Soluble bone-derived osteopontin promotes migration and stem-like behavior of breast cancer cells

Breast cancer is a leading cause of cancer death in women, with the majority of these deaths caused by metastasis to distant organs. The most common site of breast cancer metastasis is the bone, which has been shown to provide a rich microenvironment that supports the migration and growth of breast cancer cells. Additionally, growing evidence suggests that breast cancer cells that do successfully metastasize have a stem-like phenotype including high activity of aldehyde dehydrogenase (ALDH) and/or a CD44⁺CD24^- phenotype. In the current study, we tested the hypothesis that these ALDH^hiCD44⁺CD24^- breast cancer cells interact with factors in the bone secondary organ microenvironment to facilitate metastasis. Specifically, we focused on bone-derived osteopontin and its ability to promote the migration and stem-like phenotype of breast cancer cells. Our results indicate that bone-derived osteopontin promotes the migration, tumorsphere-forming ability and colony-forming ability of whole population and ALDH^hiCD44⁺CD24^- breast cancer cells in bone marrow-conditioned media (an ex vivo representation of the bone microenvironment) (p≤0.05). We also demonstrate that CD44 and RGD-dependent cell surface integrins facilitate this functional response to bone-derived osteopontin (p≤0.05), potentially through activation of WNK-1 and PRAS40-related pathways. Our findings suggest that soluble bone-derived osteopontin enhances the ability of breast cancer cells to migrate to the bone and maintain a stem-like phenotype within the bone microenvironment, and this may contribute to the establishment and growth of bone metastases.

The streptozotocin-induced diabetic nude mouse model: differences between animals from different sources

Diabetes is induced in mice by using streptozotocin (STZ), a compound that has a preferential toxicity toward pancreatic β cells. We evaluated nude male mice from various sources for their sensitivity to a single high dose (160 to 240 mg/kg) of STZ. Diabetes was induced in male mice (age: median, 12 wk; interquartile range, 11 to 14 wk; body weight, about 30 g) from Taconic Farms (TAC), Jackson Laboratories (JAX), and Charles River Laboratories (CRL). Mice were monitored for 30 d for adverse side effects, blood glucose, and insulin requirements. In CRL mice given 240 mg/kg STZ, more than 95% developed diabetes within 4 to 5 d, and loss of body weight was relatively low (mean, 0.4 g). In comparison, both TAC and JAX mice were more sensitive to STZ, as evidenced by faster development of diabetes (even at a lower STZ dose), greater need for insulin after STZ, greater body weight loss (mean: TAC, 3.5 g; JAX, 3.7 g), and greater mortality. We recommend conducting exploratory safety assessments when selecting a nude mouse source, with the aim of limiting morbidity and mortality to less than 10%.

[The influence of Ad-AVEGF165 on human malignant melanoma growth in nude mice]

OBJECTIVE

To investigate the effect of antisense VEGF165 infection on the growth of A375 cells in nude mice.

METHODS

A375 cells were injected s.c into the axilla of the nude mouse. After the tumor formed, we cut it into 16 pieces equally, then transplanted into another 15 nude mice. There were three groups: Group PBS, Group Ad-GFP, and Group Ad-aVEGF. Four weeks after interfere, the mice were sacrificed and their tumors were excised for naked eye and histological observation. The VEGF expression was checked with ISH and immunohistochemistry staining. The micro-vessel density (MVD) in tumor mass was counted by VIII factor immunohistochemistry staining.

RESULTS

The visible and palpable nodules had developed at all the injected sites. Tumor growth speed was more slowly in Group Ad-aVEGF than that in other groups. GFP gene could express effectively in tumor mass. Ad-aVEGF infection could suppress the growth of tumors, and there were no obvious side effects. Ad-aVEGF resulted more tissue necrosis, but it had no obvious effect on cell apoptosis. VEGF expression was inhibited significantly in Group Ad-aVEGF, and MVD was decreased accordingly.

CONCLUSIONS

Ad-aVEGF interfere may be a new method against human malignant melanoma, whose main mechanism is to induce ischemia, but not apoptosis.

Learning from nudity: lessons from the nude phenotype

In mice, rats, and humans, loss of function of Foxn1, a member of the winged helix/forkhead family of transcription factors, leads to macroscopic nudity and an inborn dysgenesis of the thymus. Nude (Foxn1(nu)/Foxn1(nu)) mice develop largely normal hair follicles and produce hair shafts. However, presumably because of a lack of certain hair keratins, the hair shafts that are generated twist and coil in the hair follicle infundibulum, which becomes dilated. Since hair shafts fail to penetrate the epidermis, macroscopic nudity results and generates the - grossly misleading - impression that nude mice are hairless. Here, we provide an overview of what is known on the role of Foxn1 in mammalian skin biology, its expression patterns in the hair follicle, its influence on hair follicle function, and onychocyte differentiation. We focus on the mechanisms and signaling pathways by which Foxn1 modulates keratinocyte differentiation in the hair follicle and nail apparatus and summarize the current knowledge on the molecular and functional consequences of a loss of function of the Foxn1 protein in skin. Foxn1 target genes, gene regulation of Foxn, and pharmacological manipulation of the nude phenotype (e.g. by cyclosporine A, KGF, and vitamin D3) are discussed, and important open questions as well as promising research strategies in Foxn1 biology are defined. Taken together, this review aims at delineating why enhanced research efforts in this comparatively neglected field of investigative dermatology promise important new insights into the controls of epithelial differentiation in mammalian skin.

An allograft model of androgen independent prostatic neuroendocrine carcinoma derived from a large probasin promoter-T antigen transgenic mouse line

PURPOSE

Animal models that mimic this hormone refractory prostate cancer may be useful for developing and testing novel treatment strategies.

MATERIALS AND METHODS

Using the prostate of the 12T-10 transgenic mouse an allograft model was established by transplantation into a nude mouse. To our knowledge we describe the first allograft model derived from the primary prostate tumor of a transgenic mouse.

RESULTS

The primary tumor progressed from high grade prostatic intraepithelial neoplasm to invasive, undifferentiated and metastatic cancer with loss of androgen receptor expression. After 10 passages in nude mice the allograft retained the same histological and immunohistochemical features as the primary tumors, including neuroendocrine differentiation. The allograft demonstrated androgen independent growth and metastases to liver and lung, paralleling tumor behavior in the original transgenic line. Cytogenetic characterization of the allograft revealed consistent chromosomal abnormalities for multiple in vivo passages.

CONCLUSIONS

This allograft model may give insight into the mechanism by which human prostate cancer progresses to an androgen independent state and provide a system for testing drugs that can inhibit this disease.

Inorganic Cadmium- and Arsenite-Induced Malignant Transformation of Human Bladder Urothelial Cells

Arsenic and cadmium (Cd(+2)) are human carcinogens, and epidemiological studies have implicated both pollutants in the development of urinary bladder cancer. Despite this epidemiological base, it is unknown if either Cd(+2) or arsenite (As(+3)) can directly cause the malignant transformation of human urothelial cells. The goal of this study was to determine if Cd(+2) and/or As(+3) are able to cause the malignant transformation of human urothelial cells. The strategy employed was to expose the nontumorigenic urothelial cell line UROtsa to long-term in vitro exposure to Cd(+2) and As(+3), with the endpoint being the ability of the cells to form colonies in soft agar and tumors when heterotransplanted into nude mice. It was demonstrated that a long-term exposure to either 1 M Cd(+2) or 1 M As(+3) resulted in the selection of cells that were able to form colonies in soft agar and tumors when heterotransplanted into nude mice. The histology of the tumor heterotransplants produced by UROtsa cells malignantly transformed by Cd(+2) had epithelial features consistent with those of a classic transitional-cell carcinoma of the bladder. The histology of the tumor heterotransplants produced by cells malignantly transformed by As(+3) was unique in that the cells displayed a prominent squamoid differentiation.

Complete rescue of the nude mutant phenotype by a wild-type Foxn1 transgene

In this paper we describe the production and analysis of mice carrying a 110-kb transgene that encompasses the wild-type Foxn1 genomic locus. Mutations in Foxn1 cause the nude phenotype. We show that in the hair follicles, transgenic mice with increased Foxn1 gene dosage exhibited increased Foxn1 expression that was restricted correctly to the nascent, post-mitotic cells of the differentiating hair cortex and hair cuticle lineages. We also demonstrate for the first time that a Foxn1 transgene rescues completely both the hair follicle and the thymus defects in animals that are also homozygous for the nude mutation at the endogenous Foxn1 locus, causing the development of a full coat of hair and a normal population of peripheral blood T lymphocytes. We conclude that sufficient cis-acting regulatory information resides within this 110-kb transgene to direct reliable and appropriate tissue-specific expression of the Foxn1 gene.

Expression domains in the skin of genes affected by the nude mutation and identified by gene expression profiling

Although several genes affected by the nude mutation inactivating the transcription factor Whn have recently been identified, a comprehensive molecular analysis of the nude phenotype is still missing. Gene expression profiling of wildtype and nude mice back skin reveals several so far unknown differences in mRNA levels and demonstrates that microarray hybridization is ideal to identify even quantitative changes in expression. Some genes are upregulated in the absence of Whn. Most of the differentially expressed genes are downregulated in nude skin. Our results identify metallothionein IV among these genes. This is the first report on metallothionein IV expression in the murine hair follicle; its expression domain almost completely overlaps that of Whn.

The nude gene and the skin

The nude mutation has been known for a long time. Nevertheless, the gene responsible for the defect has been identified only recently. It encodes a transcriptional activator of the family of forkhead proteins mainly expressed in thymic epithelium and distinct keratinocyte populations in the epidermis and hair follicles. The present review focuses on the molecular and functional characterization of the nude gene and its product and gives an overview as to its role in skin biology and the first identified target genes in the skin. In addition, evolutionary aspects are highlighted stressing the importance of such investigations for a comprehensive understanding of the nude gene product and the regulation of its expression. Furthermore, these studies give a hint as to when the nude gene has occurred first and how it has developed in molecular and functional terms since then.

Laser capture microdissection-based expression profiling identifies PD1-ligand as a target of the nude locus gene product

T cell development requires the interaction of developing thymocytes with thymic epithelial cells. Thymic epithelial cells acquire their unique phenotype under the control of the winged-helix transcription factor Whn, which is lacking in the nude mouse. Whn-dependent genes may therefore be important regulators of lympho-epithelial interactions. To identify Whn target genes we isolated RNA populations of wild-type and nude thymic anlagen from embryonic day 12.5 embryos by laser capture microdissection and compared them by gene expression profiling on microarrays representing 22,000 transcripts. All cDNA with expression differences confirmed by quantitative RT-PCR using RNA from individual anlagen and by in situ hybridization were found to be present in wild-type and absent in nude samples. Three of eight confirmed transcripts were of hematopoietic origin; these transcripts emanate from hematopoietic precursors which have just entered the thymic anlage. Five transcripts were of epithelial origin; one of these corresponds to the recently identified PD-1 ligand (PD-L1), the receptor of which is known to modulate positive selection and to play a role in the control of autoimmunity, and the remaining transcripts code for novel genes. The presented results support our prediction that this systematic approach by gene expression profiling yields regulators of thymopoiesis.

Hair growth pattern in nude mice

Nude mice are not bald but instead show an 'abortive' reduced hair growth on different sites of the integument. An albino (NMRI-nu) and a pigmented (C57BL/6-nu) strain of nude mice were examined as to whether the regional distribution pattern of this anagen hair proliferation is subject to the same ontogenetic development as in hairy mice. Hairy mice of both strains served as a comparison. Hair distribution was documented macroscopically by drawing and photography in a total of 415 mice of both sexes up to 421 days of age. Because of the pigmentation of the growing anagen hair follicles, the growth areas in the pigmented nude mice were distinctly visible whereas in the albino mice they were roughly recognisable from the boundaries of hair covering. The regional distribution of the 'abortive' anagen hair pattern in both nude strains corresponded to the wave-like course of the adult hair generations of hairy mice. As in older hairy mice, the hair cycle duration in nude mice was prolonged from an age of 121-180 days, the hair growth areas appeared reduced and less symmetrically orientated. Differences of up to 33% in body mass between the lighter nude and +/nu mice made ontogenetic comparison impossible so that all information is based on direct pattern or age comparison. The significance of experiments on the skin and hair follicles of nude mice is further increased if litters are examined comparatively and the temporal and spatial dimension of the follicle proliferation is considered more carefully than has been the case until now.

Antitumor activity of XR5944, a novel and potent topoisomerase poison

Inhibitors of topoisomerases are widely used in the treatment of cancer, including inhibitors of topoisomerase I (camptothecin analogs such as irinotecan and topotecan) and topoisomerase II (etoposide and doxorubicin). The novel bis-phenazine, XR5944, is a joint inhibitor of topoisomerase I and II as shown by the stabilization of topoisomerase-dependent cleavable complexes. XR5944 demonstrated exceptional activity against human and murine tumor cells in vitro and in vivo. In a range of cell lines XR5944 (IC50 0.04-0.4 nM) was significantly more potent than TAS-103, originally proposed as a joint topoisomerase I and II inhibitor, as well as agents specific for topoisomerase I or II (topotecan, doxorubicin and etoposide). In addition, XR5944 was unaffected by atypical drug resistance and retained significant activity in cells overexpressing P-glycoprotein or multidrug resistance-associated protein. Antitumor efficacy of XR5944 was demonstrated in human carcinoma xenograft models (H69 small cell lung cancer and HT29 colon). In the HT29 model, which is relatively unresponsive to chemotherapy, XR5944 (15 mg/kg i.v., q4dx3) induced tumor regression in the majority of animals (six of eight), whereas TAS-103, dosed at its maximum tolerated dose (45 mg/kg i.v., q7dx3), only induced a delay in tumor growth compared with control animals. In the H69 model, low doses of XR5944 (5 mg/kg i.v., qdx5/week for 2 weeks or 10-15 mg/kg i.v., q4dx3), induced complete tumor regression in the majority of animals. In contrast, topotecan (20 mg/kg i.v., q4dx3) or etoposide (30 mg/kg i.v., q5dx5) only slowed the tumor growth rate. These studies show that XR5944 is a highly active novel anticancer agent that is well tolerated at efficacious doses.

Regional variations in the distributions of small intestinal intraepithelial lymphocytes (IELs) in BALB/c +/+, nu/+, and nu/nu mice

Regional variations in intraepithelial lymphocytes (IELs) in the small intestine were examined in BALB/c +/+, nu/+, and nu/nu mice. The small intestine was obtained from 11- to 12-week-old mice and divided equally into three (proximal, middle, and distal) parts. The IELs were isolated from each part of the intestine, and the total numbers of IELs in nu/+ and nu/nu mice were about a fifth of those in +/+ mice. Regional variations in the distribution of the IEL alphabeta, but not the gammadelta T-cell subset were found by use of flow cytometry in +/+ and nu/+ mice. On the other hand, such differences were not found in nu/nu mice, suggesting that thymus-independent development of T cells is not different among regions. Different local expansion of thymus-dependent alphabeta T cells may cause the regional variations seen in the distribution of alphabeta T cell IELs in +/+ and nu/+ mice.

IL-7 enhances the responsiveness of human T cells that develop in the bone marrow of athymic mice

The beige/nude/xid/human (bnx/hu) model of human hematopoiesis provides a unique opportunity to study extrathymic human T lymphocyte development in an in vivo system. Purified human hematopoietic stem cells develop into mature T lymphocytes and immature progenitors in the bone marrow of athymic bnx mice. The human T cells are all TCR alpha beta(+) and display a restricted TCRV beta repertoire. In the current studies, we examined the effects of systemic human IL-7 (huIL-7) administration on the phenotype and the activation status of the bnx/hu T cells. In the majority of the mice that did not have huIL-7 administration, a higher frequency of human CD3(+)/CD8(+) than CD3(+)/CD4(+) T cells developed in the bone marrow. This phenomenon is also frequently observed in human bone marrow transplant recipients. Extremely low levels of IL-2 were expressed by human CD3(+) cells isolated from these mice, in response to PMA plus ionomycin and to CD3 and CD28 cross-linking. IL-4 was not expressed by cells exposed to either stimulus, demonstrating a profound inability of the bnx/hu T cells to produce this cytokine. Systemic production of huIL-7 from engineered stromal cells transplanted into the mice increased the human CD4 to CD8 ratios, and increased the ratio of memory to naive CD4(+) and CD8(+) T cells. The human CD3(+) cells recovered from mice that had systemic huIL-7 and equivalent numbers of CD3(+)/CD4(+) and CD3(+)/CD8(+) cells in the marrow were still unable to produce IL-4 in response to any condition tested, but were capable of normal levels of IL-2 production following stimulation.

Ectopic expression of the nude gene induces hyperproliferation and defects in differentiation: implications for the self-renewal of cutaneous epithelia

Nude mice are characterized by the absence of visible hair, epidermal defects, and the failure to develop a thymus. This phenotype results from loss-of-function mutations in Whn (Hfh11), a winged-helix transcription factor. In murine epidermis and hair follicles, endogenous whn expression is induced as epithelial cells initiate terminal differentiation. Using the promoter for the differentiation marker involucrin, transgenic mice that ectopically express whn in stratified squamous epithelia, hair follicles, and the transitional epithelium of the urinary tract were generated. Transgenic epidermis and hair follicles displayed impaired terminal differentiation and a subset of hair defects, such as delayed growth, a waved coat, and curly whiskers, correlated with decreased transforming growth factor (TGF)-alpha expression. The exogenous Whn protein also stimulated epithelial cell multiplication. In the epidermis, basal keratinocytes exhibited hyperproliferation, though transgene expression was restricted to suprabasal, postmitotic cells. Hair follicles failed to enter telogen (a resting period) and remained continuously in an abnormal anagen (the growth phase of the hair cycle). Ureter epithelium developed severe hyperplasia, leading to the obstruction of urine outflow and death from hydronephrosis. Though an immune infiltrate was present occasionally in transgenic skin, the infiltrate was not the primary cause of the epithelial hyperproliferation, as the immune reaction was not observed in all affected transgenics, and the transgene induced identical skin and urinary tract abnormalities in immunodeficient Rag1-null mice. Given the effects of the transgene on cell proliferation and TGFalpha expression, the results suggest that Whn modulates growth factor production by differentiating epithelial cells, thereby regulating the balance between proliferative and postmitotic populations in self-renewing epithelia.

Enhanced human tumor cell transplantability in a new congenic immunodeficient mouse; KSN-BNX

We introduced two mutant genes (beige; bg that induces the deficiency of natural killer (NK) activity and xid that decreases the production of immunoglobulin) into KSN nude mice with high reproductive performances. We produced KSN bg/bg(nu/nu) (KSN-bg), KSN-xid/xid(nu/nn) (KSN-xid), KSN xid/xid,bg/bg(nu/nu) (KSN-BNX) and KSN-nu/+ (KS) mice by back-cross (cross-intercross method). All strains showed as high a reproductivity rate as the parental KSN mice. KSN-xid and KSN-BNX mice had a reduced percentage of B220 positive cells in the spleens compared to KSN and KSN-bg mice, but they showed increased percentages of Thy-1 and asialo GM1 positive cells. The serum immunoglobulin concentrations of KSN-BNX were as low as KSN-xid. Both KSN-bg and KSN-BNX mice showed deficient NK activity in spleens, whereas KSN-xid mice showed an elevated NK activity. Compared to nude mice, the growth of both human tumor cell TCO-1 and BxPc-3 transplanted subcutaneously was enhanced in KSN-BNX mice. However Panc-1 cells that was rejected in nude mice was not accepted in KSN-BNX mice. Liver metastasis of human pancreatic tumor cells; Capan-1, BxPc-3 and MIAPaCa-2 were studied. No significant difference was observed in the percentage of metastasis formed mice between nude and KSN-BNX mice.

Maturation of B cell precursors is impaired in thymic-deprived nude and old mice

We have previously reported that bone marrow B cell precursors from thymic-deprived nude and old mice express less recombination-activating gene-1 (RAG-1) mRNA than they do in young euthymic mice. We now report that both nude and old mice have decreased bone marrow pre-B cells and that fewer pre-B cells express RAG protein. This combination of events appears to be the basis for the lower level of bone marrow RAG mRNA in thymic-deprived mice. A link between thymic function and B cell development was suggested by the similar kinetics of thymic involution and of declining bone marrow RAG-1 gene expression during aging. Support for this hypothesis was obtained by demonstrating that injection of supernatant medium from activated CD8+ but not CD4+ young T cells from mice increases RAG mRNA, RAG protein, and the number of bone marrow pre-B cells in nude and old mice. Furthermore, in vivo CD8+ T cells also regulate bone marrow RAG gene expression. Thus, mice deficient in CD8+ T cells expressed levels of RAG-1 mRNA in their bone marrow that were only 10% of those observed in normal or CD4+ T cell-deficient mice. IL-16 was detected in the supernatant medium from activated T cell cultures, and injection of nanogram quantities of recombinant IL-16 (rIL-16) into nude or old mice increased the levels of RAG mRNA in bone marrow B cell precursors and the number of bone marrow pre-B cells. We conclude that the impaired development of B cells within the bone marrow of thymic-deprived nude and old mice can be reversed, at least in part, by the administration of rIL-16.

Genetic typing of the mouse and rat nude mutations by PCR and restriction enzyme analysis

A genetic typing method for the mouse and rat nude mutations by PCR and restriction fragment length polymorphism (RFLP) analysis was developed. Since restriction sites useful for RFLP analysis do not exist in the mouse nu and rat rnu mutations, artificial restriction sites were introduced by PCR with modified primers. Three genotypes in the mouse (nu/nu, nu/+ and +/+) or rat (rnu/rnu, rnu/+ and +/+) are rapidly differentiated with the PCR-RFLP assay. In addition, congenic nude strains can be efficiently established by using this assay. Finally, genetic mapping of the rnu locus was performed with microsatellite markers. The locus order on rat chromosome 10 was D10Mgh14-(2.0cM)-D10Mit2-(1.4cM)-rnu-(0.7cM++ +)-D10Mgh6-(2.7cM)-D10Mit8.

The nude gene encodes a sequence-specific DNA binding protein with homologs in organisms that lack an anticipatory immune system

In the mouse, the product of the nude locus, Whn, is required for the keratinization of the hair shaft and the differentiation of epithelial progenitor cells in the thymus. A bacterially expressed peptide representing the presumptive DNA binding domain of the mouse whn gene in vitro specifically binds to a 11-bp consensus sequence containing the invariant tetranucleotide 5'-ACGC. In transient transfection assays, such binding sites stimulated reporter gene expression about 30- to 40-fold, when positioned upstream of a minimal promotor. Whn homologs from humans, bony fish (Danio rerio), cartilaginous fish (Scyliorhinus caniculus), agnathans (Lampetra planeri), and cephalochordates (Branchiostoma lanceolatum) share at least 80% of amino acids in the DNA binding domain. In agreement with this remarkable structural conservation, the DNA binding domains from zebrafish, which possesses a thymus but no hair, and amphioxus, which possesses neither thymus nor hair, recognize the same target sequence as the mouse DNA binding domain in vitro and in vivo. The genomes of vertebrates and cephalochordates contain only a single whn-like gene, suggesting that the primordial whn gene was not subject to gene-duplication events. Although the role of whn in cephalochordates and agnathans is unknown, its requirement in the development of the thymus gland and the differentiation of skin appendages in the mouse suggests that changes in the transcriptional control regions of whn genes accompanied their functional reassignments during evolution.

The product of the mouse nude locus, Whn, regulates the balance between epithelial cell growth and differentiation

Mutations in the winged-helix nude (whn) gene result in the nude mouse and rat phenotypes. The pleiotropic nude phenotype which affects the hair, skin, and thymus suggests that whn plays a pivotal role in the development and/or maintenance of these organs. However, little is known about whn function in these organs. We show here that in skin whn is specifically expressed in epithelial cells and not the mesenchymal cells, and using a hair reconstitution assay, we demonstrate that the abnormal nude mouse hair development is attributable to a functional defect of the epithelial cells. Examination of nude mouse primary keratinocytes in culture revealed that these cells have an increased propensity to differentiate in an abnormal fashion, even under conditions that promote proliferation. Furthermore, nude mouse keratinocytes displayed a 100-fold increased sensitivity to the growth-inhibitory/differentiation effects of the phorbol ester TPA. In parallel with these findings, we directly show that whn functions as a transcription factor that can specifically suppress expression of differentiation/TPA-responsive genes. The region of Whn responsible for these effects was mapped to the carboxy-terminal transactivating domain. These results establish whn as a key regulatory factor involved in maintaining the balance between keratinocyte growth and differentiation. The general implications of these findings for an epithelial self-renewal model will be discussed.

Postnatal and postpartal morphology of the mammary gland in nude mice

The object of this work was to compare the postnatal and postpartal morphology of the mammary gland of nu/nu with that of nu/(+)-mice. All studies were carried out on groups of female (athymic) nude mice with NMRI genetic background, their nu/(+)-siblings and dams. The various age groups (3, 21, 40, 55, 70 and 120 days) each consisted of 6 nu/nu- and 6 heterozygous nu/(+)-mice respectively. The morphological examination of the mammary gland tissue were made on histological sections and whole mounts. Body weights, total areas of the mammary glands and the number of the terminal end buds were compared. The mammary gland of the athymic nude mouse exhibited no essential morphological differences from the normal developing mammary gland of the hairy euthymic nu/(+)-animal. The area of the mammary gland increased with increasing body weight. Both collectives of mice differed only in their rate of mammary gland development. As a result, the terminal end buds appeared numerously as growth points of mammary gland in nu/(+)-animals as early as the 21st day of life. The athymic nude mice showed a maximum only on the 40th day of life and a lower degree of density and differentiation of specific mammary gland structures (lateral buds, lobulo-alveolar glandular endings) until the 70th day of life. The mammary gland of 120-day-old animals and dams of both animal groups reached the same state of maturity. Thus it is not the rate of development of the dam, but other, yet unidentified factors, which determine, if successful breeding of nude mice with homozygous parents is possible.

New immunodeficient mouse strains bred by introducing beige and xid mutations into the KSN nude strain

We introduced two mutant genes (beige or bg, which induces a deficiency of natural killer activity, and xid, which decreases the production of immunoglobulins) into KSN nude mice with high reproductive performance. At first we produced the KSN-bg/bg(nu/nu) (KSN-bg) and KSN-xid/xid(nu/nu) (KSN-xid) congenic strain by backcross (cross-intercross method). After we identified homozygosity at the biochemical locus and polymorphic microsatellite loci, we mated KSN-bg and KSN-xid mice, and selected the KSN-xid/xid;bg/bg(nu/nu) (KSN-BNX) mice from the progeny. Furthermore we introduced the non-nude gene, which originated from CBA/N, into the KSN strain and produced KSN-nu/+ (KS) mice that have the same genetic background except for the nu locus. All strains had as high a reproductivity rate as the parental KSN mice. The KSN-xid and KSN-BNX mice had a reduced percentage of B220-positive cells in the spleen compared with KSN and KSN-bg mice, but they had increased percentages of Thy-1 and asialo GM1-positive cells. The serum immunoglobulin concentrations of BNX were as low as those of KSN-xid mice. Both KSN-bg and KSN-BNX mice had deficient natural killer activity in the spleen, whereas KSN-xid mice had increased natural killer activity. Compared with nude mice, the growth of the human thyroid tumor cell line transplanted subcutaneously was enhanced in BNX mice. These KSN, KSN-bg, KSN-xid, KSN-BNX, and KS nice not only are of value for use in various fields as the hosts of xenograft but also are good models of the combination effect of multiple immunodeficient genes.

The nu gene acts cell-autonomously and is required for differentiation of thymic epithelial progenitors

The nude mutation (nu) causes athymia and hairlessness, but the molecular mechanisms by which it acts have not been determined. To address the role of nu in thymogenesis, we investigated whether all or part of the nude thymic epithelium could be rescued by the presence of wild-type cells in nude <--> wild-type chimeric mice. Detailed immunohistochemical analyses revealed that nude-derived cells could persist in the chimeric thymus but could not contribute to cortical or medullary epithelial networks. Nude-derived cells, present in few clusters in the medulla, expressed markers of a rare subpopulation of adult medullary epithelium. The thymic epithelial rudiment of nude mice strongly expressed these same markers, which may therefore define committed immature thymic epithelial precursor cells. To our knowledge, these data provide the first evidence that the nu gene product acts cell-autonomously and is necessary for the development of all major subpopulations of mature thymic epithelium. We propose that nu acts to regulate growth and/or differentiation, but not determination, of thymic epithelial progenitors.

Differences of nu/+ and nu/nu mice in some behaviors reflecting temperament traits

The goal of this paper is to discover a pattern of consistent behavioral differences between athymic CD1 nu/nu mice and euthymic CD1 nu/+ ones. The following behaviors, thought to be correlates of temperament traits, were measured along 3 trials: ambulation, rear, and defecation in two open fields of varying light intensity, interaction time with a conspecific, and variables in the light-darkness test (time in the lit compartment, latency to leave the dark compartment, and number of crossings between compartments). Besides, weight and (IgM and IgG) antibodies to rat erythrocytes were measured. Relative to nu/nu mice, nu/+ mice were heavier, yielded much higher antibody responses, interacted more with a conspecific (the males, but not the females), and ambulated slightly more in the open fields, although the proportion of variance in the behaviors accounted for by the nude mutation was small (< 20%). Therefore, the nude mutation participated in the expression of the activity or extraversion traits.

A high-resolution map of the chromosomal region surrounding the nude gene

The nude mutation produces the apparently disparate phenotypes of hairlessness and congenital thymic aplasia. These pleiotropic defects are the result of a single, autosomal recessive mutation that was previously mapped to a 9-cM region of murine chromosome 11 bounded by loci encoding the acetylcholine receptor beta subunit and myeloperoxidase. In this study, exclusion mapping of a panel of congenic nude strains was used to place the nude locus between the microsatellite loci D11Nds1 and D11Mit8. The relative distance from nude to each of these loci was determined by analyzing a large segregating cross. Thus, nude lies 1.4 cM distal to D11Nds1 and is 0.5 cM proximal to D11Mit8. Mice that carried recombinational breakpoints between D11Nds1 and D11Mit8 were further analyzed at the loci Evi-2 and D11Mit34, which placed nu 0.2 cM proximal to these markers. D11Nds1 and Evi-2/D11Mit34 thus define the new proximal and distal boundaries, respectively, for the nu interval. We also report the typing of the above microsatellite markers in the AKXD, AKXL, BXD, CXB, and BXH recombinant inbred strains, which confirmed the relative order and separation of loci in this region.

Immunodeficiency. Trapping the nude mouse gene

Hairless nude mice are immunodeficient because they lack a thymus. The nude gene has now been identified; it encodes a winged-helix transcription factor that is expressed specifically in skin and thymus.

Identification of genetic events involved in early steps of immortalization of mouse fibroblasts

The spontaneously immortalized early passaged fibroblasts from three different strains of mouse are observed to represent two distinct stages of immortalization. The cells at stage I are characterized by slow growth rate, contact inhibition and requisition of serum factors for their growth and proliferation. Stage II cells are marked by fast, multilayer growth that is independent of serum supplementation in growth medium and by the elevated levels of the two marker proteins, i.e., p53 and p81. The change from cytosolic distribution of mortalin, a senescence inducing protein (J. Biol. Chem. (1993) 268, 6615-6621; 22239-22242) to the perinuclear locale is detected as an early event during cellular immortalization. Furthermore, the distinct stages could be characterized by thermal analysis of intact cells, that to the best of our knowledge is employed for the first time for the analysis of cellular mortal and immortal phenotypes. The study characterizes at least two distinct end points in rodent transformation suggesting that there are multiple routes to immortalization.

New member of the winged-helix protein family disrupted in mouse and rat nude mutations

Mutations at the nude locus of mice and rats disrupt normal hair growth and thymus development, causing nude mice and rats to be immune-deficient. The mouse nude locus has been localized on chromosome 11 (refs 3, 4) within a region of < 1 megabase. Here we show that one of the genes from this critical region, designated whn, encodes a new member of the winged-helix domain family of transcription factors, and that it is disrupted on mouse nu and rat rnuN alleles. Mutant transcripts do not encode the characteristic DNA-binding domain, strongly suggesting that the whn gene is the nude gene. Mutations in winged-helix domain genes cause homeotic transformations in Drosophila and distort cell-fate decisions during vulval development in Caenorhabditis elegans. The whn gene is thus the first member of this class of genes to be implicated in a specific developmental defect in vertebrates.

The inducible form of nitric oxide synthase (NOS2) isolated from murine macrophages maps near the nude mutation on mouse chromosome 11

Nitric oxide synthase has been shown to mediate streptozocin-induced diabetes and to act as an antimicrobial agent in murine macrophages. Using a cDNA probe for the inducible form of nitric oxide synthase (Nos2) isolated from murine macrophages we have determined that the gene maps within 1 cM of the nude mutation on mouse Chromosome 11. The position of Nos2 was also mapped relative to the markers 115, Evi2, Cchlbl (previously unmapped), and Gfap. This map location is discussed relative to map locations for disease susceptibility loci involved in mediating cutaneous leishmaniasis (ScII) and autoimmune type-I diabetes (Idd4).

The human BAT3 ortholog in rodents is predominantly and developmentally expressed in testis

A partial cDNA clone, RLC34, was isolated from a rat brain cDNA library. Its sequence exhibits high identity with BAT3 (88.4% and 94.9% for DNA and the deduced amino acid sequence, respectively), a gene located within the region of human major histocompatibility complex III (MCHIII region). RLC34 detected a transcript the same size in human and rat, similar to that reported for BAT3. Southern blot analysis of RLC34 showed similar restriction patterns as those of the human BAT3 gene. A panel of rodent tissue samples were examined and the RLC34 was found to be predominantly expressed in the germ cells of rodent testes. The expression is developmentally regulated with increased transcripts seen at 17-20 days after birth. Its testicular expression, its association with spermatogenesis, and its location in MCHIII suggest a correlation of RLC34 with the growth-reproduction complex (grc). This finding may also provide a clue to study the function of other genes localized in this area of the MCHIII region.

A yeast artificial chromosome contig on mouse chromosome 11 encompassing the nu locus

Mutations at the nude locus disrupt the homing process of T cell progenitor cells to the thymic rudiment, a key aspect of T cell differentiation. Here, we map the nude locus to a set of overlapping yeast artificial chromosomes (YAC) clones covering a genetic interval of about 0.5 centi Morgan on mouse chromosome 11. These results provide a suitable starting point to molecularly clone the nude gene.

Immunological properties of heterozygous nu/+ mice: changes in antibody response and inducibility of tolerance to protein antigens

Heterozygous nu/+ mice are not fully identical in their immunological properties with the mice of wild +/+ genotype. A colony of nu/nu, nu/+ and +/+ mice from the same breeding nucleus was established and their immune reactivity to human serum albumin, inducibility of adult immune tolerance to hen egg lysozyme (HEL), sensitivity of their lymphoid cells to stimulation by mitogens and ratio of CD3, CD4 and CD8 positive cell populations was studied. Both the numbers of antibody-forming cells in regional lymph nodes and the antibody titres in sera of nu/+ mice were highly variable, between undetectable values of nu/nu and high values of +/+ homozygotes. Intravenous pretreatment with soluble HEL, leading in +/+ mice to a deep hyporeactivity to subsequent immunization with the same antigen, did not decrease the response of nu/+ mice significantly. These results indicate that the immunological alteration of nu/+ mice is not only quantitative and that T cell subpopulations might be differentially modified by the presence of nu allele. The finding of decreased CD4:CD8 ratio in nu/+ mice also supports this idea.

Direct isolation of polymorphic markers linked to a trait by genetically directed representational difference analysis

We describe a technique, genetically directed representational difference analysis (GDRDA), for specifically generating genetic markers linked to a trait of interest. GDRDA is applicable, in principle, to virtually any organism, because it requires neither prior knowledge of the chromosomal location of the gene controlling the trait nor the availability of a pre-existing genetic map. Based on a subtraction technique described recently called representational difference analysis, GDRDA uses the principles of transmission genetics to create appropriate Tester and Driver samples for subtraction. We demonstrate the usefulness of GDRDA by, for example, successfully targeting three polymorphisms to an interval of less than 1 cM of the mouse nude locus of chromosome 11.

Comparative evaluation of the immune status of congenitally athymic and euthymic rat strains bred and maintained at different institutes: 2. Athymic rats

We performed a comparative evaluation of the immune status, focused on the T-cell system, in congenitally athymic rat strains. From 11 institutes around the world, we sampled 15 groups of animals at ages of 1 1/2-2 months and 1/2 year. The analysis included weight of body and spleen; antibody response and delayed-type hypersensitivity response after immunization with ovalbumin; and (immuno)histology of spleen, lymph nodes and lymphoid tissue along the gastrointestinal tract. Morphometric analysis was done for alpha beta-T-cell receptor-bearing cells in spleen tissue as a measure of the periarteriolar lymphocyte sheath; it was also done for splenic red pulp using the antibody ED2 recognizing red pulp macrophages. For almost all variables analyzed, statistically significant differences between the groups were observed. The extent of alpha beta-T-cell receptor-bearing cells in the spleen increased with age. The functioning of these cells in immunological responses can be questioned, because an immune response to ovalbumin was invariably absent. But secondary follicles with germinal centers, reflecting T-cell-dependent B-cell reactivity, were observed in lymph nodes and Peyer's patches (up to 40% and 75%, respectively, depending on the group), with a higher prevalence in older animals. A cluster analysis on the basis of body and spleen weight and composition of spleen compartments did not yield clusters with a different profile in regard to the animals' group of origin. The data presented are useful when comparing studies performed with various athymic rat strains at different institutes.

[Athymic mice of the 101/HY strain with a new allele at the nude locus]

The spontaneous autosomal recessive mutation at locus nude (nuY) was discovered in 101/HY mice imperfect in respect to repair of induced chromosome damage and this is maintained in conventional conditions at RLEBM. Homozygous mutants have no hair and thymic differentiation. The new mutant form can be a valuable model for medical and biological experiments requiring T-cell immune deficiency.

Serum immunoglobulin isotype profile of viable and non viable lymphoid cell chimaeras made with nude athymic lpr (lymphoproliferation) mouse recipients

C57BL/6 mice (B6) which are homozygous at the nu (nude, athymic) and lpr (lymphoproliferation) locus (B6 nulpr) are short-lived. We showed previously that increased survival could be obtained by grafting lymphoid cells from euthymic lpr-homozygous B6 mice (B6 lpr) mice ([lpr----nulpr] chimaeras), but curiously enough not from normal (B6 wild) mice ([wild----nulpr] chimaeras). Moreover female, but not male, [lpr----nulpr] chimaeras developed spleen and lymph node enlargement. In the present paper the distribution and absolute concentrations of all serum immunoglobulin (Ig) isotypes have been determined in these chimaeras and their controls. All chimaeras displayed whole serum Ig levels higher than those of B6 wild mice, suggesting a successful reconstitution of the athymic recipients by the grafted lymphoid cells, but two types of chimaeras were peculiar. The short-lived [wild----nulpr] chimaeras showed a proportion of IgM as high as ungrafted B6 nulpr mice, suggesting a deficient down-regulation of IgM production by the grafted B6 wild-type lymphoid cells. The [lpr----nulpr] female chimaeras recovered a long lasting overexpression of all Ig isotypes, like B6 lpr mice, while all the other chimaeras showed a transient overexpression only. Since neither lymphadenopathy nor persistent increase of serum Ig levels were observed in [lpr----nu] chimaeras, our data confirmed the need for a genetically lpr host to allow the significant development of the lpr syndrome.

Extrathymic positive selection of gamma delta T cells. V gamma 4J gamma 1 rearrangements with "GxYS" junctions

Neither function nor Ag recognition properties of gamma delta T cells are well understood yet. A TCR gamma-chain family, characterized by distinct N region sequences that converge in coding for a "GxYS" VJ junctional sequence, appears late in ontogeny among highly diversified V gamma 4J gamma 1C gamma 1 chains of C57BL/6 and BALB/c mice. The glycine and serine codons are of germline V gamma 4 and J gamma 1 origin, respectively, whereas the N region consists of a variable amino acid residue x, followed by an invariant tyrosine Y. The high expression of V gamma 4 xYJ gamma 1C gamma 1 in the lung of BALB/c mice compared to that of C57BL/6 is apparently due to a novel pattern of strain-dependent positive selection which, unlike for alpha beta TCR, operates extrathymically. This type of selection seems to be determined by strain specific polymorphic ligands encoded outside of the classical H-2 region.

A comparative study on the xenotransplantability of human solid tumors into mice with different genetic immune deficiencies

These experiments set out to assess the role of NK and B cells in the resistance of nude mice to human tumor xenotransplantation. The transplantability of 9 fresh and 8 cultured human tumors was compared in 2 strains of mice with different genetic immune deficiencies: athymic NCr/Sed (nu/nu) nude mice, and nude-beige-xid (N:NIH-nu-bg-xid/Sed mice). Flow cytometric studies showed both strains to be deficient in Thy. 1.2 (T) cells and unresponsive to stimulation by Concanavalin A (Con A) or direct T-cell-receptor triggering with anti-CD3. The number of B cells was similar in the 2 strains, but the response to lipopolysaccharide (LPS) was markedly reduced in the nude-beige-xid animals. The number of asialoGM1-positive cells (predominantly NK) detected by flow cytometry was also reduced in the nude-beige-xid mice. The transplantability of the human tumors was found to be equivalent in the 2 strains. Quantitative cell-transplantation assays performed for 2 of the tumor cell lines did not reveal any subtle transplantation advantage for the more broadly immune-deficient animals. No evidence could, therefore, be found to suggest that NK or B cells were major determinants of human tumor xenotransplantability in these strains of mice.

Reduced tumorigenicity of murine tumor cells secreting gamma-interferon is due to nonspecific host responses and is unrelated to class I major histocompatibility complex expression

Spontaneous SP1 murine adenocarcinoma cells transfected with the murine gamma-interferon (IFN-gamma) gene expressed IFN-gamma (SP1/IFN-gamma) failed to grow in syngeneic hosts and grew in nude mice. The rejection of SP1/IFN-gamma cells was related to the amount of IFN-gamma produced and appeared to be mediated primarily by nonspecific cellular mechanisms, although some role for T-cells in the afferent arm of this response is possible. SP1 cells are H2-Kk negative but express class I antigens when producing IFN-gamma. However, class I major histocompatibility complex (MHC) expression, while likely necessary, was insufficient in itself to prevent tumor growth since secretion of greater than 64 units/ml IFN-gamma was needed to inhibit tumorigenicity while only 8 units/ml IFN-gamma could induce class I antigens. Similar results were obtained with the murine colon carcinoma CT-26, a tumor that constitutively expresses class I MHC antigens, further supporting the contention that class I MHC expression is not essential for the rejection response induced by IFN-gamma. The failure of SP1/IFN-gamma cells to protect against a challenge with parent SP1 cells argues that factors other than IFN-gamma production or class I MHC expression are needed to induce a protective response against weakly or nonimmunogenic tumor cells.

Rearrangement patterns of T-cell receptor genes in the spleen of athymic (nu/nu) young mice

Although the athymic nude mouse is grossly deficient in peripheral T cells, the number of lymphocytes bearing T-cell markers (L3T4, LyT2) and the alpha beta or gamma delta T-cell receptor (Tcr) increases steadily with age. The anatomical site(s) where these cells arise are unknown. Splenocytes from 3-5-week-old C57BL/6 (nu/nu) mice contain 2%-5% Pro-T cell progenitors identified with the Joro 37-5 and Joro 75 antibodies, but not mature T cells. To study Tcr gene rearrangement outside the thymus, we fused splenocytes from 3-5-week-old C57BL/6 nude mice with the T-cell lymphoma BW 100.129. Of 22 hybrids that grew stably in culture, four had Tcrd-VD1-D2-J1, two had Tcrd-VD2-J1, and seven had Tcrd-D1-D2 types of rearrangement. Eight hybrids had rearranged the Tcrg-2 gene cluster, but none had rearranged Tcrg-1, -3, or -4. None of the hybrids had rearranged the Tcrb gene cluster and 13 contained DJ rearrangements at the Igh locus. We conclude that the spleen is one of the extrathymic sites where T-cell progenitors can rearranged Tcrd and Tcrg genes. However, there was no evidence for Tcrb gene rearrangements in this organ. Furthermore, the analysis of this limited number of hybrids suggests that extrathymic Tcr gene rearrangements seem to be distinct and much less diverse than those found in the developing thymocytes.

Caries susceptibility in inbred mouse strains and inheritance patterns in F1 and backcross (N2) progeny from strains with high and low caries susceptibility

We studied dental caries susceptibility in various inbred mice strains infected with Streptococcus mutans and the inheritance pattern in the F1 and the N2 backcross animals. A high caries score was observed in four laboratory strains, BALB/cAJcl, C57BL/6NJcl, C57BL/10Slc and DBA/2NJcl. Three strains, C3H/HeNJcl, AKR/JSlc and CBA/JNCrj, showed less caries. Males of strain C57BL/10Slc (mean caries score = 112.2) and females of strain C3H/HeNJcl (mean caries score = 24.0) were chosen for examinations of the inheritance of the caries susceptibility. The mean caries score in (C57BL/10Slc x C3H/HeNJcl) F1 hybrids was 98.4, demonstrating that F1 progenies were susceptible. A number of N2 mice were obtained by mating the F1 male and the C3H/HeNJcl female. The caries scores of these N2 male mice had an extensive range, from 14 to 194. Assuming that a caries score over 74 (median of the scores between C57BL/10Slc and C3H/HeNJcl) belonged to the highly caries-susceptible group, N2 mice could be divided into groups with low or high caries susceptibility. Furthermore, the effect of nu/nu mutation on caries susceptibility in mice was also examined.

HNF transfection with chondrosarcoma DNA results in the development of a sarcoma cell surface-associated epitope

High molecular weight DNA, which was isolated from a chondrosarcoma cell line, was transfected into human neonatal foreskin fibroblasts and NIH/3T3 cells. Both types of transfected cells expressed anchorage-independent growth in soft agar and produced tumors in nude mice. The tumors which developed in nude mice following injection of transfected human fibroblasts grew to approximately 0.8 cm in diameter in four weeks. The tumors which developed from transfected NIH/3T3 cells grew to greater than 2.0 cm in diameter in 6 weeks. After growth in soft agar the transfected human fibroblasts expressed a cell surface sarcoma-associated epitope recognized by the monoclonal antibody 345.134S. In addition to the transfected human fibroblasts, the original human chondrosarcoma tumor, the chondrosarcoma cell line derived from the tumor, and the nude mouse tumor which developed from transfected human fibroblasts all exhibited positive reactivity with the monoclonal antibody 345.134S. Transfected NIH/3T3 cells that exhibited anchorage-independent growth and tumorigenicity did not exhibit detectable reactivity with the monoclonal antibody. These results suggest that the expression of the tumor-associated cell surface antigen appears to be an early event correlated with transformation of the transfected human cells but not directly related to the tumorigenic potential of the DNA. The transfected cells which expressed anchorage independent growth exhibited the sarcoma cell surface antigen prior to attaining the potential for tumorigenicity.

[Formation of E-rosettes in homozygous nude mice (nu/nu) and heterozygotes (nu/+)]

Nude homozygote nu/nu mice show a deficiency in their cellular immune response, due to the fact that their thymic tissue is very scarce. The purpose of this paper has been to determine whether nu/nu mice, in the presence of T lymphocytes, have the capacity of forming E rosettes with sheep erythrocytes. These mice do present them, although in significantly lower quantities when compared to the nu/+ and normal ones of Balb/c strain. This result confirms previous information which point towards the existence of other types of markers on the surface of T lymphocytes in nu/nu mice.

Establishment of DDD/1-Mtv-2/Mtv-2, nu/nu and DDD/1-Mtv-2/Mtv-2, nu/+ mice: preliminary characterization in relation to MTV antigen expression and mammary tumorigenesis

To investigate the effects of the T-cell deprivation on viral mammary tumorigenesis, two double congenic mouse strains of the DDD genetic background, DDD/1-Mtv-2/Mtv-2, nu/nu and DDD/1-Mtv-2/Mtv-2, nu/+, were produced by the cross between DDD/1-Mtv-2/Mtv-2 (DDD-Mtv-2) and DDD/1-nu/nu mice, followed by repeated intercross breedings. Expression of the mouse mammary tumor virus (MTV)-gp52 antigen was demonstrated in the mammary glands of mice from 14 days on, in both -nu/nu and -nu/+ females. Mammary gland development was comparable in both strains, but, the incidence of mammary cancer was lower in the T-cell-deprived mice.

The influence of the athymic mutation nude on the components of the circadian rhythm of activity in mice

The mutation known as nude brings about the lack of a thymus gland in mice. This immunodeficiency akes it possible to graft normally unaccepted, human cancerous tumors onto the mouse. Consequently, this animal is frequently used as a model for evaluating anti-cancer therapies. The effect of this mutation on biological rhythms constitutes a necessary step before using this model for cancer chronotherapy research. We evaluated the circadian and ultradian components of the rest-activity cycle in the following strains of mice: C57BL/6 with homozygous nu/nu, heterozygous nu/+, thymectomised +/+, and sham-operated +/+. The amount of activity was reduced in nu/nu as compared to the other groups. Nonetheless, neither the nude mutation nor thymectomy yielded any notable change in the circadian rhythm of activity.

The C57BL/6 nude, beige mouse: a model of combined T cell and NK effector cell immunodeficiency

This article describes the construction and establishment of a double congenic nude, beige C57BL/6 (B6 nu, bg) mouse strain. The mice do not show higher fragility than C57BL/6 nude mice and the double congenic strain can be maintained under conventional mouse housing conditions. Although the B6 nu, bg display a very low natural killer activity which cannot be enhanced by an interferon inducer (poly(I-C], they lack responsiveness to a T cell mitogen (concanavalin A); and they also show extremely low responsiveness to a B cell mitogen (0128: B12 Escherichia coli lipopolysaccharide) probably as a result of combined effects of the beige and nude genes in the C57BL/6 genetic context.