Biomedical subjects

S R Dillon

Publications and source records attributed to S R Dillon.

7 recordsLinked to original sources

PubMed1997

V(D)J recombinase activity in a subset of germinal center B lymphocytes.

Reexpression of the V(D)J recombinase-activating genes RAG1 and RAG2 in germinal center B cells creates the potential for immunoglobulin gene rearrangement and the generation of new antigen receptor specificities. Intermediate products of V(D)J recombination are abundant in a subset of germinal center B cells, demonstrating that the kappa immunoglobulin light-chain locus becomes a substrate for renewed V(D)J recombinase activity. This recombinationally active cell compartment contains many heavy-chain VDJ rearrangements that encode low-affinity or nonfunctional antibody. In germinal centers, secondary V(D)J recombination may be induced by diminished binding to antigen ligands, thereby limiting abrupt changes in receptor specificity to B cells that are usually eliminated from the germinal center reaction. This restriction preserves efficient antigen-driven selection in germinal centers while allowing for saltations in the somatic evolution of B cells.

Animals↗

PubMed1995

A functionally compromised intermediate in extrathymic CD8+ T cell deletion.

We have established a model system for analyzing the induction of self-tolerance among mature peripheral T cells in V beta 5 TCR Tg mice. Both CD4+V beta 5+ and CD8+ V beta 5+ cells undergo a superantigen-driven chronic deletion in the periphery of I-E mice. Prior to their disappearance, CD4+ transgene-expressing cells are activated and then rendered anergic to further stimulation through their TCRs. This scenario differs strikingly in the CD8+ cellular compartment, which is characterized by a distinct population of CD8loV beta 5lo cells localized to the blood and spleen. CD8lo cells are small, express the surface phenotype of memory cells, and rapidly incorporate BrdU in vivo. The kinetics of their appearance and disappearance in adult thymectomized mice, the rapid chasing of BrdU from labeled cells, and their in vivo cortisone sensitivity all suggest CD8lo cells are slated for deletion. Furthermore, their functional incompetence can be documented in vitro in the absence of internucleosomal DNA fragmentation. Thus, we have identified an intermediate population of T cells targeted for peripheral deletion that, although functionally compromised, has not yet undergone programmed cell death.

Animals↗

PubMed1995

Thymic selection events mediated by the pre-TCR do not depend upon a limiting ligand.

Thymocyte differentiation requires the production of a functional TCR, the culmination of a carefully orchestrated series of events in which TCR beta chain gene rearrangement precedes that of TCR alpha genes. The product of a successful rearrangement of the TCR beta locus associates with an invariant protein in immature thymocytes to form the 'pre-TCR' complex, which is required for allelic exclusion at the TCR beta locus, the expression of CD4 and CD8 co-receptors, and the clonal expansion of immature thymocytes. The pivotal role for the beta chain protein during early thymocyte development led us to investigate the relative differentiation efficiency within the same thymus of cells which do and cells which do not possess productive TCR gene rearrangements. Using mixed radiation bone marrow chimeras to establish an in vivo competition between TCR beta transgenic (Tg) and non-Tg bone marrow cells, we show that the prior productive rearrangement of a TCR beta chain gene only subtly enhances the efficiency of intrathymic differentiation. Further, we have compared the relative differentiation efficiency of TCR alpha beta and TCR beta Tg cells within the mixed chimera system by altering the proportion of TCR Tg bone marrow cells in the reconstituting inoculum. As expected, Tg cells carrying both alpha and beta chains of a selectable TCR are developmentally hindered compared with their non-Tg counterparts by the lack of ample numbers of intrathymic positively selecting ligands or niches. In contrast, parallel experiments using TCR beta Tg bone marrow cells demonstrate that the early selection events mediated by the pre-TCR do not similarly depend upon a ligand present in limiting quantities.

Animals↗

PubMed1994

V beta 5+ T cell receptors skew toward OVA+H-2Kb recognition.

T cells recognize a complex of peptide Ag bound within the groove of MHC-encoded molecules. Although many studies have attempted to correlate TCR gene expression with specificity for particular Ag/MHC combinations, it is still not clear exactly how the TCR physically interacts with its cognate ligand. We have analyzed transgenic mice that carry a rearranged gene encoding a V beta 5.2+ TCR beta-chain derived from the CD8+ CTL clone B3, which is specific for chicken OVA+H-2Kb. Surprisingly, we have found that peripheral lymphocytes isolated from naïve V beta 5.2 transgenic mice can generate a strong primary anti-OVA CTL response when stimulated in vitro with OVA+H-2b, whereas generation of even a weak anti-OVA response from nontransgenic littermates requires in vivo priming. This response is Ag specific, because the transgenic mice are unable to respond with or without priming to vesicular stomatitis virus, which contains a dominant epitope presented in the context of H-2Kb. The precursor frequency of OVA-specific CTL in unprimed V beta 5.2 transgenic mice is approximately 30-fold higher than that in nontransgenic littermate controls. Reverse transcription-PCR analyses demonstrate that OVA-specific CTL lines derived from unprimed V beta 5.2 transgenic mice express a variety of TCR V alpha elements, indicating that the transgenic anti-OVA response is not solely due to the reconstitution of the original B3 TCR. In fact, our data suggest that even a nontransgenic V beta 5+ TCR is intrinsically OVA specific. First, five separate OVA-specific oligoclonal CTL lines derived from individual nontransgenic mice demonstrate dramatic skewing toward expression of V beta 5.1+ or V beta 5.2+ TCR over the course of several in vitro stimulations. Second, sorting for V beta 5+CD8+ nontransgenic cells enriches for OVA-specific CTL. However, peptide antagonism experiments using mutant forms of the Kb-restricted OVA peptide reveal distinct differences between the recognition patterns of two individual OVA-specific CTL lines derived from unprimed V beta 5.2 transgenic mice. These experiments support the notion that a discrete portion of the responding TCR can heavily influence but not necessarily be solely sufficient for the recognition of a peptide Ag presented in the cleft of an MHC-encoded molecule.

Amino Acid Sequence↗

PubMed1991

Wocko, a neurological mutant generated in a transgenic mouse pedigree.

Naturally occurring mutations involving the nervous system have provided virtually all of our current understanding of the genetic regulation of neural development (Caviness and Rakic, 1978). The difficulty of isolating the corresponding genes, however, has precluded a molecular analysis of these mutants. Insertional mutagenesis, induced by microinjection of DNA into fertilized ova to produce transgenic animals, provides a molecular tag that marks the site of the mutational event. In this article, we describe a transgenic neurological mutation, designated wocko (Wo), which disrupts the development of the inner ear. These mutant mice display a dominant behavioral phenotype that consists of circling, hyperactivity, and head tossing, reminiscent of the shaker/waltzer class of mutants, and they display a recessive homozygous sublethal phenotype. Anatomical analyses showed that both structural and neural components of the vestibular system were disrupted, while analyses of mutant fetuses showed that these morphological abnormalities were due to aberrant development. Although low levels of transgene expression were detected using a sensitive PCR assay, several nonmutant pedigrees that contain the same construct also expressed the transgene in the inner ear, suggesting that low levels of transgene expression alone were not responsible for the wocko phenotype. Because the integrated transgene provides a marker to clone the wocko mutation, the analysis of this mutant will give unique insight into the molecular genetics of inner ear development and into a broad class of neurological mutations that affect the inner ear.

Animals↗

PubMed1985

Effectiveness of the dietitian-technician team on a burn unit.

A study was conducted to determine whether the clinical registered dietitian (R.D.) on the burn and trauma unit of an 863-bed medical center was able to perform more efficiently when a part-time dietetic technician (D.T.) was employed and whether the R.D.-D.T. team had an influence on the nutritional status of burn patients. The authors audited a random sample of medical records of burn patients from the year prior to employment of the D.T. (year 1, N = 44) and the year following her employment (year 2, N = 41) to determine the quantity and frequency of nutrition information charted. Results indicated that the percentage of records charted by the R.D. in year 2 increased significantly over the percentage in year 1, as did recommendations for nutrition support. Mean percentage of nutrition recommendations that the R.D. documented for total patient days also increased significantly. Data were insufficient to determine the influence of the R.D.-D.T. team on the nutritional status of patients. With part-time technician assistance, the dietitian had more time to screen and monitor patient records; to plan, implement, and evaluate nutrition care; and to make recommendations for aggressive nutrition support.

Alabama↗

PubMed1984

Methods of nutritional support for hospitalized patients.

Major components of intravenous nutritional solutions include crystalline amino acids as the protein source, and monohydrous dextrose and lipid emulsions as the energy sources. Intravenous nutrition is indicated in patients without gastrointestinal tract function. Patients with a functioning gastrointestinal tract may be supported enterally by tube feeding. A number of enteral feeding formulas are available, including modular components that may be combined to satisfy specific needs.

Amino Acids↗