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D W Scott

Publications and source records attributed to D W Scott.

At least 19 recordsLinked to original sources
PubMed1996

Epitope-specific tolerance induction with an engineered immunoglobulin.

Isologous and heterologous immunoglobulins have been shown to be extremely effective as tolerogenic carriers for nearly 30 years. The efficacy of these proteins is due in part to their long half-life in vivo, as well as their ability to crosslink surface IgM with Fc receptors. The concept of using IgG as a carrier molecule to induce unresponsiveness in the adult immune system has been exploited for simple haptens, such as nucleosides, as well as for peptides. To further evaluate the in vivo potential of these molecules for inducing tolerance to a defined epitope, we have engineered a fusion protein of mouse IgG1 with the immunodominant epitope 12-26 from bacteriophage lambda cI repressor protein. This 15-mer, which contains both a B-cell and T-cell epitope, has been fused in-frame to the N terminus of a mouse heavy chain IgG1 construct, thus creating a "genetic hapten-carrier" system. We describe a novel in vitro and in vivo experimental system for studying the feasibility of engineered tolerogens, consisting of a recombinant flagellin challenge antigen and a murine IgG1 tolerogen, both expressing the lambda repressor epitope 12-26. Herein, we show that peptide-grafted IgG molecules injected i.v., or expressed by transfected, autologous B cells, can efficiently modulate the cellular and humoral immune responses to immunodominant epitopes. This model displays the feasibility of "tailor-designing" immune responses to whole antigens by selecting epitopes for either tolerance or immunity.

Amino Acid Sequence↗
PubMed1996

T cells commit suicide, but B cells are murdered!

In addition to self tolerance, the immune system needs to be regulated when a response has been initiated. Recent data suggest that activated T and B cells, as well as immature lymphocytes, are susceptible to programmed cell death and that Fas:Fas ligand (FasL) interactions play an important role in this process. However, while T cells may kill themselves via a Fas-dependent pathway, we propose that B cells undergo activation-induced apoptosis independent of Fas, yet can be susceptible to T cell-mediated, FasL-induced death. Therefore, T cells can "commit suicide," but B cells are "murdered" during the regulation of an immune response! Further evidence is presented to support the hypothesis that T cell and B cell apoptosis, are initiated through fundamentally different pathways.

Animals↗
PubMed1996

Role of cyclin A and p27 in anti-IgM induced G1 growth arrest of murine B-cell lymphomas.

Cross-linking surface immunoglobulin (Ig)M on the WEHI-231 B-cell lymphoma results in decreased cell size, G1/S growth arrest, and finally DNA cleavage into oligonucleosomal fragments that are the classical features of apoptotic cells. Treatment of WEHI-231 cells with anti-IgM in early G1 phase prevents phosphorylation of the retinoblastoma gene product (pRb) and inhibits entry into S phase. Using unsynchronized cells, we previously demonstrated that cyclin A-associated and Cdk2-dependent GST-pRb kinase activity were inhibited in WEHI-231 cells treated with anti-IgM. We now show that progression of elutriated early G1 phase WEHI-231 cells from early into late G1 phase is accompanied by an increase in the abundance of cyclin A protein and cyclin A-associated kinase activity. Treatment of early G1 cells with anti-IgM prevented this increase in cyclin A-associated kinase activity at late G1, despite minimal changes in the overall level of cyclin A and Cdk2 proteins. Late G1 cells, which already possess high cyclin A-associated kinase activity, were insensitive to anti-IgM treatment and were able to complete the cell cycle. We also found that anti-IgM-treated cells contained increased amounts of the Cdk inhibitor protein p27Kip1. Essentially all of the cyclin A in treated cells was associated with p27, a result which we propose explains the lack of cyclin A/Cdk2 kinase activity. Accumulation of p27 in cyclin A kinase complexes, however, did not decrease the amount of Cdk2 bound to cyclin A. Thus, cross-linking IgM on growth-inhibitable B-cell lymphomas affects cyclin A kinase activity by increasing the levels of p27 in this complex, thus preventing productive pRb phosphorylation and leading to cell cycle arrest and subsequent apoptosis. These results are discussed in terms of the cell cycle restriction points that regulate lymphocyte function, as well as the lineage-specific differences in cell cycle control.

Animals↗
PubMed1996

Role of c-myc and CD45 in spontaneous and anti-receptor-induced apoptosis in adult murine B cells.

Although adult murine B cells can be stimulated to proliferate by Igm receptor cross-linking, we and others have shown that these cells will undergo apoptosis in vitro in a dose-, time- and temperature-dependent manner with polyclonal but not monoclonal anti-IgM, To test the role of c-myc and cell cycle progression in B cell apoptosis, we examined normal, Sp6 anti-TNP lg and E micro-myc transgenic splenocytes for receptor-mediated apoptosis in vitro. In normal mice, both spontaneous and anti-IgM-induced programmed cell death were specifically blocked by antisense oligodeoxynucleotides for the c-myc proto-oncogene, whereas nonsense myc oligonucleotides and irrelevant oligonucleotides had only a minor effect. Similarly, TNP-dextran-induced apoptosis in Sp6 anti-TNF transgenics was inhibited by antisense c-myc. This effect was not due to the mitogenic effects of unmethylated CpG-containing sequences because ones lacking this motif, as well as methylated oligonucleotides containing this motif, prevented apoptosis, and mitogenic doses of lipopolysaccharide failed to inhibit anti-IgM-driven cell death. Importantly, antisense c-myc also prevented the anti-IgM-induced increase in myc protein species. Moreover, spontaneous apoptosis in vitro was exaggerated in E micro-myc transgenic B cells. To examine the role of CD45 in anti-IgM-induced apoptosis, we treated spleen cells from CD45 knockout mice, which do not proliferate with anti-IgM, and found that B cells from these underwent apoptosis normally despite the lack of entry into S. These data suggest that anti-IgM driven apoptosis does not require CD45. Rather, apoptosis may be due to an overexpression of myc protein in the absence of signals which can drive B cells productively into S, but the failure to proliferate normally is insufficient for apoptosis to occur.

Animals↗
PubMed1996

Primary seborrhoea in English springer spaniels: a retrospective study of 14 cases.

Primary seborrhoea was diagnosed in 14 English springer spaniels over a 17-year period. Seven of the dogs developed clinical signs by two years of age. The dermatosis began as a generalised non-pruritic dry scaling which gradually worsened. Some dogs remained in this dry (seborrhoea sicca) stage, but in most cases the dermatosis became greasy and inflamed (seborrhoea oleosa and seborrhoeic dermatitis). Eight of the dogs suffered from recurrent episodes of superficial or deep bacterial pyoderma. Histological findings in skin biopsy specimens included marked orthokeratotic hyperkeratosis of surface and infundibular epithelium, papillomatosis, parakeratotic capping of the papillae, and superficial perivascular dermatitis in which lymphocytes and mast cells were prominent. The dogs with seborrhoea sicca responded more satisfactorily to therapy with topical emollient-humectant agents or oral omega-3/omega-6 fatty acid supplementation. Dogs with seborrhoea oleosa and seborrhoeic dermatitis did not respond satisfactorily to topical therapy. One dog, however, responded well to etretinate and omega-3/omega-6 fatty acid administration. No dog was cured.

Animals↗
PubMed1996

Treatment of canine scabies with milbemycin oxime.

The purpose of this study was to determine the efficacy of orally administered milbemycin oxime in the treatment of canine scabies. Forty dogs were treated. Mean drug dosage for all dogs was approximately 2 mg/kg body weight. Twenty-seven dogs received 3 doses separated by 7 d, and 13 dogs received 2 doses separated by 14 d. All dogs were clinically normal following treatment and no adverse reactions were detected.

Administration, Oral↗
PubMed1995

Clinical efficacy of increased dosages of milbemycin oxime for treatment of generalized demodicosis in adult dogs.

OBJECTIVE: To determine the efficacy of increased dosages of milbemycin oxime in the treatment of generalized demodicosis. DESIGN: Prospective clinical trial. ANIMALS: 26 adult dogs with chronic generalized demodicosis. PROCEDURE: In phase 1, milbemycin was administered daily to 13 dogs at an approximate mean dosage of 1 mg/kg of body weight (PO) until 30 days after skin scrapings failed to detect mites. If the mite count had not decreased by 25% from the prior month's examination, the drug dosage was increased to approximately 2 mg/kg. Treatment was considered a failure if the mite count had not changed on 2 successive examinations. In phase 2 involving 13 other dogs, an approximate mean dosage of 2 mg/kg was used. If mite counts had not been reduced to 0 by 180 days, treatment was considered to have failed. RESULTS: In phase 1, when milbemycin was administered at the initial low dosage, 6 dogs were considered to have been cleared of mites. One of these relapsed 2 months after discontinuation of treatment. For the 7 dogs not cleared of mites, the dosage was doubled. Two of these were never cleared of mites. In phase 2, 12 of 13 dogs were cleared of mites after 60 to 180 days of treatment. CLINICAL IMPLICATIONS: High-dose milbemycin was effective in the treatment of generalized demodicosis.

Animals↗
PubMed1995

Immunoreceptor tyrosine-based activation motif is required to signal pathways of receptor-mediated growth arrest and apoptosis in murine B lymphoma cells.

The B cell Ag receptor is a multimeric protein complex consisting of the ligand binding mlg and the Ig alpha/lg beta heterodimer. The cytoplasmic tails of Ig alpha and Ig beta both contain a consensus sequence termed the immunoreceptor tyrosine-based activation motif (ITAM). This motif is believed to play a critical role in the receptor-mediated signal transduction. To explore the role of ITAM in signaling for B cell death (apoptosis), we transfected CH31 cells, an immature B lymphoma cell line, with expression vectors encoding for the CD8 extracellular/transmembrane domains and the cytoplasmic signal-transducing domain (ITAM) of Ig alpha or Ig beta, respectively. Here, we demonstrate that cross-linking of CD8:Ig alpha or CD:Ig beta with anti-CD8 mAb effectively induced cell growth arrest and apoptosis characterized by [3H]thymidine release and DNA fragmentation; in contrast, CD8:gamma 2a or truncated CD8:Ig alpha lacking the ITAM could not do so. Moreover, selective point mutation of either of the two conserved tyrosine residues within the ITAM, but not the nonconserved tyrosine, completely abrogated the ability of this motif to mediate cell death signals. These findings clearly indicate that ITAM is a critical component required for transmitting growth arrest and apoptotic signals, and that these functions of ITAM are positively regulated by tyrosine phosphorylation.

Amino Acid Sequence↗
PubMed1995

Differential susceptibility to tolerance induction in vitro of splenic B cells from several transgenic mouse lines. Role of B1 cells.

Spleen cells from transgenic mice, whose rearranged Ig receptors reflect the repertoires of B1 (CD5+ and "sister" B cells) or normal B2 cells, were examined for their ability to be rendered unresponsive. By using an anti-Ig tolerance protocol that is independent of receptor specificity, we previously reported that peritoneal B cells, containing primarily CD5+ and "sister" B cells, were not susceptible to unresponsiveness. Herein, we show that splenic B cells from two separate transgenic mouse lines, each expressing a B1-type receptor, are resistant to tolerance induction in vitro. In contrast, splenic B cells from two other transgenic mouse lines with a large representation of conventional B cells were sensitive to anti-lg-mediated unresponsiveness. This difference does not reside in the surface Ig density, cell cycle, or activation stage of these cells, but is reflected in the initial calcium mobilization and tyrosine phosphorylation after surface Ig cross-linking. Therefore, these results support the hypothesis that the antigenic specificity of B cell receptors may drive cells toward the B1 subset, as suggested by Cong et al. (Cong, Y-Z., E. Rabin, and H. H. Wortis. 1991. Int. Immunol. 3:467-476), and that B1 cell characteristics confer the ability of B cells to withstand in vitro tolerance induction, irrespective of their anatomical location. The possibility that this results from previous antigenic experience is discussed.

Animals↗
PubMed1995

Identification of mast cells in buffy coat preparations from dogs with inflammatory skin diseases.

In 100 dogs with 4 inflammatory dermatologic diseases, buffy coat preparations from EDTA-treated blood samples were examined cytologically. Fifty-four dogs had atopy, 26 had flea-bite hypersensitivity, 17 had sarcoptic mange, and 3 had food allergy. Twenty-eight dogs had 2 or more concurrent skin diseases; most of these had secondary pyoderma. Dogs did not have mast cell tumors. Thirteen samples contained 1 or more mast cells/4 slides reviewed. This study revealed that dogs with inflammatory skin diseases can have a few to many mast cells evident on cytologic examination of buffy coat preparations.

Animals↗
PubMed1995

Lymphoma models for B-cell activation and tolerance: anti-immunoglobulin M treatment induces growth arrest by preventing the formation of an active kinase complex which phosphorylates retinoblastoma gene product in G1.

The product of the retinoblastoma gene, RB-1, is the prototype of a class of tumor suppressor genes that is expressed in most mammalian cells. The RB protein is phosphorylated in a cell cycle-dependent manner and is modulated during cellular differentiation. We have shown previously that anti-immunoglobulin M (anti-mu) treatment of WEHI-231 and CH31 B-lymphoma cells caused cell cycle blockade and apoptosis. In such arrested cells, pRB was predominantly in the underphosphorylated (active) form, in contrast to hyperphosphorylated pRB in control log phase cells. Herein we examine the modulation of pRB phosphorylation by anti-mu and its effect on a cyclin:kinase complex that can act on pRB in murine B-lymphoma cells. In unsynchronized B-lymphoma cells, anti-mu cross-linking of membrane immunoglobulin M leads to an accumulation of the hypophosphorylated form of pRB, a decrease in the abundance of one form of cyclin A, and inhibition of cyclin A and cdk2-associated kinase activity. Using centrifugal elutriation, we also show that anti-mu treatment prevents the phosphorylation of the retinoblastoma gene product only when added in early G1. In addition, there is a critical point after which membrane immunoglobulin M cross-linking is no longer effective at preventing this process. We suggest that anti-mu-mediated growth arrest is due to the direct or indirect inactivation of an active kinase complex capable of pRB phosphorylation.

Animals↗
PubMed1994

Lymphoma models for B cell activation and tolerance. X. Anti-mu-mediated growth arrest and apoptosis of murine B cell lymphomas is prevented by the stabilization of myc.

Treatment of the WEHI-2131 or CH31 B cell lymphomas with anti-mu or transforming growth factor (TGF)-beta leads to growth inhibition and subsequent cell death via apoptosis. Since anti-mu stimulates a transient increase in c-myc and c-fos transcription in these lymphomas, we examined the role of these proteins in growth regulation using antisense oligonucleotides. Herein, we demonstrate that antisense oligonucleotides for c-myc prevent both anti-mu- and TGF-beta-mediated growth inhibition in the CH31 and WEHI-231 B cell lymphomas, whereas antisense c-fos has no effect. Furthermore, antisense c-myc promotes the appearance of phosphorylated retinoblastoma protein in the presence of anti-mu and prevents the progression to apoptosis as measured by propidium iodide staining. Northern and Western analyses show that c-myc message and the levels of multiple myc proteins were maintained in the presence of antisense c-myc, results indicating that myc species are critical for the continuation of proliferation and the prevention of apoptosis. These data implicate c-myc in the negative signaling pathway of both TGF-beta and anti-mu.

Animals↗
PubMed1994

Activation-induced apoptosis in lymphocytes.

Activation-induced apoptosis has been proposed as a mechanism for purging the immune repertoire of anti-self specificities, not only in development but also during the generation of somatic mutation in germinal centers. The pathways involved in driving immature and mature T and B cells to programmed cell death are reviewed with respect to two hypotheses, the pre-emptive death model, in which certain signals are obligatory for programmed cell death, and the two signal: death/survival model. Depending on the system, some data support the former pathway, in which certain signals are obligatory for programmed cell death, whereas other data are consistent with the two signal hypothesis. Moreover, recent data suggests that the c-myc protein plays a pivotal role in controlling this process. Finally conflicting roles of protein kinases, bcl-2 and p53 are reviewed and contrasted for involvement in activation-induced cell death in T and B lymphocytes.

Animals↗
PubMed1994

Clemastine fumarate as an antipruritic agent in pruritic cats: results of an open clinical trial.

Clemastine fumarate was administered to 10 presumed or proven atopic cats to determine its efficacy in controlling their pruritus. Initially, each cat received 0.34 mg orally every twelve hours for 14 days. When none responded satisfactorily, the dosage was increased to 0.68 mg/cat every twelve hours. At that dosage, the pruritus in five cats (50%) was eliminated. Diarrhea was seen in one cat. Under the conditions of the study, clemastine was a useful antipruritic agent for the cat.

Administration, Oral↗
PubMed1994

Efficacy of tylosin tablets for the treatment of pyoderma due to Staphylococcus intermedius infection in dogs.

Tylosin tablets (20 mg/kg, q12h) were administered orally to 21 dogs with superficial or deep staphylococcal pyodermas. Response to therapy was excellent in 90.5% of the dogs, and in vitro susceptibility testing correlated perfectly with therapeutic response. Duration of therapy varied from 17 to 91 days, with an average of 33 days. Relapses occurred in 28.6% of the dogs within a three-month period. No side effects were reported. Under the conditions of the study, tylosin was an effective and safe antibiotic for the treatment of staphylococcal pyoderma in dogs.

Administration, Oral↗