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Biomedical subjects

D C Roopenian

Publications and source records attributed to D C Roopenian.

At least 19 recordsLinked to original sources
PubMed2004

Quantitative gene expression profiling implicates genes for susceptibility and resistance to alveolar bone loss.

Periodontal disease is one of the most prevalent chronic inflammatory diseases. There is a genetic component to susceptibility and resistance to this disease. Using a mouse model, we investigated the progression of alveolar bone loss by gene expression profiling of susceptible and resistant mouse strains (BALB/cByJ and A/J, respectively). We employed a novel and sensitive quantitative real-time PCR method to compare basal RNA transcription of a 48-gene set in the gingiva and the spleen and the subsequent changes in gene expression due to Porphyromonas gingivalis oral infection. Basal expression of interleukin-1 beta (Il1b) and tumor necrosis factor alpha (Tnf) mRNA was higher in the gingiva of the susceptible BALB/cByJ mice than in the gingiva of resistant A/J mice. Gingival Il1b gene expression increased further and Stat6 gene expression was turned on after P. gingivalis infection in BALB/cByJ mice but not in A/J mice. The basal expression of interleukin-15 (Il15) in the gingiva and the basal expression of p-selectin (Selp) in the spleen were higher in the resistant A/J mice than in the susceptible BALB/cByJ mice. In the resistant A/J mice the expression of no genes detectably changed in the gingiva after infection. These results suggest a molecular phenotype in which discrete sets of differentially expressed genes are associated with genetically determined susceptibility (Il1b, Tnf, and Stat6) or resistance (Il15 and Selp) to alveolar bone loss, providing insight into the genetic etiology of this complex disease.

Alveolar Bone Loss↗
PubMed2001

Efficient chromosomal mapping of a methylcholanthrene-induced tumor antigen by CTL immunoselection.

It has been difficult to genetically map the genes encoding tumor Ags because they arise as a consequence of somatic mutational events. CTL-mediated immunoselection can impose potent immunoselective pressure against tumor cells, resulting in the survival of rare tumor Ag-loss variants. We subjected a heterozygous 3-methylcholanthrene-induced murine sarcoma cell line to CTL immunoselection, selecting for the loss of a tumor-specific Ag, recognized antigen from MCA-induced tumor 1 (Ram1). Several variants eluded CTL recognition by genetic loss of the hemizygously expressed tumor-specific Ag epitope. A frequently observed genetic escape mechanism was spontaneous mitotic recombination resulting in loss of heterozygosity on chromosome 4. Higher density genetic analyses along with functional confirmation with an independently produced chromosome 4 loss of heterozygosity variant positioned the Ram1 locus to a distal 7.1 cM interval on chromosome 4. This region of the mouse genome is rich in tumor-modifier genes and this positioning of Ram1 may thus provide insight into the genetic basis of 3-methycholanthrene-induced tumor Ags.

Animals↗
PubMed2001

Naturally variant autosomal and sex-linked loci determine the severity of iron overload in beta 2-microglobulin-deficient mice.

Hereditary hemochromatosis (HH) is a common chronic human genetic disorder whose hallmark is systemic iron overload. Homozygosity for a mutation in the MHC class I heavy chain paralogue gene HFE has been found to be a primary cause of HH. However, many individuals homozygous for the defective allele of HFE do not develop iron overload, raising the possibility that genetic variation in modifier loci contributes to the HH phenotype. Mice deficient in the product of the beta(2)-microglobulin (beta(2)M) class I light chain fail to express HFE and other MHC class I family proteins, and they have been found to manifest many characteristics of the HH phenotype. To determine whether natural genetic variation plays a role in controlling iron overload, we performed classical genetic analysis of the iron-loading phenotype in beta(2)M-deficient mice in the context of different genetic backgrounds. Strain background was found to be a major determinant in iron loading. Sex played a role that was less than that of strain background but still significant. Resistance and susceptibility to iron overload segregated as complex genetic traits in F(1) and back-cross progeny. These results suggest the existence of naturally variant autosomal and Y chromosome-linked modifier loci that, in the context of mice genetically predisposed by virtue of a beta(2)M deficiency, can profoundly influence the severity of iron loading. These results thus provide a genetic explanation for some of the variability of the HH phenotype.

Aging↗
PubMed2001

Quantitative analysis of the immune response to mouse non-MHC transplantation antigens in vivo: the H60 histocompatibility antigen dominates over all others.

Minor histocompatibility Ags (minor H Ags) are substantial impediments to MHC-matched solid tissue and bone marrow transplantation. From an antigenic standpoint, transplantation between MHC-matched individuals has the potential to be remarkably complex. To determine the extent to which the immune response is simplified by the phenomenon of immunodominance, we used peptide/MHC tetramers based on recently discovered minor H Ags (H60, H13, and HY) and monitored in vivo CD8 T cell responses of female C57BL/6 mice primed with MHC-matched, but background-disparate, male BALB.B cells. CD8 T cells against H60 overwhelmed responses to the H13 and HY throughout primary and secondary challenge. H60 immunodominance was an inherent quality, overcoming a lower memory precursor frequency compared with that of H13 and evoking a T cell response with diverse TCRV beta usage. IFN-gamma staining examining congenically defined minor H Ags extended H60 dominance over additional minor H Ags, H28, H4, and H7. These four minor H Ags accounted for up to 85% of the CD8 T cell response, but H60 stood out as the major contributor. These findings show that immunodominance applies to antigenically complex transplantation settings in vivo and that the responses to the H60 minor H Ag dominates in this model. We suggest that immunodominant minor H Ags are those that result from the absence of a self analog.

Animals↗
PubMed2001

Mouse strain differences determine severity of iron accumulation in Hfe knockout model of hereditary hemochromatosis.

Hereditary hemochromatosis (HH) is a common disorder of iron metabolism caused by mutation in HFE, a gene encoding an MHC class I-like protein. Clinical studies demonstrate that the severity of iron loading is highly variable among individuals with identical HFE genotypes. To determine whether genetic factors other than Hfe genotype influence the severity of iron loading in the murine model of HH, we bred the disrupted murine Hfe allele onto three different genetically defined mouse strains (AKR, C57BL/6, and C3H), which differ in basal iron status and sensitivity to dietary iron loading. Serum transferrin saturations (percent saturation of serum transferrin with iron), hepatic and splenic iron concentrations, and hepatocellular iron distribution patterns were compared for wild-type (Hfe +/+), heterozygote (Hfe +/-), and knockout (Hfe -/-) mice from each strain. Although the Hfe -/- mice from all three strains demonstrated increased transferrin saturations and liver iron concentrations compared with Hfe +/+ mice, strain differences in severity of iron accumulation were striking. Targeted disruption of the Hfe gene led to hepatic iron levels in Hfe -/- AKR mice that were 2.5 or 3.6 times higher than those of Hfe -/- C3H or Hfe -/- C57BL/6 mice, respectively. The Hfe -/- mice also demonstrated strain-dependent differences in transferrin saturation, with the highest values in AKR mice and the lowest values in C3H mice. These observations demonstrate that heritable factors markedly influence iron homeostasis in response to Hfe disruption. Analysis of mice from crosses between C57BL/6 and AKR mice should allow the mapping and subsequent identification of genes modifying the severity of iron loading in this murine model of HH.

Animals↗
PubMed2001

T-cell contributions to alveolar bone loss in response to oral infection with Porphyromonas gingivalis.

We have previously shown that mice lacking CD4+, but not CD8+, T cells lose less alveolar bone loss in response to oral infection with Porphyromonas gingivalis than do immunocompetent mice of the same genetic background, indicating that CD4+ T cells contribute to bone resorption. The CD4+ and CD8+ T-cell knockouts were produced by targeted deletions of, respectively, major histocompatibility complex II (MHCII) or beta2-microglobulin (producing non-expression of MHCI). Because MHC deletions can have other effects in addition to those on T-cell selection, we wanted to confirm that the lessened bone loss was truly an effect of the lack of T cells. Consequently, we repeated our experiments with C57B1 /6J-Tcra mice that have a targeted deletion of the alpha chain of the T-cell receptor (Tcra). Six weeks after oral infection with P. gingivalis ATCC 53977 the total bone loss at buccal maxillary sites was 0.28 mm in infected immunocompetent mice (P=0.002 compared with sham-infected mice), whereas in Tcra knockouts the bone loss was only 0.08 mm (P=0.04 compared with shams). The T-cell-deficient mice thus lost 70% less bone after infection than did genetically matched immunocompetent mice (P =0.003). These experiments confirm that T cells, and their responses to oral infection with P. gingivalis, help to push bone remodeling in the direction of net loss of bone.

Alveolar Bone Loss↗
PubMed2000

Identification of a CD8 T cell that can independently mediate autoimmune diabetes development in the complete absence of CD4 T cell helper functions.

Previous work has indicated that an important component for the initiation of autoimmune insulin-dependent diabetes mellitus (IDDM) in the NOD mouse model entails MHC class I-restricted CD8 T cell responses against pancreatic beta cell Ags. However, unless previously activated in vitro, such CD8 T cells have previously been thought to require helper functions provided by MHC class II-restricted CD4 T cells to exert their full diabetogenic effects. In this study, we show that IDDM development is greatly accelerated in a stock of NOD mice expressing TCR transgenes derived from a MHC class I-restricted CD8 T cell clone (designated AI4) previously found to contribute to the earliest preclinical stages of pancreatic beta cell destruction. Importantly, these TCR transgenic NOD mice (designated NOD.AI4alphabeta Tg) continued to develop IDDM at a greatly accelerated rate when residual CD4 helper T cells were eliminated by introduction of the scid mutation or a functionally inactivated CD4 allele. In a previously described stock of NOD mice expressing TCR transgenes derived from another MHC class I-restricted beta cell autoreactive T cell clone, IDDM development was retarded by elimination of residual CD4 T cells. Hence, there is variability in the helper dependence of CD8 T cells contributing to the development of autoimmune IDDM. The AI4 clonotype represents the first CD8 T cell with a demonstrated ability to progress from a naive to functionally activated state and rapidly mediate autoimmune IDDM development in the complete absence of CD4 T cell helper functions.

Animals↗
PubMed2000

Development of spontaneous arthritis in beta2-microglobulin-deficient mice without expression of HLA-B27: association with deficiency of endogenous major histocompatibility complex class I expression.

OBJECTIVE: Mice deficient in beta2-microglobulin (beta2m), but expressing the human major histocompatibility complex (MHC) class I molecule HLA-B27, have been reported to develop spontaneous inflammatory arthritis (SA). We sought to determine whether, under certain conditions, beta2m deficiency alone was sufficient to cause SA, and if this might be a result of class I deficiency. METHODS: The following types of mice were produced: mice of the MHC b haplotype genetically deficient in beta2m (beta2m(0)) on several genetic backgrounds (C57BL/6J [B6], BALB/cJ, SJL/J, MRL/MpJ, and B6,129), mice deficient in the transporter associated with antigen processing (TAP1(0)) on a B6,129 background, and HLA-B27-transgenic beta2m(0) mice on a B6 background. Cohorts were transferred from specific pathogen-free (SPF) to conventional (non-SPF) animal rooms, and evaluated clinically and histologically for the development of SA. RESULTS: SA occurred in TAP1(0) and beta2m(0)/class I-deficient mice with a mixed B6,129 genome at a frequency of 30-50%, while 10-15% of B6, SJL/J, and BALB/cJ beta2m(0) mice developed this arthropathy. MRL/ MpJ beta2m(0) mice were unaffected. Expression of B27 did not increase the frequency of SA in B27-transgenic B2m(0) B6 mice compared with that in beta2m(0) B6 controls. CONCLUSION: Class I deficiency is sufficient to cause SA in mice. The frequency of disease, as well as B27-specific SA, is markedly dependent on a non-MHC genetic background. These results suggest that class I deficiency in a genetically susceptible mouse can mimic B27-associated arthropathy.

Animals↗
PubMed2000

Heterogeneity of Porphyromonas gingivalis strains in the induction of alveolar bone loss in mice.

These experiments examine alveolar bone loss in a model in which specific pathogen-free mice are exposed orally with Porphyromonas gingivalis. Alveolar bone loss was induced as a result of a specific infection with P. gingivalis, rather than other environmental antigens. Infection with live P. gingivalis was required, as significant bone loss did not follow gavage with formalin-killed P. gingivalis. The virulence of different strains of P. gingivalis was compared. Two laboratory strains of the bacteria (ATCC 53977 and W50) and a mutant strain lacking the 43-kDa fimbrillin (strain DPG3) induced bone loss. P. gingivalis 381, however, did not induce bone loss. There was a strong immunoglobulin G (IgG) antibody response to infection with each strain but a significant serum IgA response only to strain 381. These studies show that in mice with a background oral microflora bone loss is induced by a specific infection with P. gingivalis and that bacterial strain variation is important in determining whether alveolar bone loss will ensue.

Alveolar Bone Loss↗
PubMed2000

Genetic control of susceptibility to Porphyromonas gingivalis-induced alveolar bone loss in mice.

Periodontal disease affects a large percentage of the human population. Resorption of the alveolar bone of the jaw is a pivotal sequela of periodontal disease, because this bone is the attachment site for the periodontal ligaments that anchor the teeth. Using a murine model in which alveolar bone loss is induced by oral infection with Porphyromonas gingivalis, a gram-negative bacterium associated with human adult periodontal disease, we provide evidence suggesting that susceptibility to such bone loss is a genetically determined trait. AKR/J, DBA/2J, and BALB/cByJ or BALB/cJ mice were highly susceptible, while A/J, A/HeJ, 129/J, SJL/J, and C57BL/6J mice were much more resistant. When susceptible BALB/cJ and BALB/cByJ mice were crossed to resistant strains, two patterns were observed. (BALBc/ByJ x C57BL/6J)F(1) offspring were susceptible, suggesting C57BL/6J has recessive resistance alleles, while (BALB/cJ x A/J)F(1) mice were all resistant, suggesting that A/J mice have dominant resistance alleles. These results suggest a tractable genetic basis for P. gingivalis-induced alveolar bone loss and open the possibility of exploiting the mouse model to identify loci important for host susceptibility and resistance to periodontal disease.

Adult↗
PubMed2000

Adhesion molecule deficiencies increase Porphyromonas gingivalis-induced alveolar bone loss in mice.

Alveolar bone resorption can be induced in specific-pathogen-free mice by oral infection with Porphyromonas gingivalis (P. J. Baker, R. T. Evans, and D. C. Roopenian, Arch. Oral Biol. 39:1035-1040, 1994). Here we used a mouse strain, C57BL/6J, which is relatively resistant to P. gingivalis-induced bone loss to examine whether partial or complete deletion of various adhesion molecules would increase susceptibility. Complete deletion of P-selectin or nearly complete lack of expression of intercellular adhesion molecule 1 (ICAM-1) led to increased susceptibility to bone resorption after oral infection, while a hypomorphic defect in beta(2)-integrins did not. Both the total amount of bone lost and the number of sites at which there was significant loss were increased in mice deficient in either ICAM-1 or P-selectin. Each of the three adhesion molecule deficiencies was sufficient to decrease P. gingivalis-specific serum immunoglobulin G responses, but lower antibody titers did not lead to increased bone loss in partially beta(2)-integrin-deficient mice. In conclusion, P-selectin and ICAM-1 deficiencies increase susceptibility to and severity of alveolar bone loss after P. gingivalis infection. This finding underscores the importance of innate immunity in protection against P. gingivalis-induced alveolar bone resorption.

Alveolar Bone Loss↗
PubMed1999

The same genetic regions encode minor histocompatibility antigens detected in the context of different MHC haplotypes.

The mammalian genome encodes numerous autosomal minor histocompatibilty (H) antigens that act as a barrier to allogeneic tissue transplantation when donor and recipient are matched for the major histocompatibilty complex (MHC). However, most of our understanding of the genetic basis of such minor H antigens is limited to analysis of mouse strains of the H2b haplotype. To broaden our understanding, we investigated minor H antigens detected in the context of other MHC alleles. As measured by graft survival and precursor cytotoxic T lymphocytes from blood, our results suggest that chromosomal segments known to encode minor H antigens detected in the context of the H2b haplotype are antigenically complex in that they also frequently encode minor H antigens that can be detected in the context of at least the H2d and H2k haplotypes. Genetic models to account for this complexity are discussed.

Animals↗
PubMed1999

Biochemical and immunogenetic analysis of an immunodominant peptide (B6dom1) encoded by the classical H7 minor histocompatibility locus.

Of the many minor histocompatibility (H) Ags that have been detected in mice, the ability to induce graft vs host disease (GVHD) after bone marrow transplantation is restricted to a limited number of immunodominant Ags. One such murine Ag, B6dom1, is presented by the H2-Db MHC class I molecule. We present biochemical evidence that the natural B6dom1 peptide is indistinguishable from AAPDNRETF, and we show that this peptide can be isolated from a wide array of tissues, with highest levels from the lymphoid organs and lung. Moreover, we employ a novel, somatic cell selection technique involving CTL-mediated immunoselection coupled with classical genetics, to show that B6dom1 is encoded by the H7 minor H locus originally discovered approximately 40 years ago. These studies provide a molecular genetic framework for understanding B6dom1, and exemplify the fact that mouse minor H loci that encode immunodominant CTL epitopes can correspond to classical H loci originally identified by their ability to confer strong resistance to tumor transplantation. Additionally, these studies demonstrate the utility of somatic cell selection approaches toward resolving H Ag immunogenetics.

Animals↗
PubMed1999

Shaping the repertoire of cytotoxic T-lymphocyte responses: explanation for the immunodominance effect whereby cytotoxic T lymphocytes specific for immunodominant antigens prevent recognition of nondominant antigens.

The immunodominance effect, whereby the presence of immunodominant epitopes prevents recognition of nondominant determinants presented on the same antigen-presenting cell (APC) considerably restricts the repertoire of cytotoxic T lymphocyte (CTL) responses. To elucidate the molecular basis of the immunodominance effect, we compared the interactions of a dominant (B6(dom1)) and a nondominant epitope (H-Y) with their restricting class I molecule (H2-Db), and their ability to trigger cognate CTLs. We found that B6(dom1)/Db complexes behaved as optimal T-cell receptor (TCR) ligands and triggered a more rapid in vivo expansion of cognate CTLs than H-Y/Db complexes. The superiority of the dominant epitope was explained by its high cell surface density (1,012 copies/cell for B6(dom1) v 10 copies/cell for H-Y) and its optimal affinity for cognate TCRs. Based on these results, we conclude that dominant class I-associated epitopes are those that have optimal ability to trigger TCR signals in CTLs. We propose that the rapid expansion of CTLs specific for dominant antigens should enable them to compete more successfully than other CTLs for occupancy of the APC surface.

Animals↗
PubMed1999

Serum antibody response to oral infection precedes but does not prevent Porphyromonas gingivalis-induced alveolar bone loss in mice.

The purpose of this study was to determine whether humoral immunity prevents bacterially induced alveolar bone loss. BALB/cByJ mice were orally infected with the human periodontopathic bacterium Porphyromonas gingivalis, and were compared with sham-infected mice. Specific serum antibody titers to P. gingivalis were measured by enzyme-linked immunosorbent assay. Alveolar bone levels were measured as the distance from the cementoenamel junction to the alveolar bone crest and bone loss was defined as a change in bone levels over time or between infected and sham-infected animals. The specific humoral response was predominantly of the IgG isotype, although low levels of specific serum IgA were also present. Antibody titers in the infected animals were significantly different from those in the sham-infected animals by 18 days and remained at maximal levels at 47 days. Bone loss became significant by 26 days and continued to progress at 47 days. Thus the serum antibody response to oral infection with P. gingivalis preceded detectable bone loss and remained elevated while bone loss increased. The presence of specific antibody did not prevent the onset or progression of bone loss.

Alveolar Bone Loss↗
PubMed1999

Genetic modification of hearing in tubby mice: evidence for the existence of a major gene (moth1) which protects tubby mice from hearing loss.

Quantitative trait locus (QTL) analysis of genetic crosses has proven to be a useful tool for identifying loci associated with specific phenotypes and for dissecting genetic components of complex traits. Inclusion of a mutation that interacts epistatically with QTLs in genetic crosses is a unique and potentially powerful method of revealing the function of novel genes and pathways. Although we know that a mutation within the novel tub gene leads to obesity and cochlear and retinal degeneration, the biological function of the gene and the mechanism by which it induces its phenotypes are not known. In the current study, a QTL analysis for auditory brainstem response (ABR) thresholds, which indicates hearing ability, was performed in tubby mice from F(2)intercrosses between C57BL/6J- tub / tub and AKR/J-+/+ F(1)hybrids (AKR intercross) and between C57BL/6J- tub / tub and CAST/Ei.B6- tub / tub F(1)hybrids (CAST intercross). A major QTL, designated asmodifieroftubbyhearing1 ( moth1 ), was identified on chromosome 2 with a LOD score of 33.4 ( P < 10(-33)) in the AKR intercross (181 mice) and of 6.0 ( P < 10(-6)) in the CAST intercross (46 mice). This QTL is responsible for 57 and 43% of ABR threshold variance, respectively, in each strain combination. In addition, a C57BL/6J congenic line carrying a 129/Ola segment encompassing the described QTL region when made homozygous for tubby also exhibits normal hearing ability. We hypothesize that C57BL/6J carries a recessive mutation of the moth1 gene which interacts with the tub mutation to cause hearing loss in tub / tub mice. A moth1 allele from either AKR/J, CAST/Ei or 129/Ola is sufficient to protect C57BL/6J- tub / tub mice from hearing loss.

Adaptor Proteins, Signal Transducing↗