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Biomedical subjects

D Melamed

Publications and source records attributed to D Melamed.

29 records · Page 2Linked to original sources
PubMed1994

Retinoic acid receptor-alpha gene expression is modulated by dietary vitamin A and by retinoic acid in chicken T lymphocytes.

The effects of dietary vitamin A and retinoic acid in vitro on the proliferative response and gene expression of retinoic acid receptor-alpha (RAR-alpha) in chicken T lymphocytes were studied. Antigen-specific proliferative responses of T lymphocytes increased with dietary vitamin A intake from 0 to 6.6 mg/kg diet; however, at high dietary vitamin A (13.2 mg/kg diet), the proliferative response declined. RAR-alpha mRNA expression in T lymphocytes peaked in chicks fed low levels of vitamin A (830 and 1500 micrograms/kg diet) and declined at higher intakes. In vitro effects of retinoic acid on the modulation of RAR-alpha mRNA were studied in stimulated T lymphocytes. Retinoic acid (0.01 mumol/L) increased RAR-alpha mRNA levels within 2 or 16 h of incubation with concanavalin A- or beta-casein-stimulated T cells, respectively. This effect was transient. Expression of RAR-alpha mRNA in concanavalin A-stimulated T lymphocytes was up-regulated by retinoic acid in a dose-dependent manner, and maximal expression occurred in response to 1 mumol/L retinoic acid. The proliferative response of these cells was also modulated by retinoic acid in a dose-dependent manner, and highest effects were observed at 0.01 mumol/L retinoic acid. Our results indicate that RAR-alpha mRNA expression and antigen-specific proliferative responses of T lymphocytes are influenced by vitamin A status in vivo, and directly modulated by retinoic acid.

Administration, Oral↗
PubMed1994

The effect of varying levels of dietary vitamin A on immune response in the chick.

The effect of dietary vitamin A on antibody production and T cell proliferative response was determined in broilers from 21 to 39 d old. Chicks were fed soybean meal-sorghum diets with levels of supplemented vitamin A from 0 to 13,200 micrograms/kg retinol equivalents from hatching and were immunized with beta-casein at 21 d of age. T cell proliferation response to beta-casein or an acetone precipitate of antigen to Mycobacterium tuberculosis was determined in vitro at 34 to 37 d old. Antibodies to beta-casein in serum were determined every 5 d from 21 d of age. In chicks with no added dietary vitamin A, antibody production and proliferative response were depressed in comparison with chicks receiving vitamin A. Addition of small amounts of vitamin A enhanced the responses; both antibody production and proliferative responses increased with dietary vitamin A until the diet contained 6,660 micrograms/kg, above which the responses decreased. This suggests that maximal immune responses in the chick may be achieved at dietary intakes considerably higher than NRC recommendations.

Animal Feed↗
PubMed1993

Direct evidence for anergy in T lymphocytes tolerized by oral administration of ovalbumin.

The present study investigated bystander suppression, specific suppression and anergy as mechanisms for oral tolerance. Oral tolerance was induced in mice by a single gastric intubation of 20 mg ovalbumin (OVA) and was evaluated in vitro by the absence of T lymphocyte proliferative responses to OVA after priming by OVA-complete Freund's adjuvant (CFA). T lymphocyte unresponsiveness was antigen specific, systemic and was not affected by the vehicle used for immunization. T lymphocytes derived from tolerant popliteal lymph nodes (PLN) responded to an acetone precipitate (AP) of mycobacteria present in CFA; this response was not suppressed by co-culture with OVA, thereby arguing against a mechanism of bystander suppression in our system. Responses of PLN T lymphocytes derived from OVA-CFA primed, non-tolerant mice, or those of an OVA-specific T lymphocyte line, were not suppressed by PLN or spleen cells derived from OVA tolerant mice. These results excluded the possibility that oral tolerance was induced and maintained by a mechanism of specific suppression. At the cellular level, we found that OVA-tolerant T lymphocytes did not produce interleukin-2 (IL-2) nor express IL-2 receptor in response to OVA stimulation in vitro; both observations are indicative of a state of anergy. Incubation of OVA-tolerant PLN T lymphocytes together with murine recombinant IL-2 for 5 days, released anergic T lymphocytes and a concomitant OVA-specific proliferative response of CD4+ T cells was detected. Taken together, our experimental system excludes the involvement of bystander or specific suppression in the induction of oral tolerance to OVA, and provides direct evidence to show that oral tolerance results from specific T lymphocyte anergy.

Administration, Oral↗
PubMed1993

Modification of the immune response by oral tolerance: antigen requirements and interaction with immunogenic stimuli.

The present study was undertaken to define requirements for antigen in induction and maintenance of oral tolerance and to evaluate the interrelationship between simultaneously administered oral tolerogenic and parenteral immunogenic stimuli. Tolerance was induced by a single gastric intubation of OVA and was assessed by absence of OVA-specific T lymphocyte proliferation in vitro. Tolerance was short termed and held for 21 days in the absence of additional antigen; alternatively, antigen persistence enabled prolonged maintenance of tolerance. Since tolerogenic and immunogenic stimuli reflect two distinct pathways of the immune system, we investigated the consequences of their simultaneous administration. When tolerogenic stimuli preceded immunogenic stimuli up to a minimal period of 24 hr, unresponsiveness dominated. Furthermore, tolerogenic stimuli were able to reduce the level of T lymphocyte proliferation when administered at the time of, and after, immunization. The degree of reduction was inversely related to the interval between parenteral immunization and gastric intubation. Repeated tolerogenic stimuli caused a further substantial reduction in residual T lymphocyte responses. These findings indicate that prevalence of tolerance in the immune response requires rapid dissemination and long term persistence of antigen.

Administration, Oral↗
PubMed1993

Interferons and interleukin-6 suppress the DNA-binding activity of E2F in growth-sensitive hematopoietic cells.

Transcription factor E2F binds to cellular promoters of certain growth- and cell cycle-controlling genes and forms distinct heteromeric complexes with other nuclear proteins. We show here that alpha and beta interferons (alpha, beta) and interleukin-6 abolished the E2F-containing DNA-binding complexes in Daudi Burkitt lymphoma cells and in M1 myeloblastic cells, which responded to the cytokines by suppression of c-myc transcription. Time kinetics studies showed that the abolishment of E2F complexes coincided with reduction of c-myc expression and that both molecular events preceded the cell cycle block in G0/G1 phase. In contrast, the pattern of E2F complexes remained unchanged in an interferon-treated growth-resistant Daudi cell mutant that displayed relaxed regulation of c-myc. All of the DNA-binding E2F complexes, including those containing the retinoblastoma protein (pRB), cyclin A-p33cdk2, and the free forms of E2F, were reduced by interferons or interleukin-6. Their abolishment was unperturbed by pharmacological treatments that alleviated the cyclin A and pRB responses to interferon. Thus, changes in cyclin A expression and pRB phosphorylation are not primary events that influence the pattern of E2F responses to cytokines. Addition of EDTA to cell extracts of interferon-treated Daudi cells restored the DNA-binding activity of E2F, resulting in the appearance of a single E2F complex that exclusively contained pRB. It is suggested that the regulation of E2F by growth-inhibitory cytokines that induce cell cycle exit takes place at the level of the DNA-binding activity, and by that mean it differs basically from the phase-specific regulation of E2F in cycling cells.

Base Sequence↗
PubMed1993

Interleukin 6 induces DNA binding activity of AP1 in M1 myeloblastic cells but not in a growth resistant cell derivative.

The effects that three different growth inhibitory cytokines exert on expression and function of members of the Jun family were studied in this work. M1 myeloblastic cells were chosen for this purpose because of their high growth sensitivity to interleukin 6 (IL-6), transforming growth factor beta 1 and alpha- and beta-interferons. It is reported here that IL-6 elevated the junB and c-jun mRNA levels and induced the formation of a novel DNA-protein complex with high sequence specificity to 12-O-tetradecanoylphorbol-13-acetate response element (TRE) oligonucleotides. This IL-6 induced TRE binding complex was abolished by anti-Jun specific antibodies and was efficiently competed by an oligonucleotide that comprises the mouse homologue of a previously described human c-myc negative DNA element. It persisted in cells for at least 48 h after IL-6 treatment and failed to be induced by alpha- and beta-interferons or by transforming growth factor beta 1, which affected differently the pattern of jun mRNA expression. To further explore regulatory and functional aspects of this induced TRE binding activity, an IL-6 resistant M1 clone was isolated and further analyzed. This clone carried a postreceptor deficiency that abrogated completely the growth inhibitory responses to IL-6 but did not interfere with the induction of two differentiation related cell surface markers. Interestingly, the IL-6 resistant clone had lost two molecular responses to IL-6, induction of TRE binding activity and suppression of the c-myc gene. The data correlate the IL-6 induced AP1 activity with the suppression of c-myc and growth inhibition.

Animals↗
PubMedDate not supplied

A vaccine against avian colibacillosis based on ultrasonic inactivation of Escherichia coli.

Ultrasonic inactivation of Escherichia coli followed by irradiation was found to be the most efficient method for preparation of an effective vaccine against colibacillosis. Challenge experiments revealed that this vaccine provided the best protection compared with other methods of inactivation: heat, formaldehyde, and irradiation. Preparing the ultrasonicated vaccine from O2:K1 strain increased its range and also supported adequate protection against homologous strain O78:K80. The degree of protection conferred by the vaccine was positively correlated with the antibody titer against E. coli as measured on day of challenge. Low antibody titers detected 5 days post-vaccination resulted in only 20% protection. High antibody titers detected at 8 and 15 days post-vaccination correlated with a low number of chicks with lesions. In each challenged group, the live chicks that did not develop lesions had higher antibody titers than chicks with lesions, revealing a correlation between numbers of chicks with lesions and antibody titers as measured by enzyme-linked immunosorbent assay.

Animals↗
PubMedDate not supplied

An enzyme-linked immunosorbent assay for detection of antibodies against Escherichia coli: association between indirect hemagglutination test and survival.

An enzyme-linked immunosorbent assay (ELISA) was modified for detection of antibodies against the two main pathogenic serotypes of Escherichia coli: serotypes O78:K80 and O2:K1. The ELISA was a more sensitive and repeatable test than the indirect hemagglutination test (IHT), which is a common method for detecting antibodies against E. coli. Cross-reactivity between the two strains was measured by reacting antisera of each serotype against homologous and heterologous antigens. The results suggest that aside from similar determinants expressed by the two serotypes, serotype O2:K1 expresses more strain-specific determinants than does O78:K80. Comparison of mean antibody titers of immunized chicks by IHT and ELISA along the primary response revealed that during the first 15 days after immunization with inactivated E. coli, the titers in both tests were parallel. After 15 days post-immunization, antibody titers measured by IHT decreased rapidly, whereas titers measured by ELISA decreased only slightly. In addition, a higher correlation was found between titers detected by ELISA and survival through challenge with E. coli than between titers detected with IHT and survival through challenge. The results suggest that the ELISA is a better test for detection of antibody in flocks suspected of being infected with E. coli.

Animals↗