Tamburini P. Brownell E. Muller D. J. Biol. Chem. 1994; 269: 25172-25177Abstract Full Text PDF PubMed Google Scholar). Consistent with this paradigm, studies have shown that CTLA-2β is a competitive inhibitor of certain cysteine proteases including cathepsin B and L (20Delaria K. Fiorentino L. Wallace L. Tamburini P. Brownell E. Muller D. J. Biol. Chem. 1994; 269: 25172-25177Abstract Full Text PDF PubMed Google Scholar). We observed that CTLA-2β is induced in the steroid-primed uterus in response to a decidual signal. In situ hybridization analysis indicated that the expression of CTLA-2β in the pregnant uterus is localized in the uterine stroma near the vicinity of the embryo and overlapped with the decidual phase. Interestingly, our studies further revealed that cathepsin L, which is expressed in giant trophoblast cells, is one of the targets of CTLA-2β. Based on these studies, we postulate that expression of CTLA-2β in uterine stroma during PR-mediated decidualization plays a critical role in the regulation of embryo implantation. Reagents—Progesterone and 17β-estradiol were purchased from Sigma. RU 38486 (Mifepristone) was a gift of Population Council, New York, NY. Antibody against cathepsin L was purchased from Santa Cruz Biotechnology, Santa Cruz, CA. Animals and Tissue Collection—All experiments involving animals were approved by the Animal Care at the of and the studies were in with the of for the and of mice from in were with The of a after was as day of pregnancy. The animals were at of and the uteri were The mice were and were by as (18Cheon Y.P. Li Q. DeMayo F.J. Bagchi I.C. Bagchi M.K. Mol. Endocrinol. 2002; 16: 2853-2871Crossref PubMed Scopus (118) Google Scholar). was induced as DeMayo F.J. S.K. C.A. G. Dev. PubMed Scopus Google Scholar). were first following animals were with of estrogen in of for This was followed by of of progesterone for one of the uterus was by of a and of the of the uterine The other was The animals were with progesterone for days and The uteri were the two were and was from of or of was by and to were in and for 4 h at was in the containing of a CTLA-2β cDNA The were for in at for in at and to The of on the were by To for the were with to the glyceraldehyde-3-phosphate in the this the were of the by for in at The were with a as In from pregnant animals were and were in at 4 were at and to In situ hybridization was with or to CTLA-2β were from CTLA-2β cDNA or and to the was in a at for in hybridization was at in a To the were in and for in at were with was and the and was were to in the and the was of were The was and the were in for The were in and utilized a and were against cathepsin L Cruz Biotechnology, Santa Cruz, was for uteri were at 7 on and in in were in for and in a containing for in at 4 was a for the of and of CTLA-2β express recombinant CTLA-2β in the was and the at was to A of CTLA-2β with and was generated by and into the and of a the end of CTLA-2β, was The of this into a was following the cells were in with fetal The recombinant CTLA-2β was expressed in were with the recombinant at a of of to at were at h the was with a of protease The was with to a against for 3 h at 4 on a The was with of The proteins to the were at 4 with a containing in protein expression was by a The analysis of purified CTLA-2β was by and was by the RU486 CTLA-2β in the role of progesterone during early pregnancy is to be by a of PR-induced genes 1994; PubMed Scopus Google Scholar). Consistent with this treatment of pregnant or during the phase with RU486, which function of PR, implantation D. M. I. D. J. E.E. S.J. The RU486 and Plenum Press, New Scholar). To identify the downstream targets of PR during pregnancy, we have recently the in uterine mRNA expression in response to RU486 (18Cheon Y.P. Li Q. DeMayo F.J. Bagchi I.C. Bagchi M.K. Mol. Endocrinol. 2002; 16: 2853-2871Crossref PubMed Scopus (118) Google Scholar). mice on day 3 of pregnancy were with or RU486 and uterine were on day the day of implantation. The uterine were to high-density oligonucleotide Santa containing gene We a of a in expression between and for progesterone-regulated this we a of whose expression was in the uterus at the time of implantation in response to RU486 (18Cheon Y.P. Li Q. DeMayo F.J. Bagchi I.C. Bagchi M.K. Mol. Endocrinol. 2002; 16: 2853-2871Crossref PubMed Scopus (118) Google Scholar). We one of these genes as that encoding CTLA-2β, a cysteine protease To the results of we from uteri of day 4 pregnant mice with or RU486 the was with CTLA-2β a in the from mice on day 4 of pregnancy mRNA was observed in the uterine from mice of the with a indicated of in these therefore, the of the of CTLA-2β mRNA as by the of CTLA-2β in during next the of CTLA-2β gene expression in the uterus at of We analysis of from uteri of mice at days and of pregnancy uteri of were used for this The uteri were of embryonic by or by the from the implantation The was with a CTLA-2β and a in to CTLA-2β mRNA was observed in the pregnant animals on days of A expression of this mRNA was detected on day 4 of pregnancy The of CTLA-2β further on days and to by day of pregnancy and The of expression of CTLA-2β was by followed by with to the mRNA signal. The of CTLA-2β mRNA on day 4 was that on day 3 of results indicated that CTLA-2β expression in the pregnant uterus is between days 4 and of that precisely with the decidual phase. We localized the expression of CTLA-2β by in situ hybridization Consistent with the expression the CTLA-2β were between days and 3 of pregnancy The expression of CTLA-2β was observed on day of pregnancy and this expression was localized in the stroma the implanted embryo The of this protease inhibitor in the further on days and on day with the of the decidual phase of pregnancy. We the expression of CTLA-2β in the uterine of day pregnant animals at implantation and implantation Whereas expression was observed in the uterine of day pregnant animals at the implantation near the CTLA-2β was detected at the implantation these results indicated that CTLA-2β is induced in the at the of implantation. The of CTLA-2β from the decidua in the vicinity of the embryo the that this regulates embryo-uterine interactions during early pregnancy. of CTLA-2β of PR-mediated of CTLA-2β expression in the pregnant uteri in response to RU486 indicated that progesterone PR plays a role in this gene expression. Interestingly, we found that administration of progesterone to estrogen-primed ovariectomized mice failed to induce CTLA-2β mRNA in the uterus CTLA-2β was expressed in the decidua the we a decidual is for CTLA-2β expression. To induce decidualization, mice were following mice were a hormonal regimen of estrogen and progesterone as and hormone decidualization was initiated in the by it with a the was the decidual response the was of decidual response. The uteri from animals were or were and was from these for analysis CTLA-2β cDNA as a shown in to CTLA-2β was observed in the from the uterine In a of was detected in the that was in response to the artificial stimulation To further the role of PR in CTLA-2β expression in the we the expression of this gene in the uteri of PR and mice of the shown in when these animals were to decidualization the we failed to to CTLA-2β mRNA in the PR mice The uterine from mice, as the CTLA-2β mRNA Collectively, these results that a PR-induced decidual is essential for expression of CTLA-2β in the uterus. L a of CTLA-2β in the Previous studies indicated that CTLA-2β is a cysteine protease inhibitor (19Denizot F. Brunet J.-F. Roustan P. Harper K. Suzan M. Luciani F. Golstein P. Eur. J. Immunol. 1989; 19: 631-635Crossref PubMed Scopus (71) Google Scholar, K. Fiorentino L. Wallace L. Tamburini P. Brownell E. Muller D. J. Biol. Chem. 1994; 269: 25172-25177Abstract Full Text PDF PubMed Google Scholar). A of the CTLA-2β is highly homologous to the of cysteine including B and L. Consistent with this CTLA-2β and the activity of these proteases in vitro (20Delaria K. Fiorentino L. Wallace L. Tamburini P. Brownell E. Muller D. J. Biol. Chem. 1994; 269: 25172-25177Abstract Full Text PDF PubMed Google Scholar). It therefore, that this protease inhibitor play a role in the activity of one or more cysteine proteases by the trophoblast in the decidual uterus. To determine CTLA-2β targets one or more cysteine in the pregnant we analyzed its interaction with proteins present in soluble extracts prepared from uteri from mice at days and 7 of pregnancy. The extracts prepared from day pregnant which express CTLA-2β, were to target(s) of this protein and as In the extracts from day 7 pregnant which expressed CTLA-2β mRNA, were to the target(s) of this To determine the of CTLA-2β in the decidual is of embryonic or we prepared extracts from two of day 7 pregnant one containing implanted and the other of A protein affinity strategy employing a recombinant CTLA-2β was used to these uterine this we expressed and purified CTLA-2β in cells The protein was used to proteins from the day and 7 uterine The proteins were on to a and by a of against cysteine including and L. We that CTLA-2β interaction with cathepsin B or in of the uterine extracts We failed to interaction of this protease inhibitor with cathepsin L in the extracts of day pregnant uteri or the day 7 pregnant uteri of embryo 3 and A cathepsin was, however, in the proteins that associated with CTLA-2β in the day 7 uterine extracts containing the embryonic Our therefore, indicated that cathepsin L is one of the targets of CTLA-2β in the pregnant uterus. Our results indicated that embryo is the most of cathepsin L. We the of cathepsin L in day 7 pregnant uterus by We observed that cathepsin L was expressed in the day 7 pregnant uteri and its expression was localized to the invasive giant trophoblast cells of the ectoplacental cone Collectively, these results our hypothesis that decidual expression of CTLA-2β in the pregnant uterus may to embryo implantation by neutralizing the activities of cysteine cathepsin L, generated by the proliferating trophoblast. In the endometrial stroma in response to blastocyst implantation, a as the decidua V.J. Wynn R.M. Cellular Biology of the Uterus. North Holland Publishing Co., Amsterdam1967: 191-290Google Scholar, J.C. Werb Z. Fisher S.J. Science. 1994; 266: 1508-1518Crossref PubMed Scopus (1188) Google Scholar, 13Irwin J.C. Giudice D. Knobil E. Neill J.D. Encyclopedia of Reproduction. Academic Press, New York1999: 823-835Google Scholar, 14Gu Y. Gibori G. Knobil E. Neill J.D. Encyclopedia of Reproduction. Academic Press, New York1999: 836-842Google Scholar). The decidua the blastocyst and which the trophoblast cells and The interactions of these two results in the establishment of a highly that and the growth and of the V.J. Wynn R.M. Cellular Biology of the Uterus. North Holland Publishing Co., Amsterdam1967: 191-290Google Scholar, J.C. Werb Z. Fisher S.J. Science. 1994; 266: 1508-1518Crossref PubMed Scopus (1188) Google Scholar, 13Irwin J.C. Giudice D. Knobil E. Neill J.D. Encyclopedia of Reproduction. Academic Press, New York1999: 823-835Google Scholar, 14Gu Y. Gibori G. Knobil E. Neill J.D. Encyclopedia of Reproduction. Academic Press, New York1999: 836-842Google Scholar). The progesterone-induced signaling molecules that participate in the formation of the decidual and its function remain poorly understood. We by analysis a cysteine protease inhibitor, CTLA-2β, which is induced in the uteri of pregnant mice precisely during the decidual phase. The CTLA-2β were induced in the on day of pregnancy following embryo attachment to the uterine a during days and to after day with the of the decidual phase. In situ hybridization analysis revealed that CTLA-2β mRNA expression in the It is that with the of implantation, a variety of cells, including cells, cells, and in the decidua near the implanted embryo B.A. Chantakru S. Esadeg S. Ashkar A.A. Wei Q. J. Reprod. Immunol. 2002; 57: 151-168Crossref PubMed Scopus (122) Google Scholar). we the of cells in the decidua that CTLA-2β. the that CTLA-2β is in the vicinity of embryo is and with the role of this in embryo-uterine interactions during early pregnancy. of the embryo in A role of protease in embryo-uterine interactions is with the that the of implantation involves invasion of the by the invasion endometrial as well as the are precisely regulated and a between the factors that and trophoblast protease which are by endometrial during pregnancy, have been for and R.M. Full Text PDF PubMed Scopus Google Scholar, A.T. R.M. J. Biol. Chem. Full Text PDF PubMed Google Scholar) a uterine inhibitor from uterine of during pregnancy R.M. Full Text PDF PubMed Scopus Google Scholar, A.T. R.M. J. Biol. Chem. Full Text PDF PubMed Google Scholar). expression was the of and to and The inhibitor a well of which with inhibitor R.M. J. Biol. Chem. 1994; 269: Full Text PDF PubMed Google Scholar). are with the hypothesis that the progesterone-regulated protease function by neutralizing the activities of one or more proteases generated by the proliferating trophoblast R.M. N. Dey S.K. and Cellular of U. S. New Scholar). In that factors that invasion are Biol. 1989; Google Scholar, S. Full Text PDF PubMed Scopus Google Scholar). Consistent with this trophoblast been shown to and proteases and and the cysteine proteases F. D. Dev. PubMed Scopus Google Scholar, M.B. Biol. Reprod. PubMed Scopus Google Scholar, Y. M. J. Biol. Scholar, P. P. PubMed Google Scholar, Werb Z. PubMed Google Scholar). The decidual is to participate in the of invasion by the of these proteases. Our studies that cathepsin L, by the giant is one of the targets of CTLA-2β in the pregnant uterus Based on these we that CTLA-2β during the decidual phase regulates trophoblast invasion by neutralizing the activity of cathepsin L. role of cathepsin L during implantation is by the studies of and S. L. PubMed Google Scholar). observed that of a inhibitor of cathepsin L, to pregnant mice implantation in a Whereas treatment of mice with a dose of in a of implantation, administration of a dose of this to and a decidual response. studies support the that action of cathepsin L the decidua is critical for the decidualization and implantation CTLA-2β was in the of identification of gene for the function of cytotoxic T (19Denizot F. Brunet J.-F. Roustan P. Harper K. Suzan M. Luciani F. Golstein P. Eur. J. Immunol. 1989; 19: 631-635Crossref PubMed Scopus (71) Google Scholar, Denizot F. Golstein P. Immunol. 1988; PubMed Scopus Google Scholar). It therefore, that uterine CTLA-2β may play a role in the regulation of T action during early pregnancy. the time of embryo implantation, the response to the embryo the of A. Immunol. 2002; 2: PubMed Scopus Google Scholar, E. PubMed Scopus Google Scholar). the embryo this response and the of the a that from the fetal A. Immunol. 2002; 2: PubMed Scopus Google Scholar, E. PubMed Scopus Google Scholar). Consistent with this studies have shown that which of T cells, implantation and of early pregnancy A. E. S. G. A. Immunol. 2: PubMed Scopus Google Scholar, J. P. K. D. Immunol. 2: PubMed Scopus Google Scholar). It is that response to the embryo is in regulation of T Interestingly, a of studies indicated that cathepsin L plays role in T P. A. A. J. Science. PubMed Scopus Google Scholar, K. J. 2002; PubMed Scopus Google Scholar). A critical in complex is of the L was found to be necessary for and cathepsin L mice a of T cells in the and P. A. A. J. Science. PubMed Scopus Google Scholar, K. J. 2002; PubMed Scopus Google Scholar). Consistent with this a T was found to a of the cathepsin L gene F. A. E. A. M. N. PubMed Scopus Google Scholar). Interestingly, our in this the that CTLA-2β in the decidua the implanting embryo may inhibit the activity of cathepsin L by the leading to of complex This in may to a in the of certain of T cells, the of response to the studies determine the function of CTLA-2β in the pregnant uterus is to with cathepsin L to trophoblast invasion T function to response at the time of implantation.