Integrity of the interface between denture base and soft liner: a scanning electron microscopic study

Aims and objectives of the study was to study the integrity of the interface between the denture base and the soft liner when the thickness of the soft liner was 0.5, 1.0 and 2.0 mm, and to study the integrity of the soft liner and denture base interface as influenced by aging process. 80 rectangular based specimens were fabricated using heat cured acrylic resin. The heat cured component of the specimen was fabricated from stainless steel template form by compression molding technique. Different thickness of silicone soft layer component was added to heat cured acrylic resin component of the specimen following the manufacturer's instructions to fabricate the group A, group B, group C and group D specimens. All the specimens were subjected to the same finishing and polishing procedures. The group A specimens was immediately scanned in scanning electron microscope after processing. A thermo statically controlled artificial saliva bath designed to maintain the temperature between 38 ± 4°C was used to simulate the oral condition and to age the group B, group C and group D specimens for 3 months after which they were subjected to scanning under a scanning electron microscope. All the aged specimens demonstrated two types of failures namely adhesive which occurred along the bond interface between the soft liner and the acrylic resin and adhesive and cohesive type of failure which occurred not only at the interface but also within the soft liner material itself. When the data was subjected to ANOVA, the group A specimens showed statistical significance with group B (P = 0.006), group C (P = 0.007) and group D specimens (P = 0.004), the level of significance being (P < 0.05). However, there was no statistical significance between group B and C (P = 0.98), group C and D specimens (P = 0.52), group B and D specimens (P = 0.70), the level of significance being (P < 0.05). Based on the results, statistical analysis of the results and within the limitations of this in vitro study the following conclusions can be drawn: The thickness of the liner did not show a statistically significant rate of failure on the integrity of the interface between the denture base resin and the soft liner and aging conditions simulating the clinical environment showed a statistically significant rate of failure on the integrity of the interface between the denture base resin and the soft liner.

CD4 T cell anergy in murine AIDS: costimulation via CD28 and the addition of IL-12 are not sufficient to rescue anergic CD4 T cells

Murine acquired immunodeficiency syndrome (MAIDS) is a fatal disease induced by a mixture of retroviruses known as BM5. It is characterized by splenomegaly, lymphadenopathy, hypergammaglobulinemia, loss of T and B cell function, and development of B cell lymphomas. As the disease progresses, by wk 8 of infection, CD4 T cell response to Ags and mitogens is severely curtailed and the CD4 T cell population becomes anergic. We examined responses of anergic CD4 T cells upon addition of a costimulatory signal (anti-CD28) and a cytokine (IL-12), which might help to restore the function of cells. We report that proliferation and cytokine production were restored in the early stages of infection by the strategies we tested, but not at later stages when anergy was well established. We also examined the effect of the same treatments on anergy of CD4 T cells from thymectomized, BM5-infected mice to determine whether the rescue seen was due to cells freshly derived from the thymus. We report that proliferation and cytokine production decreased in thymectomized mice even at wk 4 of infection, indicating that cells that are freshly derived from thymus are the ones responding to treatment. This study indicates that once anergy has been established in MAIDS, it cannot be reversed by providing costimulation via CD28 and IL-12. Anergy of CD4 T cells in MAIDS appears to be different from that seen in other systems, both in underlying cause and in the ability of the cells to revert to a normal state.

CD4 T cell anergy in murine AIDS: costimulation via CD28 and the addition of IL-12 are not sufficient to rescue anergic CD4 T cells

Murine acquired immunodeficiency syndrome (MAIDS) is a fatal disease induced by a mixture of retroviruses known as BM5. It is characterized by splenomegaly, lymphadenopathy, hypergammaglobulinemia, loss of T and B cell function, and development of B cell lymphomas. As the disease progresses, by wk 8 of infection, CD4 T cell response to Ags and mitogens is severely curtailed and the CD4 T cell population becomes anergic. We examined responses of anergic CD4 T cells upon addition of a costimulatory signal (anti-CD28) and a cytokine (IL-12), which might help to restore the function of cells. We report that proliferation and cytokine production were restored in the early stages of infection by the strategies we tested, but not at later stages when anergy was well established. We also examined the effect of the same treatments on anergy of CD4 T cells from thymectomized, BM5-infected mice to determine whether the rescue seen was due to cells freshly derived from the thymus. We report that proliferation and cytokine production decreased in thymectomized mice even at wk 4 of infection, indicating that cells that are freshly derived from thymus are the ones responding to treatment. This study indicates that once anergy has been established in MAIDS, it cannot be reversed by providing costimulation via CD28 and IL-12. Anergy of CD4 T cells in MAIDS appears to be different from that seen in other systems, both in underlying cause and in the ability of the cells to revert to a normal state.

TCR triggering of anergic CD4 T cells in murine AIDS induces apoptosis rather than cytokine synthesis and proliferation

Murine AIDS (MAIDS) induced by infection of C57BL/6 mice with a mixture of retroviruses known as LP-BM5 is characterized by lymphadenopathy, splenomegaly, and T and B cell dysfunction. By labeling with bromodeoxyuridine in vivo, we found vigorous CD4 T cell proliferation during the initial stages of infection, yet a loss in their ability to function both in vivo and in vitro. In addition, a significant fraction of the CD4 T cell population in infected mice undergoes spontaneous apoptosis in vivo. Upon in vitro stimulation with anti-CD3 plus PMA, anergic CD4 T cells from mice with MAIDS fail to progress through the cell cycle (G0/G1 arrest), and a fraction of the cells undergoes apoptosis. The addition of IL-2 along with TCR-mediated stimulation not only fails to rescue CD4 T cells from apoptosis, but enhances activation-induced cell death. To further understand the regulation of the suicide pathway(s) of anergic CD4 T cells vs the cytokine synthesis pathway(s) of normal CD4 T cells, we evaluated their expression of Bcl-2 protein. As infection progresses, the expression of Bcl-2 among CD4 T cells declines and drops further when CD4 T cells are restimulated through the TCR in vitro. These results suggest that this CD4 T cell immunodeficiency in MAIDS includes a TCR-induced program of activation-induced cell death and an uncoupling from cytokine synthesis pathways and proliferation of CD4 T cells. The decline in Bcl-2 expression may be in part responsible for this reprogramming.

TCR triggering of anergic CD4 T cells in murine AIDS induces apoptosis rather than cytokine synthesis and proliferation

Murine AIDS (MAIDS) induced by infection of C57BL/6 mice with a mixture of retroviruses known as LP-BM5 is characterized by lymphadenopathy, splenomegaly, and T and B cell dysfunction. By labeling with bromodeoxyuridine in vivo, we found vigorous CD4 T cell proliferation during the initial stages of infection, yet a loss in their ability to function both in vivo and in vitro. In addition, a significant fraction of the CD4 T cell population in infected mice undergoes spontaneous apoptosis in vivo. Upon in vitro stimulation with anti-CD3 plus PMA, anergic CD4 T cells from mice with MAIDS fail to progress through the cell cycle (G0/G1 arrest), and a fraction of the cells undergoes apoptosis. The addition of IL-2 along with TCR-mediated stimulation not only fails to rescue CD4 T cells from apoptosis, but enhances activation-induced cell death. To further understand the regulation of the suicide pathway(s) of anergic CD4 T cells vs the cytokine synthesis pathway(s) of normal CD4 T cells, we evaluated their expression of Bcl-2 protein. As infection progresses, the expression of Bcl-2 among CD4 T cells declines and drops further when CD4 T cells are restimulated through the TCR in vitro. These results suggest that this CD4 T cell immunodeficiency in MAIDS includes a TCR-induced program of activation-induced cell death and an uncoupling from cytokine synthesis pathways and proliferation of CD4 T cells. The decline in Bcl-2 expression may be in part responsible for this reprogramming.

Both naive and memory CD4 T cell subsets become anergic during MAIDS and each subset can sustain disease

Infection of C57BL/6 mice with the LP-BM5 mixture of retroviruses causes a severe murine acquired immunodeficiency syndrome (MAIDS). After infection, the entire CD4 T cell population shifts to a memory/activated phenotype and the CD4 cells become anergic to further stimulation. This drastic shift in phenotype could result either from a response of naive cells to the virus or its products and/or from the selective expansion of cells already having a memory phenotype. We have investigated whether both naive and memory CD4 T cells can be anergized during BM5 infection and whether each subset is sufficient for disease development. We show that V beta 3/V alpha 11 TCR transgenic mice that have > 98% CD4 T cells with naive phenotype develop MAIDS. Their spleens and lymph nodes become enlarged, their CD4 population expressing the TCR transgene shifts to a memory/activated phenotype, and the CD4 cells neither proliferate nor secrete IL-2 in response to specific Ag, a fragment of pigeon cytochrome C, or to mitogens. Adult thymectomized mice, having memory but not naive CD4 T cells, also developed MAIDS and anergy of the CD4 T cell population at a rate and extent comparable to normal control mice. Furthermore, CD4 T cells from mice primed with keyhole limpet hemocyanin 6 wk before infection with BM5 also became unresponsive to KLH during MAIDS. Thus, both naive and memory CD4 T cells are rendered anergic by the BM5 virus infection and it is likely that each subset is sufficient to sustain the development of MAIDS.

Both naive and memory CD4 T cell subsets become anergic during MAIDS and each subset can sustain disease

Infection of C57BL/6 mice with the LP-BM5 mixture of retroviruses causes a severe murine acquired immunodeficiency syndrome (MAIDS). After infection, the entire CD4 T cell population shifts to a memory/activated phenotype and the CD4 cells become anergic to further stimulation. This drastic shift in phenotype could result either from a response of naive cells to the virus or its products and/or from the selective expansion of cells already having a memory phenotype. We have investigated whether both naive and memory CD4 T cells can be anergized during BM5 infection and whether each subset is sufficient for disease development. We show that V beta 3/V alpha 11 TCR transgenic mice that have &gt; 98% CD4 T cells with naive phenotype develop MAIDS. Their spleens and lymph nodes become enlarged, their CD4 population expressing the TCR transgene shifts to a memory/activated phenotype, and the CD4 cells neither proliferate nor secrete IL-2 in response to specific Ag, a fragment of pigeon cytochrome C, or to mitogens. Adult thymectomized mice, having memory but not naive CD4 T cells, also developed MAIDS and anergy of the CD4 T cell population at a rate and extent comparable to normal control mice. Furthermore, CD4 T cells from mice primed with keyhole limpet hemocyanin 6 wk before infection with BM5 also became unresponsive to KLH during MAIDS. Thus, both naive and memory CD4 T cells are rendered anergic by the BM5 virus infection and it is likely that each subset is sufficient to sustain the development of MAIDS.

Restricted IgH V gene usage in the response to the ese epitope on "Hi" sheep red blood cells

We had previously shown that the in vitro antibody response to a single epitope (ese; extra sheep E Ag) present on some sheep E but absent from others could be monitored by assay of the plaque-forming cell response on both Lo3 and Hi SRBC. We had shown also that the response was seen only in certain strains of mice and that the gene(s) controlling the response mapped to the IgH V region of the IgH chain complex. An additional feature of the response is that it is only seen in vitro and is absent and, we hypothesize, is suppressed in vivo. The strain distribution of the response to the ese determinant suggested that the response may only use one V gene (or a small set of closely related V genes) that would be present in the responder strains and absent from the nonresponder strains. To test this hypothesis, we made hybridomas with specificity for the ese determinant and for the shared determinants. cDNA from these hybridomas were sequenced. All four anti-ese hybridomas were almost identical in V region sequence, but varied considerably in D and J segment usage, thus confirming the hypothesis that the ese response would be limited at the V segment. The four anti-ese hybridomas used two Vh J558 genes that differed only by one, or possibly two, nucleotide(s). Importantly, these genes are quite different from most other published J558 sequences. The sequence is very similar to an unexpressed sequence from a C57Bl/6 perinatal mouse and slightly less similar to two other Vhb sequences. It was quite similar to two sequences from autoantibodies, one an anti-DNA hybridoma antibody, BXW-14, isolated from an NZB x NZWF1 mouse, and the other, an NZB hybridoma, G8, with specificity for a mouse E Ag. We speculate that the Ig encoded by the V ese gene react with an autoantigen, that the B cells persist in the animal, but that the secretion of Ig is somehow suppressed.

Restricted IgH V gene usage in the response to the ese epitope on "Hi" sheep red blood cells

We had previously shown that the in vitro antibody response to a single epitope (ese; extra sheep E Ag) present on some sheep E but absent from others could be monitored by assay of the plaque-forming cell response on both Lo3 and Hi SRBC. We had shown also that the response was seen only in certain strains of mice and that the gene(s) controlling the response mapped to the IgH V region of the IgH chain complex. An additional feature of the response is that it is only seen in vitro and is absent and, we hypothesize, is suppressed in vivo. The strain distribution of the response to the ese determinant suggested that the response may only use one V gene (or a small set of closely related V genes) that would be present in the responder strains and absent from the nonresponder strains. To test this hypothesis, we made hybridomas with specificity for the ese determinant and for the shared determinants. cDNA from these hybridomas were sequenced. All four anti-ese hybridomas were almost identical in V region sequence, but varied considerably in D and J segment usage, thus confirming the hypothesis that the ese response would be limited at the V segment. The four anti-ese hybridomas used two Vh J558 genes that differed only by one, or possibly two, nucleotide(s). Importantly, these genes are quite different from most other published J558 sequences. The sequence is very similar to an unexpressed sequence from a C57Bl/6 perinatal mouse and slightly less similar to two other Vhb sequences. It was quite similar to two sequences from autoantibodies, one an anti-DNA hybridoma antibody, BXW-14, isolated from an NZB x NZWF1 mouse, and the other, an NZB hybridoma, G8, with specificity for a mouse E Ag. We speculate that the Ig encoded by the V ese gene react with an autoantigen, that the B cells persist in the animal, but that the secretion of Ig is somehow suppressed.

CD4 T cells in murine acquired immunodeficiency syndrome: polyclonal progression to anergy

We have examined the kinetics of changes that occur in the helper T cell subset during murine acquired immunodeficiency syndrome, which occurs after infection with the mix of viruses known as BM5. We find that there is expansion of the CD4 T cells by 2 wk, 50% of the CD4 T cells become large as the disease progresses, and the CD4 T cell population is increasingly comprised of cells with a memory/activated phenotype. These effects are apparent by 2 wk postinfection, and the change is nearly complete by 6-8 wk. The phenotypic shift is paralleled by the loss of the ability of the CD4 T cells to proliferate or to produce interleukin 2 (IL-2), IL-3, IL-4, and interferon gamma in response to stimulation with mitogens, superantigen, or anti-CD3. There is no obvious expansion or deletion of CD4 T cells expressing particular V beta genes, as might be expected if a conventional superantigen were driving the changes. The results suggest, however, that the total CD4 population has been driven to anergy by some potent polyclonal stimulus directly associated with viral infection.

Frequency and organization of papA homologous DNA sequences among uropathogenic digalactoside-binding Escherichia coli strains

The frequency of selected papA DNA sequences among 89 digalactoside-binding, uropathogenic Escherichia coli strains was evaluated with 12 different synthetic 15-base probes corresponding to papA genes from four digalactoside-binding piliated recombinant strains (HU849, 201B, and 200A). The papA probes encode amino acids which are common at the carboxy terminus of all strains, adjacent to the proximal portion of the intramolecular disulfide loop of strain 210B, or predicted to constitute the type-specific epitope for each of the four recombinant strains or other epitopes of strain HU849. The presence among the strains of DNA sequence homology to the papA probes was determined by in situ colony hybridization. Hybridization data suggest that there is a high frequency of homologous papA DNA sequences corresponding to selected regions of the papA gene from strain HU849 among the clinical strains. The following nucleotide locations which encode portions of the mature HU849 PapA are detected in a high percentage (42 to 70%) of clinical isolates: 208 to 222, 310 to 324, 478 to 492, 517 to 531, 553 to 567, and 679 to 693. These sequences encode portions of the predicted protective, immunogenic, and/or antigenic epitopes of this PapA. The data also indicate considerable heterogeneity of papA sequences among the strains, especially in the region of nucleotide bases corresponding to positions 391 to 418. These oligonucleotides encode the predicted PapA type-specific immunogenic dominant epitope. Determination of the extent of genetic variability in the papA gene among digalactoside-binding strains will require more extensive DNA sequencing of prototypic papA genes, additional hybridization studies employing other papA gene oligonucleotide probes, and assessment of the different pap operons and their copy number in each strain.

Altered queuine modification of transfer RNA involved in the in vitro transformation of Chinese hamster embryo cells

Altered queuine modification of tRNA has been correlated to neoplastic transformation, but no direct cause and effect relationship has been defined. In the present study, a potential role for this alteration has been assigned. The tRNA in normal Chinese hamster embryo cells is significantly more queuine modified than the tRNA in their transformed Chinese hamster embryo counterparts, even though the specific activity of the queuine modification enzyme is much lower in Chinese hamster embryo cells than in transformed Chinese hamster embryo cells. Substrate availability appears to be responsible for the queuine hypomodification of tRNA in the transformed cells, since addition of excess exogenous queuine to the culture medium results in incorporation of queuine into the anti-codon of the undermodified tRNAs. Most importantly, the excess queuine inhibits anchorage-independent growth of transformed Chinese hamster embryo cells, thereby implicating queuine hypomodification of tRNA in the expression of this transformed phenotype.

Identifying inhibitors of queuine modification of tRNA in cultured cells

Altered queuine modification of tRNA has been associated with cellular development, differentiation, and neoplastic transformation. Present methods of evaluating agents for their ability to induce queuine hypomodification of tRNA are tedious, time-consuming, and not readily amenable to examining cell-type or tissue specificity. Therefore, a rapid, small-scale assay was developed to identify agents that alter queuine modification of tRNA in cultured cells. Monolayer cultures (2cm2) of Chinese hamster embryo cells depleted of queuine for 24 h were evaluated for their ability to incorporate [3H]dihydroqueuine into acid precipitable material (tRNA) in the presence and absence of potential inhibitors. Known inhibitors of the queuine modification enzyme tRNA-guanine ribosyltransferase (e.g., 7-methylguanine, 6-thio-guanine, and 8-azaguanine) were very effective in blocking incorporation of the radiolabel, and the dose-dependent results exhibited small standard deviations in independent experiments. The data indicate that the method is rapid, reliable, and potentially useful with a variety of cell types.

Enhancement of the chemical transformation of Chinese hamster embryo cells in vitro by 7-methylguanine

The RNA catabolite 7-methylguanine has been shown to inhibit queuine modification of tRNA in Chinese hamster embryo cells under conditions leading to in vitro transformation. Phorbol ester tumor promoters also induce queuine hypomodification of tRNA in normal human cells, and this effect was reported to be correlated directly to the appearance of an altered (transformed) cell phenotype. Based on this common macromolecular alteration, 7-methylguanine was evaluated for its ability to enhance the chemically induced transformation of cultured cells. Two-stage initiation-promotion experiments were undertaken with Chinese hamster embryo cells in vitro to compare the effects of 7-methylguanine to known tumor promoters subsequent to initiation with 3-methylcholanthrene. 7-Methylguanine was able to increase significantly the expression of type III foci as well as anchorage-independent growth, thereby confirming that it can act as a promoting agent in vitro. Methylated guanines that do not induce queuine hypomodification of tRNA were not capable of enhancing these characteristics of in vitro transformation. The results suggest that 7-methylguanine may be a natural, endogenous promoting agent, and that changes in queuine modification of tRNA may play a fundamental role in the promotion of carcinogenesis.

Hematopoiesis and the inosine modification in transfer RNA

Human promyelocytic leukemia (HL-60) cells were used to begin to evaluate the role in hematopoiesis of inosine biosynthesis in the tRNA anticodon wobble position; a reaction involving the enzymatic insertion of performed hypoxanthine. Dimethyl sulfoxide (DMSO) and hypoxanthine were found to induce the differentiation of HL-60 cells in a synergistic manner, and the induced differentiation was independent of changes in the purine catabolic enzymes adenosine deaminase and purine nucleoside phosphorylase. The short-term exposure of HL-60 cells to DMSO plus hypoxanthine resulted in enhanced leucine incorporation, and a model is presented showing how the inosine modification reaction in tRNA may be involved. A means by which hypoxanthine insertion into tRNA may modulate the synthesis of regulatory proteins (e.g., lymphokines and cell surface receptors) is also outlined.