A human anti-IL-2 antibody that potentiates regulatory T cells by a structure-based mechanism

Interleukin-2 (IL-2) has been shown to suppress immune pathologies by preferentially expanding regulatory T cells (T_regs). However, this therapy has been limited by off-target complications due to pathogenic cell expansion. Recent efforts have been focused on developing a more selective IL-2. It is well documented that certain anti-mouse IL-2 antibodies induce conformational changes that result in selective targeting of T_regs. We report the generation of a fully human anti-IL-2 antibody, F5111.2, that stabilizes IL-2 in a conformation that results in the preferential STAT5 phosphorylation of T_regs in vitro and selective expansion of T_regs in vivo. When complexed with human IL-2, F5111.2 induced remission of type 1 diabetes in the NOD mouse model, reduced disease severity in a model of experimental autoimmune encephalomyelitis and protected mice against xenogeneic graft-versus-host disease. These results suggest that IL-2-F5111.2 may provide an immunotherapy to treat autoimmune diseases and graft-versus-host disease.

Discovery of a novel human anti-IL-2 antibody that potentiates Regulatory T cells by a structure-based mechanism

Interleukin-2 (IL-2) has been shown to suppress immune pathologies by preferentially expanding regulatory T cells (Treg). However, this therapy has been limited by off-target complications due to pathogenic cell expansion. Recent efforts have been focused on developing a more selective IL-2. It is well documented that certain anti-mouse IL-2 antibodies induce conformational changes that result in selective targeting of Treg cells. We report the generation of the first fully human anti-IL-2 antibody, F5111.2 that stabilizes IL-2 in a conformation that results in the preferential STAT5 phosphorylation of Tregs in vitro and selective expansion of Tregs in vivo. When complexed with human IL-2, F5111.2 induced remission of type 1 diabetes in the NOD mouse model, reduced disease severity in a model of experimental autoimmune encephalitis, and protected mice against xenogeneic Graft-versus-Host-Disease (GvHD). These results suggest that IL-2-F5111.2 may provide a new immunotherapy to treat autoimmune diseases and GvHD.

IL-22 bridges the lymphotoxin pathway with the maintenance of colonic lymphoid structures during infection with Citrobacter rodentium

Colonic patches (CLPs) and isolated lymphoid follicles (ILFs) are two main lymphoid structures in the colon. Lymphoid tissue-inducer cells (LTi cells) are indispensable for the development of ILFs. LTi cells also produce interleukin 17 (IL-17) and IL-22, signature cytokines secreted by IL-17-producing helper T cells. Here we report that IL-22 acted downstream of the lymphotoxin pathway and regulated the organization and maintenance of mature CLPs and ILFs in the colon during infection with Citrobacter rodentium. Lymphotoxin (LTα(1)β(2)) regulated the production of IL-22 during infection with C. rodentium, but the lymphotoxin-like protein LIGHT did not. IL-22 signaling was sufficient to restore the organization of CLPs and ILFs and host defense against infection with C. rodentium in mice lacking lymphotoxin signals, which suggests that IL-22 connects the lymphotoxin pathway to mucosal epithelial defense mechanisms.

Regulation and functions of the IL-10 family of cytokines in inflammation and disease

The IL-10 family of cytokines consists of nine members: IL-10, IL-19, IL-20, IL-22, IL-24, IL-26, and the more distantly related IL-28A, IL-28B, and IL-29. Evolutionarily, IL-10 family cytokines emerged before the adaptive immune response. These cytokines elicit diverse host defense mechanisms, especially from epithelial cells, during various infections. IL-10 family cytokines are essential for maintaining the integrity and homeostasis of tissue epithelial layers. Members of this family can promote innate immune responses from tissue epithelia to limit the damage caused by viral and bacterial infections. These cytokines can also facilitate the tissue-healing process in injuries caused by infection or inflammation. Finally, IL-10 itself can repress proinflammatory responses and limit unnecessary tissue disruptions caused by inflammation. Thus, IL-10 family cytokines have indispensable functions in many infectious and inflammatory diseases.

Regulation of cytokine secretion in human CD127(+) LTi-like innate lymphoid cells by Toll-like receptor 2

Lymphoid tissue inducer cells are members of an emerging family of innate lymphoid cells (ILC). Although these cells were originally reported to produce cytokines such as interleukin-17 (IL-17) and IL-22, we demonstrate here that human CD127(+)RORC(+) and CD56(+)CD127(+) LTi-like ILC also express IL-2, IL-5, and IL-13 after activation with physiologic stimuli such as common γ-chain cytokines, Toll-like receptor (TLR) 2 ligands, or IL-23. Whereas TLR2 signaling induced IL-5, IL-13, and IL-22 expression in a nuclear factor κB (NF-κB)-dependent manner, IL-23 costimulation induced only IL-22 production. CD127(+) LTi-like ILC displayed clonal heterogeneity for IL-13 and IL-5 production, suggesting in vivo polarization. Finally, we identified a role for autocrine IL-2 signaling in mediating the effects of TLR2 stimulation on CD56(+)CD127(+) and CD127(+) LTi-like ILC. These results indicate that human LTi-like ILC can directly sense bacterial components and unravel a previously unrecognized functional heterogeneity among this important population of innate lymphoid cells.

Human NKp44+IL-22+ cells and LTi-like cells constitute a stable RORC+ lineage distinct from conventional natural killer cells

Lymphoid tissue inducer (LTi) cells are required for lymph node formation during fetal development, and recent evidence implies a role in mucosal immunity in the adult. LTi cells share some phenotypic features of conventional natural killer (NK; cNK) cells; however, little is known to date about the relationship between these two cell types. We show that lineage(-) (Lin(-)) CD127(+)RORC(+) LTi-like cells in human tonsil are precursors to CD56(+)CD127(+)RORC(+)NKp46(+) cells, which together comprise a stable RORC(+) lineage. We find that LTi-like cells and their CD56(+) progeny can be expanded and cloned ex vivo without loss of function and without conversion into cNK cells. Clonal analysis reveals heterogeneity of cytokine production within the CD127(+) LTi-like population. Furthermore, we identify within the tonsil a cNK precursor population that is characterized as Lin(-)CD117(+)CD161(+)CD127(-) cells. Overall, we propose that CD127(+)RORC(+) cells, although they share some characteristics with cNK cells, represent a functionally and developmentally distinct lineage.

Identification of a human helper T cell population that has abundant production of interleukin 22 and is distinct from T(H)-17, T(H)1 and T(H)2 cells

Interleukin 22 (IL-22) is a member of the IL-10 cytokine family that is involved in inflammatory and wound healing processes. Originally considered a T helper type 1 (T(H)1)-associated cytokine, IL-22 has since been shown to be produced mainly by IL-17-producing helper T cells (T(H)-17 cells). Here we describe a previously uncharacterized IL-22-producing human helper T cell population that coexpressed the chemokine receptor CCR6 and the skin-homing receptors CCR4 and CCR10. These cells were distinct from both T(H)-17 cells and T(H)1 cells. Downregulation of either the aryl hydrocarbon receptor (AHR) or the transcription factor RORC by RNA-mediated interference affected IL-22 production, whereas IL-17 production was affected only by downregulation of RORC by RNA-mediated interference. AHR agonists substantially altered the balance of IL-22- versus IL-17-producing cells. This subset of IL-22-producing cells may be important in skin homeostasis and pathology.

Human fetal lymphoid tissue-inducer cells are interleukin 17-producing precursors to RORC+ CD127+ natural killer-like cells

The human body contains over 500 individual lymph nodes, yet the biology of their formation is poorly understood. Here we identify human lymphoid tissue-inducer cells (LTi cells) as lineage-negative RORC+ CD127+ cells with the functional ability to interact with mesenchymal cells through lymphotoxin and tumor necrosis factor. Human LTi cells were committed natural killer (NK) cell precursors that produced interleukin 17 (IL-17) and IL-22. In vitro, LTi cells gave rise to RORC+ CD127+ NK cells that retained the ability to produce IL-17 and IL-22. Postnatally, similar populations of LTi cell-like cells and RORC+ CD127+ NK cells were present in tonsils, and both secreted IL-17 and IL-22 but no interferon-gamma. Our data indicate that lymph node organogenesis is controlled by an NK cell precursor population with adaptive immune features and demonstrate a previously unappreciated link between the innate and adaptive immune systems.

Flow cytometry-based methods for studying signaling in human CD4+CD25+FOXP3+ T regulatory cells

T regulatory (Treg) cells have a fundamental role in the establishment and maintenance of peripheral tolerance. It is well established that Treg cells have a phenotype and function that is distinct from conventional T effector cells, although how these two T cell subsets differ in terms of molecular signaling cascades remains largely unknown. Analysis of signaling events in Treg cells using classical biochemistry has been hampered due to difficulties in isolating homogeneous populations and limited cell numbers. In order to overcome these challenges, we defined the optimal conditions for culture, in vitro expansion, and stimulation of human CD4(+)CD25(+) Treg and T effector cells to study intracellular signaling events by flow cytometry. In order to avoid the pitfalls associated with cell isolation based on CD25 expression, we developed methodology to analyze subpopulations of FOXP3 positive and negative cells from ex vivo CD4(+) T cells. In addition to examination of ex vivo cells, we optimized expansion conditions for analysis of signaling in Treg and T effector cell lines. Using these methods, we found that human FOXP3(+) Treg cells displayed a greater capacity to phosphorylate the extracellular regulated kinase (ERK) compared to T effector cells, upon TCR-mediated activation. In contrast, FOXP3(+) Treg cells showed a significantly diminished capacity to phosphorylate AKT. This methodology provides a foundation for future investigation into the molecular events that regulate the phenotype and function of Treg cells, and may ultimately lead to the identification of Treg-cell specific therapeutic targets.

Activation-induced FOXP3 in human T effector cells does not suppress proliferation or cytokine production

Forkhead box P3 (FOXP3) is currently thought to be the most specific marker for naturally occurring CD4(+)CD25(+) T regulatory cells (nTregs). In mice, expression of FoxP3 is strictly correlated with regulatory activity, whereas increasing evidence suggests that in humans, activated T effector cells (Teffs) may also express FOXP3. In order to better define the role of FOXP3 in human Teff cells, we investigated the intensity and kinetics of expression in ex vivo Teff cells, suppressed Teff cells and Teff cell lines. We found that all dividing Teff cells expressed FOXP3, but only transiently, and at levels that were significantly lower than those in suppressive nTregs. This temporary expression in Teff cells was insufficient to suppress expression of reported targets of FOXP3 repressor activity, including CD127, IL-2 and IFN-gamma, and was not correlated with induction of a nTreg phenotype. Thus expression of FOXP3 is a normal consequence of CD4(+) T cell activation and, in humans, it can no longer be used as an exclusive marker of nTregs. These data indicate that our current understanding of how FOXP3 contributes to immune tolerance in humans needs to be re-evaluated.

Altered activation of AKT is required for the suppressive function of human CD4+CD25+ T regulatory cells

Suppression by T regulatory cells (Treg cells) is a major mechanism by which the immune system controls responses to self and nonharmful foreign proteins. Although there are many different types of Treg cells, the best characterized are those that constitutively express cell-surface IL-2Ralpha (CD25). We investigated whether altered T-cell-receptor (TCR)-mediated signaling in pure populations of ex vivo human CD4+CD25+ Treg cells might underlie their unique phenotype, including hyporesponsiveness to TCR-mediated activation and lack of cytokine production. CD4+CD25+ Treg cells displayed a consistent defect in phosphorylation of AKT at serine 473 and reduced phosphorylation of the AKT substrates FOXO and S6. Restoration of AKT activity via lentiviral-mediated expression of an inducibly active form of the kinase revealed that reduced activity of this pathway was necessary for the suppressive function of CD4+CD25+ Treg cells. These data represent the first demonstration of a causal association between altered signaling and the function of CD4+CD25+ Treg cells. Moreover, we have created the first system allowing inducible abrogation of suppression through manipulation of the suppressor cells. This system will be a powerful tool to further study the mechanism(s) of suppression by CD4+CD25+ Treg cells.

Human CD4+ T cells express TLR5 and its ligand flagellin enhances the suppressive capacity and expression of FOXP3 in CD4+CD25+ T regulatory cells

Germline encoded pattern recognition receptors, such as TLRs, provide a critical link between the innate and adaptive immune systems. There is also evidence to suggest that pathogen-associated molecular patterns may have the capacity to modulate immune responses via direct effects on CD4+ T cells. Given the key role of both CD4+CD25+ T regulatory (Treg) cells and the TLR5 ligand flagellin in regulating mucosal immune responses, we investigated whether TLR5 may directly influence T cell function. We found that both human CD4+CD25+ Treg and CD4+CD25- T cells express TLR5 at levels comparable to those on monocytes and dendritic cells. Costimulation of effector T cells with anti-CD3 and flagellin resulted in enhanced proliferation and production of IL-2, at levels equivalent to those achieved by costimulation with CD28. In contrast, costimulation with flagellin did not break the hyporesponsiveness of CD4+CD25+ Treg cells, but rather, potently increased their suppressive capacity and enhanced expression of FOXP3. These observations suggest that, in addition to their APC-mediated indirect effects, TLR ligands have the capacity to directly regulate T cell responses and modulate the suppressive activity of Treg cells.

Inhibition of basal and stimulated progesterone synthesis by dichlorodiphenyldichloroethylene and methoxychlor in a stable pig granulosa cell line

The effects of the insecticide dichlorodiphenyldichloroethylene (DDE) and methoxychlor in a stable pig granulosa cell line, JC-410, were investigated. The studies of DDE and methoxychlor were conducted in combination with studies of cholera toxin, the protein kinase A activator that stimulates cAMP and progesterone synthesis and gene expression of P450 cholesterol side chain cleavage (P450scc), which converts cholesterol to pregnenolone. Administration of DDE at 3000 and 10 000 ng ml (-1) was found to decrease progesterone synthesis 0.49- and 0.25-fold, respectively, and to block the stimulatory effect of 100 ng cholera toxin ml (-1), after 24 h incubation. At 1-100 ng ml (-1), methoxychlor did not affect progesterone synthesis after 48 h incubation. However, 1000 ng methoxychlor ml (-1) decreased progesterone synthesis 0.32-fold, and both 100 and 1000 ng methoxychlor ml (-1) blocked the stimulatory effect of cholera toxin. At 3000 and 10 000 ng ml(-1), DDE decreased cAMP synthesis 0.66-and 0.36-fold, respectively. At 300, 3000 and 10 000 ng ml (-1), DDE also decreased cholera toxin-stimulated cAMP synthesis 0.84-, 0.68-, and 0.52-fold, respectively. Administration of 1-100 ng methoxychlor ml (-1) did not affect basal or cholera toxin-stimulated cAMP synthesis. Cholera toxin increased P450scc mRNA 1.4-fold after 24 h incubation, while 3000 and 10 000 ng DDE ml (-1) led to 0.39- and 0.18-fold reductions, respectively. The stimulatory effect of cholera toxin on P450scc mRNA was blocked by 3000 and 10 000 ng DDE ml(-1). Cholera toxin increased P450scc mRNA 3.48-fold after 48 h incubation, while 100 and 1000 ng methoxychlor ml (-1) increased P450scc mRNA 1.79- and 3.0-fold, respectively, and further increased the stimulatory effect of cholera toxin 6.47- and 5.44-fold, respectively. The results of the present study indicate that DDE inhibits granulosa cell steroidogenesis by affecting cAMP production and P450scc gene expression. However, methoxychlor appears to inhibit steroidogenesis by a mechanism occurring before the conversion of cholesterol into pregnenolone.

Inhibition of basal and stimulated progesterone synthesis by dichlorodiphenyldichloroethylene and methoxychlor in a stable pig granulosa cell line

The effects of the insecticide dichlorodiphenyldichloroethylene (DDE) and methoxychlor in a stable pig granulosa cell line, JC-410, were investigated. The studies of DDE and methoxychlor were conducted in combination with studies of cholera toxin, the protein kinase A activator that stimulates cAMP and progesterone synthesis and gene expression of P450 cholesterol side chain cleavage (P450scc), which converts cholesterol to pregnenolone. Administration of DDE at 3000 and 10 000 ng ml (-1) was found to decrease progesterone synthesis 0.49- and 0.25-fold, respectively, and to block the stimulatory effect of 100 ng cholera toxin ml (-1), after 24 h incubation. At 1-100 ng ml (-1), methoxychlor did not affect progesterone synthesis after 48 h incubation. However, 1000 ng methoxychlor ml (-1) decreased progesterone synthesis 0.32-fold, and both 100 and 1000 ng methoxychlor ml (-1) blocked the stimulatory effect of cholera toxin. At 3000 and 10 000 ng ml(-1), DDE decreased cAMP synthesis 0.66-and 0.36-fold, respectively. At 300, 3000 and 10 000 ng ml (-1), DDE also decreased cholera toxin-stimulated cAMP synthesis 0.84-, 0.68-, and 0.52-fold, respectively. Administration of 1-100 ng methoxychlor ml (-1) did not affect basal or cholera toxin-stimulated cAMP synthesis. Cholera toxin increased P450scc mRNA 1.4-fold after 24 h incubation, while 3000 and 10 000 ng DDE ml (-1) led to 0.39- and 0.18-fold reductions, respectively. The stimulatory effect of cholera toxin on P450scc mRNA was blocked by 3000 and 10 000 ng DDE ml(-1). Cholera toxin increased P450scc mRNA 3.48-fold after 48 h incubation, while 100 and 1000 ng methoxychlor ml (-1) increased P450scc mRNA 1.79- and 3.0-fold, respectively, and further increased the stimulatory effect of cholera toxin 6.47- and 5.44-fold, respectively. The results of the present study indicate that DDE inhibits granulosa cell steroidogenesis by affecting cAMP production and P450scc gene expression. However, methoxychlor appears to inhibit steroidogenesis by a mechanism occurring before the conversion of cholesterol into pregnenolone.

Generation of stable cell lines by spontaneous immortalization of primary cultures of porcine granulosa cells

We report the generation of stable cell lines obtained by spontaneous immortalization of primary cultures of porcine granulosa cells. Three hundred stable cell lines were obtained from three independent immortalization trials. Two of these cell lines retained the steroidogenic capabilities characteristic of granulosa cells, such as de novo synthesis of progesterone and conversion of androstenedione into estradiol-17beta. All the stable cell lines expressed the P450arom and 3betaHSD genes, confirming their granulosa origin. Moreover, the steroidogenic stable granulosa cells also expressed StAR and P450scc genes. Stable cells were developed in cultures using Medium 199 supplemented with 5% newborn calf serum (NBCS). The surviving cells overcame the senescent phase and entered a stage of continuous growth for over one hundred generations. No stable colonies were obtained from cultures grown in MEM or DMEM or media supplemented with 10% NBCS or 5 and 10% fetal calf serum (FCS). Medium 199 is a formulation richer in nutrients compared to MEM or DMEM and the cell growth capability of NBCS is lower than that of FCS, probably due to deficiency of growth factors. We speculate that spontaneous immortalization of granulosa cells may be facilitated by using a rich culture formulation supplemented with low concentrations of serum deficient in growth factors. We have validated the stable cell lines for studying the effect of hormonal steroids on granulosa cell steroidogenesis and the expression of the steroidogenic genes. Therefore, we believe that they are useful models to study the molecular mechanism involved in granulosa cell differentiation and steroidogenesis.

Repression of myosin isoforms in developing and denervated skeletal muscle fibers originates near motor endplates

During development of chicken pectoralis muscle, a neonatal myosin heavy-chain isoform is supplanted progressively by an adult isoform. This expression is under neuronal control. In this study we test the hypothesis that developmental myosin transformations are initiated near the motor endplate of each muscle fiber, thereafter progressing toward the fiber ends. By using immunocytochemical methods, pectoralis muscle from chickens aged 1-115 days after hatching were labeled by antibody against neonatal isoform. Ellipse minor axis and mean optical density of labeled and/or unlabeled fiber profiles from each bird were measured by computer image analysis. Acetylcholinesterase (AChE) activity was demonstrated histochemically. Using serial cross sections, we show that smaller fiber profiles are the tapered ends of larger fiber profiles. The largest fiber profiles (central regions of the fibers) were the first to lose their neonatal myosin during development. Motor endplates were localized by AChE activity to the central regions of the fibers. The pectoralis of mature chickens was denervated for 3, 7, 15, or 21 days. After 2 weeks' denervation, neonatal myosin is first reexpressed in the fiber ends. Dev Dyn 2000;217:50-61.

Dichlorodiphenyldichloroethylene potentiates the effect of protein kinase A pathway activators on progesterone synthesis in cultured porcine granulosa cells

The insecticide dichlorodiphenyltrichloroethane (DDT) and its major metabolite p,p'-dichlorodiphenyldichloroethylene (DDE) have been implicated as endocrine-modulating chemicals. The DDT metabolite p, p'-DDE has been found contaminating human tissues and follicular fluid because of dietary exposure. We investigated the effects of DDE on progesterone synthesis in a stable porcine granulosa cell line, JC-410, and in primary cultures of porcine granulosa cells. Progesterone synthesis was not affected by 0.1-100 ng/ml DDE in the JC-410 cells. However, 10 ng/ml DDE increased 8-bromo-cAMP (8-Br-cAMP)-stimulated progesterone synthesis 0.4-fold (P < 0.05) over the levels observed with 1 mM 8-Br-cAMP alone. The effect of cholera toxin (CT) on progesterone synthesis was increased 0.7-fold (P < 0.05) by 10 ng/ml DDE over the value observed with 30 ng/ml CT alone. In primary cultures of porcine granulosa cells, 10 ng/ml DDE potentiated CT-stimulated progesterone synthesis 1.2-fold over the value observed with CT alone. In the JC-410 cells, 1 and 10 ng/ml DDE increased CT-stimulated cytochrome P450-cholesterol side-chain cleavage (P450(scc)) mRNA levels 0.3- and 0.4-fold, respectively, over the values obtained with CT alone. Neither basal nor CT-stimulated cAMP levels were changed by DDE. We conclude that DDE affects granulosa cell response to protein kinase A activators by altering the expression of the P450(scc) gene.

Steroid regulation of progesterone synthesis in a stable porcine granulosa cell line: a role for progestins

The objective of this investigation was to determine the effect of steroid hormones on the synthesis of progesterone in a stable porcine granulosa cell line, JC-410. We also examined the effect of steroid hormones on expression of the genes encoding the steroidogenic enzymes, cytochrome P450-cholesterol side chain cleavage (P450scc) and 3beta-hydroxy-5-ene steroid dehydrogenase (3beta-HSD). We observed that 48 h exposure of the JC-410 cells to estradiol-17beta (estradiol), androstenedione, 5alpha-dihydrotestosterone, levonorgestrel, and 5-cholesten-3beta, 25-diol (25-hydroxycholesterol) resulted in stimulation of progesterone synthesis. 25-Hydroxycholesterol augmented progesterone synthesis stimulated by estradiol, 5alpha-dihydrotestosterone, levonorgestrel and 8-bromoadenosine 3':5'-cyclic monophosphate (8-Br-cAMP). This increase in progesterone synthesis was additive with estradiol, 5alpha-dihydrotestosterone and levonorgestrel, and synergistic with 8-Br-cAMP. Cholera toxin, progesterone, levonorgestrel and androstenedione increased P450scc mRNA levels, whereas estradiol had no effect. Cholera toxin, progesterone and levonorgestrel increased 3beta-HSD mRNA levels, but estradiol and androstenedione had no effect. The results were interpreted to mean that estrogens, androgens and progestins regulate progesterone synthesis in the JC-410 cells. The effect of androgens appears to be mediated by stimulation of P450scc gene expression while progestins stimulate both P450scc and 3beta-HSD gene expression. Our results support the concept that progesterone is an autocrine regulator of its own synthesis in granulosa cells.

Regulation of steroidogenesis in jc-410, a stable cell line of porcine granulosa origin

We investigated the regulation of steroidogenesis in a cell line of porcine granulosa origin, JC-410. Cells responded to the protein kinase-A activators, cholera toxin and forskolin, with increased accumulation of intracellular cAMP. Histochemically, cells were shown to contain 3beta-HSD, the enzyme which converts pregnenolone to progesterone. The JC-410 cells produced progesterone and responded to the protein kinase-A activators with an increase in progesterone synthesis. Progesterone levels were also increased by 25-hydroxycholesterol, pregnenolone, estradiol and androstenedione. Follicle-stimulating hormone and luteinizing hormone had no effect on cAMP or progesterone accumulation. Androstenedione was required for the synthesis of estradiol by JC-410 cells. Steady-state levels of mRNA for the steroidogenic enzymes 3beta-HSD and P450scc were increased by treatment with cholera toxin, whereas P450arom was not changed. These cells express the steroidogenic enzymes genes in a similar fashion to primary cultures of porcine granulosa cells. The JC-410 cells may represent a valuable model to study second messenger regulation and the molecular mechanisms involved in steroidogenesis in granulosa cells.