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Biomedical subjects

R M Thorn

Publications and source records attributed to R M Thorn.

At least 19 recordsLinked to original sources
PubMed2001

Effects of goal-setting and feedback on memory performance and beliefs among older and younger adults.

This research examined the impact of goal-setting conditions on memory beliefs and performance among older and younger adults. After baseline recall and assessment of beliefs, participants were assigned to goal-setting, goals plus feedback, or control. Then, additional recall trials were followed by repeated memory beliefs assessments. For both younger and older adults, performance, motivation, and self-efficacy were affected positively by goal-setting. The impact of goals plus feedback was mixed and varied as a function of age and dependent measure. Success rates for reaching memory goals, which were low for the older adults, may have been a factor in these results. Adults' self-set recall goals were predicted initially by baseline performance and self-efficacy. On the final trial, goals were predicted by last trial performance, self-efficacy, and control beliefs.

Adolescent↗
PubMed1989

Assessment of HIV-1 screening test sensitivities using serially diluted positive sera can give misleading results.

Three FDA licensed HIV-1 viral lysate and two nonlicensed recombinant antigen assays were used to evaluate six serially diluted plasma samples and 2 highly characterized seroconversion series. The sensitivity as measured by serial dilution did not necessarily correlate with the sensitivity as measured by seroconversion performance with the lysate and the recombinant assays. It is concluded that national licensing agencies should arrange to share seroconversion panels to evaluate accurately the sensitivity of new HIV-1 screening tests.

Diagnostic Errors↗
PubMed1987

Enzyme immunoassay using a novel recombinant polypeptide to detect human immunodeficiency virus env antibody.

A unique antigen, CBre3, has been synthesized from a genetically engineered clone to detect human immunodeficiency virus (HIV) env antibodies with high sensitivity and specificity. The antigen contains sequences derived from both envelope proteins of HIV, i.e., gp120 and gp41, and was purified free of Escherichia coli proteins detectable by Coomassie stain or immunoblotting with E. coli antiserum. The purified recombinant polypeptides were used as antigen in an enzyme immunoassay (EIA) to screen serum samples from healthy and HIV-infected individuals. The same samples were also tested by radioimmunoprecipitation (RIP) for gp120 and gp160 HIV antibodies. All samples containing gp120 and gp160 antibodies by RIP had CBre3 EIA values greater than 0.35 (n, 122; range, 0.37 to 2.1+; median, 1.65). All RIP HIV antibody-negative samples had CBre3 EIA values less than 0.25 (n, 140; mean, 0.052; standard deviation, 0.045; range, 0.00 to 0.22). The endpoint titer of a standard positive control serum was 1:10,000 by RIP and by CBre3 EIA. The assay was 100% accurate in three proficiency panels. It easily detected six samples from individuals whose infections were confirmed by culture; these samples were reactive only with p24 by Western blot. The samples also were positive for gp120 and gp160 antibodies by RIP. These data suggest that the CBre3 EIA can detect env antibodies as sensitively and specifically as RIP and with more sensitivity than Western blot.

Acquired Immunodeficiency Syndrome↗
PubMed1987

Detection of antibodies to human immunodeficiency virus by latex agglutination with recombinant antigen.

Recombinant human immunodeficiency virus (HIV) env antigen was attached to polystyrene particles, and these complexes were used to develop the first latex agglutination assay for antibodies to HIV. A total of 95 positive and 116 negative human serum samples were assayed for antibodies to HIV by latex agglutination, and results were compared with those of a commercial enzyme immunoassay. Latex agglutination was also compared with, and found to be completely concordant with, Western blot (immunoblot) analysis with virion antigens.

Antibodies, Viral↗
PubMed1987

Diagnosis of human immunodeficiency virus infection by immunoassay using a molecularly cloned and expressed virus envelope polypeptide. Comparison to Western blot on 2707 consecutive serum samples.

To detect human immunodeficiency virus (HIV) antibodies in a simple enzyme-linked immunoassay (CBre3-EIA), we used an Escherichia coli-expressed polypeptide antigen, representing the carboxy-terminal third of the external membrane glycoprotein gene fused with the amino-terminal half of the transmembrane glycoprotein gene. Over a 3-month period, 2707 consecutive serum samples referred for confirmatory testing for human T-lymphotrophic virus type III (HTLV-III) antibodies were evaluated by both Western blot and CBre3-EIA. On a single determination for each sample, the CBre3-EIA was found to have an estimated sensitivity (99.9%) and specificity (99.1%) similar or superior to the more cumbersome Western blot method. This study shows that all HIV-seropositive subjects have antibodies to the virus envelope protein; no other virus antigens are required for construction of highly sensitive immunoassays.

Acquired Immunodeficiency Syndrome↗
PubMed1985

Characterization of the blood lymphocyte population in cattle infected with the bovine leukemia virus.

Blood leukocytes of cattle characterized in terms of bovine leukemia virus (BLV) infection and persistent lymphocytosis (PL) were examined for the presence of lymphocyte subpopulation markers and viral antigens. The percentages of cells with surface and intracytoplasmic immunoglobulin M (IgM) and erythrocyte-antibody-rosetting cells agreed closely in all infected cattle. This correlation and the results of double labeling experiments indicate that virtually all the surface IgM-positive B-lymphocytes in the blood of these animals carry Fc receptors. In PL cattle, the percentages of surface IgM-positive cells were more than twice those of normal cells and accounted for all the increase in peripheral blood lymphocytes. B-cells accounted for most of the increase in peripheral blood lymphocytes seen in cattle with PL. In contrast, most BLV-infected, nonlymphocytotic cattle had normal percentages of B-cells. Thus, the expansion of the B-cell population in blood, while being a conspicuous characteristic of PL, is not necessarily a consequence of BLV infection per se. Comparisons of the percentages of IgM-positive and erythrocyte-antibody complement-rosetting cells, together with the results of double labeling experiments, indicate that about one-half the B-cells in the blood of cattle with PL lacked C-3 receptors. The proportion of these cells (most likely immature B-lymphocytes) was smaller in the blood of BLV-infected nonlymphocytotic cattle. Direct comparison showed that, in BLV-infected cattle with or without PL, and in BLV-free cattle, virtually all erythrocyte-rosetting blood cells had peanut agglutinin receptors. With only one exception, the numbers of erythrocyte-positive cells in the blood of BLV-infected cattle with or without PL were within normal values. The "null" blood cell population, estimated as the difference between the IgM-positive and erythrocyte-positive populations, was essentially unaffected in BLV-infected cattle without PL, but it was absent in PL cattle. The large majority of the B-lymphocytes present in the blood of cattle with PL were infected with BLV. The proportion of infected B-lymphocytes in the blood of BLV-positive nonlymphocytotic cattle was much lower. Even in cattle with low or moderate levels of BLV-infected blood lymphocytes, the percentages of these cells were remarkably constant during the 12-month period of the study. The data indicate that most of the BLV-infected B-lymphocytes of cattle with PL lack C-3 receptors.

Animals↗
PubMed1985

An amplified immunoperoxidase assay to detect bovine leukemia virus expression: development and comparison with other assays.

An amplified immunoperoxidase (AIP) assay using an avidin:biotin complex was developed to detect bovine leukemia virus (BLV) antigen expression in lymphocytes which had been cultured 24 h and fixed with acetone. Nonspecific reactions were eliminated by absorbing the test serum with 100% horse or cow serum. DNA synthesis inhibition did not decrease the number of AIP-positive cells, and there were no apparent preferential losses of major lymphocyte subpopulations during culture. Both viable and nonviable BLV-expressing cells were detected. Thus, the number of AIP-positive cells seems to be a good estimate of the minimum number of infected lymphocytes present in the uncultured blood cells. In direct comparisons, twice as many BLV-expressing cells were detected with the AIP assay as with an indirect immunofluorescence test. The AIP assay is as sensitive as the syncytia infectivity assay and only slightly less sensitive than an immunoperoxidase infectivity assay for detecting BLV-infected lymphocytes in the blood of infected cattle that were in early stages of infection and/or had low titers of antiviral antibodies. The AIP assay is the most sensitive, rapid, and reproducible procedure available for the identification of individual cells infected with BLV. This assay may be of great value in studies on the biology of BLV infection.

Animals↗
PubMed1982

Haemagglutination by bovine leukaemia virus.

Bovine leukaemia virus (BLV) was found to agglutinate mouse erythrocytes. Under optimal conditions, including the use of neuraminidase-treated erythrocytes, 200 microgram/ml of BLV purified from the supernatant fluid of BLV-infected bat cells had haemagglutinating titres of about 512 units. BLV haemagglutination was drastically affected by pH and temperature; maximum agglutination occurred at pH 6 and 4 degrees C. That the BLV haemagglutinin is a glycoprotein was suggested by the fact that trypsin, potassium periodate or neuraminidase, but not lipid solvents or phospholipase C, significantly reduced the haemagglutinating (HA) activity of purified BLV. Furthermore, purified BLV glycoprotein of mol. wt. 51 000 (gp51) had HA activity. The receptors for BLV on mouse erythrocytes were inactivated by proteolytic enzymes but not by sodium deoxycholate or potassium periodate. Neuraminidase treatment of erythrocytes increase their agglutinability fourfold. Haemagglutination is a relatively sensitive test for detecting BLV glycoprotein because 0.4 microgram/ml of glycoprotein can be detected by this method. The pH and temperature sensitivity of the BLV HA reaction and specificity for mouse erythrocytes distinguish BLV from that of equine infectious anaemia virus and murine leukaemia virus, the other C type retroviruses known to have HA activity.

Animals↗
PubMed1981

Further characterization of immunological unresponsiveness induced in mice by ultraviolet radiation. II. Studies on the origin and activity of ultraviolet-induced suppressor lymphocytes.

We are studying the development and mode of action of suppressor T cells induced by ultraviolet (UV) radiation, which prevent the rejection of syngeneic UV-induced tumors. Suppressor cells were induced in C3H mice by exposure to FS40 sunlamps for 1 hr, three times per week for 3 months. Neither thymectomy nor splenectomy prior to UV irradiation prevented the development of these suppressor T cells in other lymphoid tissues. The UV-induced suppressor cells functioned when injected s.c. with mixtures of normal lymphocytes and tumor cells in a Winn-type assay in immunodeficient recipients. When UV T cells were mixed with syngeneic UV-induced tumor cells they did not increase the incidence or growth rate of the tumors relative to tumor cells alone, suggesting that the suppressor cells function by interacting with normal lymphocytes and not by directly stimulating tumor growth. Although the suppressor cells were effective in vivo when injected i.v. or when injected locally with normal lymphocytes, they did not suppress cytotoxic effector lymphocytes in a short-term 51Cr release assay in vitro.

Animals↗
PubMed1981

Evidence that the spontaneous blastogenesis of lymphocytes from bovine leukemia virus-infected cattle is viral antigen specific.

Cattle lymphocytes cultured for 3 days were found to spontaneously incorporate thymidine (3STI). Under optimal conditions of culture, the median magnitude of 3STI activity in lymphocytes from bovine leukemia virus (BLV)-infected cattle was higher than that of BLV-free cattle, but the ranges of the values overlapped. However, the 3STI activity of most BLV-infected cattle was specifically inhibited by serum containing BLV antibodies, whereas the 3STI activity of BLV-free cattle was not. The 3STI inhibitor copurified with immunoglobulin, and its activity could be absorbed with BLV. Rabbit anti-BLV serum inhibited 3STI, but rabbit anti-BLV p25 did not. These results indicate that BLV infection induces or expands a BLV-specific lymphocyte population. Spontaneous blastogenesis may be indicative of an immune response which controls virus spread.

Animals↗
PubMed1979

Further characterization of immunological unresponsiveness induced in mice by ultraviolet radiation. Growth and induction of nonultraviolet-induced tumors in ultraviolet-irradiated mice.

Ultraviolet (UV)-irradiated mice were compared with unirradiated mice for their susceptibility to primary and transplanted tumors etiologically unrelated to UV radiation. Although UV-irradiated mice are unable to reject transplants of highly antigenic syngeneic tumors induced by UV light, the growth of syngeneic, non-UV-induced tumors generally was not accelerated in these animals. Furthermore, UV-irradiated mice were no more susceptible to the induction of primary leukemias, mammary tumors, or sarcomas than were unirradiated animals. Tests of immune responses to weak transplantation antigens showed that UV-irradiated mice rejected H-Y-incompatible skin grafts as vigorously as did normal animals, and that the primary in vitro cytotoxic responses of spleen cells from UV-irradiated mice to trinitrophenyl (TNP)-modified syngeneic cells and to Hh antigens were unaffected. We conclude that the susceptibility of UV-irradiated mice to challenge with UV-induced tumors represents a selective unresponsiveness, and that it is not attributable to a generalized deficiency in the immune response to tumor-specific antigens or to weak transplantation antigens.

Animals↗
PubMed1978

Specific inhibition of cytotoxic memory cells produced against UV-induced tumors in UV-irradiated mice.

Cytotoxic responses of UV-irradiated mice against syngeneic UV-induced tumors were measured by using a 51Cr-release assay to determine if UV treatment induced a specific reduction of cytotoxic activity. The in vivo and in vitro primary responses against syngeneic tumors and allogeneic cells were unaffected, as was the "memory" response (in vivo stimulation, in vitro restimulation) against alloantigens. In contrast, the memory response of UV-treated mice against syngeneic, UV-induced tumors was consistently and significantly depressed. The cytotoxicity generated by tumor cell stimulation in vivo or in vitro was tumor-specific and T cell-dependent. Since the primary response against syngeneic UV-induced tumors produces apparently normal amounts of tumor-specific cytotoxic activity, UV-treated mice may not reject transplanted syngeneic tumors because of too few T effector memory cells. These results imply that, at least in this system, tumor rejection depends mostly on the secondary responses against tumor antigens and that at least one carcinogen can, indirectly, specifically regulate immune responses.

Animals↗
PubMed1976

Studies on the mechanism of lymphocyte-mediated cytolysis. VI. A reappraisal of the requirement for protein synthesis during T cell-mediated lysis.

The role of protein synthesis in the mechanism of T cell-mediated cytolysis has been re-investigated. Cytolytically active (C57BL/L anti-DBA/2) spleen cells treated with pactamycin (10-7 M to 10-6 M) exhibited suppressed protein synthesis (100 +/- 5%), but unimpeded lytic activity. Drug-treated effector cells, incubated for prolonged (up to 24 hr) periods of time in the presence and absence of antigen, showed no siginificant diminution of lytic activity although the incorporation of 3H-leucine into protein was totally ablated. Studies with emetine, another irreversible inhibitor of protein synthesis, gave identical results. These findings are difficult to reconcile with the hypothesis that effector T cells lysis via a soluble protein mediator.

Animals↗
PubMed1976

Kinetic analysis of target cell destruction by effector T cells. I. Delineation of parameters related to the frequency and lytic efficiency of killer cells.

Murine cytotoxic T cell activity was evaluated in analogy with the methods used to characterize enzymes. Concordant with this analogy, the relationship between "steady-state" lytic rates and target cell ("substrate") number was described by a hyperbola, the asymptote of which was the maximum rate of lysis ("V") and was directly proportional to the number of killer cells. The number of target cells required to reach a rate of one-half V ("K") was independent of the number of effector cells, but was found to vary with the total cell concentration in the cultures. The kinetic analogy was extended to analyze this variability by studying the inhibition of cytolysis caused by normal syngeneic lymphocytes. A value for K in the absence of non-killer cells ("Kh") was evaluated. This term, which was independent of effector cell frequency, was a measure of lytic efficiency and, as such, was used to compare various effector cell populations. The Kh value for a number of lymphoid cell populations from identically immunized C57BL/6 mice was found to vary considerably, thereby providing direct evidence that effector populations have different lytic efficiencies. Because of this variability, the widely used practice of comparing killer cell populations solely on the basis of their relative lytic activity may often be invalid.

Animals↗