Search PubMed⌕ Search

Biomedical subjects

J D Marks

Publications and source records attributed to J D Marks.

At least 91 records · Page 5Linked to original sources
PubMed1992

By-passing immunization: building high affinity human antibodies by chain shuffling.

Diverse antibody libraries can be displayed on the surface of filamentous bacteriophage, and selected by panning of the phage with antigen. This allows human antibodies to be made directly in vitro without prior immunization, thus mimicking the primary immune response. Here we have improved the affinity of one such "primary" antibody by sequentially replacing the heavy and light chain variable (V) region genes with repertoires of V-genes (chain shuffling) obtained from unimmunized donors. For a human phage antibody for the hapten 2-phenyloxazol-5-one (phOx) (Kd = 3.2 x 10(-7) M), we shuffled the light chains and isolated an antibody with a 20 fold improved affinity. By shuffling the first two hypervariable loops of the heavy chain, we isolated an antibody with a further 15-fold improved affinity. The reshuffled antibody differed in five of the six hypervariable loops from the original antibody and the affinity for phOx (Kd = 1.1 x 10(-9) M) was comparable to that of mouse hybridomas from the tertiary immune response. Reshuffling offers an alternative to random point mutation for affinity maturation of human antibodies in vitro.

Amino Acid Sequence↗
PubMed1992

Germline variable region gene segment derivation of human monoclonal anti-Rh(D) antibodies. Evidence for affinity maturation by somatic hypermutation and repertoire shift.

To date, there has been no systematic study of the process of affinity maturation of human antibodies. We therefore sequenced the variable region genes (V genes) of 14 human monoclonal antibodies specific for the erythrocyte Rh(D) alloantigen and determined the germline gene segments of origin and extent of somatic hypermutation. These data were correlated with determinations of antibody affinity. The four IgM antibodies (low affinity) appear to be derived from two germline heavy chain variable region gene segments and one or two germline light chain variable region gene segments and were not extensively mutated. The 10 IgG antibodies (higher affinity) appear to be derived from somatic hypermutation of these V gene segments and by use of new V gene segments or V gene segment combinations (repertoire shift). Affinity generally increased with increasing somatic hypermutation; on average, there were 8.9 point mutations in the V gene segments of the four IgM antibodies (Ka = 1-4 x 10(7)/M-1) compared with 19 point mutations in the V gene segments of the 10 IgG antibodies. The four highest affinity antibodies (Ka = 0.9-3 x 10(9)/M-1) averaged 25.5 point mutations. The use of repertoire shift and somatic hypermutation in affinity maturation of human alloantibodies is similar to data obtained in inbred mice immunized with haptens.

Antibodies, Monoclonal↗
PubMed1991

By-passing immunization. Human antibodies from V-gene libraries displayed on phage.

We have mimicked features of immune selection to make human antibodies in bacteria. Diverse libraries of immunoglobulin heavy (VH) and light (V kappa and V lambda) chain variable (V) genes were prepared from peripheral blood lymphocytes (PBLs) of unimmunized donors by polymerase chain reaction (PCR) amplification. Genes encoding single chain Fv fragments were made by randomly combining heavy and light chain V-genes using PCR, and the combinatorial library (greater than 10(7) members) cloned for display on the surface of a phage. Rare phage with "antigen-binding" activities were selected by four rounds of growth and panning with "antigen" (turkey egg-white lysozyme (TEL) or bovine serum albumin) or "hapten" (2-phenyloxazol-5-one (phOx], and the encoding heavy and light chain genes were sequenced. The V-genes were human with some nearly identical to known germ-line V-genes, while others were more heavily mutated. Soluble antibody fragments were prepared and shown to bind specifically to antigen or hapten and with good affinities, Ka (TEL) = 10(7) M-1; Ka (phOx) = 2 x 10(6) M-1. Isolation of higher-affinity fragments may require the use of larger primary libraries or the construction of secondary libraries from the binders. Nevertheless, our results suggest that a single large phage display library can be used to isolate human antibodies against any antigen, by-passing both hybridoma technology and immunization.

Amino Acid Sequence↗
PubMed1991

Oligonucleotide primers for polymerase chain reaction amplification of human immunoglobulin variable genes and design of family-specific oligonucleotide probes.

In recent work, the polymerase chain reaction (PCR) has been used to amplify rearranged mouse and human immunoglobulin heavy and kappa light chain variable (V) genes. Here we have optimized the design of the PCR primers for human V genes and used them to amplify cDNA from human peripheral blood lymphocytes. Cloning and sequencing revealed a diverse repertoire of V genes, and the presence of members of each human V gene family. After alignment of the sequences, we identified a region conserved within V gene families, but differing between families, and used this to design family-specific oligonucleotide probes.

Base Sequence↗
PubMed1990

Cloning and sequencing of human lambda immunoglobulin genes by the polymerase chain reaction.

Universal oligonucleotide primers, designed for amplifying and sequencing genes encoding the rearranged human lambda immunoglobulin variable region, were validated by amplification of the lambda light chain genes from four human heterohybridoma cell lines and in the generation of a cDNA library of human V lambda sequences from Epstein-Barr virus-transformed human peripheral blood lymphocytes. This technique allows rapid cloning and sequencing of human immunoglobulin genes, and has potential applications in the rescue of unstable human antibody-producing cell lines and in the production of human monoclonal antibodies.

Amino Acid Sequence↗
PubMed1990

Plasma tumor necrosis factor in patients with septic shock. Mortality rate, incidence of adult respiratory distress syndrome, and effects of methylprednisolone administration.

We assayed serial plasma samples from 86 patients, who were enrolled in a prospective randomized trial of the effects of methylprednisolone (MPSS) in septic shock, for the presence of cytokine tumor necrosis factor (TNF) using an enzyme-linked immunosorbent assay. TNF was present in the plasma of 27 of the 74 patients with septic shock, but in only 1 of the 12 patients with shock due to other causes. TNF was detected with equal frequency in patients with shock from gram-negative or from gram-positive bacillary sepsis. TNF levels were highest on the initial sample and decreased significantly over the subsequent 24 h in both the patients treated with MPSS and in those given placebo. Patients with detectable TNF had a higher incidence and severity of the adult respiratory distress syndrome and a higher mortality rate than did patients without detectable TNF.

Humans↗
PubMed1990

Elevated von Willebrand factor antigen is an early plasma predictor of acute lung injury in nonpulmonary sepsis syndrome.

In this prospective study of 45 patients, we tested the hypothesis that markedly elevated levels of plasma von Willebrand antigen (vWf-Ag) a marker of endothelial cell injury, might predict the development of acute lung injury in patients with nonpulmonary sepsis syndrome. Acute lung injury was quantified on a four-point scoring system. At the time of entry into the study, none of the 45 patients had evidence of lung injury. Subsequently, 15 patients developed lung injury and 30 patients did not develop lung injury. The mean plasma vWf-Ag level was markedly elevated in the 15 patients who developed lung injury compared with the 30 patients who did not develop lung injury (588 +/- 204 vs. 338 +/- 196, percentage of control, P less than 0.01). Furthermore, a plasma vWf-Ag level greater than or equal to 450 was 87% sensitive and 77% specific for predicting the development of acute lung injury in the setting of nonpulmonary sepsis. In addition, the combination of a plasma vWf-Ag greater than 450 and nonpulmonary organ failure at the time of entry into the study had a positive predictive value of 80% for acute lung injury. Also, a plasma vWf-Ag level greater than 450 had a positive predictive value of 80% for identifying nonsurvivors. Thus, in patients with nonpulmonary sepsis, an elevated level of plasma vWf-Ag is a useful, early biochemical marker of endothelial injury and it has both predictive and prognostic value.

Acute Disease↗
PubMed1990

Factors affecting perioperative pulmonary function in acute respiratory failure.

To determine the magnitude, duration, and associated factors of perioperative changes in pulmonary function, we retrospectively reviewed the medical records of 145 patients who required preoperative mechanical ventilation for acute respiratory failure before undergoing 200 surgical procedures. Patients were grouped into five pulmonary diagnostic categories: (1) adult respiratory distress syndrome (ARDS) (n = 49); (2) pneumonia (n = 20); (3) atelectasis (n = 65); (4) congestive heart failure (n = 11); and (5) acute ventilatory failure (n = 55). Sixty patients underwent intra-abdominal surgery, 135 patients required surgery on the periphery, and five patients had a thoracotomy. For all patients, PaO2/FIO2 declined significantly from 321 mm Hg (mean) preoperatively to 258 mm Hg intraoperatively, and shunt fraction (Qs/QT) increased from 0.16 to 0.23 without a significant change in PaCO2. The magnitude of the increase in Qs/QT did not differ among pulmonary diagnostic groups. Preoperatively, patients undergoing laparotomy had lower PaO2/FIO2 (278 vs 340) and higher Qs/QT (0.19 vs 0.14) than patients requiring surgery on the periphery. Intraoperatively, Qs/QT increased more during abdominal procedures than during peripheral procedures. Intraoperative hypoxemia (PaO2/FIO2 less than 80 mm Hg) occurred during 13 procedures. Hypoxemic patients had a mean increase in Qs/QT of 0.20 (0.25 preoperatively to 0.45 intraoperatively), and a significant increase in PaCO2 from 38 mm Hg to 45 mm Hg intraoperatively). In general, these patients had ARDS (n = 10), sepsis (n = 10), a laparotomy (n = 9), and intraoperative mechanical ventilation via the Ohio Anesthesia ventilator (n = 8), a commonly used operating room ventilator. Their preoperative peak airway pressure (54 cm H2O) and minute ventilation (20 L/min) requirements exceeded the capabilities of the Ohio Anesthesia ventilator and likely contributed to impaired gas exchange intraoperatively. Within the first several hours postoperatively, PaO2/FIO2 recovered to preoperative levels in all patients, even in those who had severe intraoperative hypoxemia develop and who underwent laparotomy. We conclude that most patients with acute respiratory failure receiving preoperative mechanical ventilation experienced mild-to-moderate deterioration in intraoperative pulmonary oxygen exchange that rapidly returned to preoperative levels after surgery. We recommend that necessary surgery not be postponed by concern that pulmonary function will be worsened by surgery and anesthesia.

Acute Disease↗
PubMed1989

Perioperative pulmonary function in acute respiratory failure: effect of ventilator type and gas mixture.

Whether maintaining pulmonary nitrogenation and/or a stable ventilatory pattern during surgery would minimize changes in perioperative pulmonary function in two groups of patients with acute respiratory failure (ARF) whose lungs were being mechanically ventilated was examined. Group 1 (n = 39 cases) (inspired oxygen fraction [FIO2] less than or equal to 0.5, minute ventilation less than or equal to 15 l/min, peak inspiratory pressure less than or equal to 50 cmH2O, positive end-expiratory pressure [PEEP] less than or equal to 10 cmH2O) were assigned randomly to one of four intraoperative ventilator-gas mixture (FIO2 approximately 0.5) combinations: 1) Siemens 900C ventilator, N2/O2; 2) Siemens 900C ventilator, N2O/O2; 3) Ohio anesthesia ventilator, N2/O2; or 4) Ohio anesthesia ventilator, N2O/O2. Group 2 (n = 15 cases) (ventilatory requirements exceeding any of those in Group 1) had their lungs ventilated intraoperatively with the Siemens 900C ventilator and a gas mixture determined by their anesthesiologist (FIO2 approximately 0.6-1.0). In patients whose lungs were ventilated with the Ohio N2O/O2 combination, PaO2/FIO2 decreased significantly (P less than 0.05) from 358 +/- 93 mmHg (mean +/- SD) preoperatively to 282 +/- 77 mmHg intraoperatively. The level of PEEP increased significantly from 5 +/- 3 cmH2O preoperatively to 9 +/- 4 cmH2O intraoperatively (P less than 0.05). In patients whose lungs were ventilated with the Ohio N2/O2 combination, PaO2/FIO2 decreased significantly from 270 +/- 86 mmHg preoperatively to 174 +/- 74 mmHg intraoperatively. These variables did not change significantly in patients ventilated with the Siemens ventilator (groups 1 and 2). Pulmonary oxygen gas exchange returned to preoperative values by the first hour postoperatively.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Disease↗
PubMed1989

Pressure and flow limitations of anesthesia ventilators.

The effect of increasing airway pressure on the mean inspiratory flow and maximum minute ventilation (VE) capabilities of five anesthesia ventilators (Ohio Anesthesia, Airshields Ventimeter, Ohmeda 7000, Draeger AV-E and Siemens 900D) was compared to identify mechanical factor(s) limiting intraoperative ventilation of the lungs of patients with acute respiratory failure. The effect of increasing airway pressure on mean inspiratory flow was determined by cycling each ventilator through increasing restrictors. Maximum VE was measured under three study conditions using a test lung: 1) low compliance (10-30 ml/cmH2O) and minimal airflow resistance; 2) positive end-expiratory pressure (PEEP) of 0, 10, and 20 cmH2O at a compliance of 20 ml/cmH2O with minimal airflow resistance; and 3) increased resistance (19 +/- 11 cmH2O.1(-1).s-1) and compliance of 30 ml/cmH2O. As airway pressure increased from 0 to 80 cmH2O, mean inspiratory flow decreased markedly for all ventilators except the Siemens. The Siemens ventilator delivered the greatest VE under all three conditions and maintained VE when airway pressure increased due to decreased compliance or the application of PEEP; all other ventilators markedly decreased VE under these conditions. The addition of airway resistance reduced maximal VE for all ventilators by limiting the maximal inspiratory duty cycle (T1/TTOT). Thus, mean inspiratory flow of conventional anesthesia ventilators decreases with increasing airway pressure. The decreased inspiratory flow limits maximum VE when airway pressure is elevated because of decreased lung-thorax compliance and/or increased airway resistance, such as that characterizing patients with acute respiratory failure. Significant airway resistance further limits maximum VE by limiting the maximal T1/TTOT that can be used without increasing end-expiratory lung pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Airway Resistance↗
PubMed1988

Ineffectiveness of high-dose methylprednisolone in preventing parenchymal lung injury and improving mortality in patients with septic shock.

We conducted a prospective, randomized, double-blind study to determine whether high-dose methylprednisolone could prevent parenchymal lung injury, including the adult respiratory distress syndrome (ARDS), or improve mortality when administered early in septic shock. All patients already hospitalized in or newly admitted to the medical and surgical intensive care units at San Francisco General Hospital between September 1, 1983 and August 29, 1986 were eligible for admission to the study if they had either (1) an increase in temperature of 1.5 degrees C and a decrease in systolic blood pressure of 20 mm Hg or more from baseline values (in already hospitalized patients), or (2) a temperature greater than 38.5 degrees C or less than 35.5 degrees C and a systolic blood pressure of less than 90 mm Hg (in newly admitted patients). Patients meeting these criteria were excluded if they (1) had severe immunodeficiency, (2) were less than 18 or greater than 76 yr of age, (3) had multilobar roentgenographic infiltrates, or (4) were already receiving corticosteroids. Eighty-seven patients enrolled in the study received either methylprednisolone, 30 mg/kg per dose, or mannitol placebo for a total of 4 doses every 6 h, following the presumptive diagnosis of septic shock. Of these patients, 75 ultimately were determined on the basis of culture results to have actually had septic shock at the time of entry. Thirteen of the patients who received methylprednisolone developed ARDS, compared to 14 patients who received placebo. Lesser degrees of parenchymal lung injury did not differ between the 2 groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1988

Development of smaller artificial ventricles and valves made by vacuum forming.

Implantable prosthetic ventricles and trileaflet valves made by vacuum forming have been developed and implant tested. All components are made from Pellethane. Recognizing the need for smaller as well as larger ventricles, designs with effective stroke volumes of 50, 85, 100 and 130 cc have been tested with several valve types. The pneumatically driven Utah ventricular assist device (UVAD) can be used as a total artificial heart (TAH) or ventricular assist device (VAD) by using the appropriate inflow and outflow adapters. In vitro durability testing has demonstrated ventricular lifetime beyond two years and valve lifetime to nearly one and one half years. The polymer valves have lower regurgitation than mechanical valves. Animal implantation experience includes 21 TAH implants and 16 left ventricular assist device (LVAD) implantations. TAH survival ranges from 2 to 210 days. LVAD animals have lived up to 116 days before elective termination. The animal were healthy and grew normally. The devices exhibit a "Starling's Law" response. One TAH animal survived 72 days before successful explantation followed by transplantation. At autopsy, this animal had no renal infarcts. Hematology data has demonstrated the existance of little or no intravascular hemolysis (PF Hb less than 5 mg%). The "Philadelphia" version of the UVAD vacuum formed ventricles are small enough to be implanted without thrombus provoking connectors. Eight animals have received this TAH and survived up to 120 days. Vacuum forming offers a rapid and inexpensive way to produce reliable and effective total artificial hearts and valves for widespread, temporary clinical application in any size adult human.

Animals↗
PubMed1988

Hemodynamic and energetic assessment of calves implanted with a left ventricular assist device (LVAD).

Hemodynamic and ventricular energetic parameters were measured in calves implanted with the air driven Utah Ventricular Assist Device (UVAD). Uptake site was varied to determine the effect of control mode and vacuum augmentation of filing. Uptake was drawn solely from the left atrium or combined with a left ventricular apical vent. LVAD outflow returned to the descending, thoracic aorta. Control modes examined included asynchronous pumping as well as 1:1 and 1:2 synchronous diastolic counterpulsation. The 85cc LVAD, vacuum formed from PELLETHANE, was implanted acutely in four animals and chronically in six (7, 49 and 116 days paracorporeally, 1, 28 and 32 days intrathoracically). Instantaneous blood pressures, intramyocardial pressure, aortic outflow, oxygen consumption, LVAD output and drive parameters were recorded. LVAD output was independent of control mode when the natural heart rate was greater than or equal to 80 beats per minute. Intrathoracically positioned LVADs pumped a mean flow of approximately equal to 5 liters/min without vacuum augmentation of filling. Paracorporeally positioned LVADs pumped approximately equal to 3 liters/min mean flow without vacuum augmentation and up to approximately equal to 6 liters/min with 38 mm Hg of vacuum augmentation of filling. Instantaneous ascending aortic pressure and flow showed distinct beat-to-beat variation depending on LVAD control mode. Lower average ventricular afterload was observed when pumping the LVAD asynchronously or 1:2 synchronously. In one acute preparation, left ventricular myocardial oxygen consumption was reduced from the unassisted average control level by 37% for the asynchronous and 1:1 synchronous control modes with left atrial uptake.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

State-dependent respiratory depression elicited by stimulation of the orbital frontal cortex.

The effect of electrical stimulation of the orbital frontal cortex on respiration was studied in unanesthetized, freely moving cats across sleep-waking states. Single trains of forty 300-microA, 0.5-ms, constant-current pulses at 60 Hz were delivered to the orbital frontal cortex at four points in the respiratory cycle. Stimuli delivered during expiration produced an immediate switch to inspiration. Stimuli delivered during inspiration reduced inspiratory EMG slope and peak EMG amplitude, and prolonged inspiration. Stimuli delivered during early inspiration produced greater effects than stimuli delivered during late inspiration. Stimulation effects were elicited during quiet waking and quiet sleep but not during rapid-eye-movement sleep. These results suggest that the orbital frontal cortex may contribute to respiratory phase switching, and that its influence on brain stem structures is attenuated during rapid-eye-movement sleep.

Animals↗