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Biomedical subjects

D Nixon

Publications and source records attributed to D Nixon.

At least 19 recordsLinked to original sources
PubMed2000

An antigenic threshold for maintaining human immunodeficiency virus type 1-specific cytotoxic T lymphocytes.

BACKGROUND: Using the lymphocytic choriomeningitis virus (LCMV) model in mice, a number of studies show that memory cytotoxic T-lymphocyte (CTL) responses are maintained in the presence of continuous antigenic stimulation. Yet, other groups found that memory CTL specific for LCMV could last for a lifetime in mice without viral antigens. Thus, the extent to which an antigen is required for the maintenance of virus-specific CTL remains controversial. In humans, very few studies have been conducted to investigate the relationship between the quantity of antigen and the magnitude of CTL responses. MATERIALS AND METHODS: We quantified CTL precursors (CTLp) using a limiting-dilution analysis (LDA) and CTL effectors (CTLe) using a new Major Histocompatibility Complex (MHC) class I tetramer technology in six long-term nonprogressors (LTNPs) with human immunodeficiency virus type-1 (HIV-1) infection, as well as in eight patients whose viral loads were well suppressed by antiretroviral therapy. The viremia levels in these patients were measured using an reverse transcription polymerase chain reaction (RT-PCR) assay. The proviral DNA load in peripheral blood mononuclear cell (PBMC) was also measured by PCR in four LTNPs. RESULTS: The LTNPs had high levels of HIV-1-specific memory CTLp and CTLe, while maintaining a low plasma viral load. Despite also having low viral loads, patients whose plasma viremia was well-suppressed by effective therapy had low levels of CTLe. CONCLUSIONS: Our findings suggest that a complex, rather than a monotonic, relationship exists between CTL levels and HIV-1 viremia, including what appears to be an antigenic threshold for the maintenance of CTL at a measurable level. Under conditions of "antigen excess,", CTLe levels correlate inversely with viral load. On the other hand, under conditions that are "antigen limited," the correlation appears to be direct.

Adult↗
PubMed1999

A recombinant vaccinia virus based ELISPOT assay detects high frequencies of Pol-specific CD8 T cells in HIV-1-positive individuals.

OBJECTIVES: HIV-1-specific CD8 T cells are considered to be critical in anti-HIV responses. It is important to quantify these cells and to determine their antigenic targets. Here quantification of interferon (IFN)-gamma secreting, virus-specific cells was achieved with an enzyme linked immuno spot (ELISPOT) assay. METHODS: Peripheral blood mononuclear cells (PBMC) were infected with recombinant vaccinia vectors expressing HIV-1 genes (gag, pol, env or nef) and added to wells precoated with anti-IFN-gamma monoclonal antibodies. Spot forming cells (SFC), i.e. antigen-specific T cells were detected 24 h later by the addition of biotinylated anti-IFN-gamma monoclonal antibodies, followed by avidin-bound biotinylated horseradish peroxidase. RESULTS: In a cohort of 19 patients, of whom 15 were on highly active antiretroviral therapy, 18 had primed T cells directed against one or more HIV-1 antigens (P < 0.0001). Pol-specific T cells routinely dominated the CD8 response with frequencies up to 2000 SFC per 10(6) PBMC. In HLA A*0201-positive patients, the vaccinia vectors detected much higher frequencies of SFC than haplotype-restricted peptides. Elimination of CD8 T cells resulted in > 90% loss of antigen-specific SFC when vaccinia virus was used as a vector. The number of CD8 SFC exceeded the number of memory cells detected in limiting dilution assays by > 1 log10, whereas a correlation was found between the frequency of effector cells detected by both ELISPOT and MHC class I peptide tetramer assays. CONCLUSIONS: Vaccinia virus vectors used in ELISPOT assays are useful for determining the frequency and specificity of CD8 T cells for individual HIV-1 gene products. The dominance of cytolytic T lymphocytes (CTL) recognizing pol proteins suggests that this antigen should be considered in vaccine strategies.

Adult↗
PubMed1998

Pleural body cavity-based lymphoma.

We report a case of recurrent body cavity-based non-Hodgkin's lymphoma in a patient with advanced acquired immunodeficiency syndrome who presented with bilateral pleural effusions, without evidence of an associated tumor mass. The lymphoma cells were large and pleomorphic, lacking pan-T- and pan-B-cell markers, but expressing activation markers (CD30, CD38, and HLA-DR). The purpose of this article is to discuss the radiological-pathological correlation of body cavity-based lymphoma with a review of the entities that should be included in the differential diagnosis of patients with malignant pleural effusions.

Acquired Immunodeficiency Syndrome↗
PubMed1998

Silicon analysis of breast and capsular tissue from patients with saline or silicone gel breast implants: II. Correlation with connective-tissue disease.

The silicone breast implant controversy rages on. Recent work has demonstrated that normal or baseline breast tissue silicon levels in women who had had no prior exposure to any type of breast implant may be as high as 446 microg/gm of tissue. These data ranged from 4 to 446 microg/gm of tissue, with a median of 27.0 microg/gm of tissue. In addition, numerous other epidemiologic and rheumatologic studies have demonstrated no association between silicone breast implants and any connective-tissue diseases. Despite these reports, the use of silicone implants remains restricted. The present study measured breast and capsular tissue silicon levels from 23 breasts in 14 patients with saline implants, and from 42 breasts in 29 patients with silicone implants. No patient in the saline implant group presented with signs or symptoms of connective-tissue disease. Patients with silicone implants, however, were divided into three groups based on the presence or absence of signs or symptoms of connective-tissue disease: group I, no symptoms or signs; group II, + symptoms, no signs; and group III, + symptoms, + signs. Six patients in group III were diagnosed with a specific connective-tissue disease, including systemic lupus erythematosus, rheumatoid arthritis, or scleroderma. The most common indications for implant removal or exchange were capsular contracture and implant rupture, although 41 percent of patients with silicone implants expressed media-related concern over the implant issue. The most common symptoms described by patients in groups II and III were joint pain and stiffness, arm pain and numbness, and fatigue. In all groups, capsular tissue silicon levels were significantly greater than breast tissue levels. This finding may indicate that the capsule serves as a barrier to the distribution of silicone from the implant into adjacent breast tissue. Although breast tissue silicon levels in patients with silicone implants were not significantly greater than those in patients with saline implants (p = 0.48), capsular tissue levels in patients with silicone implants were, indeed, significantly greater than those in patients with saline implants (p < 0.001). However, no statistically significant differences in tissue silicon levels were observed with relation to the presence or absence of connective-tissue disease signs or symptoms in patients with silicone implants (groups I to III). Therefore, these data strengthen the conclusion that there is no association between tissue silicon levels and connective-tissue disease.

Breast↗
PubMed1996

Comparison of numerous delivery systems for the induction of cytotoxic T lymphocytes by immunization.

A variety of vaccine delivery systems including peptides with various adjuvants, recombinant particles, live recombinant viruses and bacteria and plasmid DNA were tested for their ability to induce CD8+ cytotoxic T lymphocytes (CTL) against a well-defined epitope (amino acids 252-260) from the circumsporozoite (CS) protein of Plasmodium berghei. We compared routes of immunization that would be applicable for the administration of a malaria vaccine in humans. The majority of these vaccines did not induce high CTL responses in the spleens of immunized mice. However, both a yeast-derived Ty virus-like particle expressing the optimal nine-amino acid epitope SYIPSAEKI from the CS protein (CSP-VLP) and a lipid-tailed peptide of this same sequence induced high levels of the major histocompatibility complex (MHC) class I-restricted CTL with one and three subcutaneous immunizations, respectively. Moreover, these CTL were able to recognize naturally processed antigen expressed by a recombinant vaccinia virus. The levels of CTL induced by CSP-VLP could be augmented by co-immunization with certain cytokines. Target cells pulsed with CSP-VLP were recognized and lysed, showing that the particles were effectively processed and presented through MHC class I presentation pathway. The levels of CTL induced using CSP-VLP and lipopeptides are comparable to those observed after immunization with multiple doses of irradiated sporozoites.

Amino Acid Sequence↗
PubMed1996

Silicon analysis of breast and periprosthetic capsular tissue from patients with saline or silicone gel breast implants.

The ubiquitousness of silicon is well known. Recent work has demonstrated measurable baseline levels of silicon in nonaugmented cadavers, subsequent to numerous reports of significant elevations of such levels within patients with silicone breast implants and even more reports alleging a causal relation between silicone gel prostheses and connective-tissue diseases. Despite the lack of scientifically substantiated data that such a relation exists, the calamitous silicone breast implant controversy has ensued. Saline-filled breast implants are constructed with a silicone elastomer envelope that remains in direct contact with periprosthetic capsular tissue following implantation. Although there is no evidence to link saline implants with any disorders, it is important to know if saline breast implants contribute any silicon to human body baseline silicon levels. The present study measured tissue silicon levels in 28 breasts of 16 patients with saline-filled implants to determine if the silicone envelope of these prostheses can contribute to the elevation of such levels. These data were compared with data from 116 breasts of 65 patients with silicone gel-filled prostheses as well as breast tissue from 17 patients (controls) who had never been exposed to either type of implant. Samples of breast tissue and periprosthetic capsular tissue were obtained from patients with both intact and ruptured implants. Silicon levels of breast tissue specimens from patients with saline-filled implants were within the range of the controls if the implants were intact. Silicon levels in periprosthetic capsular tissue from patients with intact saline-filled implants were significantly higher than controls (p < 0.02); however, they were still 100-fold less than capsular tissue levels from patients with intact gel-filled implants. Silicon levels measured in both types of tissue were significantly elevated in patients with silicone gel-filled implants compared with controls (p < 0.01). In the case of ruptured gel implants, breast tissue demonstrated higher silicon levels than did similar specimens from patients with intact implants (p < 0.054); periprosthetic capsular tissue levels also were elevated, although the differences were not statistically significant (p = 0.54). These findings are independent of the implant brand or length of exposure to the particular prosthesis. The finding of elevated levels of silicon in both breast and periprosthetic capsular tissue in patients with silicone gel-filled implants in no way implies or substantiates any claim of a causal relationship between silicone and any reported illnesses.

Adult↗
PubMed1993

A sequence pattern for peptides presented to cytotoxic T lymphocytes by HLA B8 revealed by analysis of epitopes and eluted peptides.

HLA B8-restricted cytotoxic T lymphocytes (CTL) specific for influenza A virus were generated and shown to recognize the nucleoprotein (NP). The dominant epitope was mapped using recombinant vaccinia viruses that expressed fragments of the NP and then synthetic peptides based on the NP amino acid sequence. The peptide 380-393 was first identified and further refined; it was shown that the glutamic acid at position 380 was essential for recognition by CTL and that the nonamer 380-388 was the optimum peptide. Six HLA B8-positive influenza immune donors that we have tested respond to this peptide as part of their influenza-specific CTL response. The amino acid sequence of the peptide epitope was compared to six other known virus peptides known to be restricted by HLA B8 and a sequence homology was identified, which predicted nonamer and octamer epitope sequences. Probable anchor residues were identified at peptide residues 3 (lysine/arginine), 5 (lysine/arginine) and 9 (leucine/isoleucine). Support for this pattern came from sequencing peptides eluted from purified HLA B8 molecules, where lysines were predominant at positions 3 and 5. One of the predicted epitope peptides was made and shown to be recognized by specific CTL. These and the two others were shown to compete with NP 380-388 for binding to HLA B8. A model was made of the HLA B8 molecule and negatively charged pockets predicted, which could accommodate the positively charged side chains of the peptide anchor residues.

Amino Acid Sequence↗
PubMed1992

Measuring the albumin excretion rate: agreement between methods and biological variability.

A timed urine collection is necessary to determine the excretion rate of albumin (AER) but such specimens are tedious to collect and frequently inaccurate. Albumin excretion can also be quantified by the use of the albumin:creatinine ratio in randomly obtained specimens. In the present study the agreement between AER as measured on a 24-h urine collection and as estimated from the albumin:creatinine ratio is determined. Previously published studies have examined the correlation rather than the agreement between these methods and not taken into account the biological variability of AER. Thirty patients with diabetes who had normal renal function, but varying degrees of albuminuria, produced two 24-h specimens and two random daytime specimens of urine. AER was measured on the former and estimated from the latter by multiplying the albumin:creatinine ratio by an estimate of that individual's creatinine excretion rate. Agreement between the methods and the biological variability was determined by using appropriate statistical methodology, the main outcome measure being the limits of agreement between repeat values for both measurements and both estimates of AER, and between the averages of the measurements and the estimates. The limits of agreement between repeated 24-h measurements were wide, the second specimen being 33 to 490% of the first. The estimates of AER gave values numerically similar to the measurements. The limits of agreement between the two estimates did not differ significantly from those of the measurements, nor did the limits of agreement when the average of the measurements and the average of the estimates were compared (all NS).(ABSTRACT TRUNCATED AT 250 WORDS)

Albuminuria↗
PubMed1991

Modified levator aponeurosis recession for upper eyelid retraction in Graves' disease.

Recession of the levator aponeurosis has proved to be an excellent operation to correct upper eyelid retraction in Graves' disease. Harvey and Anderson's original description included recession of the levator aponeurosis along its entire width and complete extirpation of Müller's muscle. In a modification of the technique, we recess only the lateral two thirds of the levator/Müller's complex. Also, rather than excising Müller's muscle, we simply recess it en bloc with the levator aponeurosis. The lateral horn of the levator is cut, as previously advocated, to relieve the marked temporal elevation of the eyelid characteristic of Graves' lid retraction. This modified procedure provides good upper lid lengthening, with less surgical manipulation, less bleeding, and avoids medial over-corrections. Of 22 upper lids (12 patients) treated with this procedure, 19 (86.3%) were considered "good" after the operation.

Adult↗
PubMed1989

A national study of state-supported psychiatric research institutes.

States have funded psychiatric research through a variety of mechanisms, including psychiatric research institutes. The authors identified and surveyed 33 such institutes to obtain information on their organizational characteristics. Twenty-nine institutes responded; more than half were organizationally located within a university setting, and a similar number were involved in research, education, and direct services. Clinical research was the most prevalent type of research conducted, and annual state revenue appropriations were the major source of funding. Because budgetary problems have threatened their future funding in some states, the authors believe the institutes should increase efforts to demonstrate their relevance to state mental health needs.

Academies and Institutes↗
PubMed1987

Indomethacin in streptozocin-induced nephrogenic diabetes insipidus.

A 14-year-old female patient with metastatic carcinoid developed streptozocin-induced glomerular, proximal, and distal tubular dysfunction. The latter was in the form of nephrogenic diabetes insipidus, with urine volumes in excess of 11 L/24 h. The prostaglandin synthetase inhibitor, indomethacin, rapidly corrected the polyuria both initially and on rechallenge, independent of change in glomerular filtration rate.

Administration, Oral↗
PubMed1987

Depression among alcoholics.

The relationships of cognition, health status, and age to depression among alcoholics were studied. Eighty male alcoholics in an alcohol treatment unit were rated on health status and given a battery of psychological tests and scales. These included the Hooper VOT (cognition) and several self-rated depression indices: MMPI-Depression, MCMI-Dysthymic, BDI-Total (BDI-Somatic and BDI-Psychological), and the Geriatric Depression Scale (GDS). Results showed that depression was present in this sample at mild clinical levels. Regression analyses showed that age was the most influential factor on the MMPI-D and BDI-Somatic. Age also was most influential on the GDS, with health status contributing. However, except for somatic depression, the amount of explained variance was small. Despite this, it is argued that age is a contributing factor to depression among alcoholics, especially the somatic elements of depression.

Adult↗
PubMed1986

Plasma L-dopa in the diagnosis of malignant melanoma.

We determined the concentration of L-dopa in the plasma of 98 patients with biopsy-proven melanoma, a dermatological neoplasm that is characterized biochemically by abnormal tyrosine metabolism. For 21 patients previously diagnosed as having melanoma but who were clinically free of disease (stage I), the mean concentration of L-dopa in plasma, 1.01 (SD 0.12) micrograms/L, was not significantly different from that of 32 normal controls, 1.23 (SD 0.16) micrograms/L. However, L-dopa was increased significantly (p less than 0.001) in the plasma of all of 65 patients with active disease (stage II), 2.08 (SD 0.46) micrograms/L, and was highest in 12 patients with stage III malignant melanoma, 8.40 (SD 3.50) micrograms/L. The development of metastases in four patients with stage II melanoma was accompanied by an increase in the concentration of plasma L-dopa. These studies suggest that measurement of plasma L-dopa may be useful in the diagnosis of melanoma.

Adult↗