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Biomedical subjects

L L Johnson

Publications and source records attributed to L L Johnson.

At least 73 records · Page 4Linked to original sources
PubMed1995

Gamma delta T cells and acute primary Toxoplasma gondii infection in mice.

A murine model of Toxoplasma gondii infection was used to investigate whether gamma delta T cells are required to resist primary acute toxoplasmosis. The surface phenotype of peritoneal exudate and spleen cells obtained from T. gondii-infected mice was examined using anti-gamma delta T cell-specific reagents and flow cytometry. Survival of mice depleted of gamma delta T cells was also followed during the acute phase of toxoplasmosis. Numbers of gamma delta T cells did not increase in spleen or peritoneal exudates of mice infected with T. gondii. Moreover, infected mice depleted of gamma delta T cells survived as long as untreated infected mice. These results indicate that gamma delta T cells do not play an important role in host defense against T. gondii infection in mice.

Acute Disease↗
PubMed1995

Role of tumor necrosis factor and gamma interferon in acquired resistance to Cryptococcus neoformans in the central nervous system of mice.

Although naive C.B-17 and BALB/cBy mice die of meningoencephalitis within 5 weeks of intravenous infection with an opportunistic strain of Cryptococcus neoformans, immunized mice express an acquired, CD4+ T-cell-dependent immunity and survive an intravenous infection. Infusion of lymphocytes from immune mice into severe combined immunodeficiency (SCID) mice renders these mice more resistant to cryptococcal brain infection than uninfused controls. We have investigated the role of gamma interferon (IFN-gamma) and tumor necrosis factor (TNF) in acquired resistance to C. neoformans. Neutralization of either IFN-gamma or TNF impaired resistance of immune BALB/cBy or C.B-17 mice to cryptococci. At 10 days postinfection, there were approximately 10 times as many yeast cells in the brains of mice treated with either anticytokine antibody as in the brains of mice treated with control antibody. Simultaneous neutralization of IFN-gamma and TNF further exacerbated infection. Neutralization of IFN-gamma or TNF also impaired resistance in immune lymphocyte-infused SCID mice, resulting in significantly higher yeast burdens in brains of cytokine-neutralized mice than in brains of controls. Concurrent neutralization of IFN-gamma and TNF rendered SCID recipients of immune cells equivalent to uninfused SCID mice with respect both to brain yeast burdens at 10 days and to survival. Anti-TNF treatment alone also curtailed survival. Histological examination of the brains of cytokine-neutralized mice revealed deficiencies in ability to focus inflammatory cells at brain lesions. These data demonstrate that both IFN-gamma and TNF are important mediators of acquired resistance to cryptococcal meningoencephalitis.

Animals↗
PubMed1995

Preimmune resistance to Toxoplasma gondii in aged and young adult mice.

Aged individuals are more susceptible to certain infections than are young adults. To investigate the relative resistance capabilities of aged and young adult mice, responses that are induced within the first week of a Toxoplasma gondii infection, which are known to be involved in preimmune resistance, were compared in young adult and aged mice. Aged mice did not differ reproducibly from young adults in numbers of induced Thy-1+ CD4- CD8- cells or interferon-gamma levels. Numbers of induced CD4+ and CD8+ T cells, associated with acquired immunity, were as high in aged mice as in young adults. Natural killer cell activity, although induced to a high level, was lower in aged mice. Aged mice thus are capable of inducing a mechanism of preimmune resistance to T. gondii and presumably other infectious agents. Nonetheless, aged mice died within 8-12 days after intraperitoneal or peroral inoculation of 500 T. gondii cysts, whereas young adult mice survived. Causes other than an age-related impairment in preimmune resistance mechanisms are apparently responsible for the increased susceptibility of aged mice to T. gondii infection.

Aging↗
PubMed1995

Strong cytolytic activity of natural killer cells is neither necessary nor sufficient for preimmune resistance to Toxoplasma gondii infection.

That strong cytolytic activity of natural killer (NK) cells is neither necessary nor sufficient for defense against acute Toxoplasma gondii infection is demonstrated. T. gondii-infected anti-interferon (IFN)-gamma-treated mice and IFN-gamma gene knockout mice died despite good induction of NK activity, while infected beige mice, deficient in NK cytolytic activity, survived.

Animals↗
PubMed1994

Bacteriophage lambda N-dependent transcription antitermination. Competition for an RNA site may regulate antitermination.

Bacteriophage lambda controls the expression of its early genes in a temporal manner by a series of transcription termination and antitermination events. This antitermination requires the lambda N protein as well as host proteins called Nus, and cis-acting sites called nut. Following transcription of the nut site, N and Nus proteins bind to the nut RNA and modify the transcription complex to a termination-resistant form. The nut site is a composite of at least two components; one is the boxB hairpin structure which interacts with N. The other is boxA, a nine-nucleotide sequence upstream of boxB. To understand more about the formation of the antitermination complex, we have characterized the effect of point mutations in and deletions of boxA on antitermination. Point mutations in boxA were found to either enhance or reduce N-mediated antitermination. Several boxA deletions, on the other hand, had little effect on antitermination other than to eliminate the requirement for the NusB host protein. To explain these observations, we propose that at least two factors compete to interact with boxA, NusB and an inhibitor of the antitermination reaction. In addition, we propose that NusB is required to prevent the inhibitor from binding at boxA. The results with various nusB and boxA mutations can be explained by this model of competition between NusB and an inhibitor for boxA RNA.

Bacterial Proteins↗
PubMed1994

A recombinant human stromelysin catalytic domain identifying tryptophan derivatives as human stromelysin inhibitors.

The human stromelysin catalytic domain (SCD) has been expressed in Escherichia coli and purified to homogeneity (Ye et al. Biochemistry 1992, 31, 11231). We have used this recombinant SCD for inhibitor screening and identified tryptophan derivatives as competitive inhibitors of SCD. Both Cbz-L-Trp-OH (1, IC50 2.5 microM, Ki 2.1 microM) and Boc-L-Trp-OH (3, IC50 10 microM, Ki 8 microM) showed good inhibitory activity. Modification at the indole nitrogen with formyl or mesitylene-2-sulfonyl group (16, IC50 34 microM, Ki 28 microM; 17, IC50 63 microM, Ki 52 microM) showed reduced activity. The amide Cbz-L-Trp-NH2 (13) was not active, but esters Cbz-L-Trp-OSu (14, IC50 13 microM, Ki 11 microM) and Boc-L-Trp-OSu (15, IC50 102 microM, Ki 84 microM) showed activity. Aromatic amino acid derivatives Cbz-L-Tyr-OH (18, IC50 24 microM, Ki 20 microM) and Cbz-L-Phe-OH (26, IC50 40 microM, Ki 33 microM) were also active, but other amino acid derivatives had no activity. Although Cbz-D-Trp-OH (2, IC50 86 microM, Ki 71 microM) was active, the L-configuration is consistently preferred for inhibitory activity. Some of the SCD inhibitors were tested on full-length human stromelysin purified from cultured human cells, and they showed the same potency rank order. These results demonstrate the usefulness of recombinant DNA technology in generating the authentic human protein with improved properties for drug discovery.

Amino Acid Sequence↗
PubMed1994

An alternative health-care reimbursement system--application of arthroscopy and financial warranty: results of a 2-year pilot study.

The results of a 2-year pilot study on an alternative health-care reimbursement system are presented. This innovative system includes a 2-year warranty by the providers to protect the insured and insurer from additional expenses. It is based on the advantages of arthroscopy. This system provided access, choice, and affordability for 111 patients from a managed care environment who were predetermined to be orthopedic surgical candidates. The unique features included unlimited free consultations and office radiographs. Payment was made only if a patient had surgery. This single fee included all related physician and hospital charges for surgery and any subsequent service for the next 2 years under the warranty. The profit margin for the providers was based on the application of arthroscopy, which anticipated reduction in the customary hospitalization. Accountability was provided by reporting of surgical indications and incidence. The surgical incidence of 42% was less than what was projected. The health maintenance organization insurer saved in excess of $125,000.00. Both the hospital and the surgeon earned more than under existing reimbursement systems.

Arthroscopy↗
PubMed1994

Resistance to Toxoplasma gondii in mice infected as neonates or exposed in utero.

Mice were exposed to the protozoan parasite Toxoplasma gondii in utero or were infected as neonates in order to identify and characterize resistance mechanisms that function protectively during the first weeks after birth. About one-half of the mice born of mothers fed T. gondii cysts at 11 days of gestation survived to weaning age or beyond. No effect of major histocompatibility complex (MHC) haplotype on early survival was observed in a group of backcross progeny; however, long-term survival was strongly dependent on MHC haplotype. The ability of mice infected as neonates to survive until weaning was found to depend on gamma interferon and on Thy-1+ cells but not on CD4+ or CD8+ cells. Mice that survived to maturity after infection as neonates were slightly more resistant to challenge with virulent T. gondii parasites than were sham-infected controls but were less resistant than were mice infected as adults. Together the results indicate the following. (i) Mice congenitally infected with T. gondii have a gamma interferon-dependent mechanism of early resistance that involves Thy-1+ cells but not CD4+ or CD8+ cells. (ii) This mechanism is not under MHC-linked genetic control. (iii) Mice that exhibit long-term survival after congenital infection acquire a modest degree of protection against reinfection with virulent organisms. (iv) The extent of long-term survival of congenitally infected neonates, like that in mice infected as adults, is influenced by MHC genes, presumably via MHC-restricted CD4+ and/or CD8+ cells.

Animals↗
PubMed1994

Role for 10Sa RNA in the growth of lambda-P22 hybrid phage.

Certain lambda-P22 hybrids, providing that they express the P22 C1 protein, fail to grow in Escherichia coli with the sipB391 mutation. We show that sipB391, previously located to the 57-min region of the E. coli chromosome, is a large deletion that extends into the 3' end of ssrA, a gene encoding the small stable 10Sa RNA. This deletion, apparently created by the excision of a cryptic prophage, CP4-57 (identified by Kirby et al. [J. E. Kirby, J. E. Trempy, and S. Gottesman, J. Bacteriol. 176:2068-2081]), leaves most of ssrA intact but removes the sequence encoding the 3' end of the precursor form of 10Sa RNA. The lack of functional 10Sa RNA, resulting from either the excision of CP4-57 or insertional inactivation of ssrA, appears to be responsible for the inhibition of lambda-P22 growth in E. coli with the sipB391 mutation. We propose that 10Sa RNA acts either directly or indirectly to facilitate removal of C1 protein from its DNA target site.

Bacteriophage P22↗
PubMed1994

Relationships between toxicopathic hepatic lesions and exposure to chemical contaminants in English sole (Pleuronectes vetulus), starry flounder (Platichthys stellatus), and white croaker (Genyonemus lineatus) from selected marine sites on the Pacific Coast, USA.

Relationships between hepatic lesions and chemical contaminant concentrations in sediments, stomach contents, liver tissue, and bile were statistically evaluated in three species of bottomfish, English sole (Pleuronectes vetulus), starry flounder (Platichthys stellatus), and white croaker (Genyonemus lineatus), captured from 27 urban and nonurban sites on the Pacific Coast from Alaska to southern California. Lesions detected were neoplasms, preneoplastic foci of cellular alteration, nonneoplastic proliferative lesions, unique or specific degenerative/necrotic lesions, nonspecific degenerative/necrotic lesions, and hydropic vacuolation of biliary epithelial cells and hepatocytes. In general, lesion prevalences were significantly higher in all three species captured at chemically contaminated urban sites, and certain lesions had significantly higher relative risks of occurrence at urban sites in Puget Sound, San Francisco Bay, the vicinity of Los Angeles, and San Diego Bay. Concentrations of polycyclic aromatic hydrocarbons, polychlorinated biphenyls, DDT and its derivatives, and chlordanes and dieldrin in sediment, stomach contents, liver, and fluorescent aromatic compounds in bile were significant risk factors for the occurrence of neoplastic, preneoplastic, nonneoplastic proliferative, and specific degenerative/necrotic lesions, as well as hydropic vacuolation. Fish age also had a significant influence on occurrence of several hepatic lesions, but gender was rarely a significant risk factor. These relationships provide strong evidence for the involvement of environmental contaminants in the etiology of hepatic lesions in several marine bottomfish species and clearly indicate the utility of these lesions as biomarkers of contaminant-induced effects in wild fish.

Animals↗
PubMed1994

Role of imaging in assessment of ischemic heart disease.

We review recent advances in cardiac imaging for the evaluation of patients with ischemic heart disease. Noninvasive imaging modalities discussed include radionuclide perfusion imaging, new applications of echocardiography, metabolic imaging with positron-emission tomography, and magnetic resonance imaging and ultrafast computed tomography. New clinical applications in radionuclide perfusion imaging include prognostic assessment of normal perfusion scans in patients who do and do not reach target heart rate, new pharmacologic stress modalities including dobutamine stress and adenosine vasodilation, and improved assessment of patients with left bundle branch block using pharmacologic stress. In addition, new radiotracers, technical considerations, and new imaging protocols are discussed. Assessment of myocardial viability using conventional radionuclide perfusion imaging agents, positron-emission tomography, and echocardiographic techniques is reviewed. Cine magnetic resonance imaging and ultrafast computed tomography are evolving technologies; their application to the noninvasive diagnosis of coronary artery disease has received recent attention.

Animals↗
PubMed1994

Myocardial perfusion imaging with technetium-99m-teboroxime.

Technetium-99m-teboroxime is a myocardial perfusion imaging radiotracer that, although not widely used in clinical practice, has the potential to provide valuable diagnostic information. Teboroxime's high myocardial extraction and rapid in vivo myocardial clearance make stress/rest studies possible using very short imaging protocols. In addition, differential washout of 99mTc-teboroxime produces defect filling on early delayed images in a high percentage of patients, potentially eliminating the need for a second rest injection. Finally, because of its rapid myocardial clearance, serial injections of 99mTc-teboroxime in an acute myocardial infarction (MI) setting can provide information on infarct vessel patency based on defect size and can help document the success or failure of reperfusion therapy.

Exercise Test↗
PubMed1993

Assignments for the main-chain nuclear magnetic resonances and delineation of the secondary structure of the catalytic domain of human stromelysin-1 as obtained from triple-resonance 3D NMR experiments.

We report the NMR assignments for the main-chain 13C, 15N, and 1H resonances (1HN, 1H alpha, 15N alpha, 13C alpha, 13CO) for the 19.5-kDa catalytic domain of human stromelysin-1, a zinc endoproteinase thought to be involved in pathologic tissue degradation. The assignments were predominantly obtained from triple-resonance three-dimensional NMR experiments using double-labeled (15N/13C) samples. The secondary structure of the molecule was determined from analysis of 3D 15N-resolved NOESY experiments. It was found to consist of a five-stranded mixed beta-sheet with four parallel and one antiparallel strand and three helices. The topological arrangement of the secondary structure elements of stromelysin catalytic domain is remarkably similar to that found for astacin, a Zn proteinase for which the tertiary structure was recently determined from X-ray diffraction data [Bode et al. (1992) Nature 358, 164-167].

Amino Acid Sequence↗
PubMed1993

A single-base-pair mutation changes the specificities of both a transcription activation protein and its binding site.

The C1 protein of bacteriophage P22 binds to a unique site in the -35 region of the PRE promoter and activates transcription of the phage c2 repressor gene. This -35 target has an approximate direct repeat that overlaps the 5' end of the c1 coding region. We have isolated a single-base-pair mutation in this region that changes the PRE -35 target as well as the amino-terminal region of the C1 protein. Although the mutant C1 protein activates the mutant PRE promoter, it fails to activate the wild-type PRE promoter. This suggests that a single-base-pair mutation changes the specificities of both a protein and its target site. These studies also indicate that C1 binding to DNA is influenced by contacts made through residues near the amino terminus.

Amino Acid Sequence↗
PubMed1993

Induction of long-term H-Y-specific tolerance in female mice given male lymphoid cells while transiently depleted of CD4+ or CD8+ T cells.

Rejection of H-Y-bearing primary skin grafts and generation of H-Y-specific cytolytic T cells by female mice requires the participation of both CD4+ and CD8+ T lymphocytes. Studies were conducted to investigate long-term tolerance of H-Y antigen induced in female mice by transiently depleting them of CD4+ and/or CD8+ T cells and, at the same time, giving them an injection of male lymphoid cells. We confirmed that after recovery of CD4+ to normal levels, female mice that had been transiently depleted of CD4+ cells and concurrently given an injection of male spleen cells were unable to generate H-Y-specific cytolytic T cells. Tolerance was also manifest by greatly extended survival (probably permanent in most cases) of male skin grafts. Further investigations revealed that female mice transiently depleted of CD8+ cells, and concurrently given an injection of male spleen cells, were similarly tolerant of H-Y antigen later when numbers of CD8+ T cells returned to normal. Moreover, small numbers of male cells were detectable in spleen and lymph nodes of tolerant females long after they had been given an injection of male cells and depleted of either CD4+ or CD8+ T cells, whereas no male cells were detected in (nontolerant) females given male cells and control antibodies. These findings show that tolerance of the relatively weak transplantation antigen, H-Y, can be achieved simply by giving male antigen-bearing spleen cells to the host while it is transiently depleted of a type of cell it needs in order to reject those cells, thus allowing the male cells to persist in the host. Furthermore, depletion of helper cells is not obligatory to achieve tolerance. It has been hypothesized that tolerance of H-Y antigen in females given male lymphoid cells while temporarily depleted of CD4+ lymphocytes results from unresponsiveness (anergy) induced in H-Y-specific CD8+ cells that are exposed to H-Y antigen in the absence of help from CD4+ cells. Interpretations of our findings are discussed in relation to this hypothesis.

Animals↗
PubMed1993

The outcome of a free autogenous semitendinosus tendon graft in human anterior cruciate reconstructive surgery: a histological study.

This report illustrates the outcome of a free human autogenous semitendinosus tendon graft placed in the knee under arthroscopic control for anterior cruciate ligament reconstruction. The tendon graft showed signs of injury by localized loss of normal histochemical staining properties. The cellularity was not diminished in an early (3-week) specimen. The resultant composite anterior cruciate ligament consisted of two distinct areas: tendon graft and surrounding fibrous tissue. The tendon maintained gross and microscopic characteristics of the original tendon. The tissue surrounding the tendon graft had a disorganized cellular pattern and hypervascularity. The tendon graft in this study did not show gross or microscopic evidence of death and reorganization. Previous reports have led to erroneous conclusions concerning the outcome of a free tendon graft due to inaccurate biopsy site of the reorganizing fibrous tissue surrounding the tendon graft.

Adult↗