Enhancement of specific antitumor immunity in mice fed a diet enriched in vitamin A acetate

Synergistic activation of Arg1 gene by retinoic acid and IL-4 involves chromatin remodeling for transcription initiation and elongation coupling

All-trans Retinoic acid (RA) and its derivatives are potent therapeutics for immunological functions including wound repair. However, the molecular mechanism of RA modulation in innate immunity is poorly understood, especially in macrophages. We found that topical application of RA significantly improves wound healing and that RA and IL-4 synergistically activate Arg1, a critical gene for tissue repair, in M2 polarized macrophages. This involves feed forward regulation of Raldh2, a rate-limiting enzyme for RA biosynthesis, and requires Med25 to coordinate RAR, STAT6 and chromatin remodeler, Brg1 to remodel the +1 nucleosome of Arg1 for transcription initiation. By recruiting elongation factor TFIIS, Med25 also facilitates transcriptional initiation-elongation coupling. This study uncovers synergistic activation of Arg1 by RA and IL-4 in M2 macrophages that involves feed forward regulation of RA synthesis and dual functions of Med25 in nucleosome remodeling and transcription initiation-elongation coupling that underlies robust modulatory activity of RA in innate immunity.

Leukocyte homing, fate, and function are controlled by retinoic acid

Although vitamin A was recognized as an "anti-infective vitamin" over 90 years ago, the mechanism of how vitamin A regulates immunity is only beginning to be understood. Early studies which focused on the immune responses in vitamin A-deficient (VAD) animals clearly demonstrated compromised immunity and consequently increased susceptibility to infectious disease. The active form of vitamin A, retinoic acid (RA), has been shown to have a profound impact on the homing and differentiation of leukocytes. Both pharmacological and genetic approaches have been applied to the understanding of how RA regulates the development and differentiation of various immune cell subsets, and how RA influences the development of immunity versus tolerance. These studies clearly show that RA profoundly impacts on cell- and humoral-mediated immunity. In this review, the early findings on the complex relationship between VAD and immunity are discussed as well as vitamin A metabolism and signaling within hematopoietic cells. Particular attention is focused on how RA impacts on T-cell lineage commitment and plasticity in various diseases.

The role of retinoic acid in tolerance and immunity

Vitamin A elicits a broad array of immune responses through its metabolite, retinoic acid (RA). Recent evidence indicates that loss of RA leads to impaired immunity, whereas excess RA can potentially promote inflammatory disorders. In this review, we discuss recent advances showcasing the crucial contributions of RA to both immunological tolerance and the elicitation of adaptive immune responses. Further, we provide a comprehensive overview of the cell types and factors that control the production of RA and discuss how host perturbations may affect the ability of this metabolite to control tolerance and immunity or to instigate pathology.

Nanoscale domains with nematic order in supercooled vitamin-A acetate: molecular dynamics studies

Vitamin-A acetate is one of the most versatile vitamins. It is applied in medicine because of its antioxidative properties, in tumor therapy because of its cytostatic activity, and in cosmetics because of its nutritional additives. Herein, using broadband dielectric spectroscopy, the molecular dynamics of supercooled and glassy vitamin-A acetate was investigated. It was shown that dielectric measurements carried out at ambient and elevated pressures reveal a number of relaxation processes associated with different types of molecular motions: α, δ, and ν processes-observed above the glass transition temperature and the next two modes: β and γ identified in the glassy state. The occurrence of the δ mode in the dielectric spectrum may imply the existence of nanoscale domains with nematic order. This hypothesis is further checked by atomic force microscopy measurements. Finally, we have determined the value of the glass transition temperature (T(g)) as well as the steepness index (m(P)) at various T-P conditions.

Retinoic acid: a key player in immunity

For the past 100 years, vitamin A has been implicated as an essential dietary component in host resistance to infectious disease. However, only recently have studies begun to elucidate the cellular and molecular mechanisms of how vitamin A regulates cell-mediated and humoral-mediated immunity. In this review, we present an overview of the recent discoveries of the role that vitamin A and its metabolite, retinoic acid (RA), play in the regulation of immune cells. How RA impacts on leukocyte growth, differentiation, and homing is discussed with special attention to inflammatory responses and solid tumor microenvironment.

Immunostimulation by retinoic acid

Retinoids have been shown to inhibit tumour growth in several model systems. In this paper evidence that immune effectors are important for this effect is discussed. Injection of retinoic acid (RA) into mice before challenge with allogeneic or syngeneic tumour cells results in a strong increase in cell-mediated cytotoxicity specific for the respective tumour. This stimulation appears to be due to effects taking place before or during the induction phase rather than the effector phase of cell-mediated cytolysis. The effector cells responsible for cytotoxicity express the Thy 1 antigen, are H-2 specific and are therefore T killer cells. The induction of T cell-mediated cytotoxicity requires the participation of the lymphokine interleukin 2 (IL-2). The possibility was tested that RA directly or indirectly influences the production of IL-2 and thereby stimulates the induction of T killer cells. Results indeed show that RA-injected mice display an increased capacity to produce IL-2 upon stimulation of their splenocytes in a mixed lymphocyte reaction. It appears therefore that RA has an effect on T cells that are destined to produce IL-2 upon antigenic challenge. Since IL-2 plays a role not only in the induction of specific cytotoxic T cells but also in the induction of natural killer (NK) cells, RA was also tested in a model system in which NK cells appear to play an important protective role. Results showed that split-dose irradiated mice that lose their NK activity and subsequently develop leukaemia can be protected from leukaemogenesis either by reconstitution with NK cells or by injection with RA. The question of whether this effect is due to stimulation of immune effectors or is a direct effect on the preleukaemic cells is discussed.

Retinoids regulate survival and antigen presentation by immature dendritic cells

Maturation of dendritic cells (DCs) is a critical step for the induction of an immune response. We have examined the role of retinoid nuclear receptor pathways in this process. Retinoids induce DC apoptosis, in the absence of inflammatory signals, through retinoic acid receptor (RAR)alpha/retinoic X receptor (RXR) heterodimers. In contrast, via a cross talk with inflammatory cytokines, retinoids increase DNA binding activity of nuclear factor kappaB in DCs, trigger membrane major histocompatibility complex class II and costimulatory molecule expression, induce the differentiation of immature DCs into mature DCs, and enhance antigen-specific T cell response. This maturation of DCs is mediated via a RXR-dependent/RAR-independent pathway and via an RARalpha/RXR pathway distinct from the one responsible for apoptosis. Apoptosis and activation, mediated through distinct nuclear retinoid receptor pathways, can be dissociated from each other with selective synthetic retinoids. We identify a novel cellular function for retinoids and suggest that selective retinoids might be of interest for controlling antigen presentation.

Effect of all-trans and 9-cis retinoic acid on growth and metastasis of xenotransplanted canine osteosarcoma cells in athymic mice

OBJECTIVE

To determine effects of all-trans and 9-cis retinoic acid (RA) on tumor growth and metastatic ability of canine osteosarcoma cells transplanted into athymic (nude) mice.

ANIMALS

Forty-five 5-week-old female BALB/c nude mice.

PROCEDURE

1 X 10(7) POS osteosarcoma cells were transplanted subcutaneously into the intrascapular region of mice. All-trans RA (3 or 30 microg/kg of body weight in 0.1 ml of sesame oil), 9-cis RA (3 or 30 mg/kg in 0.1 ml of sesame oil), or sesame oil (0.1 ml; control treatment) were administered intragastrically 5 d/wk for 4 weeks beginning 3 days after transplantation (n = 4 mice/group) or after formation of a palpable tumor (5 mice/group). Tumor weight was estimated weekly by measuring tumor length and width, and retinoid toxic effects were evaluated daily. Two weeks after the final treatment, mice were euthanatized, and number of mice with pulmonary metastases was determined.

RESULTS

Adverse treatment effects were not detected. Tumor weight was less in mice treated with either dose of 9-cis RA than in control mice, although this difference was not significant. Treatment with 30 mg of 9-cis RA/kg initiated after tumor formation significantly reduced the incidence of pulmonary metastasis, compared with the control group.

CONCLUSIONS AND CLINICAL RELEVANCE

9-cis RA decreased the incidence of pulmonary metastasis in nude mice transplanted with canine osteosarcoma cells and may be a potential adjunct therapy for treatment of osteosarcoma in dogs.

Schiff base forming drugs: mechanisms of immune potentiation and therapeutic potential

CD4 T-lymphocytes, which orchestrate immune responses, receive a cognitive signal when clonally distributed receptors are occupied by MHC class II bound peptides on antigen-presenting cells. The latter provide costimulatory or accessory signals through macromolecules such as B7.1 and B7.2 which interact with coreceptors on T-cells to regulate outcomes in terms of T-cell activation or specific non-responsiveness. Complementary studies at the chemical level have implicated Schiff base formation between specialised carbonyls and amines, constitutively expressed on antigen-presenting cell and T-cell surfaces, as an essential element in specific T-cell activation. The small xenobiotic Schiff base forming molecule tucaresol, which substitutes for the physiological donor of carbonyl groups to provide a costimulatory signal to CD4 T-helper lymphocytes (Th-cells), has been developed for testing as an immunopotentiatory drug. Tucaresol, which is orally bioavailable and systemically active, enhances CD4 Th-cell and CD8 cytotoxic T-cell responses in vivo and selectively favours a Th1-type profile of cytokine production. In murine models of virus infection and syngeneic tumour growth it has substantial therapeutic activity. Schiff base formation by tucaresol on T-cell surface amines provides a costimulatory signal to the T-cell through a mechanism that activates clofilium-sensitive K+ and Na+ transport. The signalling pathway utilised by tucaresol converges with T-cell receptor signalling at the level of MAP kinase, promoting the tyrosyl phosphorylation of ERK2 by MEK (mitogen-activated protein kinase kinase). The Schiff base forming class of immunopotentiatory drug provides the first orally active, mechanism-based immunopotentiatory agents for therapeutic testing. Tucaresol is currently undergoing pilot phase I/II clinical trials as an immunopotentiator in chronic hepatitis B virus infection, HIV infection and malignant melanoma.

Antiviral activity of primate gamma delta T lymphocytes isolated by magnetic cell sorting

The exposure of human or rhesus monkey peripheral blood mononuclear cells (PBMCs) to interleukin 2 (IL-2) in vitro resulted in a selective outgrowth of gamma delta lymphocytes. Using positive selection by monoclonal antibodies and magnetic beads, gamma delta T lymphocytes were isolated from these cultures. Without priming by viral antigens, the purified gamma delta T lymphocytes lyse immunodeficiency virus-infected cells substantially better than the uninfected counterparts.

Approaches to the identification and classification of chemical allergens in mice

During the last 10 years understanding of the immunobiological mechanisms whereby chemicals induce allergy has increased significantly. In parallel there have emerged opportunities to develop alternative methods for the prospective identification and classification of chemical contact and respiratory allergens. Attention has focused largely on the mouse, and several novel approaches to the identification of contact allergens have been described, among them the local lymph node assay, the mouse ear swelling test and, most recently, the noninvasive mouse ear swelling assay (MESA). Progress has been made also in defining methods for measuring respiratory sensitization potential in mice. Recent evidence indicates that respiratory and contact allergens provoke qualitatively different immune responses characteristic of selective T helper (Th) cell activation. Evaluation of the nature of immune responses induced in mice by chemicals may permit not only assessment of allergenic potential, but also prediction of the form allergic reactions will take.

Inhibition by retinoic acid of hepatocarcinogenesis induced by N-nitrosomorpholine and of expression of myc oncogene protein in Sprague-Dawley rats

The effects of all-trans-retinoic acid (RA) on hepato-carcinogenesis induced by N-nitrosomorpholine (NNM) and on the expression of myc p110 proteins were investigated in male Sprague-Dawley rats. Rats received i.m. injections of RA twice a week and, from the beginning of the experiment, were given drinking water containing NNM for 8 weeks. Pre-neoplastic and neoplastic lesions staining positively for gamma-glutamyl transpeptidase (GGT), glutathione-S-transferase placental type (GST-P) or myc p110 protein were examined histochemically. At week 18, quantitative histological analysis showed that prolonged administration of RA resulted in a significant reduction in the number, size and volume of GGT-positive and GST-P-positive hepatic lesions. Administration of RA also caused a significant increase in the proportion of myc p110-negative lesions to the total pre-neoplastic lesions observed. Myc p110-negative lesions had a significantly lower mitotic index than myc p110-positive lesions. These findings indicate that RA inhibits hepatocarcinogenesis and suggest that this effect may be related to its influence in reducing the expression of myc gene proteins and its subsequent inhibition of cell proliferation in pre-neoplastic lesions.

Retinoic acid protects Langerhans' cells from the effects of the tumour promotor 12-O-tetradecanoylphorbol 13-acetate

Retinoic acid prevents the decrease in epidermal Langerhans' cell (LC) density which occurs upon application of the tumour promotor 12-O-tetradecanoylphorbol 13-acetate (TPA) to murine skin. This occurred very rapidly, after only 1 week, and was still observed after 4 weeks of treatment. Retinoic acid alone increased the LC density, indicating that it could affect LC density independently of TPA. The induction of a contact sensitivity response which was inhibited by prior treatment with TPA due to the low LC density was also protected by retinoic acid. The anti-carcinogenic activity of retinoic acid is partially the result of its ability to inhibit tumour promotion. The loss of LC may be one of the important steps in tumour promotion as this would allow developing tumours to escape immune destruction. Our studies suggest that the ability of retinoic acid to suppress tumour promotion may be in part by protecting local antigen-presenting cells, thus allowing an immune response to be generated against tumours.

Infection of B lymphocytes by the human immunodeficiency virus and their susceptibility to cytotoxic cells

The T4 molecule (CD4) is an important component of the human immunodeficiency virus (HIV) receptor. As yet, no other component has been demonstrated. We report here that two cell lines, a B lymphoblastoid cell line (Gupta) and a glial cell line (HEB) derived from human embryonal brain tissue, are productively infectable with two distinct isolates of HIV as judged by electron microscopy and immunological and virological studies. These two cell lines do not display detectable surface CD4 glycoprotein. However, using S1 nuclease analysis, we have found that both cell lines do express low levels of CD4 mRNA. Neither of them produced syncytia formation upon HIV infection, a recognized feature of HIV-infected cells strongly expressing the CD4 glycoprotein. It is conceivable that the CD4 mRNA is translated, resulting in meager surface expression of CD4 molecules undetectable by conventional techniques. Therefore, infection with HIV may be one of the most sensitive methods of demonstrating low levels of CD4 expression by human cells. Furthermore, HIV-infected Gupta cells have here been shown to be more susceptible to the lytic activity of natural killer (NK) cells than their uninfected counterparts. These phenomena may be important for pathogenesis of HIV-associated disorders.

Lymphokine-activated killer cell activity in rheumatoid arthritis

The lymphokine-activated killer (LAK) cell activity in the peripheral blood of 23 patients with rheumatoid arthritis has been studied. Two control groups comprised (a) nine patients with another chronic inflammatory disease (sarcoidosis) and (b) 19 normal healthy volunteers. The LAK activity induced by human recombinant IL-2 was very similar in controls and patients with rheumatoid arthritis but was significantly decreased in patients with sarcoidosis, although the frequency of LAK-cell precursors measured using a limiting dilution assay was comparable in all three groups. The DNA synthetic response of peripheral blood mononuclear (PBM) cells to IL-2 was slightly decreased in patients with both rheumatoid arthritis and sarcoidosis as compared to controls, but this decrease was not statistically significant. Spontaneous DNA synthesis in PBM cells cultured in the absence of IL-2 was essentially identical in all three groups. We conclude on the basis of these results that the higher risk of non-Hodgkin's lymphomas in patients with rheumatoid arthritis cannot be attributed to an impairment of LAK activity. Furthermore, the doses of gamma-irradiation, which abolished the 'background' cytotoxicity of PBM cells cultured without IL-2 and also blocked effectively both spontaneous and exogenous IL-2-dependent DNA synthesis, had little effect on the generation of LAK activity. These observations are discussed in regard to the role of non-specific cytotoxic cells and the therapeutic efficacy of antiproliferative drugs in rheumatoid arthritis.

Generation of lymphokine-activated killer cells does not require DNA synthesis

We studied the role of DNA synthesis in the induction of lymphokine-activated killer (LAK) cells by recombinant interleukin-2 (IL-2) and the dependence of this phenomenon on DNA synthesis. Doses of gamma-irradiation (1000-5000 rads) that profoundly reduced DNA synthesis in human peripheral blood mononuclear leucocytes (PBL) also effectively suppressed the development of cytotoxic activity in the absence of IL-2. However, the same doses of irradiation affected the induction of LAK activity by IL-2 to a much lesser extent. Blocking the formation of deoxyribonucleotides by hydroxyurea, which resulted in a complete inhibition of DNA synthesis in PBL or purified T lymphocytes, had virtually no effect on the generation of LAK cells. These results indicate that the expression of LAK activity is not dependent on DNA synthesis.

Recombinant interleukin-2 directly augments the cytotoxicity of human monocytes

Interleukin-2 (IL-2), originally described as a growth factor required for sustained proliferation of T cells in vitro is a glycoprotein hormone of known structure which appears to be important for the generation of immune responses in vivo. As well as T lymphocytes, B lymphocytes and large granular lymphocytes with natural killer activity (NK cells) can also respond to IL-2. The action of IL-2 seemed to be limited specifically to lymphocytes, however, and the term 'T-lymphocytotrophic hormone' was used. Here we provide evidence that human monocytes display a substantially increased cytotoxic activity as a direct and rapid response to human recombinant IL-2 but not to human recombinant glycosylated interferon-gamma (IFN-gamma) or lipopolysaccharide. Our results reveal a previously unknown function of IL-2 and suggest its possible involvement in monocyte-T cell interactions.

Effects of orally administered retinol on natural killer cell activity in wild type BALB/c and congenitally athymic BALB/c mice

Retinoids have been shown to inhibit the growth and development of neoplastic cells in many systems. One mechanism of action may be through activation of the immune system, specifically natural killer (NK) cell activity. The effect of retinol on NK cell cytotoxicity was examined in three groups of mice: BALB/c (wild-type), BALB/c nu/nu (athymic), and BALB/c nu/nu previously injected with human tumor cells. In untreated mice, NK activity was highest in athymic mice without tumors and lowest in wild-type mice, although serum and liver retinol concentrations were identical in all three groups. In mice fed graded, nontoxic doses of retinol daily for 3 weeks, serum retinol levels in all three groups exhibited a sharp peak and decline following daily bolus retinol administration. Retinol stores in the livers showed a dose-dependent increase in all treated animals. However, NK cell activity, differed for each group. Athymic mice without tumors exhibited no change in NK activity as a result of retinol treatment. Athymic mice with tumors had NK levels that tended to increase with increasing retinol doses, but these changes were not statistically significant. Wild-type mice, on the other hand, demonstrated significantly higher NK levels after treatment with retinol doses of 300 and 600 micrograms/day. In subsequent time course experiments, there was a peak in NK activity 1 h following bolus retinol administration similar to the peak seen in serum retinol concentrations, suggesting either an acute activation or recruitment of cytotoxic cells. Retinol thus appears to increase NK activity in wild-type BALB/c mice, and this activity may be an important component of its antineoplastic activity.

Influence of dendritic cells on tumor growth

Dendritic cells (DC) exposed to antigen are potent initiators of immune responses, and the numbers of DC and the dose of antigen control the level of response. The influence of these variables was tested on the growth of mouse sarcoma cells in vivo. When normal syngeneic DC (100,000) were given to mice with palpable tumors, tumor regression or delay in tumor growth was obtained. DC exposed to increasing doses of tumor extract in vitro before administration had progressively less effect. DC exposed to antigen delayed tumor growth significantly only when given on the same day as 500 tumor cells. The studies suggested that low doses of antigen on DC elicit immune responses and that high doses block them. The numbers of antigen-presenting cells and the dose of antigen modulate the degree of immunity to mouse sarcoma in vivo.

Augmentation of interleukin-2 production and delayed hypersensitivity in mice infected with Mycobacterium bovis and fed a diet supplemented with vitamin A acetate

High-dose Mycobacterium bovis-infected mice fed a vitamin A acetate-supplemented diet developed a positive skin reaction to purified protein derivative of mycobacteria, and their spleen cells showed an increased IL-2 production in vitro.

Acquired immunological tolerance of foreign cells is impaired by recombinant interleukin 2 or vitamin A acetate

The susceptibility of newborn mice to the inception of tolerance after exposure to antigen is associated with their deficiency in the production of endogenous interleukin 2 (IL-2). As further evidence of the complicity of IL-2 in the inception and maintenance of tolerance, it is shown here that a solid and long-lasting state of tolerance induced by the intravenous injection into newborn CBA mice of lymphoid cells from (CBA X C57BL/10ScSn)F1 hybrids can be brought to an end by the administration of exogenous IL-2 or by supplementing an otherwise normal diet with vitamin A acetate, the effect of which is to increase the proportion of the moiety of the T-cell population that produces IL-2. These results indicate that certain nonspecific stimuli can influence whether immunological tolerance is maintained.

A diet enriched in vitamin A acetate or in vivo administration of interleukin-2 can counteract a tolerogenic stimulus

A conventional diet enriched in retinyl acetate (vitamin A acetate; VAA) or in vivo administration of exogenous interleukin-2 (IL-2) can effectively annul the otherwise tolerogenic stimulus represented by (CBA X C57BL/10ScSn) F1 cells injected intraperitoneally into newborn CBA mice. On the basis of these data and results of others, we postulate that an antigenic stimulus associated with a relative lack of IL-2 (or generally the lack of a 'secondary stimulus') can be tolerogenic rather than immunogenic. However, the tolerogenicity of the antigenic stimulus can be substantially reduced or even converted to sensitization (R. P. Cleveland & H. N. Claman, J. Immun. 124, 474-480, 1980), when the antigenic signal is appropriately associated with a concomitant or additional stimulus possibly mediated through IL-2.