Release of vasoactive substances during cardiopulmonary bypass

Cardiopulmonary bypass is associated with bleeding and thrombotic complications, massive fluid shifts, and cellular and hormonal defense reactions that are collectively termed "the whole body inflammatory response." A host of vasoactive substances are produced, released or altered during cardiopulmonary bypass. These hormones, autacoids, and cytokines react with specific receptor proteins distributed throughout the body, and mediate the vascular smooth muscle and endothelial cell contractions that are responsible for much of the morbidity associated with open heart operations. This essay briefly reviews the actions, sources, and perturbations of the approximately 25 vasoactive substances known or believed to be altered by cardiopulmonary bypass, and provides an introductory reference list.

Cystinuria: biochemical evidence for three genetically distinct diseases

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Myocardial electrical impedance mapping of ischemic sheep hearts and healing aneurysms

BACKGROUND

This study was designed to examine the bulk electrical properties of myocardium and their variation with the evolution of infarction after coronary occlusion. These properties may be useful in distinguishing between normal, ischemic, and infarcted tissue on the basis of electrophysiological parameters.

METHODS AND RESULTS

The electrical impedance of myocardial tissue was studied in a sheep model of infarction. The animal model involved a one-stage ligation of the left anterior descending and second diagonal arteries at a point 40% of the distance from the apex to the base. By use of a four-electrode probe, an epicardial mapping system was developed that allowed for cardiac cycle gated and signal-averaged measurements. Subthreshold current (15 microA) was injected through two of the electrodes at frequencies of 1, 5, and 15 kHz and the induced potential measured with the other two electrodes. Epicardial maps of the left ventricle were obtained during acute infarction and at 1-, 2-, and 6-week intervals after occlusion. Results showed the average specific impedance of the myocardium before infarction to be 158 +/- 26 omega-cm independent of location on the epicardium. By 60 minutes after coronary occlusion, the specific impedance had increased by 199% (p < 0.005, n = 9); it remained elevated for up to 4 hours. One week after infarction, the specific impedance decreased to 59% of the control value (p < 0.025, n = 8). Six weeks after occlusion, the specific impedance remained low at 57% of that of the noninfarcted tissue (p < 0.005, n = 9). The phase angle of the complex impedance was also measured and revealed similar changes. The hydroxyproline content of the tissue was assayed to assess infarct healing.

CONCLUSIONS

In this animal model, impedance is a bulk electrical property of tissue that varies with the evolution of myocardial infarction. Impedance mapping revealed significantly different values for normal, ischemic, and infarcted tissue and may prove useful in better defining the electrophysiological characteristics of such tissue.

Experience with spiral computed tomography as the sole diagnostic method for traumatic aortic rupture

BACKGROUND

Spiral computed tomographic (CT) scan is an excellent screen for aortic trauma. Traditionally, aortography is performed when injury is suspected to confirm the diagnosis. We hypothesized that it is safe and expeditious to forgo aortography when the spiral CT demonstrates aortic injury.

METHODS

Retrospective review of 54 patients undergoing aortic repair from July 1994 to December 1999. Spiral CT was the initial diagnostic study in 52 patients. Pseudoaneurysm or aortic wall defect in the presence of mediastinal hematoma was considered diagnostic. Angiography, initially routine, was later performed only when requested by the surgeon, and for all "nonnegative" studies (periaortic hematoma without detectable aortic injury).

RESULTS

Twenty-six patients underwent angiography before operation (group 1). Nineteen group 1 spiral CTs were unequivocally diagnostic; 7 were nonnegative and angiography was required. Twenty-eight other patients underwent repair based on spiral CT alone (group 2). There was one false-positive result in both groups. There were no unexpected operative findings. Mean time from admission to diagnosis was 5.7+/-3.4 hours for group 1 and 1.7+/-1.7 hours for group 2 (p < 0.01).

CONCLUSIONS

Operating on the basis of a diagnostic spiral CT is safe and expeditious. Aortography may be reserved for those with equivocal studies.

Factor V Leiden and thermolabile methylenetetrahydrofolate reductase gene variants in an East Anglian preeclampsia cohort

Preeclampsia is a heritable condition that develops as a result of widespread vascular endothelial dysfunction. The thrombotic tendency in this condition has suggested a number of candidate genes, and there have been recent reports of positive association with the Leiden variant of factor V and the thermolabile variant of methylenetetrahydrofolate reductase. We attempted to reproduce these results in a large cohort of well-characterized women with preeclampsia, recruited prospectively within the East Anglian region of the United Kingdom. Women in the preeclampsia cohort (n=283) were genotyped for both the Leiden variant (G1691A) of factor V and the thermolabile variant (C677T) of methylenetetrahydrofolate reductase. Genotype and allele frequencies were compared with those of 2 control groups, one consisting of women recruited prospectively (n=100) from the same maternity hospital as the subjects and another consisting of normotensive women (n=100) from East Anglia. No significant differences were detected. Specifically, the carrier rate for the Leiden variant was 5.3% in the preeclampsia group and 5. 5% in the combined control group. T677 homozygotes for methylenetetrahydrofolate reductase were 11% and 11.5% in the 2 groups, respectively. We conclude that there is no evidence of association of preeclampsia with either of these 2 polymorphisms in our study population.

Threads in the Hagfish Slime Gland Thread Cells: Organization, Biochemical Features, and Length

Scanning electron microscopy in conjunction with cell isolation procedures revealed details of the packing of threads in hagfish slime gland thread cells. Biochemical studies indicate that the thread is largely composed of a protein subunit with a molecular weight of 63,500. Mathematical calculations suggest that the thread may attain lengths of 60 centimeters or more.

Chronic dietary copper deficiency alters biochemical and morphological properties of mouse lymphoid tissues

Chronic copper deficiency in mice impairs both humoral and cell-mediated immunity, but the mechanisms are unknown. Copper deficiency was produced in C58 mice by feeding dams a diet low in copper throughout lactation and weaning the pups to this diet. Control mice were from dams fed the same diet but with copper supplementation the drinking water. Six-week-old mice were sampled for biochemical and morphological studies. Compared to copper-supplemented mice, copper-deficient animals were smaller, anemic and exhibited hypoceruloplasminemia. The copper-deficient mice have small thymus glands, enlarged spleens, and livers equivalent in size to copper-supplemented mice. Thymic atrophy is not caused by elevated serum corticosterone. Liver, spleen, and thymus tissues from copper-deficient mice exhibit low cytochrome oxidase (56, 38, and 45%, respectively) and superoxide dismutase activities (61, 60, and 43%, respectively) compared to tissues from copper-supplemented mice, indicating a functional copper deficiency. Electron micrographs taken of thymus and spleen from copper-deficient mice demonstrate altered morphology characterized by abnormal mitochondria and misshapen nuclei. Chronic copper deficiency alters the size, biochemistry and morphology of primary (thymus) and secondary (spleen) lymphoid tissue.

Distinguishing the cyanobacterial neurotoxin β-N-methylamino-L-alanine (BMAA) from other diamino acids

β-N-methylamino-L-alanine (BMAA) is produced by diverse taxa of cyanobacteria, and has been detected by many investigators who have searched for it in cyanobacterial blooms, cultures and collections. Although BMAA is distinguishable from proteinogenic amino acids and its isomer 2,4-DAB using standard chromatographic and mass spectroscopy techniques routinely used for the analysis of amino acids, we studied whether BMAA could be reliably distinguished from other diamino acids, particularly 2,6-diaminopimelic acid which has been isolated from the cell walls of many bacterial species. We used HPLC-FD, UHPLC-UV, UHPLC-MS, and triple quadrupole tandem mass spectrometry (UHPLC-MS/MS) to differentiate BMAA from the diamino acids 2,6-diaminopimelic acid, N-2(amino)ethylglycine, lysine, ornithine, 2,4-diaminosuccinic acid, homocystine, cystine, tryptophan, as well as other amino acids including asparagine, glutamine, and methionine methylsulfonium.

The hagfish slime gland thread cell. I. A unique cellular system for the study of intermediate filaments and intermediate filament-microtubule interactions

Thread cell differentiation in the slime gland of the Pacific hagfish Eptatretus stouti has been studied using light microscopy and scanning and transmission electron microscopy. Thread cell differentiation is remarkable in that the life history of the cell is largely dedicated to the production of a single, tapered, cylindrical, highly coiled, and precisely packaged cytoplasmic thread that may attain lengths of 60 cm and diameters approaching 1.5 micron. Each tapered thread, in turn, is comprised almost entirely of large numbers of intermediate filaments (IFs) bundled in parallel. During differentiation of the thread, the IFs become progressively more tightly packed. Various numbers of microtubules (MTs) are found among the bundled IFs during differentiation of the thread but disappear during the latter stages of thread differentiation. Observations of regularly spaced dots in longitudinal bisections of developing threads, diagonal striations in tangential sections of developing threads, and circumferentially oriented, filament-like structures observed at the periphery of developing threads cut in cross section have led us to postulate a helically oriented component(s) wrapped around the periphery of the developing thread. The enormous size of the fully differentiated thread cell, its apparent singular dedication to the production of IFs, the ease of isolating and purifying the threads and IF subunits (see accompanying paper), and the unique position of the hagfish in the phylogenetic scheme of vertebrate evolution all contribute to the attractiveness of the hagfish slime gland thread cell as a potential model system for studying IF subunit synthesis, IF formation from IF subunits, aggregation of IFs into IF bundles and the interaction(s) of IFs and MTs.

Traumatic aortic rupture: recent outcome with regard to neurologic deficit

BACKGROUND

Traumatic aortic rupture is highly lethal, and its surgical treatment is complicated by a high rate of paraplegia.

METHODS

The charts of 263 patients with traumatic aortic rupture from vehicular accidents treated between 1971 and 1998 were reviewed. Patients were grouped according to four periods: group 1, 1971 to 1975, (n = 31); group 2, 1976 to 1985, (n = 83); group 3, 1986 to 1994, (n = 82); and group 4, 1994 to 1998 (n = 67). Seventy-one patients died of exsanguination before definitive care. One hundred-ninety two patients had surgical repair with the following techniques: clamp and sew, 6 in group 1, 22 in group 2, 54 in group 3, none in group 4; shunt, 23 in group 1, 39 in group 2, 2 in group 3; cardiopulmonary bypass, 2 in group 1, 1 in group 3. Forty-three patients had partial bypass with the centrifugal pump and heparin-coated circuits in group 4.

RESULTS

Operative mortality was 6 of 31 (19%) in group 1, 22 of 61 (36%) in group 2, 15 of 57 (26%) in group 3, and 7 of 43 (16%) in group 4. There was one case of paraplegia in group 1 (4%), ten in group 2 (18%), 11 in group 3 (26%), and none in group 4. This difference of paraplegia between the groups was significant (p<0.002). Significant factors for paraplegia were intraoperative hypotension (p<0.000002), cross-clamp time longer than 30 minutes (p<0.008), pump versus no pump (p<0.008), and younger age group (28+/-11 versus 39+/-17 years) (p<0.03).

CONCLUSIONS

There were no statistically significant improvements in mortality rate over the four periods, although, the mortality rate was lowest in the last period when partial bypass with the centrifugal pump was used exclusively. Further, the use of the centrifugal pump with heparin-coated circuits, with femoral vein cannulation into the right atrium and distal aortic perfusion, reduced paraplegia significantly.

The hagfish slime gland: a model system for studying the biology of mucus

The hagfish slime gland may provide a model system for studying certain aspects of the biology of mucus. Mucus is obtained in nonhydrated form by electrically stimulating the anesthetized hagfish and the secretions are stirred into ammonium sulfate. Centrifugation and filtration are than used to isolate the two major secretory products, mucous vesicles and threads. Specific advantages of the model and potential applications for research are discussed.

Hagfish slime gland thread cells. II. Isolation and characterization of intermediate filament components associated with the thread

The slime glands of hagfish have two major cell types, gland thread cells (GTCs) and gland mucous cells (GMCs), both of which upon contact with water contribute to the formation of an abundant quantity of viscous mucus. In previous studies we reported a method for the isolation of GTCs and showed that each ellipsoidal thread cell normally contains a single tapered thread which is uniquely coiled into a space-saving conformation and occupies most of the cell volume. Subsequently, the developing thread was found to consist mainly of intermediate filaments (IFs) aligned in parallel not only to one another but also to a far fewer number of interspersed microtubules (see accompanying paper). In the present report, urea extracts of GTCs were purified and characterized to establish the properties of thread components. One major (alpha) and two minor (beta, gamma) components prepared by anion exchange chromatography were shown to have similar apparent molecular weights of 63,500 +/- 500 daltons but different isoelectric pH values (alpha, 7.56; beta, 5.67; gamma, 5.31). Although the amino acid content of alpha differed significantly from beta and gamma, each of the three was highest in Gly, relatively high in Glx, Ser, Thr, Asx, Ala, Val, and Leu, and relatively low in Cys/2 and Trp. The amino acid compositions of beta and gamma were very similar, and only beta showed evidence of carbohydrate. The threonine content of the alpha component was higher than has been reported for IFs of different origin, and the high content of hydroxyamino acids (18, 19 residues per 100) in alpha, beta, and gamma has been approached only by several IF polypeptides from human or bovine epidermal keratins. Mixtures of the purified components formed 9-11-nm filaments in vitro. The results indicate that the hagfish thread cell is a rich source of IFs, which have a structure that facilitates formation of macrofibrils within the cell.

Keratin-like components of gland thread cells modulate the properties of mucus from hagfish (Eptatretus stouti)

The hagfishes (cyclostomes) are known to secrete copious amounts of mucus mainly by the holocrine mode from the slime glands. Stressed animals release two types of cells (gland thread cells, GTCs; gland mucous cells. GMCs) which rupture on contact with water and rapidly form a mass of viscous mucus. Herein we report some key sequential events of this process and document a novel role for cytoskeletal polymers. After electrostimulation of Pacific hagfish (Eptatretus stouti), the exudate was collected in a stabilization buffer and GTCs segregated from GMC vesicles. Water was added progressively to mixtures of known quantities of these entities. The changing mucous composition and properties were monitored by light- and electron microscopy, viscometry and immunogold assay. Sequentially, the threads uncoil from GTCs, aggregate with the vesicles, the vesicles rupture and release mucin-like substances, at least some of which adhere to the thread. It was found that the intermediate filament (IF)-rich threads markedly facilitate hydration and modulate the viscoelastic and cohesive properties of the resultant mucus. It was speculated that the thread abets localization of mucus in an aqueous environment and promotes adhesion of mucus to surfaces such as the fish integument. As judged by immunostaining in situ, GTCs, as well as several cell-types in the epidermis, contain keratin-like components. The role of biopolymers on the properties of teleost and mammalian mucus is discussed.

Maturation of hagfish gland thread cells: composition and characterization of intermediate filament polypeptides

Previous studies with the hagfish, a primitive vertebrate, have shown that the gland thread cells (GTCs) each contain a single thread (approximately 60 cm long in average-sized cells) in the form of a concisely coiled cytoskeletal entity destined for export by holocrine secretion. The thread in relatively immature GTCs consists almost entirely of intermediate filaments (IFs) bundled in parallel alignment with far fewer microtubules (MTs). The three thread polypeptides described earlier (alpha, basic; beta, acidic; gamma, most acidic; each with a Mr of 63-64 kD) are now further evaluated with respect to in vitro assembly, cross-reactivity with IF polypeptides from higher vertebrates, and peptide sequence homology with known IF polypeptides. The overall results mainly suggest that the hagfish polypeptides are keratinlike substances but lamins or a new type of IF is not ruled out. However, cross-reactivity is weak with mammalian keratins; the 8-11-nm filaments formed from mixtures of alpha and gamma in vitro are generally linear rather than the curvilinear structures usually formed by keratin and nonkeratin IFs; and mixtures of alpha and beta tend to yield 9-12-nm granules or granular strings. Polypeptide analyses on GTCs segregated on the basis of maturational stage show a progressive increase in beta/gamma values which correlates with cell maturation, but the alpha/(beta + gamma) ratios remain near 1. Inasmuch as beta and gamma have many similar properties, the documented increase in the amount of the beta component in aging GTCs might in part be the result of a failure in a posttranslational modification system and may contribute to the ultrastructural changes that accompany thread maturation in preparation for holocrine secretion and subsequent modulation of the viscoelastic properties of mucus.

Mechanical dysfunction in the border zone of an ovine model of left ventricular aneurysm

BACKGROUND

The pathophysiology of regional mechanical dysfunction in the border zone (BZ) region of left ventricular aneurysm was studied in an ovine model using magnetic resonance imaging tissue-tagging and regional deformation analysis.

METHODS

Transmural infarcts were created in adult Dorsett sheep (n = 8) by ligation of the distal homonymous coronary artery and were allowed to mature into left ventricular aneurysms for 8 to 12 weeks. Animals were imaged subsequently using double oblique magnetic resonance imaging with radiofrequency tissue tagging. Short axis slices were selected for analysis that included predominantly the septal component of the aneurysm as well as adjacent BZ regions in the anterior and posterior ventricular walls. Dark grid patterns of magnetic presaturations were placed on the myocardium and tracked as they deformed during the diastolic, isovolumic systolic, and systolic ejection phases of the cardiac cycle. Regional ventricular wall strains were calculated in BZ regions and regions remote from the aneurysm and compared with strains measured in corresponding regions from normal control sheep (n = 6).

RESULTS

Diastolic midwall circumferential strains (fiber extensions) were relatively preserved, but abnormal circumferential lengthening strains were observed in the BZ regions during isovolumic systole. Peak circumferential strains ranged from 0.04 to 0.07 in the BZ regions but averaged -0.05 in the normal hearts (p = 0.002 for the anterior BZ and p = 0.001 for the posterior BZ). Midwall end-systolic fiber strains were depressed in the anterior BZ (-0.03 to -0.09 for the BZ versus -0.11 for the normal heart, p < 0.0001) but not in the posterior BZ (p = 0.19).

CONCLUSIONS

Our data support the theory that the stretching of BZ fibers during isovolumic systole contributed to a reduction in fiber shortening during systolic ejection and thus reduced the overall contribution of these fibers to forward ventricular output.

Metastatic cancer. A relative contraindication to vena cava filter placement

From October 1979 to November 1984, 41 patients underwent placement of vena cava filters for prevention of pulmonary emboli. After filter placement, no pulmonary emboli were documented. No patient died due to filter placement. However, 20 of these 41 patients are dead. Eighteen deaths were caused by cancer. Ten (24%) patients died within 2 months of filter placement. Five (12%) patients died prior to hospital discharge. All ten of these patients had known, widely metastatic cancer. Among the ten patients who died more than 2 months after filter placement, six had well-differentiated, slow growing tumors. Only three of these patients had brain metastases. Among the 21 survivors only two suffered from cancer. Strict adherence to accepted indications for vena cava filter placement required operative procedures on a small but significant number of patients who demonstrated no significant improvement in quality of life or time out of hospital. Filter placement in patients with aggressive cancers and proven metastases should be performed only after analysis of predicted survival and after detailed discussions with patients and referring physicians. Filter placement in patients with aggressive metastatic cancer may cause discomfort, risk, and expense with little hope for improvement of hospital course, longevity, or quality of life.

Spline surface interpolation for calculating 3-D ventricular strains from MRI tissue tagging

A method is developed and validated for approximating continuous smooth distributions of finite strains in the ventricles from the deformations of magnetic resonance imaging (MRI) tissue tagging "tag lines" or "tag surfaces." Tag lines and intersections of orthogonal tag lines are determined using a semiautomated algorithm. Three-dimensional (3-D) reconstruction of the displacement field on tag surfaces is performed using two orthogonal sets of MRI images and employing spline surface interpolation. The 3-D regional ventricular wall strains are computed from an initial reference image to a deformed image in diastole or systole by defining a mapping or transformation of space between the two states. The resultant mapping is termed the measurement analysis solution and is defined by determining a set of coefficients for the approximating functions that best fit the measured tag surface displacements. Validation of the method is performed by simulating tag line or surface deformations with a finite element (FE) elasticity solution of the heart and incorporating the measured root-mean-square (rms) errors of tag line detection into the simulations. The FE-computed strains are compared with strains calculated by the proposed procedure. The average difference between two-dimensional (2-D) FE-computed strains and strains calculated by the measurement analysis was 0.022 +/- 0.009 or 14.2 +/- 3.6% of the average FE elasticity strain solution. The 3-D displacement reconstruction errors averaged 0.087 +/- 0.002 mm or 2.4 +/- 0.1% of the average FE solution, and 3-D strain fitting errors averaged 0.024 +/- 0.011 or 15.9 +/- 2.8% of the average 3-D FE elasticity solution. When the rms errors in tag line detection were included in the 2-D simulations, the agreement between FE solution and fitted solution was 24.7% for the 2-D simulations and 19.2% for the 3-D simulations. We conclude that the 3-D displacements of MRI tag lines may be reconstructed accurately; however, the strain solution magnifies the small errors in locating tag lines and reconstructing 3-D displacements.

Heparinless partial cardiopulmonary bypass for the repair of aortic trauma

OBJECTIVE

We hypothesized that partial cardiopulmonary bypass with a heparin-bonded system would be a technically simple, effective adjunct for reducing paraplegia during repair of traumatic aortic rupture. It avoids the risk of heparin, but, unlike left atrial-arterial bypass, it can heat, cool, oxygenate, and rapidly infuse volume if needed.

METHODS

A retrospective review was conducted of patients admitted for aortic trauma from July 1994 to December 1999. Bypass consisted of femoral venous (right atrial) cannulation, a centrifugal pump, and an oxygenator-heater/cooler. Arterial return was to the femoral artery or distal aorta. The entire system was heparin-bonded and no systemic heparin was given.

RESULTS

Heparin-bonded partial bypass was established in 50 patients (mean age 43 +/- 17 years). Crossclamp time was 32 +/- 11 minutes (range 14-70 minutes), mean flow 3.0 +/- 0.8 L/min, and bypass time 64 +/- 43 minutes. During repair, 58% of patients received volume through the system (mean 1.1 +/- 1.9 L). Core temperature rose slightly (35.9 degrees C +/- 0.7 degrees C to 36.3 degrees C +/- 0.8 degrees C). Three of the 15 patients who underwent percutaneous femoral arterial and venous cannulation concomitant with their angiograms had vessel injury, with one limb loss, and this procedure was discontinued. Thirty-five patients underwent percutaneous femoral vein and direct distal aortic cannulation without event. The mortality rate for patients supported by bypass was 10%, and all deaths were due to other injuries. There were no new cases of paraplegia and no worsening of intracranial or pulmonary injuries.

CONCLUSIONS

Heparin-bonded bypass is technically simple to use and avoids the risk of anticoagulation. Paraplegia was avoided. The ability to correct hypothermia, oxygenate, and rapidly infuse volume may simplify management and improve outcomes.

Myocardial material property determination in the in vivo heart using magnetic resonance imaging

OBJECTIVES

To determine nonlinear material properties of passive, diastolic myocardium using magnetic resonance imaging (MRI) tissue-tagging, finite element analysis (FEA) and nonlinear optimization.

BACKGROUND

Alterations in the diastolic material properties of myocardium may pre-date the onset of or exist exclusive of systolic ventricular dysfunction in disease states such as hypertrophy and heart failure. Accordingly, significant effort has been expended recently to characterize the material properties of myocardium in diastole. The present study defines a new technique for determining material properties of passive myocardium using finite element (FE) models of the heart, MRI tissue-tagging and nonlinear optimization. This material parameter estimation algorithm is employed to estimate nonlinear material parameter sin the in vivo canine heart and provides the necessary framework to study the full complexities of myocardial material behavior in health and disease.

METHODS AND RESULTS

Material parameters for a proposed exponential strain energy function were determined by minimizing the least squares difference between FE model-predicted and MRI-measured diastolic strains. Six mongrel dogs underwent MRI imaging with radiofrequency (RF) tissue-tagging. Two-dimensional diastolic strains were measured from the deformations of the MRI tag lines. Finite element models were constructed from early diastolic images and were loaded with the mean early to late left ventricular and right ventricular diastolic change in pressure measured at the time of imaging. A nonlinear optimization algorithm was employed to solve the least squares objective function for hte material parameters. Average material parameters for the six dogs were E = 28,722 +/- 15984 dynes/cm2 and c = 0.00182 +/- 0.00232 cm2/dyne.

CONCLUSION

This parameter estimation algorithm provides the necessary framework for estimating the nonlinear, anisotropic and non-homogeneous material properties of passive myocardium in health and disease in the in vivo beating heart.

Biaryl acids: novel non-nucleoside inhibitors of HIV reverse transcriptase types 1 and 2

A series of biaryl acids has been found to show micromolar inhibition of the HIV reverse transcriptase (RT) from types 1 and 2 with IC50S in the micromolar range. The series was discovered by consideration of the polymerase active site and sub-structure searching of the company compound collection. Synthesis of analogues to investigate the SAR is described. Two of these compounds have shown inhibition of HIV-2 RT only.