The role of active immunization against inhibin α-subunit on testicular development, testosterone concentration and relevant genes expressions in testis, hypothalamus and pituitary glands in Yangzhou goose ganders.

The present study was designed to investigate the potential role of immunization against inhibin on testicular development, plasma testosterone concentration and expression of relevant genes in hypothalamus, pituitary, Leydig and Sertoli cells in Yangzhou ganders. For this purpose, Yangzhou ganders, n = 30 were divided into groups A and B. Group B ganders were actively immunized against inhibin α-subunit, while group A ganders were immunized with bovine serum albumin (BSA), which served as control. Immunization against inhibin elevated testes weights. In addition, immunization against inhibin elevated GnRH, StAR, CYP11A1 and AMH mRNA transcription expressions as depicted by qRT-PCR. Furthermore, hypothalamic GnRH-I mRNA expressions were up regulated, while GnIH mRNA transcription expression showed reciprocal expression on day 227. LH-ß mRNA transcription expression remained unaffected. In conclusion, our findings suggest that active immunization against inhibin affect spermatogenesis and testicular development through regulations of hypothalamic, pituitary and testicular genes expressions.

Goose toll-like receptor 3 (TLR3) mediated IFN-γ and IL-6 in anti-H5N1 avian influenza virus response.

Induction of the innate immune pathways is critical for early anti-viral defense. How geese recognize viral molecules and activate these pathways is not well understood. In mammals, Toll-like receptor 3 (TLR3) recognizes double-stranded RNA. Activation of TLR3 induces the activation of NF-кB and the production of type-I interferon. In this study, the goose TLR3 gene was cloned using rapid amplification of cDNA ends. Goose TLR3 encoded an 896-amino-acid protein, containing a signal secretion peptide, 14 extracellular leucine-rich repeat domains, a transmembrane domain, a Toll/interleukin-1 receptor signaling domain, and shared 46.7-84.4% homology with other species. Tissue expression of goose TLR3 varied markedly and was highest in the pancreas and lowest in the skin. Human embryonic kidney 293 cells transfected with goose TLR3 and NF-κB-luciferase-containing plasmids responded significantly to poly i:c. The expression of TLR3, IL-6 and IFN-γ mRNA, but not IL-1 mRNA, was significantly upregulated after poly i:c or high pathogenic avian influenza virus (H5N1) stimulation in goose peripheral blood mononuclear cells cultured in vitro. Furthermore, geese infected with H5N1 showed significant upregulation of TLR3, especially in the lung and brain. We conclude that goose TLR3 is a functional TLR3 homologue of the protein in other species and plays an important role in virus recognition.

Immunopotentiators Improve the Efficacy of Oil-Emulsion-Inactivated Avian Influenza Vaccine in Chickens, Ducks and Geese.

Combination of CVCVA5 adjuvant and commercial avian influenza (AI) vaccine has been previously demonstrated to provide good protection against different AI viruses in chickens. In this study, we further investigated the protective immunity of CVCVA5-adjuvanted oil-emulsion inactivated AI vaccine in chickens, ducks and geese. Compared to the commercial H5 inactivated vaccine, the H5-CVCVA5 vaccine induced significantly higher titers of hemaglutinin inhibitory antibodies in three lines of broiler chickens and ducks, elongated the antibody persistence periods in geese, elevated the levels of cross serum neutralization antibody against different clade and subclade H5 AI viruses in chicken embryos. High levels of mucosal antibody were detected in chickens injected with the H5 or H9-CVCA5 vaccine. Furthermore, cellular immune response was markedly improved in terms of increasing the serum levels of cytokine interferon-γ and interleukine 4, promoting proliferation of splenocytes and upregulating cytotoxicity activity in both H5- and H9-CVCVA5 vaccinated chickens. Together, these results provide evidence that AI vaccines supplemented with CVCVA5 adjuvant is a promising approach for overcoming the limitation of vaccine strain specificity of protection.

Development of a Cell Marker ELISA for the Detection of Goose T Cell Surface CD8α Molecules.

CD8 molecule is a key marker on T cell surface and is connected with the antigen recognition and activation of T lymphocytes. In order to provide a detection method for quantifying goose CD8α expression, this study raised the protein and antibody for goose CD8α and developed a feasible cell marker enzyme-linked immunoabsorbent assay (ELISA) method. Recombinant protein of the extracellular region gene of goCD8α was expressed in prokaryotic expression system, and specific polyclonal antibodies for goCD8α were raised and purified, which was further confirmed by Western-blot, immunofluorescence assay (IFA), and immunohistochemistry (IHC). A cell marker ELISA was established and optimized to detect the change of goCD8α expression between goose parvovirus (GPV)-infected and mock-infected goose peripheral blood mononuclear cells (PBMCs), which is consistent with our previously results of real-time quantitative PCR (qPCR). Cell marker ELISA can provide a new method to detect goCD8α in protein level and in a sensitive, specific, and simple way. This may provide a convenient and novel method for the detection of goCD8α expression.

Transcriptome Analysis and Identification of Differentially Expressed Transcripts of Immune-Related Genes in Spleen of Gosling and Adult Goose.

The goose (Anser cygnoides), having high nutritional value, high-quality feathers and high economic benefit, is an economically important poultry species. However, the molecular mechanisms underlying the higher susceptibility to pathogens in goslings than in adult geese remains poorly understood. In this study, the histological sections of spleen tissue from a two-week-old gosling and an adult goose, respectively, were subjected to comparative analysis. The spleen of gosling was mainly composed of mesenchyma, accompanied by scattered lymphocytes, whereas the spleen parenchyma was well developed in the adult goose. To investigate goose immune-related genes, we performed deep transcriptome and gene expression analyses of the spleen samples using paired-end sequencing technology (Illumina). In total, 50,390 unigenes were assembled using Trinity software and TGICL software. Moreover, these assembled unigenes were annotated with gene descriptions and gene ontology (GO) analysis was performed. Through Kyoto encyclopedia of genes and genomes (KEGG) analysis, we investigated 558 important immune-relevant unigenes and 23 predicted cytokines. In addition, 22 immune-related genes with differential expression between gosling and adult goose were identified, among which the three genes showing largest differences in expression were immunoglobulin alpha heavy chain (IgH), mannan-binding lectin serine protease 1 isoform X1 (MASP1) and C-X-C chemokine receptor type 4 (CXCR4). Finally, of these 22 differentially expressed immune-related genes, seven genes, including tumor necrosis factor receptor superfamily member 13B (TNFRSF13B), C-C motif chemokine 4-like (CCL4), CXCR4, interleukin 2 receptor alpha (IL2RA), MHC class I heavy chain (MHCIα), transporter of antigen processing 2 (TAP2) IgH, were confirmed by quantitative real-time PCR (qRT-PCR). The expression levels of all the candidate unigenes were up-regulated in adult geese other than that of TNFRSF13B. The comparative analysis of the spleen transcriptomes of gosling and adult goose may promote better understanding of immune molecular development in goose.

Molecular cloning, tissue distribution, and immune function of goose TLR7.

TLR7 is a transmembrane endosomal protein that plays an essential role in innate antiviral responses via the recognition of conserved viral molecular patterns. Here, we cloned the full-length cDNA of goose TLR7 and carried out a molecular characterization of goose TLR7. The goose TLR7 gene is 3900 bp and encodes a 1045 amino acid protein with high homology to poultry (93% to duck and 83% to chicken). Similar conclusions were made by phylogenetic analysis. The predicted protein secondary structure of goose TLR7 contained a conserved Toll/interleukin-1 receptor domain and characteristic leucine-rich repeat regions, which has also been reported for duck TLR7. Additionally, the tissue distribution of goose TLR7 suggests that immune-associated tissues, especially the cecal tonsil and bursa of Fabricius, have high goose TLR7 expression levels. Goose TLR7 is abundantly expressed in lung tissues, which is distinct from its expression in chickens. Similar to duck TLR7, goose spleen mononuclear cells (MNCs) exposed to the mammalian TLR7 agonists R848 and Imiquimod showed significant induction of the production of proinflammatory cytokines and IFN-α. New type gosling viral enteritis virus (NGVEV) infection resulted in high mRNA expression levels of goose TLR7 in the spleen. By contrast, no direct interaction between NGVEV and goose TLR7 was detected after infecting goose spleen MNCs with NGVEV in vitro. However, triggering of goose TLR7 resulted in the rapid up-regulation of proinflammatory cytokines and anti-viral molecules, suggesting that goose TLR7 plays an important role in anti-viral defense.

Cloning and characterization of goose interleukin-17A cDNA.

Interleukin-17 (IL-17 or IL-17A) is a proinflammatory cytokine produced by activated T cells. IL-17A plays important roles in inflammation and host defense. In this study, the cDNA of the goose IL-17A (GoIL-17A) gene was cloned from thymocytes. Recombinant GoIL-17A (rGoIL-17A) was expressed using a baculovirus expression system and then biologically characterized. The complete open reading frame (ORF) of GoIL-17A contains 510 base pairs that encode 169 amino acid residues, including a 29-amino acid signal peptide and a single potential N-linked glycosylation site. This protein has a molecular weight of 18.9kDa. The amino acid sequence showed 95.9%, 84.6%, 45.0% and 38.4% similarity with the corresponding duck, chicken, rat, and human IL-17A sequences, respectively. The six conserved cysteine residues were also observed in GoIL-17A. A recombinant, mature form of GoIL-17A was produced and its biological activities in goose embryonic fibroblasts were investigated. RT-PCR analysis revealed a marked up-regulation of IL-6 and IL-8 mRNA expression in goose embryonic fibroblasts treated with 1-50 µg of rGoIL-17A for 12h. The GoIL-17A gene sequence and the biologically active recombinant protein may be useful for understanding the role of IL-17A in immune regulation.

Identification and expression profiling analysis of goose melanoma differentiation associated gene 5 (MDA5) gene.

Melanoma differentiation associated gene 5 (MDA5) is an important cytoplasmic receptor that recognizes long molecules of viral double-stranded RNA and single-stranded RNA with 5' triphosphate and mediates type I interferon secretion. In this study, the full-length MDA5 gene in the goose was identified and characterized. The cDNA of goose MDA5 was 3,306 bp in length with an open reading frame of 3,018 bp, which encoded a polypeptide of 1,005 amino acids. The deduced amino acid sequence contained 6 main structure domains including 2 caspase activation and recruitment domains, one DExD/H-box helicase domain, one type III restriction enzyme domain, one helicase conserved C-terminal domain, and one RIG-I C-terminal domain. Quantitative real-time PCR analysis indicated that goose MDA5 mRNA was constitutively expressed in all sampled tissues. It was highly expressed in the jejunum, trachea, ileum, colon, and kidney, and lowly expressed in the muscular stomach, glandular stomach, and muscle. A significant increase in the transcription of MDA5 was detected in the brain, spleen, and lungs of geese after infection with H5N1 highly pathogenic avian influenza virus compared with uninfected tissues. These findings indicated that goose MDA5 was an important receptor, involved in the antiviral innate immune defense to H5N1 highly pathogenic avian influenza virus in geese.

Molecular cloning, characterization and expression of goose Toll-like receptor 5.

Toll-like receptors (TLRs) are pattern recognition receptors (PRRs) that are vital to activation of the innate immune system in response to invading pathogens through their recognition of pathogen-associated molecular patterns (PAMPs). TLR5 is responsible for the recognition of bacterial flagellin in vertebrates. In this study, we cloned the goose TLR5 gene using rapid amplification of cDNA ends (RACE). The open reading frame (ORF) of goose TLR5 cDNA is 2583 bp in length and encodes an 860 amino acid protein. The entire coding region of the TLR5 gene was successfully amplified from genomic DNA and contained a single exon. The putative amino acid sequence of goose TLR5 consisted of a signal peptide sequence, 11 leucine-rich repeat (LRR) domains, a leucine-rich repeat C-terminal (LRR-CT) domain, a transmembrane domain and an intracellular Toll-interleukin-1 receptor (TIR) domain. The amino acid sequence of goose TLR5 shared 50.5% identity with human (Homo sapiens), 49.8% with mouse (Mus musculus) and 82.7% with chicken (Gallus gallus). The goose TLR5 gene was highly expressed in the spleen, liver and brain; moderately expressed in PBMCs, kidney, lung, heart, bone marrow, small intestine and large intestine; and minimally expressed in the cecum. HEK293 cells transfected with goose TLR5 and NF-κB-luciferase containing plasmids significantly responded to flagellin from Salmonella typhimurium indicating that it is a functional TLR5 homologue. In response to infection with S. enterica serovar Enteritidis (SE), the level of TLR5 mRNA significantly increased over the control in PBMCs at 1 d post infection (p.i.) and was slightly elevated in the spleen at 1 d or 3 d p.i. IL-6 was expressed below control levels in PBMCs but was upregulated in the spleen. In contrast to IL-6, an evident decrease in the expression level of IL-8 was observed in both PBMCs and spleens at 1 d or 3 d p.i. SE challenge also resulted in an increase in the mRNA expression of IL-18 and IFN-γ in PBMCs and the spleen. These results imply that the expression of goose TLR5 is differentially regulated in various tissues and may participate in the immune response against bacterial pathogens.

Localization of linear B-cell epitopes on goose parvovirus structural protein.

Goose parvovirus (GPV), a small non-enveloped ssDNA virus, can cause Derzsy's disease, a highly contagious and lethal disease in goslings and muscovy ducklings, leading to a huge economic loss. However, little is known about the localization of B-cell epitopes on GPV structural protein. To address the issue, the structural protein of GPV was dissected into sets of partially overlapping fragments and expressed in Escherichia coli. Then Western blot reactivity of these glutathione S-transferase (GST) fusion short peptides to viral infected sera was surveyed. The results showed linear immunodominant epitopes, which were found in seven fragments covering amino acid residues 35-71, 123-198, 423-444, 474-491, 531-566, 616-669, 678-732. Our findings may provide the basis for the development of immunity-based prophylactic, therapeutic, and diagnostic clinical techniques for Derzsy's disease.

Molecular cloning, expression and regulation analysis of the interleukin-6 (IL-6) gene in goose adipocytes.

1. Interleukin-6 (IL-6) is a multifunctional cytokine involved in lipid metabolism in adipose tissue. The objective of the study was to identify and characterize the IL-6 gene in the goose. 2. A full-length coding sequence (CDS) of the goose (Anser anser) IL-6 gene was cloned that encoded a 234-amino acid peptide containing a 38-amino acid signal peptide, an IL-6/G-CSF/MGF family consensus pattern and four conserved α-helices. The mature goose IL-6 showed 74% and 39% identities to that of chicken and human, respectively. 3. Quantitative real-time PCR analysis showed that the goose IL-6 was predominantly expressed in liver and was up-regulated in adipocytes by lipopolysaccharide (LPS) and oleic acid.

Effects of yeast selenium supplementation on the growth performance, meat quality, immunity, and antioxidant capacity of goose.

The aim was to investigate the effects of yeast selenium (YS) supplementation on the growth performance, meat quality, immunity, and antioxidant variables of geese. A total of 96 one-day-old geese with similar body weight were randomly divided into four groups, with three replicates per group and eight geese in each replicate. The birds were fed basal diets supplemented with 0, 0.10, 0.30, 0.50 mg/kg YS (on selenium basis) during the 63-day experiment. Yeast selenium supplementation showed no effect on the growth performance of geese, but significantly improved the meat quality. No changes in ash or fat content were observed in breast muscle, but significant (p < 0.05) protein content increase was detected in the 0.1 and 0.5 mg/kg groups. Yeast selenium supplementation significantly (p < 0.05 or p < 0.01) promoted Se deposition in liver, kidney, pancreas, and muscle and the highest increases were all detected in the 0.5 mg/kg group. Yeast selenium supplementation enhanced the organ and cellular immunity of geese, but did not alter the humoral immunity. Furthermore, dietary YS significantly (p < 0.05) promoted the antioxidant capacity of both muscle and liver, but the effects varied with YS levels and organs. Hence, dietary YS supplementation was a good measure to improve the meat quality, Se content, immunity function, and antioxidant capacity of goose.

Safety and efficacy of an inactivated Carbopol-adjuvanted goose haemorrhagic polyomavirus vaccine for domestic geese.

Haemorrhagic nephritis enteritis of the goose (HNEG) is an epizootic viral disease in domestic geese. The causal agent is a polyomavirus, namely goose haemorrhagic polyomavirus. To help control the disease, an inactivated vaccine was developed, based on viral particles produced in goose kidney cells. Viral material was quantified using real-time quantitative polymerase chain reaction, inactivated with beta-propiolactone and adjuvanted with Carbopol, an acrylic acid polymer. Carbopol proved to be more immunogenic than aluminium hydroxide and was totally safe when administered to young goslings and breeders alike. Carbopol-adjuvanted vaccine induced a high serological response. Moreover, goslings hatched from vaccinated breeders were protected against viral challenge, indicating that maternally-derived neutralizing antibodies (MDA) were efficiently transferred. MDA were still detectable 15 days post-hatch. Clinical trials will be necessary to accurately evaluate a vaccine-based HNEG control strategy under field conditions.

Presenting features of feather duvet lung.

BACKGROUND: Feather duvet lung (FDL) is a rare subgroup of bird fancier's lung. It is caused by inhalation of organic dust due to goose or duck feathers in duvets or pillows. METHODS: A retrospective review of the medical records of 13 patients with FDL was performed to assess the specific history and review clinical characteristics of patients with this disease. RESULTS: All patients were female with a mean age of 53 years (26-71). They were recently exposed to feather duvets (6), pillows (1) or both (6). Specific histories were duvets or pillows filled with raw goose feathers from their own farms (4), intensive contact with goose feathers in youth (3), and bird exposure prior to symptom onset (5). In all patients specific IgG antibodies to goose and/or duck feathers were detected. Pulmonary function tests revealed a moderate to severe reduced diffusion capacity and a mild restrictive pattern. High-resolution computed tomography was performed in 11 patients and demonstrated predominantly ground-glass opacities (10) and fibrosis (6). In bronchoalveolar lavage fluid, lymphocytic alveolitis was demonstrated in all patients. Lung biopsies were obtained in 9 patients and demonstrated lymphocytic alveolitis (8), granulomas (3), bronchiolitis obliterans organizing pneumonia pattern (2), and usual interstitial pneumonia pattern (1). CONCLUSIONS: The clinical findings of FDL are typical of extrinsic allergic alveolitis. Primary sensitization could be due to former exposure to bird antigens at home or goose/duck feather exposure in youth. In view of the increasing popularity of feather duvets, FDL should be considered in the differential diagnosis of patients with extrinsic allergic alveolitis.

Chimeric West Nile/dengue virus vaccine candidate: preclinical evaluation in mice, geese and monkeys for safety and immunogenicity.

A live attenuated virus vaccine is being developed to protect against West Nile virus (WN) disease in humans. Previously, it was found that chimeric West Nile/dengue viruses (WN/DEN4 and WN/DEN4Delta30) bearing the membrane precursor and envelope protein genes of WN on a backbone of dengue type 4 virus (DEN4) with or without a deletion of 30 nucleotides (Delta30) in the 3' noncoding region of the DEN4 part of the chimeric genome were attenuated and efficacious in mice and monkeys against WN challenge. Here, we report the generation of a clinical lot of WN/DEN4Delta30 virus and its further preclinical evaluation for safety and immunogenicity in mice, geese and monkeys. The vaccine candidate had lost neuroinvasiveness in highly sensitive immunodeficient mice inoculated intraperitoneally and had greatly reduced neurovirulence in suckling mice inoculated intracerebrally (IC). Compared to the wild-type WN parent, the chimeric virus was highly restricted in replication in both murine and human neuroblastoma cells as well as in brains of suckling mice. The WN/DEN4Delta30 virus failed to infect geese, indicating that chimerization of WN with DEN4 completely attenuated WN for this avian host. This observation suggests that the WN/DEN4 chimeric viruses would be restricted in their ability to be transmitted from vaccinees to domestic or wild birds. In monkeys, the WN/DEN4Delta30 vaccine candidate was highly immunogenic despite its low level of replication with undetectable viremia. Furthermore, the WN/DEN4Delta30 vaccine virus was safe and readily induced neutralizing antibodies against WN in monkeys immune to each of the four serotypes of dengue virus. These studies confirm the attenuation of WN/DEN4Delta30 for non-human primates, including dengue-immune monkeys, and demonstrate both a highly restricted replication (>10(8)-fold decrease) in the brain of mice inoculated IC and an absence of infectivity for birds, findings that indicate this vaccine should be safe for both the recipient and the environment.

cDNA cloning, genomic structure and expression analysis of the goose (Anser cygnoides) MHC class I gene.

To provide data for studies on avian disease resistance, goose MHC class I cDNA (Ancy-MHC I) was cloned from a goose cDNA library, it's genomic structure and expression analysis were investigated. The mature peptides of Ancy-MHC I cDNA encoded 333 amino acids. The genomic organization is composed of eight exons and seven introns. Based on the genetic distance, six Ancy-MHC I genes from six individuals can be classified into four lineages. A total of nineteen amino acid positions in peptide-binding domain showed high scores by Wu-kabat index analysis. The Ancy-MHC I amino acid sequence displayed seven critical HLA-A2 amino acids that bind with antigen polypeptides, and have an 85.4-98.9% amino acid homology with each genes, and a 59.8-66.0% amino acid homology with chicken MHC class I. Expression analyses using Q-RT-PCR to detect the tissue-specific expression of Ancy-MHC I mRNA in an adult goose. The result appeared that Ancy-MHC I cDNA was expressed in the liver, spleen, intestine, kidney, lung, pancreas, heart, brain, and skin. The phylogenetic tree appears to branch in an order consistent with accepted evolutionary pathways.

Sorodiagnóstico da Doença de Chagas: novo reagente para o teste de hemaglutinaçäo indireta (THAIIAL) / Chagas' disease serological diagnosis: a new reagent to the indirect hemagglutination test (IHATIAL)

A new reagent was designed to the indirect hemagglutination test (IHATIAL), utilizing goose red blood cells as inert matrix and standardized for the field diagnosis of American trypanosomiasis. The objective was to substitute the lyophilized or frozen reagent of IHAT produced routinely using human erythrocytes in the Adolfo Lutz Institute (Säo Paulo/Brazil). The standardized reagent presented a long stability in liquid suspension, and was evaluated in 137 serum samples from patient with and without Chagas' disease, by IHATIAL. The diagnostic performance of this test was similar to the IHAT utilizing human erythrocytes and to that of a commercial IHAT kit. The sensitivity was 1.00, specificity 0.98, predictive value of positive 0.96 and of negative 1.00. Different batches of reagent successively produced proved to be reproducible in a quality control method. The new reagent is more economic than the former reagent, it can be produced easily and may be applicable to the seroepidemiologic studies.

Effects of amino-acids on pancreatic hormones and gut glucagon-like immunoreactivity in the goose.

In the goose, alanine and arginine, intravenously or orally administered, act in the same way on pancreatic hormones; they both stimulate insulin and glucagon secretions. Conversely, whereas alanine treatment has no effect on plasma gut GLI, oral arginine stimulates gut GLI secretion. Since stimulation of gut GLI secretion does not occur with i.v. arginine, it may be assumed that this secretion depends on the intestinal transit of arginine and, as already described (Sitbon and Mialhe 1979), of glucose. The results, compared with studies on a similar species (duck) and on mammals, point out that i.v. infusion of alanine stimulates IRI and GLI secretions in the goose and not in the duck. In the same way, arginine i.v. infusion, contrarily to the observation made in the duck, is without effect on gut GLI secretion in the goose. Furthermore, insulin seems to be able to inhibit the alpha cell response to arginine infusion, as in mammals, whereas this is not the case in ducks.

Serological investigations into the presence of antibodies to Yaba 1--Lednice 110 virus in Romania.

Sera collected from several migratory birds of the Danube Delta, from humans and domestic birds and animals of three Romanian counties were tested by hemagglutination-inhibition reaction for the presence of antibodies to Yaba 1--Lednice 110 virus. Antibodies could be detected in only 8 of the 14 species of migratory birds included in the study, especially in wild geese and ducks.

Studies of the regulatory effects of the sex hormones on antibody formation and stem cell differentiation.

The primary and secondary immune responses to thymus-dependent and -independent antigens were evaluated in normal male and female mice and in castrated male mice. Both IgM antibody production in the primary response and IgG antibody production in the secondary response were enhanced in females vs. males of equivalent age. Castration of the male converted this animal to a female in terms of responsiveness to the thymus-dependent group of antigens, while inducing equivalent or even greater enhanced responsiveness over the female to the thymus-independent antigen, polyvinylpyrrolidone. Further characteristics of the changes in lymphoid organs were determined in the castrated animal vs. normal males and females. It was shown that the spleen and thymus became markedly hyperplastic, the organ weights exceeding the female, which in turn were greater than in the male. The enhanced weight of the thymus was shown to be due to increased numbers of cortisone-sensitive cells, the absolute number of cortisone-resistant cells remaining equivalent to normal males and females. Thus, the increased thymic weight of the female also resided in the cortisone-sensitive population. Peripheral lymphocyte counts in castrated animals exceeded both normal males and females. Further experiments in gonadectomized males provided evidence that increased thymic cell activity per se played a role in enhanced response to thymus-dependent antigens, but that a thymic-derived hormone mediated the enhanced effect to the thymus-independent antigen in the castrated animal. The capacity for loss of androgenic hormone-producing tissue to generate enhanced differentiation of stem cells was denoted by experiments in which numbers of spleen colonies and uptake of (59)Fe, employed as an index of hematopoiesis 1 wk after reconstitution of lethally irradiated castrated and normal recipients, were enhanced in gonadectomized male animals. Thus, in summary, changes in sex hormone levels exerted a marked influence on immune responsiveness and stem cell differentiation, by increasing numbers of functioning cells, by promoting cellular differentiation, as well as by promoting cellular function via hormonal effects.