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Biomedical subjects

R H Stevens

Publications and source records attributed to R H Stevens.

At least 19 recordsLinked to original sources
PubMed1992

Inhibition of B cell proliferation by antisense DNA to both alpha and beta forms of Fc epsilon R II.

Epstein-Barr Virus (EBV) infection activates B lymphocyte proliferation through partially understood mechanisms, resulting in phenotypic changes, including the appearance of new antigens. One such antigen is Fc epsilon R II/CD-23 which may be relevant for B cell proliferation. We have used anti-sense oligonucleotides to study the importance of the two forms of this molecule for proliferation in the EBV-transformed, Fc epsilon R II +ve lymphoblastoid B cell line, RPMI 8866. Anti-sense oligodeoxynucleotides were generated to the two forms of Fc epsilon R II; Fc epsilon R IIa (alpha) and IIb (beta) which differ only in their intracytoplasmic domains. Addition of increasing concentrations of anti-sense oligonucleotides, ranging from 1 to 30 microM, significantly decreased cellular proliferation as measured by the incorporation of [3H]thymidine (inhibition range 8-88%). Optimum inhibition of cellular proliferation was apparent at 15 microM concentration of both anti-sense Fc epsilon R IIa and IIb (Fc epsilon R IIa, mean +/- SE = 75 +/- 7% inhibition, p less than 0.001; Fc epsilon R IIb, mean +/- SE = 71 +/- 7% inhibition, p less than 0.001). Anti-sense oligonucleotides complementary to the common part of Fc epsilon R II resulted in a similar inhibition of proliferation. Sense oligonucleotides did not induce significant inhibition. Preincubation of sense and anti-sense oligonucleotides resulted in an abrogation of proliferation inhibition. Moreover, none of these oligonucleotides had any effect on a Fc epsilon R II -ve cell line. Incubation with both anti-sense IIa and IIb resulted in additive, but not synergistic inhibition of proliferation. Addition of soluble Fc epsilon R II did not reverse inhibition of proliferation, suggesting that membrane-bound or intracellular rather than soluble Fc epsilon R II was important for the induced proliferation. Analysis of cell surface expression for Fc epsilon II indicated that while there was a pronounced effect on cell number following incubation with anti-sense oligonucleotides, surface expression of Fc epsilon R II was consistent as measured over different time points. PCR analysis revealed that while most cells expressed either the alpha or the beta form of Fc epsilon R II, EBV-transformed cell lines, particularly RPMI 8866, were found to express both alpha and beta forms simultaneously. This may constitute a mechanism whereby EBV infection confers an immortal state to the cell, resulting in its uncontrolled proliferation. Cell lines expressing only one receptor form, either alpha or beta, were unaffected after incubation with anti-sense oligonucleotides.(ABSTRACT TRUNCATED AT 400 WORDS)

B-Lymphocytes↗
PubMed1992

Can artificial neural networks provide an "expert's" view of medical students performances on computer based simulations?

Artificial neural networks were trained to recognize the test selection patterns of students' successful solutions to seven immunology computer based simulations. When new student's test selections were presented to the trained neural network, their problem solutions were correctly classified as successful or non-successful > 90% of the time. Examination of the neural networks output weights after each test selection revealed a progressive increase for the relevant problem suggesting that a successful solution was represented by the neural network as the accumulation of relevant tests. Unsuccessful problem solutions revealed two patterns of students performances. The first pattern was characterized by low neural network output weights for all seven problems reflecting extensive searching and lack of recognition of relevant information. In the second pattern, the output weights from the neural network were biased towards one of the remaining six incorrect problems suggesting that the student mis-represented the current problem as an instance of a previous problem.

Allergy and Immunology↗
PubMed1991

In vitro regulation of B cell differentiation by interleukin-6 and soluble CD23 in systemic lupus erythematosus B cell subpopulations and antigen-induced normal B cells.

Polyreactive systemic lupus erythematosus (SLE) B cells were compared with antigen-induced SLE and normal B cells for their interleukin-6 (IL-6) and soluble CD23 requirements. Unlike normal B cells, secretion of antibody by SLE B cells in serum-free medium was not enhanced by exogenous IL-6. Anti-IL-6 antibodies inhibited immunoglobulin production in cultures of normal and SLE B cells, which suggests that IL-6 is required for B cell differentiation. SLE culture supernatants had elevated levels of IL-6, which explains the poor response of the SLE cells to exogenous IL-6. Soluble CD23 enhanced the responses of cells from normal subjects and SLE patients.

Adult↗
PubMed1990

Interleukin 6 is essential for antibody secretion by human in vivo antigen-induced lymphoblastoid B cells.

In vivo immunization of normal subjects with a variety of antigens generates circulating lymphoblastoid (LB) B cells, which in vitro spontaneously secrete significant levels of specific antibody. Since activation and initial differentiation of these cells occurs in vivo, they provide a useful model for the study of the later stages of B cell maturation. In the present study, we investigated the requirement of interleukin 6 (IL-6) for the "spontaneous" in vitro production of IgG-Tet by LB B cells. Addition of IL-6 to cultures of LB B cells in medium supplemented with 10% fetal calf serum failed to increase the levels of IgG-Tet produced in vitro. However, addition of anti-IL-6 antibodies decreased IgG-Tet production as much as 70%, and this inhibition could be reversed by the addition of IL-6. LB B cells cultured in serum-free medium in order to restrict endogenous IL-6 production secreted only low levels of antibody, unless exogenous IL-6 was added. Addition of 2.5 units/ml of IL-6 to serum-free cultures induced an increase in IgG-Tet secretion nearly comparable to that seen in cultures supplied with serum. The magnitude of the increase in IgG-Tet secretion in response to exogenous IL-6 was inversely related to the number of cells in culture, which was due in part to increased endogenous IL-6 production in cultures with higher cell concentrations. Experiments including hydroxyurea in serum-free cultures indicated that IL-6-dependent enhancement of LB B cells' IgG-Tet secretion was not primarily mediated by cell growth. These observations suggest that in vivo generated LB B cells are not totally committed to antibody secretion, and that IL-6 is essential for in vivo antigen-induced LB B cells to reach the antibody-secreting stage.

Antibodies↗
PubMed1990

Soluble CD23 containing B cell supernatants induce IgE from peripheral blood B-lymphocytes and costimulate with interleukin-4 in induction of IgE.

The role of soluble fragments of CD23 and their relationship to interleukin-4 (IL-4) in the in vitro production of IgE by normal human peripheral blood mononuclear cells was examined. Most donors' cells were induced to produce IgE in vitro by IL-4 during a 9- to 21-day culture. This stimulation was not observed in the absence of T cells. Inability of IL-4 to induce IgE in nonresponding cultures was associated with a failure to express CD23 on Lev-19+ natural killer cells; CD23 expression on B cells and monocytes was equivalent in responding and nonresponding subjects. Concentrated supernatants from Epstein-Barr virus-transformed B cell lines containing soluble fragments (sCD23) of the low-affinity Fc epsilon R (Fc epsilon R-II, CD23) induced IgE from all donors' cells in the absence of T cells. The sCD23 containing supernatants were demonstrated to be devoid of IL-4, and their effect could not be abrogated by anti-IL-4. IgE induction by both IL-4 and sCD23-containing supernatant were blocked by anti-CD23 monoclonal antibody. Affinity absorption of sCD23 removed the IgE-inducing activity. The cells most responsive to the sCD23 material were small, resting B cells rather than large in vivo activated cells. IL-4 synergized with sCD23-containing supernatant in the T cell-depleted cultures, and limiting dilution analyses demonstrated that IL-4 caused a more than tenfold increase in the precursor frequency of cells capable of responding to sCD23-containing supernatant with IgE production. These data are consistent with the hypothesis that IL-4 has multiple effects in the ultimate induction of human IgE including (1) commitment of B cells to IgE and (2) the generation of natural killer cell sCD23 fragments that subsequently drive IgE-committed cells to IgE synthesis.

Adult↗
PubMed1990

AIDS Kaposi sarcoma-derived cells produce and respond to interleukin 6.

Cell lines derived from Kaposi sarcoma lesions of patients with AIDS (AIDS-KS cells) produce several cytokines, including an endothelial cell growth factor, interleukin 1 beta, and basic fibroblast growth factor. Since exposure to human immunodeficiency virus increases interleukin 6 (IL-6) production in monocytes and endothelial cells produce IL-6, we examined IL-6 expression and response in AIDS-KS cell lines and IL-6 expression in AIDS Kaposi sarcoma tissue. The AIDS-KS cell lines (N521J and EKS3) secreted large amounts of immunoreactive and biologically active IL-6. We found both IL-6 and IL-6 receptor (IL-6-R) RNA by slot blot hybridization analysis of AIDS-KS cells. The IL-6-R was functional, as [3H]thymidine incorporation by AIDS-KS cells increased significantly after exposure to human recombinant IL-6 (hrIL-6) at greater than 10 units/ml. When AIDS-KS cells (EKS3) were exposed to IL-6 antisense oligonucleotide, cellular proliferation decreased by nearly two-thirds, with a corresponding decrease in the production of IL-6. The decrease from IL-6 antisense in AIDS-KS cell proliferation was reversed by the addition of hrIL-6. We confirmed that AIDS-KS cells produced IL-6 in vivo by preparing RNA and tissue sections from involved and uninvolved skin from a patient with AIDS Kaposi sarcoma. We detected immunoreactive IL-6 in the involved tumor areas and to a lesser extent in the surrounding normal epidermis. Slot blot hybridization showed a great excess of IL-6 and IL-6-R RNA in involved skin compared to uninvolved skin. These results show that both IL-6 and IL-6-R are produced by AIDS-KS cells and that IL-6 is required for optimal AIDS-KS cell proliferation, and they suggest that IL-6 is an autocrine growth factor for AIDS-KS cells.

Acquired Immunodeficiency Syndrome↗
PubMed1990

Human IgG anti-F(ab')2 antibodies possess rheumatoid factor activity.

Individual preparations of affinity purified anti-F(ab')2 antibodies and anti-Fc antibodies isolated from the sera of patients with rheumatoid arthritis (RA), were examined for reactivity with the Fab and Fc fragments of human IgG. Western blot assays demonstrated specific interaction of affinity-purified anti-Fab antibodies with both Fab and Fc molecules. Approximately one-half of the anti-Fab antibody preparations studied contained IgG antibodies reactive with Fab and Fc fragments in ELISA, suggesting the existence of naturally occurring epibody-like autoantibodies in these patients. Thirteen of 14 affinity-purified anti-Fc antibody preparations contained IgG cross-reactive with Fab molecules in ELISA. Double-adsorption assays on affinity columns demonstrated that a minimum of 14%, and possibly as much as 50%, of the IgG anti-Fab antibodies reacted with the Fc of IgG. Conversely, a minimum of 12%, and possibly as much as 70%, of the IgG anti-Fc antibodies reacted with IgG Fab molecules. Anti-Fab antibodies isolated from non-RA individuals also exhibited anti-Fc reactivity in ELISA, demonstrating the presence of these dual-reactive antibodies in other autoimmune and normal individuals. These studies establish the presence of naturally occurring IgG autoantibodies reactive with both the Fab and Fc fragments of human IgG. Their existence emphasizes the potential of anti-immunoglobulin antibodies to recognize a multiplicity of antigens, possibly including other members of the immunoglobulin supergene family.

Antibody Specificity↗
PubMed1990

Structural proteins of the Actinobacillus actinomycetemcomitans bacteriophage phi Aa.

øAa is an A1 morphotype bacteriophage which infects certain strains of Actinobacillus actinomycetemcomitans. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis of dissociated, purified phi Aa particles revealed 7 major structural proteins (P1-P7) ranging in size from 17.5 to 52.7 kilodaltons (Kd). Treatment of the intact phage particles with 67% dimethyl sulfoxide (DMSO) resulted in the separation of the virion head and tail subunits. Purification of the head subunits was accomplished by sucrose density gradient centrifugation of the DMSO-treated phage particles. The purified head subunits were composed of a single protein having an electrophoretic mobility which corresponded to a 39.5 Kd protein (P3) of the intact virus. Raising the pH of a purified phi Aa suspension to 12.7 disrupted the head subunits, as well as the tail tube and tail fibers, releasing intact contractile tail sheaths. The tail sheaths were collected by centrifugation. The purified tail sheaths were analyzed by SDS-PAGE and were found to be composed of two proteins (P1 and P2) having molecular weights of 52.7 and 41.2 Kd respectively. The location of each of the 4 remaining major structural proteins in the phi Aa virion remains to be determined.

Actinobacillus↗
PubMed1990

Administering a microcomputer-based problem-solving examination.

Administering a microcomputer-based problem-solving examination in the basic sciences to medical students poses a series of practical concerns not associated with traditional types of testing. This article reviews the issues of planning, student preparation, exam scheduling, student verification, and software security. Also discussed are the effects on student scores of exam scheduling and of students' familiarity with computers, student evaluations of the exam, and security and technical difficulties.

Allergy and Immunology↗
PubMed1989

Animal model of conjunctival primary acquired melanosis.

A condition clinically identical to human conjunctival primary acquired melanosis (PAM) was induced in 16 of 20 Dutch (pigmented) rabbits after weekly topical 60-microliters applications of a 1% solution of 7,12-dimethylbenz[a]anthracene (DMBA) in acetone. Pigment stippling appeared in the conjunctiva as early as 5 weeks after the initial carcinogen application. Confluent patches of flat pigmentation appeared over the palpebral conjunctiva 18 weeks after the onset of treatment and showed progressive lateral enlargement and darkening. Histologically, a spectrum of changes from increased melanin production and melanocytic hyperplasia without atypia (resembling the human condition of PAM without atypia) through atypical melanocytic hyperplasia (resembling human PAM with atypia) was identified. The development of this model permits further investigations to explore and explain the clinically observed phenomenon of waxing and waning of PAM and its promotion to conjunctival malignant melanoma.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1989

Evaluating preclinical medical students by using computer-based problem-solving examinations.

A study was designed to determine the feasibility of creating and administering computer-based problem-solving examinations for evaluating second-year medical students in immunology and to determine how students would perform on these tests relative to their performances on concurrently administered objective and essay examinations. The results indicate that problem-solving questions of uniform difficulty can be created and that correct solution of the problems correlates with the early selection of the most relevant data. The mean scores on the three types of tests were not significantly different. The scores on the essay and objective examinations were most highly correlated, those on the computer-based and objective examinations were minimally correlated, and those on the computer-based and essay examinations were not correlated.

Allergy and Immunology↗
PubMed1988

Serum IgG4 anti-Fab antibodies in rheumatoid arthritis are constitutively expressed.

IgG4 comprises a significant proportion of the total anti-Fab antibody (aFABA) response in many but not all patients with rheumatoid arthritis (RA). Analyses of the dynamics of IgG aFABA subclass expression in 11 RA patients for periods of up to 11 months demonstrated that IgG4 aFABA was restricted to 6 of the 11 RA patients' sera initially studied and comprised approximately 25% (or more) of the total IgG aFABA response. Quantities of IgG4 aFABA in subsequent, serially obtained serum samples from these patients remained stable throughout the study period, whereas the remaining RA patients whose initial sera possessed small quantities of serum IgG4 aFABA failed to generate any augmented IgG4 aFABA response during the study. Elevated expression of IgG4 aFABA did not appear to be a consequence of a generalized polyclonal gammopathy or a generalized increase in autoantibody expression, though patients with higher total IgG4 serum levels expressed significantly greater quantities of IgG4 aFABA. These results indicate that the differential expression of IgG4 aFABA among RA patients reflects constitutive production within a subset of RA patients in whom IgG4 appears to comprise a significant proportion of the total IgG aFABA response.

Antibodies, Anti-Idiotypic↗
PubMed1988

Recognition by anti-Fab antibodies in rheumatoid arthritis of structure(s) widely distributed on human Fab molecules.

Anti-Fab antibodies (aFABA) of restricted clonality and acidic spectrotypes were isolated from the sera of patients with rheumatoid arthritis (RA). These aFABA reacted with multiple populations of pooled human Fab molecules, which had been charge separated by chromatofocusing techniques (CF), indicating that the structures recognized by these aFABA were present on a polyclonal population of Fab molecules. The structures were also widely distributed among the Fab repertoires of normal individuals, as well as individual autologous and heterologous RA patients. Thus, the aFABA did not appear to recognize highly restricted epitope(s), i.e. a private idiotope, limited in its expression to RA individuals. The determinants of the Fab molecules recognized by affinity purified aFABA could be defined by linear and/or conformational structures, depending upon the individual from which the aFABA were isolated. Additionally, some of the affinity purified aFABA also reacted with Fc fragments, suggesting the presence of epibody-like autoantibodies in this population. Lastly, size analysis of the circulating IgG4 aFABA complexes indicated that these autoantibodies were not complexed with intact IgG, but rather with a molecule of 40-60 kDa, further suggesting the potential for these autoantibodies to react with multiple antigens.

Arthritis, Rheumatoid↗
PubMed1988

The comparative cytotoxicity of periodontal bacteria.

The direct cytotoxicity of sonic extracts (SE) from nine periodontal bacteria for human gingival fibroblasts (HGF) was compared. Equivalent dosages (in terms of protein concentration) of SE were used to challenge HGF cultures. The cytotoxic potential of each SE was assessed by its ability to (1) inhibit HGF proliferation, as measured by direct cell counts; (2) inhibit 3H-thymidine incorporation in HGF cultures; or (3) cause morphological alterations of the cells in challenged cultures. The highest concentration (500 micrograms SE protein/ml) of any of the SEs used to challenge the cells was found to be markedly inhibitory to the HGFs by all three of the criteria of cytotoxicity. At the lowest dosage tested (50 micrograms SE protein/ml); only SE from Actinobacillus actinomycetemcomitans, Bacteroides gingivalis, and Fusobacterium nucleatum caused a significant effect (greater than 90% inhibition or overt morphological abnormalities) in the HGFs as determined by any of the criteria employed. SE from Capnocytophaga sputigena, Eikenella corrodens, or Wolinella recta also inhibited cell proliferation and thymidine incorporation at this dosage; however, the degree of inhibition (5-50%) was consistently, clearly less than that of the first group of three organisms named above. The SE of the three other organisms tested (Actinomyces odontolyticus, Bacteroides intermedius, and Streptococcus sanguis) had little or no effect (0-10% inhibition) at this concentration. The data suggest that the outcome of the interaction between bacterial components and normal resident cells of the periodontium is, at least in part, a function of the bacterial species.

Bacterial Physiological Phenomena↗