The Toll-Like Receptor 5 Agonist Entolimod Mitigates Lethal Acute Radiation Syndrome in Non-Human Primates

There are currently no approved medical radiation countermeasures (MRC) to reduce the lethality of high-dose total body ionizing irradiation expected in nuclear emergencies. An ideal MRC would be effective even when administered well after radiation exposure and would counteract the effects of irradiation on the hematopoietic system and gastrointestinal tract that contribute to its lethality. Entolimod is a Toll-like receptor 5 agonist with demonstrated radioprotective/mitigative activity in rodents and radioprotective activity in non-human primates. Here, we report data from several exploratory studies conducted in lethally irradiated non-human primates (rhesus macaques) treated with a single intramuscular injection of entolimod (in the absence of intensive individualized supportive care) administered in a mitigative regimen, 1-48 hours after irradiation. Following exposure to LD50-70/40 of radiation, injection of efficacious doses of entolimod administered as late as 25 hours thereafter reduced the risk of mortality 2-3-fold, providing a statistically significant (P<0.01) absolute survival advantage of 40-60% compared to vehicle treatment. Similar magnitude of survival improvement was also achieved with drug delivered 48 hours after irradiation. Improved survival was accompanied by predominantly significant (P<0.05) effects of entolimod administration on accelerated morphological recovery of hematopoietic and immune system organs, decreased severity and duration of thrombocytopenia, anemia and neutropenia, and increased clonogenic potential of the bone marrow compared to control irradiated animals. Entolimod treatment also led to reduced apoptosis and accelerated crypt regeneration in the gastrointestinal tract. Together, these data indicate that entolimod is a highly promising potential life-saving treatment for victims of radiation disasters.

Identification of granulocyte colony-stimulating factor and interleukin-6 as candidate biomarkers of CBLB502 efficacy as a medical radiation countermeasure

Given an ever-increasing risk of nuclear and radiological emergencies, there is a critical need for development of medical radiation countermeasures (MRCs) that are safe, easily administered, and effective in preventing and/or mitigating the potentially lethal tissue damage caused by acute high-dose radiation exposure. Because the efficacy of MRCs for this indication cannot be ethically tested in humans, development of such drugs is guided by the Food and Drug Administration's Animal Efficacy Rule. According to this rule, human efficacious doses can be projected from experimentally established animal efficacious doses based on the equivalence of the drug's effects on efficacy biomarkers in the respective species. Therefore, identification of efficacy biomarkers is critically important for drug development under the Animal Efficacy Rule. CBLB502 is a truncated derivative of the Salmonella flagellin protein that acts by triggering Toll-like receptor 5 (TLR5) signaling and is currently under development as a MRC. Here, we report identification of two cytokines, granulocyte colony-stimulating factor (G-CSF) and interleukin-6 (IL-6), as candidate biomarkers of CBLB502's radioprotective/mitigative efficacy. Induction of both G-CSF and IL-6 by CBLB502 1) is strictly TLR5-dependent, 2) occurs in a CBLB502 dose-dependent manner within its efficacious dose range in both nonirradiated and irradiated mammals, including nonhuman primates, and 3) is critically important for the ability of CBLB502 to rescue irradiated animals from death. After evaluation of CBLB502 effects on G-CSF and IL-6 levels in humans, these biomarkers will be useful for accurate prediction of human efficacious CBLB502 doses, a key step in the development of this prospective radiation countermeasure.

Prevention and mitigation of acute radiation syndrome in mice by synthetic lipopeptide agonists of Toll-like receptor 2 (TLR2)

Bacterial lipoproteins (BLP) induce innate immune responses in mammals by activating heterodimeric receptor complexes containing Toll-like receptor 2 (TLR2). TLR2 signaling results in nuclear factor-kappaB (NF-κB)-dependent upregulation of anti-apoptotic factors, anti-oxidants and cytokines, all of which have been implicated in radiation protection. Here we demonstrate that synthetic lipopeptides (sLP) that mimic the structure of naturally occurring mycoplasmal BLP significantly increase mouse survival following lethal total body irradiation (TBI) when administered between 48 hours before and 24 hours after irradiation. The TBI dose ranges against which sLP are effective indicate that sLP primarily impact the hematopoietic (HP) component of acute radiation syndrome. Indeed, sLP treatment accelerated recovery of bone marrow (BM) and spleen cellularity and ameliorated thrombocytopenia of irradiated mice. sLP did not improve survival of irradiated TLR2-knockout mice, confirming that sLP-mediated radioprotection requires TLR2. However, sLP was radioprotective in chimeric mice containing TLR2-null BM on a wild type background, indicating that radioprotection of the HP system by sLP is, at least in part, indirect and initiated in non-BM cells. sLP injection resulted in strong transient induction of multiple cytokines with known roles in hematopoiesis, including granulocyte colony-stimulating factor (G-CSF), keratinocyte chemoattractant (KC) and interleukin-6 (IL-6). sLP-induced cytokines, particularly G-CSF, are likely mediators of the radioprotective/mitigative activity of sLP. This study illustrates the strong potential of LP-based TLR2 agonists for anti-radiation prophylaxis and therapy in defense and medical scenarios.

Accelerated thymic atrophy as a result of elevated homeostatic expression of the genes encoded by the TNF/lymphotoxin cytokine locus

TNF, lymphotoxin (LT)-alpha, LT-beta and LIGHT are members of a larger superfamily of TNF-related cytokines that can cross-utilize several receptors. Although LIGHT has been implicated in thymic development and function, the role of TNF and LT remains incompletely defined. To address this, we created a model of modest homeostatic overexpression of TNF/LT cytokines using the genomic human TNF/LT locus as a low copy number Tg. Strikingly, expression of Tg TNF/LT gene products led to profound early thymic atrophy characterized by decreased numbers of thymocytes and cortical thymic epithelial cells, partial block of thymocyte proliferation at double negative (DN) 1 stage, increased apoptosis of DN2 thymocytes and severe decline of T-cell numbers in the periphery. Results of backcrossing to TNFR1-, LTbetaR- or TNF/LT-deficient backgrounds and of reciprocal bone marrow transfers implicated both LT-alpha/LT-beta to LTbetaR and TNF/LT-alpha to TNFR1 signaling in accelerated thymus degeneration. We hypothesize that chronic infections can promote thymic atrophy by upregulating LT and TNF production.

Mls: A Link Between Immunology and Retrovirology

The nature of the mysterious minor lymphocyte stimulating (Mls) antigens has recently been clarified. These molecules which were key elements for our current understanding of immune tolerance, have a strong influence on the mouse immune system and are encoded by the open reading frame (orf) of endogenous and exogenous mouse mammary tumor viruses (MMTV's). The knowledge that these antigens are encoded by cancerogenic retroviruses opens an interdisciplinary approach for understanding the mechanisms of immune responses and immune tolerance, retroviral carcinogenesis, and retroviral strategies for infection.

Immune response to MMTV infection

Mouse mammary tumor virus (MMTV) has developed a strategy of exploitation of the immune response. It infects dendritic cells and B cells and requires this infection to establish an efficient chronic infection. This allows transmission of infection to the mammary gland, production in milk and infection of the next generation via lactation. The elaborate strategy developed by MMTV utilizes several key elements of the normal immune response. Starting with the infection and activation of dendritic cells and B cells leading to the expression of a viral superantigen followed by professional superantigen-mediated priming of naive polyclonal T cells by dendritic cells and induction of superantigen-mediated T cell B cell collaboration results in long-lasting germinal center formation and production of long-lived B cells that can later carry the virus to the mammary gland epithelium. Later in life it can induce transformation of mammary gland epithelium by integrating close to proto-oncogenes leading to their overexpression. Genes encoding proteins of the Wnt-pathway are preferential targets. This review will put these effects in the context of a normal immune response and summarize important facts on MMTV biology.

Novel tumor necrosis factor-knockout mice that lack Peyer's patches

We generated a novel tumor necrosis factor (TNF) null mutation using Cre-loxP technology. Mice homozygous for this mutation differ from their "conventional" counterparts; in particular, they completely lack Peyer's patches (PP) but retain all lymph nodes. Our analysis of these novel TNF-knockout mice supports the previously disputed notion of the involvement of TNF-TNFR1 signaling in PP organogenesis. Availability of TNF-knockout strains both with and without PP enables more definitive studies concerning the roles of TNF and PP in various immune functions and disease conditions. Here, we report that systemic ablation of TNF, but not the presence of PP per se, is critical for protection against intestinal Listeria infection in mice.

Distinct and nonredundant in vivo functions of TNF produced by t cells and macrophages/neutrophils: protective and deleterious effects

Tumor necrosis factor (TNF, TNFalpha) is implicated in various pathophysiological processes and can be either protective, as in host defense, or deleterious, as in autoimmunity or toxic shock. To uncover the in vivo functions of TNF produced by different cell types, we generated mice with TNF ablation targeted to various leukocyte subsets. Systemic TNF in response to lipopolysaccharide was produced mainly by macrophages and neutrophils. This source of TNF was indispensable for resistance to an intracellular pathogen, Listeria, whereas T-cell-derived TNF was important for protection against high bacterial load. Additionally, both T-cell-derived TNF and macrophage-derived TNF had critical and nonredundant functions in the promotion of autoimmune hepatitis. Our data suggest that T-cell-specific TNF ablation may provide a therapeutic advantage over systemic blockade.

SMUCKLER/TIM4 is a distinct member of TIM family expressed by stromal cells of secondary lymphoid tissues and associated with lymphotoxin signaling

Lymphotoxin-alpha (LTalpha) was originally linked to delayed-type hypersensitivity and its production was later attributed to Th1, but not Th2 cells. Studies employing knockout mice demonstrated that LT signaling is essential for the development and functional compartmentalization of lymphoid tissues. Here, using gene expression profiling, we identified a novel gene termed SMUCKLER (spleen, mucin-containing, knockout of lymphotoxin), that is selectively down-regulated in spleens of LTalpha- or LTbeta-deficient mice. The encoded transmembrane protein contains immunoglobulin V and mucin domains and is identical to TIM4, a predicted member of recently identified TIM family (T cell immunoglobulin- and mucin-domain-containing molecule). Unlike TIM1 and TIM3, which were implicated in T cell-mediated functions, SMUCKLER lacks tyrosine phosphorylation motif in its intracellular domain and is not expressed by bone marrow-derived cells. In situ hybridization of spleen sections demonstrated SMUCKLER expression by stromal cells predominantly in the marginal zone and to a lesser extent throughout the white pulp. Similarly to other TIM genes, SMUCKLER maps to a locus associated with predisposition to asthma both in mice and in humans (11.b1 and 5q33, respectively) and shows coding sequence variations between BALB/c and DBA mice. Therefore, SMUCKLER/TIM4 may be considered as a candidate disease-predisposition gene for asthma.

Dissecting the role of lymphotoxin in lymphoid organs by conditional targeting

Mice with inactivation of lymphotoxin beta receptor (LTbetaR) system have profound defects in the development and maintenance of peripheral lymphoid organs. As surface LT is expressed by lymphocytes, natural killer cells, and lymphoid tissue-initiating cells as well as by some other cell types, we dissected cell type-specific LT contribution into the complex LT-deficient phenotype by conditional gene targeting. B-LTbeta knockout (KO) mice displayed an intermediate phenotype in spleen as compared with mice with complete LTbeta deficiency. In contrast, T-LTbeta KO mice displayed normal structure of the spleen. However, inactivation of LTbeta in both T and B cells resulted in additional defects in the structure of the marginal zone and in the development of follicular dendritic cells in spleen. Structure of lymph nodes (LN) and Peyer's patches (PP) was normal in both B-LTbeta KO and T- and B-LTbeta KO mice, except that PPs were of reduced size. When compared across the panel of lymphocyte-specific LT KOs, the defects in antibody responses to T-cell-dependent antigens correlated with the severity of defects in spleen structure. Expression of CCL21 and CCL19 chemokines was not affected in spleen, LN and PP of B-LTbeta KO and T- and B-LTbeta KO mice, while CXCL13 was slightly reduced only in spleen. Collectively, our data suggest the following: (i). requirements for LT signaling to support architecture of spleen, LN and PP are different; (ii). LT complex expressed by B cells plays a major role in the maintenance of spleen structure, while surface LT expressed by T cells provides a complementary but distinct signal; and (iii). in a non-transgenic model, expression of lymphoid tissue chemokines is only minimally dependent on the expression of surface LT complex on B and T lymphocytes.

Distinct contributions of TNF and LT cytokines to the development of dendritic cells in vitro and their recruitment in vivo

TNF/LTalpha/LTbeta (tumor necrosis factor/lymphotoxin-alpha/lymphotoxin-beta) triple knockout (KO) mice show a significant reduction of dendritic cell (DC) number in the spleen, presumably due to defective recruitment and/or production. To distinguish between these possibilities, DCs were generated from bone marrow (BM) cultures prepared from wild-type (wt) and mutant mice in the presence of granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-4 (IL-4). The yield of CD11c(+) major histocompatibility complex (MHC) class II(+) DCs generated from TNF/LTalpha/LTbeta(-/-) BM culture was significantly reduced compared with wt BM culture. In order to further dissect the individual pathways responsible for defective DC properties observed in TNF/LTalpha/LTbeta(-/-) mice, the panel of TNF/LT ligand and receptor single KO mice were used. The production of DCs from BM culture was significantly reduced in TNF(-/-) and TNF receptor (TNFR) p55(-/-) mice, but normal in LTalpha(-/-), LTbeta(-/-), LTbetaR(-/-) mice. Recombinant TNF (rTNF) exogenously added to TNF/LTalpha/LTbeta(-/-) BM cultures could reverse this defect, and blocking antibodies showed partial effect on BM cultures of wt mice. Conversely, numbers of mature DCs in spleen were significantly decreased in LTalpha(-/-), LTbeta(-/-), LTbetaR(-/-) mice, but not in TNF(-/-) and TNFRp55(-/-) mice. These results reveal 2 distinct contributions of TNF/LT cytokines. First, TNF acting through TNF receptor is involved in the development/maturation of DCs in BM progenitor cultures, but this function appears to be redundant in vivo. Second, the microenvironment in peripheral lymphoid organs associated with LTalpha/LTbeta-LTbetaR signaling and chemokine production is critical for recruitment efficiency of DCs, and this pathway is indispensable.

Redundancy in tumor necrosis factor (TNF) and lymphotoxin (LT) signaling in vivo: mice with inactivation of the entire TNF/LT locus versus single-knockout mice

Homologous genes and gene products often have redundant physiological functions. Members of the tumor necrosis factor (TNF) family of cytokines can signal activation, proliferation, differentiation, costimulation, inhibition, or cell death, depending on the type and status of the target cell. TNF, lymphotoxin alpha (LTalpha), and LTbeta form a subfamily of a larger family of TNF-related ligands with their genes being linked within a compact 12-kb cluster inside the major histocompatibility complex locus. Singly TNF-, LTalpha-, and LTbeta-deficient mice share several phenotypic features, suggesting that TNF/LT signaling pathways may regulate overlapping sets of target genes. In order to directly address the issue of redundancy of TNF/LT signaling, we used the Cre-loxP recombination system to create mice with a deletion of the entire TNF/LT locus. Mice with a triple LTbeta/TNF/LTalpha deficiency essentially manifest a combination of LT and TNF single-knockout phenotypes, except for microarchitecture of the spleen, where the disorder of lymphoid cell positioning and functional T- and B-cell compartmentalization is severer than that found in TNF or LT single-knockout mice. Thus, our data support the notion that TNF and LT have largely nonredundant functions in vivo.

Transcriptional Regulation of the Gene, Encoding p40 Subunit of IL-12 and IL-23, in Murine Macrophages

Interleukin-12 (IL-12) is an immunomodulatory cytokine with broad spectrum of activities, central of which are stimulation of NK cells, and promoting differentiation of T helper cells towards Th1 phenotype. IL-12 consists of two unrelated subunits, p35 and p40. Recently discovered cytokine, IL-23, which has both unique properties and those overlapping with IL-12, also contains p40 associated with another subunit, p19. Both IL-12 and IL-23 transmit the signal through receptors associated with JAK-STAT pathways. One of the critical components in the control of both IL-12 and IL-23 regulation is the transcriptional control of p40 gene which is induced in macrophages and dendritic cells in response to bacterial endotoxin, IFN-gamma and other stimuli. In the present study we report on the structure of the transcriptional unit of the murine p40 gene, its promoter and inducible expression of p40 in murine macrophages. Our findings are consistent with multi-level regulation of p40 expression.

Expression profiling in knockout mice: lymphotoxin versus tumor necrosis factor in the maintenance of splenic microarchitecture

Expression profiling provides a powerful approach to define the underlying molecular mechanisms in disease. Several techniques referred collectively to as gene profiling may be also helpful in the analysis of the phenotype of mice with targeted mutations, especially if applied to distinct histological compartments, to specific cell types or to evaluate the effect of specific challenges, such as infection. Here we review several of the existing techniques applicable to genetic knockout studies, and share our experience from the study of mice with tumor necrosis factor (TNF) and lymphotoxin (LT) deficiencies, with specific emphasis on the distinction between TNF- and LT-mediated signalling pathways in vivo. Gene expression profiling analysis of TNF/LT-deficient mice supports the notion that TNF and LT, originally discovered as distinct biological activities, manifest both distinct and redundant functions in vivo.

Gene profiling approach in the analysis of lymphotoxin and TNF deficiencies

Mice with combined lymphotoxin-alpha (LTalpha) and tumor necrosis factor (TNF) deficiencies show defects in the structure of peripheral lymphoid organs such as spleen, lymph nodes, and gut-associated lymphoid tissues. To identify genes associated with this defective phenotype in spleen, we applied a gene profiling approach, including subtractive cloning and gene array hybridizations, to mice with combined TNF/LT deficiency. The differentially expressed genes identified by these techniques was then evaluated by Northern blot analysis for splenic expression in knockout mice with single LTalpha or single TNF deficiency. Most of the genes detected in this analysis are directly or indirectly associated with disrupted LT and not TNF signaling.

SPLASH (PLA2IID), a novel member of phospholipase A2 family, is associated with lymphotoxin deficiency

Lymphotoxin (LT) deficient mice have profound defects in the splenic microarchitecture associated with defective expression on certain gene products, including chemokines. By using subtraction cloning of splenic cDNA from wild-type and LT alpha or TNF/LT alpha double deficient mice we isolated a novel murine gene encoding a secretory type phospholipase A2, called SPLASH. The two major alternative transcripts of SPLASH gene are predominantly expressed in lymphoid tissues, such as spleen and lymph nodes. SPLASH maps to the distal part of chromosome 4, to which several cancer-related loci have been also mapped.

Mice with a Targeted Mutation in Lymphotoxin-α Exhibit Enhanced Tumor Growth and Metastasis: Impaired NK Cell Development and Recruitment

Mice deficient in lymphotoxin (LT)-α lack peripheral lymph nodes and Peyer’s patches and have profound defects in development of follicular dendritic cell networks, germinal center formation, and T/B cell segregation in the spleen. Although LTα is known to be expressed by NK cells as well as T and B lymphocytes, the requirement of LTα for NK cell functions is largely unknown. To address this issue, we have assessed NK cell functions in LTα-deficient mice by evaluating tumor models with known requirements for NK cells to control their growth and metastasis. Syngeneic B16F10 melanoma cells inoculated s.c. grew more rapidly in LTα−/− mice than in the wild-type littermates, and the formation of experimental pulmonary metastases was significantly enhanced in LTα−/− mice. Although LTα−/− mice exhibited almost a normal total number of NK cells in spleen, they showed an impaired recruitment of NK cells to lung and liver. Additionally, lytic NK cells were not efficiently produced from LTα−/− bone marrow cells in vitro in the presence of IL-2 and IL-15. These data suggest that LTα signaling may be involved in the maturation and recruitment of NK cells and may play an important role in antitumor surveillance.

Mice with a targeted mutation in lymphotoxin-alpha exhibit enhanced tumor growth and metastasis: impaired NK cell development and recruitment

Mice deficient in lymphotoxin (LT)-alpha lack peripheral lymph nodes and Peyer's patches and have profound defects in development of follicular dendritic cell networks, germinal center formation, and T/B cell segregation in the spleen. Although LTalpha is known to be expressed by NK cells as well as T and B lymphocytes, the requirement of LTalpha for NK cell functions is largely unknown. To address this issue, we have assessed NK cell functions in LTalpha-deficient mice by evaluating tumor models with known requirements for NK cells to control their growth and metastasis. Syngeneic B16F10 melanoma cells inoculated s.c. grew more rapidly in LTalpha-/- mice than in the wild-type littermates, and the formation of experimental pulmonary metastases was significantly enhanced in LTalpha-/- mice. Although LTalpha-/- mice exhibited almost a normal total number of NK cells in spleen, they showed an impaired recruitment of NK cells to lung and liver. Additionally, lytic NK cells were not efficiently produced from LTalpha-/- bone marrow cells in vitro in the presence of IL-2 and IL-15. These data suggest that LTalpha signaling may be involved in the maturation and recruitment of NK cells and may play an important role in antitumor surveillance.

Interferon-gamma enhances tumor necrosis factor-alpha production by inhibiting early phase interleukin-10 transcription

The ability of cytokine synthesis inhibitory factor or interleukin-10 (IL-10) and interferon-gamma (IFN-gamma) to modulate the production of tumor necrosis factor (TNF-alpha) induced by lipopolysaccharide (LPS) was examined in mouse bone marrow-derived macrophages (BMDM). IFN-gamma profoundly enhances LPS-stimulated TNF-alpha production, whereas IL-10 is markedly inhibitory, demonstrating the opposing effects of IFN-gamma and IL-10 on BMDM. Early neutralization of endogenously produced, LPS-stimulated IL-10 markedly enhanced short term TNF-alpha production, an effect further amplified by the absence of IFN-gamma priming. The regulatory effects of IFN-gamma and IL-10 apparently occurred at the translational (or post-translational) level, with TNF-alpha mRNA steady-state levels remaining unchanged. Furthermore, IFN-gamma exerts its enhancing effect on TNF synthesis by the transcriptional inhibition of IL-10. This in vitro finding was also confirmed in vivo. In the absence of LPS, IFN-gamma was not capable of inducing TNF-alpha production in BMDM, indicating that LPS or other signals are necessary for transcriptional activation. Reduced but significant TNF-alpha production in LPS-injected IFN-gamma receptor -/- mice suggests that IFN-gamma is not an absolute requirement and that other cytokines or cell types contribute in a secondary fashion to the priming of LPS-induced TNF-alpha production in vivo.

Role of interferon-gamma in interleukin 12-induced pathology in mice

Interleukin 12 (IL-12) activates natural killer (NK) and T cells with the secondary synthesis and release of interferon-gamma (IFN-gamma) and other cytokines. IL-12-induced organ alterations are reported for mice and the pathogenetic role of IFN-gamma is investigated by the use of mice deficient in the IFN-gamma receptor (IFN-gamma R-/-). IL-12 caused a rapid infiltration of liver and splenic red pulp with activated macrophages; this and increased NK cells resulted in a fivefold increase of splenic weight in wild-type mice. Splenomegaly was associated with myelosuppression and decreasing peripheral leukocyte counts. IL-12-induced changes in wild-type mice were associated with markedly increased IFN-gamma serum levels and up-regulation of major histocompatibility complex (MHC) class I and II expression in various epithelia. IL-12 induced a qualitatively similar macrophage infiltration in IFN-gamma R-/- mice, less marked splenomegaly (to 2 x normal), and no MHC upregulation. Strikingly increased vascular endothelial intercellular adhesion molecule-1 expression was apparent in both IFN-gamma R-/- and IFN-gamma R+/+ mice. Restricted to mutant mice was a severe, invariably lethal, interstitial, and perivascular pulmonary macrophage infiltration with diffuse pulmonary edema. Extensive quantitative reverse transcriptase polymerase chain reaction analysis revealed an increase of only IL-6 and IL-10 pulmonary gene transcripts in IFN-gamma R-/- mice compared with wild-type mice. IL-12-induced myelosuppression is due to IFN-gamma-release from NK cells and T cells, and is associated with macrophage activation and distinct MHC class I and II antigen upregulation. The pulmonary pathology in IFN-gamma R-/- mice, however, reveals a toxic potential for IL-12 and suggests that endogenous IFN-gamma plays a protective role in preventing fatal pulmonary disease in these mice.

Retroviral infection of neonatal Peyer's patch lymphocytes: the mouse mammary tumor virus model

Mouse mammary tumor virus is known to infect newborn mice via mother's milk. A proposed key step for viral spread to the mammary gland is by the infection of lymphocytes. We show here that although in suckling mice retroviral proteins are found in all epithelial cells of the gut, viral DNA is exclusively detectable in the Peyer's patches. As early as 5 d after birth the infection leads to a superantigen response in the Peyer's patches but not in other lymphoid organs draining the intestine. Viral DNA can be detected before the superantigen response and becomes first evident in the Peyer's patches followed by mesenteric lymph nodes and finally all lymphoid organs.

New infectious mammary tumor virus superantigen with V beta-specificity identical to staphylococcal enterotoxin B (SEB)

Only few infectious mouse mammary tumor viruses (MMTV) have been characterized which induce a potent superantigen response in vivo. Here we describe the characterization of an MMTV which was isolated from milk of the highly mammary tumor-prone SHN mouse strain. Exposure of newborn mice to milk-borne MMTV (SHN) results in a very slow deletion of V beta 7, 8.1, 8.2 and 8.3 expressing peripheral T cells. Subcutaneous injection of adult mice with this virus induces a rapid and strong stimulation of all four affected V beta-subsets in vivo. Besides the strong T cell effect we observed an early proliferation and activation of the local B cell pool leading to the initial secretion of IgM followed by preferential secretion of IgG2a by day 6. Sequence comparison of the polymorphic C terminus with known open reading frames revealed high homology to the endogenous provirus Mtv-RCS. This is the first report of a virus having a complete overlap in V beta-specificity with a bacterial superantigen stimulating as many as 35% of the whole CD4+ T cell repertoire including V beta 8.2.

A new infectious mammary tumor virus in the milk of mice implanted with C4 hyperplastic alveolar nodules

We have previously characterized an infectious mouse mammary tumor virus [(MMTV(SW)] which induces a strong superantigen response in vivo. Here we describe the isolation and characterization of MMTV(C4) which was derived from milk of mice implanted with hyperplastic alveolar nodules. MMTV(C4) stimulates V beta 2 expressing T cells after local injection in vivo. Comparison with known open reading frame (orf) sequences revealed high homology to Mtv-6, an endogenous virus interacting with V beta 3-expressing T cells. The carboxyl-terminal amino acids were, however, altered. High homology including the carboxyl-terminal orf amino acids were found with MMTV(C3H-K). We show here that MMTV(C3H-K) has lost its superantigen function. Sequence comparisons permitted the characterization of few key amino acids which could be important for T cell receptor interaction and superantigen processing.

Superantigen-induced immune stimulation amplifies mouse mammary tumor virus infection and allows virus transmission

Endogenous and infectious mouse mammary tumor viruses (MMTVs) encode in their 3' long terminal repeat a protein that exerts superantigen activity; that is, it is able to interact with T cells via the variable domain of the T cell receptor (TCR) beta chain. We show here that transmission of an infectious MMTV is prevented when superantigen-reactive cells are absent through either clonal deletion due to the expression of an endogenous MTV with identical superantigen specificity or exclusion due to expression of a transgenic TCR beta chain that does not interact with the viral superantigen. A strict requirement for superantigen-reactive T cells is also seen for a local immune response following MMTV infection. This immune response locally amplifies the number of MMTV-infected B cells, most likely owing to their clonal expansion. Collectively, our data indicate that a superantigen-induced immune response is critical for the MMTV life cycle.

Peripheral T cell activation and deletion induced by transfer of lymphocyte subsets expressing endogenous or exogenous mouse mammary tumor virus

Murine T cell reactivity with products of the minor lymphocyte stimulatory (Mls) locus correlates with the expression of particular variable (V) domains of the T cell receptor (TCR) beta chain. It was recently demonstrated that Mls antigens are encoded by an open reading frame (ORF) in the 3' long terminal repeat of either endogenous or exogenous mouse mammary tumor virus (MMTV). Immature thymocytes expressing reactive TCR-V beta domains are clonally deleted upon exposure to endogenous Mtv's. Mature T cells proliferate vigorously in response to Mls-1a (Mtv-7) in vivo, but induction of specific anergy and deletion after exposure to Mtv-7-expressing cells in the periphery has also been described. We show here that B cells and CD8+ (but not CD4+) T cells from Mtv-7+ mice efficiently induce peripheral deletion of reactive T cells upon transfer to Mtv-7- recipients, whereas only B cells stimulate specific T cell proliferation in vivo. In contrast to endogenous Mtv-7, transfer of B, CD4+, or CD8+ lymphocyte subsets from mice maternally infected with MMTV(SW), an infectious homologue of Mtv-7, results in specific T cell deletion in the absence of a detectable proliferative response. Finally, we show by secondary transfers of infected cells that exogenous MMTV(SW) is transmitted multidirectionally between lymphocyte subsets and ultimately to the mammary gland. Collectively our data demonstrate heterogeneity in the expression and/or presentation of endogenous and exogenous MMTV ORF by lymphocyte subsets and emphasize the low threshold required for induction of peripheral T cell deletion by these gene products.

Superantigen-reactive CD4+ T cells are required to stimulate B cells after infection with mouse mammary tumor virus

Superantigens are defined by their ability to stimulate a large fraction of T cells via interaction with the T cell receptor (TCR) V beta domain. Endogenous superantigens, classically termed minor lymphocyte-stimulating (Mls) antigens, were recently identified as products of open reading frames (ORF) in integrated proviral copies of mouse mammary tumor virus (MMTV). We have described an infectious MMTV homologue of the classical endogenous superantigen Mls-1a (Mtv-7). The ORF molecules of both the endogenous Mtv-7 and the infectious MMTV(SW) interact with T cells expressing the TCR V beta 6, 7, 8.1, and 9 domains. Furthermore, the COOH termini of their ORF molecules, thought to confer TCR specificity, are very similar. Since successful transport of MMTV from the site of infection in the gut to the mammary gland depends on a functional immune system, we were interested in determining the early events after and requirements for MMTV infection. We show that MMTV(SW) infection induces a massive response of V beta 6+ CDC4+ T cells, which interact with the viral ORF. Concomitantly, we observed a B cell response and differentiation that depends on both the presence and stimulation of the superantigen-reactive T cells. Furthermore, we show that B cells are the main target of the initial MMTV infection as judged by the presence of the reverse-transcribed viral genome and ORF transcripts. Thus, we suggest that MMTV infection of B cells leads to ORF-mediated B-T cell interaction, which maintains and possibly amplifies viral infection.

Inhibition of mouse mammary tumor virus-induced T cell responses in vivo by antibodies to an open reading frame protein

Minor lymphocyte stimulating (Mls) antigens specifically stimulate T cell responses that are restricted to particular T cell receptor (TCR) beta chain variable domains. The Mls phenotype is genetically controlled by an open reading frame (orf) located in the 3' long terminal repeat of mouse mammary tumor virus (MMTV); however, the mechanism of action of the orf gene product is unknown. Whereas predicted orf amino acid sequences show strong overall homology, the 20-30 COOH-terminal residues are strikingly polymorphic. This polymorphic region correlates with TCR V beta specificity. We have generated monoclonal antibodies to a synthetic peptide encompassing the 19 COOH-terminal amino acid residues of Mtv-7 orf, which encodes the Mls-1a determinant. We show here that these antibodies block Mls responses in vitro and can interfere specifically with thymic clonal deletion of Mls-1a reactive V beta 6+ T cells in neonatal mice. Furthermore, the antibodies can inhibit V beta 6+ T cell responses in vivo to an infectious MMTV that shares orf sequence homology and TCR specificity with Mtv-7. These results confirm the predicted extracellular localization of the orf COOH terminus and imply that the orf proteins of both endogenous and exogenous MMTV interact directly with TCR V beta.

Infectious minor lymphocyte stimulating (Mls) antigens

Minor lymphocyte stimulating (Mls) antigens have profound effects on the murine immune system and have been very important for our current understanding of immune tolerance. It has recently been discovered that these Mls antigens are encoded in an open reading frame located in the 3' long terminal repeat of endogenous and infectious mouse mammary tumor viruses (MMTV). In this review we will discuss the effects of a novel infectious MMTV with properties of Mls-1a on the neonatal and adult immune system in comparison to the effects of endogenous Mtv-7 (Mls-1a).

trans activation of the tumor necrosis factor alpha promoter by the human T-cell leukemia virus type I Tax1 protein

In a cotransfection assay, the human T-cell leukemia virus type I Tax1 gene product specifically activated transcription from the mouse tumor necrosis factor alpha promoter. The activation patterns of 5' deletion mutants, artificial enhancer constructs, and point mutations in the promoter indicate that the major Tax1-responsive element is a site at position -655 which binds the NF-kappa B/rel and NF-GMa transcription factors.

An exogenous mouse mammary tumor virus with properties of Mls-1a (Mtv-7)

The classical minor lymphocyte stimulating (Mls) antigens, which induce a strong primary T cell response in vitro, are closely linked to endogenous copies of mouse mammary tumor viruses (MMTV). Expression of Mls genes leads to clonal deletion of T cell subsets expressing specific T cell receptor (TCR) V beta chains. We describe the isolation and characterization of a new exogenous (infectious) MMTV with biological properties similar to the Mls antigen Mls-1a. In vivo administration of either Mls-1a-expressing B cells or the infectious MMTV (SW) led to an increase of T cells expressing V beta 6 followed by their deletion. Surprisingly, different kinetics of deletion were observed with the exogenous virus depending upon the route of infection. Infection through the mucosa led to a slow deletion of V beta 6+ T cells, whereas deletion was rapid after subcutaneous infection. Sequence analysis of the open reading frames in the 3' long terminal repeat of both this exogenous MMTV (SW) and of Mtv-7 (which is closely linked to Mls-1a) revealed striking similarities, particularly in the COOH terminus, which has been implicated in TCR V beta recognition. The identification of an infectious MMTV with the properties of a strong Mls antigen provides a new, powerful tool to study immunity and tolerance in vivo.

Enhancers and transcription factors controlling the inducibility of the tumor necrosis factor-alpha promoter in primary macrophages

In macrophages, the TNF-alpha promoter is specifically induced by bacterial endotoxin, and provides a good model for gene regulation during bacterial infections. We have analyzed the protein-binding characteristics and enhancer activity of four kappa B-like enhancers and of a MHC class II-like Y box found in the mouse TNF-alpha promoter. In addition to members of the NF-kappa B/rel transcription factor family, at least two of the kappa B sites also bound a nuclear protein identified as NF-GMa, a factor that binds to promoter sequences from many cytokines. When inserted upstream of an enhancer-less promoter, two of the kappa B sites were active as LPS-inducible enhancers in primary macrophages, whereas the other two were not. Mutations in nucleotides known to contact nuclear factors severely reduced affinity of the kappa B sites for NF-kappa B. Introduction of the same mutations into a construct containing 1059 bp of the TNF-alpha promoter coupled to a CAT reporter gene resulted in a stepwise reduction in inducibility by LPS; mutation of all four sites (11 bp of 1059) reduced inducibility by 90%, providing compelling evidence for the role of transcription factors belonging to the NF-kappa B/rel family in the activation of the TNF-alpha promoter. The TNF-alpha Y box bound an abundant nuclear factor, but had no detectable activity in our assays, either as an enhancer or as a mutation-sensitive controlling element.

Enhancers and transcription factors controlling the inducibility of the tumor necrosis factor-alpha promoter in primary macrophages

In macrophages, the TNF-alpha promoter is specifically induced by bacterial endotoxin, and provides a good model for gene regulation during bacterial infections. We have analyzed the protein-binding characteristics and enhancer activity of four kappa B-like enhancers and of a MHC class II-like Y box found in the mouse TNF-alpha promoter. In addition to members of the NF-kappa B/rel transcription factor family, at least two of the kappa B sites also bound a nuclear protein identified as NF-GMa, a factor that binds to promoter sequences from many cytokines. When inserted upstream of an enhancer-less promoter, two of the kappa B sites were active as LPS-inducible enhancers in primary macrophages, whereas the other two were not. Mutations in nucleotides known to contact nuclear factors severely reduced affinity of the kappa B sites for NF-kappa B. Introduction of the same mutations into a construct containing 1059 bp of the TNF-alpha promoter coupled to a CAT reporter gene resulted in a stepwise reduction in inducibility by LPS; mutation of all four sites (11 bp of 1059) reduced inducibility by 90%, providing compelling evidence for the role of transcription factors belonging to the NF-kappa B/rel family in the activation of the TNF-alpha promoter. The TNF-alpha Y box bound an abundant nuclear factor, but had no detectable activity in our assays, either as an enhancer or as a mutation-sensitive controlling element.

Clonal deletion of V beta 14-bearing T cells in mice transgenic for mammary tumour virus

Autoreactive T lymphocytes are clonally deleted during maturation in the thymus. Deletion of T cells expressing particular receptor V beta elements is controlled by poorly defined autosomal dominant genes. A gene has now been identified by expression of transgenes in mice which causes deletion of V beta 14+ T cells. The gene lies in the open reading frame of the long terminal repeat of the mouse mammary tumour virus.

[Cloning and expression of the CD4 receptor gene from human T-lymphocytes in Escherichia coli cells]

The gene for the CD4-membrane glycoprotein-receptor for HIV has been cloned. The 179 amino acids fragment of the CD4-receptor responsible for binding of gp120 HIV glycoprotein has been fused with beta-galactosidase and shown to be expressed in Escherichia coli cells. The recombinant protein in ELISA and immunoblotting techniques reacts with the monoclonal antibodies OKT4A and Leu3A known to block the interaction between the CD4 and gp120 HIV glycoprotein. The recombinant protein can be used for different scientific and practical purposes including studying of the mechanisms for HIV interaction with the sensitive cells as well as for viral gp120 protein purification, etc.

Structural analysis of the rabbit TNF locus, containing the genes encoding TNF-beta (lymphotoxin) and TNF-alpha (tumor necrosis factor)

The genes coding for 20-kDa lymphotoxin (TNF-beta) and tumor necrosis factor (TNF-alpha) have been cloned from a rabbit genomic library. The two genes are tandemly arranged and separated by only 1 kb of DNA, as previously observed in human and mouse genomes. We have sequenced the entire rabbit lymphotoxin-encoding gene and inferred the primary structure of rabbit TNF-beta, whose cDNA is not yet cloned. We also analysed the upstream sequences of the rabbit TNF-beta and TNF-alpha genes and identified a number of potential binding sites for known nuclear transcription factors, and in particular several putative kappa B-type sequences.

Kappa B-type enhancers are involved in lipopolysaccharide-mediated transcriptional activation of the tumor necrosis factor alpha gene in primary macrophages

We have explored the cis-acting elements necessary for the LPS-mediated activation of the mouse TNF-alpha promoter by transfecting a set of 5' deletion mutants linked to the CAT reporter gene into primary bone marrow-derived macrophages. A major drop in inducibility by LPS was seen upon deletion of a region mapping between nt -655 and nt -451. Gel retardation assays revealed that LPS induced the appearance in this region of several specific DNA-protein complexes mapping to sequence motifs with strong homology to the kappa B enhancer. Constructs containing two or more copies of one of the kappa B enhancer motifs linked to a heterologous promoter were inducible by LPS. Additional deletion of a region between nt -301 and nt -241, which contains a MHC class II-like "Y box" and formed a Y box-specific complex with a protein whose concentration was increased by LPS, caused a nearly complete loss of inducibility by LPS. We speculate that NF-kappa B and/or related proteins are involved in the LPS-induced transcriptional activation of the TNF-alpha gene, and that factors interacting with the Y box can additionally modulate the activity of the gene in macrophages.

[Cloning and structural analysis of genes coding for tumor necrosis factor and lymphotoxin in rabbits]

Genes, coding for tumor necrosis factor (TNF-alpha) and lymphotoxin (TNF-beta), have been cloned from the rabbit genomic library. The two genes are tandemly arranged and separated only by 1 kb of DNA as previously observed in human and mouse genomes. We have sequenced the entire rabbit lymphotoxin gene (LT) and calculated the amino acid sequence of the rabbit LT whose cDNA is not yet cloned. We also analyzed the upstream sequences of this gene and revealed a number of recognition sites for the known transcriptional factors. The rabbit TNF gene comprised in the cloned genomic region has been sequenced earlier.

[Mapping the genome locus containing genes for mouse tumor necrosis factor by means of hybridization end labelling with the use of synthetic oligonucleotides]

We have developed a technique for restriction nuclease sites mapping in genomic DNA cloned into phage lambda vectors. Synthetic oligonucleotides homologous to the vector sequences and adjacent to the cloning site were used as hybridisation probes for indirect end labelling procedure. In addition, a number of oligonucleotides homologous to the sequences of tumour necrosis factor genes were used for mapping from the internal sites. As a result, a map of 35 kb genomic region on the chromosome 17 inside major histocompatibility complex and surrounding mouse tumour necrosis factor genes was constructed.

Control region of SV40 minichromosomes is preferentially cleaved by single-strand specific S1 nuclease

We have analysed S1 sensitivity of SV40 minichromosomes isolated from the nuclei of infected cells at the late stage of infection. We show that a fraction of purified minichromosomes is sensitive towards double-strand cleavage by S1 nuclease. The pattern of specific cleavage reminiscent of that found for subcloned fragment under supercoiling is superimposed upon apparently random double-strand cuts along the entire regulatory region. Therefore, the cleavage sites are not exclusively confined to the regions with the reported alternate DNA conformation.

Molecular control of tissue-specific expression at the mouse TNF locus

We have examined the patterns of mRNA accumulation and transcription of the tandemly linked genes for tumor necrosis factor (TNF)-beta and TNF-alpha. In spite of their tandem arrangement and close linkage, the two TNF genes utilize separate promoters. Our results show that, while levels of mRNA correlate with patterns of TNF-alpha and TNF-beta secretion by lymphocytes and macrophages, the transcriptional levels of the corresponding genes do not. The TNF-alpha gene is transcribed much more heavily than the TNF-beta gene in T lymphocytes, even though the TNF-beta mRNA is more abundant. Resting T lymphocytes and macrophages, which do not accumulate any TNF mRNA, nevertheless transcribe the TNF-alpha gene actively. On the other hand, the TNF-beta gene is transcriptionally silent in macrophages. Our results are consistent with a model where tissue specificity is controlled transcriptionally, whereas post-transcriptional events differentially control mRNA abundance.

[Molecular cloning of genes coding for tumor necrosis factor. Complete nucleotide sequence of the genome copy of TNF-alpha in mice]

Using Sanger's technique and synthetic oligonucleotides derived from the known structure of cDNA, complete nucleotide sequence of the genomic copy of the mouse TNF-alpha gene has been determined. The length of the gene from transcription initiation site down to polyadenylation signal is about 2620 bp. Comparison with the previously described cDNA sequence revealed existence of 4 exons and 3 introns in the positions homologous to those of human TNF gene. The fourth exon codes for 88% amino acids of mature TNF-alpha.

The genes for tumor necrosis factor (TNF-alpha) and lymphotoxin (TNF-beta) are tandemly arranged on chromosome 17 of the mouse

We have isolated clones containing the gene for tumor necrosis factor (TNF-alpha) from a mouse genomic library. Four out of five clones containing the TNF-alpha gene also hybridized to a human lymphotoxin (TNF-beta) probe. We constructed a restriction enzyme cleavage map of a 6.4 kb region from one of the genomic clones. From partial sequencing data and hybridizations with exon-specific oligonucleotide probes, we conclude that this region contains the mouse TNF-alpha and TNF-beta genes in a tandem arrangement, that they are separated by only about 1100 bases, and that their intron-exon structure is very similar to that seen in man. We probed genomic blots of DNA from human/mouse hybrids containing single mouse chromosomes for the presence of the mouse TNF genes. The results show that the genes are located on mouse chromosome 17, which also contains the major histocompatibility complex. Therefore, both the mouse and the human TNF genes are tandemly arranged and located on the same chromosome as the MHC.

[Structuro-functional organization of the SV40 virus chromosome. IV. Specific organization of regulatory sequences of the SV40 genome in the mini-chromosome]

Using previously described technique of hybridization end-labeling, we analysed nucleosomal organization of the regulatory region of SV40 minichromosome. We showed that DNAase II, in spite of certain specificity observed on the naked DNA, cut the minichromosome in a highly specific manner with the major hypersensitive site inside the enhancer. This hypersensitivity and that to micrococcal nuclease were not found when the chromosome of mature SV40 virions was tested.