Elevation of corticosteroid-binding globulin in obese strain (OS) chickens: possible implications for the disturbed immunoregulation and the development of spontaneous autoimmune thyroiditis

Basal plasma levels of corticosterone and corticosteroid-binding globulin (CBG) have been investigated in Obese strain (OS) chickens afflicted with spontaneous autoimmune thyroiditis (SAT). Corticosterone was determined radioimmunologically, and CBG by using a highly sensitive radioligand saturation assay. OS chickens displayed total corticosterone levels not different from healthy normal White Leghorn (NWL) chickens. CBG, however, was found to be twice as high in OS chickens as compared with their healthy counterparts, irrespective of sex or age. This quantitative difference in the CBG level is not compensated for by either altered affinity or specificity of the molecule. Furthermore, no differences were found in the response of OS and NWL lymphocytes to the suppressive effect of glucocorticoids in vitro. We therefore assume that OS animals are deficient in free, hormonally active corticosterone. An additional indication for such a diminished glucocorticoid tonus was that in vivo treatment of OS chickens with glucocorticoid hormones, thus increasing the free and active hormone fraction, normalizes the T cell hyperreactivity and significantly reduces thyroid infiltration. Possible pathophysiological implications of a diminished glucocorticoid tonus for spontaneous autoimmunity, as well as possible explanations for the beneficial effects of glucocorticoid treatment on the development of SAT, are discussed.     

Diminished glucocorticoid tonus in obese strain (OS) chickens with spontaneous autoimmune thyroiditis: increased plasma levels of a physicochemically unaltered corticosteroid-binding globulin but normal total corticosterone plasma concentration and normal glucocorticoid receptor contents in lymphoid tissues

Obese strain (OS) chickens afflicted with spontaneous autoimmune thyroiditis (SAT) display several signs of a general immune dysbalance, some of which may be related to altered endocrine mechanisms such as the glucocorticoid tonus. The latter is the combined result of corticosterone (CN) production, metabolism as well as excretion, and the binding of CN to corticosteroid binding globulin (CBG) and glucocorticoid receptors (GR). The present study deals with the comparative investigation of these parameters in OS and normal White Leghorn (NWL) chickens. The results obtained with radioimmunoassay for CN and radioligand saturation assays for plasma CBG as well as GR in the thymus were as follows: (1) both OS and NWL have equal total CN levels; (2) however, OS chickens exhibit elevated CBG levels, whereas the physicochemical parameters (equilibrium affinity, specificity spectrum) of CBG were equal in OS and NWL; (3) the GR capacities and affinities were equal in both OS and NWL throughout development until thymic involution. Similarly, the specificity, affinity, and sedimentation behaviour were equal in OS and NWL. (4) Furthermore, no differences were found in the response of OS and NWL splenocytes to the suppressive effect of glucocorticoids in vitro, also excluding postreceptor alterations at the cellular level in the OS. From these findings we conclude that the increased CBG levels, which are not compensated for by either increased CN plasma levels or by increased receptor capacities or affinities in lymphatic organs, represent a diminished glucocorticoid tonus in OS chickens. This may have immunoregulatory consequences which, in turn, may contribute to the development of SAT.     

AT-1.1: A thymus-specific alloantigen of chickens

A thymocyte-specific alloantigen, designated AT (avian thymus) –1.1, has been detected in Cornell C strain (CS) and Obese strain (OS) chickens, the latter being a strain derived from CS which develops a spontaneous form of autoimmune thyroiditis (SAT). Antisera specific for this antigen were developed first in a turkey immunized with thymocytes from an OS chicken and, later, in AT-1.1-negative CS chickens immunized with AT-1.1-positive thymocytes. AT-1.1 was detected in 50–70% of cells in a thymus cell suspension, but was not seen on peripheral blood lymphocytes, erythrocytes, or cells from bursa, spleen, kidney, liver, or brain. It was present on thymocytes of chickens at all ages tested, from 1 day to 6 months of age. AT-1.1 was not detected in six chicken lymphoid tumor cell lines tested, and birds expressing it were found to be negative for the presence of Marek's disease viral antigens. Pedigree studies on 287 (OS × CS)F₂ chickens demonstrated that AT-1.1 is expressed in a dominant or codominant manner, and the gene coding for this antigen was not linked to the B (major histocompatibility) complex. The genetics and tissue distributions of AT-1.1 indicate that it differs from thymus cell surface antigens, avian or mammalian, previously described.     

Materno-embryonally transferred antibodies precipitate autoimmune thyroiditis in obese strain (OS) chickens

In Obese strain (OS) chickens the role of maternal antibodies, passively transferred through the egg to the developing chick, was evaluated as a causative factor in the early development of spontaneous autoimmune thyroiditis (SAT). In the egg, passive antibody titers were highest in the yolk and lower in the allantoic fluid and sera of developing embryos. This passage of antibodies was documented by use of radiolabeled antibodies. In dams with high antibody titers, antibodies could be found in the sera of chicks at the time of hatch. Thyroglobulin was absent in the yolk of OS eggs during embryonal life, as compared with its detection in normal eggs. Immune complexes (thyroglobulin-autoantibody) detected in the thyroids of OS, but not CS, chicks at the time of hatch, or earlier, appear to reflect the presence of the maternally transferred antibodies. A pair of crosses between OS chickens, with thyroiditis, and the C strain (CS), without thyroiditis, was made to evaluate the role of transferred antibodies in the pathogenesis of autoimmune disease. When an OS chicken was the dam, maternal antibodies could be passively transferred; when a CS chicken was the dam, no maternal antibodies were present to be transferred. Nevertheless, both hybrids developed full-blown thyroiditis, demonstrating that binding of transferred maternal antibody to thyroglobulin is not a prerequisite for the induction of SAT. However, presence of maternal antibodies precipitated the onset of disease. Immune complexes formed in the embryonic thyroid are likely to participate in early autoimmune disease, although the development of full-blown thyroiditis may await the competency of the chick's immune system to provide the characteristic cellular infiltrate.     

Enhanced response to Con A and production of TCGF by lymphocytes of obese strain (OS) chickens with spontaneous autoimmune thyroiditis

The mitogenic response to Con A and the production of T cell growth factor or interleukin 2 (IL 2) by splenic and peripheral blood lymphocytes of obese strain (OS) chickens with spontaneous autoimmune thyroiditis have been investigated. By using an optimized method with Con A-coated chicken erythrocytes (MRC), lymphocytes of OS chickens were found to exhibit significantly elevated mitogenic responses as compared with cells from either Normal White Leghorn chickens (NWL) or animals of the Cornell C-Strain (CS), from which the OS has originally been developed. This difference was observed throughout ontogeny up to 15 mo of age, and was associated with increased levels of IL 2 activity in the culture supernatants. The elevated responsiveness of OS T lymphocytes was also found to be manifested in the expression of receptors for IL 2, because Con A-stimulated lymphocytes of OS birds were significantly more effective than those from normal controls in absorbing IL 2 activity from conditioned media (CM) of stimulated spleen cells. High concentrations of CM were suppressive in IL 2 assays, signaling the presence of an inhibitory factor(s) in addition to IL 2. An additional indication for defective immunoregulation was that CM from OS lymphocyte cultures showed significantly less of this suppressive activity in comparison with CM of normal (NWL and CS) lymphocyte cultures. Finally, the spontaneous uptake of 125IUdR of embryonic and early post hatching OS spleen lymphocytes was consistently and significantly enhanced. This difference, however, in contrast to the one observed in Con A responses, was found to decrease with age. The data are discussed in view of the contradictory results concerning T cell functions reported for several autoimmune states in mammals.     

Analysis of lymphocytes infiltrating the thyroid gland of Obese strain chickens

Lymphocytes were isolated from the infiltrated thyroid glands of 2- to 5-wk-old Obese strain (OS) chickens with spontaneous autoimmune thyroiditis (SAT). Immunofluorescence analysis performed by using a panel of monoclonal and polyclonal antibodies revealed that 60% of thyroid infiltrating leukocytes (TIL) were mature T cells, a large portion of which seemed to be in an activated state bearing Ia-like antigens (10%) as well as a surface determinant associated with T cell activation (16%), i.e., possibly the receptor for interleukin 2 (IL 2). Furthermore, a relatively high plasma cell content (5%) was observed. TIL exhibited high proliferative responses to T cell mitogens (concanavalin A, phytohemagglutinin) and IL 2, but only weak responses to the B cell mitogen LPS from Salmonella typhimurium. When injected into newly hatched, MHC-identical, irradiated normal chickens, TIL induced both the production of autoantibodies and thyroid infiltration. Peripheral lymphocytes from spleen and blood and thymocytes from the same OS donors had no effect. Analysis of chemically (cyclophosphamide) bursectomized OS chickens suggested that an intact B cell system was not obligatory for the induction of SAT. TIL from these chickens consisted of 77% T cells and less than 1% B lymphocytes, yet were capable of inducing severe thyroid infiltration upon transfer into normal recipients. These findings emphasize the importance of the T cell system in the initiation of SAT.     

Mechanisms of T cell hyperreactivity in obese strain (OS) chickens with spontaneous autoimmune thyroiditis: lack in nonspecific suppression is due to a primary adherent cell defect

The disturbed homeostasis of the immune system in Obese strain (OS) chickens with spontaneous autoimmune thyroiditis consists in a general T cell hyperreactivity (concanavalin A hyperresponsiveness, interleukin 2 (IL 2) hypersecretion), particularly expressed by those lymphocytes which infiltrate the diseased thyroid gland. This abnormality has been attributed to a defective regulation of both IL 2 production and IL 2 function by low m.w. factors, which are present in serum and splenocyte culture supernatants of normal chickens, but deficient in the OS. In the present study we identified the cellular origin of IL 2 antagonistic activity as a nonlymphoid, adherent cell. Suppressor factor production in vitro was confined to the plastic adherent fraction of spleen cells and preincubation of splenocytes with nylon wool, silica particles, or carbonyl iron significantly reduced the nonspecific suppressive activity of the culture supernatant. Kinetic studies revealed the defect in nonspecific suppression to entail prolonged IL 2 production by concanavalin A-activated OS spleen cells. In vivo treatment of normal White Leghorn chickens with silica led to a decrease in suppressive serum activity down to the OS level, whereas neither neonatal thymectomy nor bursectomy had any effect. The defective suppressor factor production in autoimmune chickens appeared to be due to a functional, but not numeric defect of macrophages as revealed by phenol red staining. The possibility that this aberration in adherent cell function might be a secondary phenomenon to the recently described reduced corticosterone tonus in OS chickens was excluded by in vivo substitution with exogenous glucocorticoids which did not normalize the suppressor defect in serum or in conditioned medium. Finally, we present evidence that T lymphoblasts from OS animals are less susceptible to IL 2 antagonistic regulation than normal cells, which possibly further contributes to the T cell hyperfunction of this autoimmune strain.     

Characterization of estrogen receptors in the hamster brain

Although the hamster is frequently used as an experimental animal for studying reproductive neuroendocrinology and sex behavior, estrogen receptors (ER) in the central nervous system have not been fully characterized. Using Sephadex LH-20 gel filtration and DNA-cellulose affinity chromatography, estrogen binding macromolecules having the physicochemical properties of classical ER were identified in cytosolic and nuclear extracts of brain tissues. These receptors exhibited high affinity for estradiol (Kd = 10(-9) M), limited capacity (30-50 fmol/g tissue), and estrogen specificity; however, competition studies indicate that brain and uterine ER have different binding kinetics. The neuroanatomic distribution of ER was similar in males and females with highest levels in the limbic brain and consistently low levels in remaining forebrain and mid/hindbrain. No sex differences in receptor number or other binding parameters were evident. Sucrose gradient centrifugation showed that cytosolic ER sedimented in the 7-8S region of a 5-20% linear gradient (no salt), whereas nuclear ER had a sedimentation coefficient of 5S under high ionic strength. On DNA-cellulose affinity columns, these receptors had an elution maximum of 0.18 M NaCl. After a single injection of estradiol, nuclear ER increased and cytosolic ER were depleted. The lower estradiol binding affinity and receptor levels in hamster brain as compared to the rat are consistent with observed species differences in neural sensitivity to estrogen. We expect these data in hamsters, a markedly photosensitive species, to provide a basis for future studies examining the role of receptors in mediating the effects of day-length on steroid dependent feedback and behavioral responses.     

Disturbed immune-endocrine communication in autoimmune disease. Lack of corticosterone response to immune signals in obese strain chickens with spontaneous autoimmune thyroiditis

Antigenic challenge as well as injection of lymphokine-containing media lead to a transient increase of serum glucocorticoids, a phenomenon that has been implicated in the regulation of the specificity of immune responses. In the present study we examined the dialogue between the immune and the neuroendocrine systems in Obese strain (OS) chickens, an animal model for human Hashimoto thyroiditis. The following results were obtained: A) OS and normal White Leghorn (NWL) chickens, 5-mo-old, were immunized with sheep red blood cells followed by daily monitoring of corticosterone (CN) serum levels. Whereas in NWL animals CN serum levels markedly increase 3 to 4 days after immunization, OS animals did not respond with CN elevation. B) A single i.v. injection of conditioned medium (CM) from concanavalin A-stimulated spleen cells also led to a transient, dose-dependent peak in plasma CN (maximum after 30 min). This CN response to a given CM preparation was significantly lower in OS than in NWL animals. C) CM, whether obtained from OS or NWL splenocytes, were equally effective to stimulate CN production. D) A single i.v. injection of CM leads--concomitantly to the CN peak--to a decrease of the concanavalin A-mediated proliferative response of peripheral blood lymphocytes in both OS and NWL chickens. This suppression, however, was significantly more pronounced in NWL chickens. In summary, these data suggest a disturbance of the immune-neuroendocrine communication in OS chickens with spontaneous thyroid autoimmunity. The possible implications for the generation of "forbidden" autoimmune responses are discussed.     

Immunogenetic and ontogenetic studies of chickens with selective IgA deficiency and autoimmune thyroiditis

In addition to spontaneous hypothyroidism and autoimmune thyroiditis, chickens of the obese strain (OS) have a high incidence of selective IgA deficiency. Elevated levels of serum IgM also occur in many OS chickens. The IgA deficiency begins by 2 weeks, the age when hypothyroidism is developing. Like thyroiditis, a greater incidence of IgA deficiency was noted in OS birds homozygous for the B¹ allele than for the B⁴ allele of the major histocompatibility locus. Although IgA deficiency occurs in both sexes, it is found in a higher frequency in females than males (2:1). An abnormal ontogenesis of immunological competence may influence both traits.     

“Natural” chicken antibodies to red blood cells are mainly directed against the B-G antigen,and their occurrence is independent of spontaneous autoimmune thyroiditis

Using an indirect hemagglutination assay we tested sera from 94 healthy normal White Leghorn (NWL) and 117 Obese strain (OS) chickens with spontaneous autoimmune thyroiditis for the presence of natural antibodies against major histocompatibility complex (MHC) antigens expressed on red blood cells (RBC). In both groups older animals had a significantly increased frequency of such antibodies, but the titer was age-independent. OS chickens showed almost the same frequency of natural antibodies as NWL, and a comparison between OS birds with high antithyroglobulin autoantibody (Tg-AAb) titers and those with low titers also did not reveal a significant difference. We conclude that the occurrence of natural antibodies has no relation to Tg-AAb. The specificity of natural antibodies for MHC-encoded antigens was investigated in indirect immunofluorescence tests including absorption experiments with RBC and white blood cells (WBC). This analysis revealed that of 14 MHC-specific sera 13 were reacting with the B-G antigen, which is present on RBC only. One serum reacted with the B-F antigen, expressed on all somatic cells, i. e., both on RBC and WBC.     

禽呼肠孤病毒感染对鸡法氏囊及免疫应答的影响

研究LY株禽呼肠孤病毒(ARV)感染1日龄SPF鸡后对法氏囊发育影响,对传染性法氏囊病毒(IBDV)、禽流感病毒(AIV)、新城疫病毒(NDV)疫苗免疫诱发的抗体的影响,及对强毒株IBDV致病作用的影响。结果表明,LY株ARV感染1日龄SPF鸡可引起法氏囊萎缩和部分淋巴细胞减少,但对增重及AIV和NDV疫苗免疫后抗体滴度却没有显著影响。ARV感染可降低弱毒IBDV疫苗免疫后的抗体反应,但对随后IBDV强毒株攻毒的抵抗力却与对照鸡无显著差异。经IBDV弱毒疫苗免疫后,再接种强毒株IBDV,不会引起死亡,但却仍能显著抑制对AIV、NDV疫苗免疫后的抗体滴度。然而,对于1~7日龄经ARV感染的鸡,IBDV强毒的这种免疫抑制作用又显著低于未经ARV感染的对照鸡。     

Biochemical characterization of the progesterone receptor in the chick bursa of Fabricius

In a previous work we demonstrated estrogen-inducible progesterone binding sites in the bursa of Fabricius. In the present study these were characterized and compared to the progesterone receptor (PR) in the chick oviduct. When the size of the binding sites was analyzed with sucrose gradient centrifugation, 2 peaks of bound progesterone were obtained. The sedimentation coefficients of the peaks were 8-9 S and 3-4 S. In size exclusion HPLC only 1 peak was seen with a size corresponding to the 8-9 S in the sucrose gradient. The Stokes radius was 7.7 nm. When the ionic strength was elevated or CaCl2 was added, smaller steroid binding forms were detected. The sizes of these progesterone binding molecules at low and high ionic strength and in the presence of CaCl2 were equal in bursa and oviduct when analyzed with HPLC. The Stokes radii of these forms were 5.6 nm in high salt and 2.1 nm with CaCl2. The steroid binding components in the bursa cytosol eluated as 2 peaks from the DEAE column with KCl gradient. The peaks corresponded to the so-called A and B components in the chick oviduct. In the presence of molybdate, bound progesterone eluated as one peak from DEAE in both oviduct and bursa. The progesterone binding capacity was shown to be heat labile with equal half-lives in the bursa and the oviduct. Progesterone and ORG 2058 had a high affinity for the binding site and their binding was specific for progestins. It is concluded that the estrogen-inducible progesterone binding site in the bursa of Fabricius resembles the oviductal progesterone receptor in structural and binding properties.     

A role for IL-15 in driving the onset of spontaneous autoimmune thyroiditis?

The obese strain (OS) of chickens, which suffers from spontaneous autoimmune thyroiditis, is an excellent animal model for Hashimoto's thyroiditis and provides a unique opportunity to investigate the mechanisms underlying and driving the onset of the disease. Following recent advances in cloning chicken cytokines, we can now begin to investigate the role of cytokines in driving the lymphoid infiltration of the thyroid seen in these birds from day 7 posthatch. Using real-time quantitative RT-PCR, we characterized the expression of IFN-gamma, IL-1beta, IL-2, IL-6, IL-8, IL-15, and IL-18 in thyroids from OS birds and control CB line birds, both in the embryo just before hatch (embryonic day 20) and at 3 and 5 days posthatch. All of these cytokines were up-regulated compared with levels in thyroids from CB birds, at least at some time points, with some evidence for coordination of regulation, e.g., for the proinflammatory cytokines IL-1beta and IL-8. Only IL-15 was up-regulated at all time points. IL-15 was also shown to be up-regulated in spleens of OS birds at embryonic day 20 and 5 days posthatch, suggesting that IL-15 is constitutively up-regulated in this line of birds. This could explain the general immune system hyperreactivity exhibited by OS chickens and may be a factor driving the lymphoid infiltration of the thyroid.     

Depot differences in steroid receptor expression in adipose tissue: possible role of the local steroid milieu

Sex hormones play an important role in adipose tissue metabolism by activating specific receptors that alter several steps of the lipolytic and lipogenic signal cascade in depot- and sex-dependent manners. However, studies focusing on steroid receptor status in adipose tissue are scarce. In the present study, we analyzed steroid content [testosterone (T), 17beta-estradiol (17beta-E2), and progesterone (P4)] and steroid receptor mRNA levels in different rat adipose tissue depots. As expected, T levels were higher in males than in females (P = 0.031), whereas the reverse trend was observed for P4 (P < 0.001). It is noteworthy that 17beta-E2 adipose tissue levels were higher in inguinal than in the rest of adipose tissues for both sexes, where no sex differences in 17beta-E2 tissue levels were noted (P = 0.010 for retroperitoneal, P = 0.005 for gonadal, P = 0.018 for mesenteric). Regarding steroid receptor levels, androgen (AR) and estrogen receptor (ER)alpha and ERbeta densities were more clearly dependent on adipose depot location than on sex, with visceral depots showing overall higher mRNA densities than their subcutaneous counterparts. Besides, expression of ERalpha predominated over ERbeta expression, and progesterone receptor (PR-B form and PR-A+B form) mRNAs were identically expressed regardless of anatomic depot and sex. In vitro studies in 3T3-L1 cells showed that 17beta-E2 increased ERalpha (P = 0.001) and AR expression (P = 0.001), indicating that estrogen can alter estrogenic and androgenic signaling in adipose tissue. The results highlighted in this study demonstrate important depot-dependent differences in the sensitivity of adipose tissues to sex hormones between visceral and subcutaneous depots that could be related to metabolic situations observed in response to sex hormones.     

The estrogen binding protein in human pancreas: concentrations in subcellular fractions of normal pancreatic tissue, in duodenal juice during pancreatic stimulation and in peripheral serum in normal and pathological conditions

The steroid binding properties of the human pancreatic estrogen binding protein (hEBP) in cytosol were studied by equilibrium dialysis. A high ligand specificity of the protein was revealed. hEBP in cytosol binds unconjugated steroid estrogens with a medium affinity (Kd = 10(-7) M) but does not bind conjugated estrogens or unconjugated androgens, gestagens, glucocorticoids or cholesterol. Quantitation of hEBP by radioimmunoassay in subcellular fractions of human pancreatic tissue indicated that the protein is translocated into different subcellular compartments. Duodenal juice taken from patients following stimulation of pancreatic secretion by food ingestion (Lund's test) showed high hEBP concentrations, and the levels of hEBP changed concomitantly with the levels of pancreatic isoamylase, indicating that hEBP secretion was stimulated by food ingestion. The levels of hEBP in peripheral serum from healthy subjects showed no sex difference, but were positively correlated to age. Highly elevated (10-20-fold) hEBP levels were found in serum from patients with acute pancreatitis, while normal serum hEBP values were found in other abdominal diseases. It is speculated that hEBP might have a specific role in the transport of estrogens from the peripheral circulation via the pancreas to the duodenum. The elevated hEBP levels in patients with acute pancreatitis indicate that this protein may be used as a marker of cellular damage in the pancreas.     

Diminished hepatic growth hormone receptor binding in sex-linked dwarf broiler and leghorn chickens

Hepatic growth hormone (GH) receptor binding was compared in normal and sex-linked dwarfs (SLD) from both Hubbard and Cornell strain chickens. At 6, 8, and 20 weeks of age, hepatic GH receptor binding in the Hubbard SLD chickens was significantly lower than that of normal fast-growing birds. At 20 weeks of age, only 2 of 22 SLD chickens in the Hubbard broiler strain showed positive binding at a high enough level to allow for Scatchard analysis. The affinity constants and binding capacities of these two SLD chickens were numerically (but not significantly) lower than those of the normal fast-growing birds. We further examined hepatic GH receptor binding in two closely related White Leghorn strains of chickens that have been maintained as closed breeding populations for many years. We observed no detectable hepatic GH binding in the Cornell SLD chickens (N = 20), as compared to the normal-growing control strain (K strain). In both SLD strains, pretreatment with 4 M MgCl2 did not enhance GH binding, suggesting that there was no endogenous GH binding to the receptor. Based on these data, we suggest that the lack, or greatly reduced number, of GH receptors may be a major contributing factor to the dwarfism observed in these strains.     

Sex steroid sensitivity of developing bursa of Fabricius

Sex steroid sensitivity of the bursa of Fabricius (BF) was studied from the early embryonic time until its regression. Expression of progesterone receptor (PR) served as a dual marker: first, as a marker for progesterone sensitivity and second, as a marker for estrogen action, since it is an estrogen-induced protein. The progesterone binding molecule in the bursa was characterized by different chromatography methods and by steroid binding studies. We showed that it fulfils the criteria of a progesterone receptor by binding, structural and immunological properties. With immunohistochemistry and with the combined techniques of immunohistochemistry and autoradiography we demonstrated two cell types which express the PR: smooth muscle cells surrounding the BF and stromal cells located under the bursal epithelium and between the lymphoid follicles. The epithelium and the cells inside the lymphoid follicles were negative. Using immunoelectron microscopy the PR-expressing stromal cells were shown to be fibroblasts. The cloacal mesenchyme, from which the BF develops, was shown to be sensitive to exogenous estrogen very early during the embryonic time. The mesenchyme around and inside the developing BF reached estrogen sensitivity a few days later. The estrogen-sensitive mesenchymal cells were first seen surrounding the bursal primordium and later in the center of the plicae. During a natural sexual maturation without exogenous estradiol an expression of the PR was detected much later, at the age of 10-12 weeks after hatching. This expression correlates with the onset of the bursal regression and with the increase of the sex steroid levels in the blood. In the oviduct stroma PR was undetectable before the onset of sexual maturation. In the oviduct stroma PR becomes detectable a few weeks earlier than in the bursa.