System identification of tendon reflex dynamics

Patellar tendon reflexes were evaluated in 12 healthy adult subjects using several measures of the reflex responses and of the system input-output relationship. A hand-held instrumented hammer was used to tap the patellar tendon and to elicit the reflex response. Tendon reflex dynamics were estimated using the recorded tapping force (as input) and the quadriceps muscle electromyogram and knee joint extension torque signals (as output). A dome-shaped rubber pad was mounted onto the most sensitive spot on the patellar tendon, where it served as a tapping target, and helped to reduce the reflex variability significantly (p < 0.01). The input-output properties of the system relating the reflex torque to the tapping force were characterized using several measures: the tendon reflex gain (Gtr), contraction rate (Rc), and half-relaxation rate (Rhr). Reflex loop delay (t(d)) was estimated using the delay from the onset of tapping force to the onset of reflex torque. We determined that these system parameters provided significantly more repeatable and consistent characterization of tendon reflexes than did reflexive torque or EMG signals alone (p < 0.025). The input-output relationship relating the EMG signals of the stretched muscle to the tapping force was also identified to help characterize neuromuscular dynamics of tendon reflexes. The observed sensitivity and consistency of the reflex system measures suggest that with appropriate simplification of the instrumentation, these methods may prove useful in routine clinical practice, and may allow more precise quantification of the tendon jerk than is currently feasible with standard clinical tests.

A PstI polymorphism detects the mutation of serine128 to arginine in CD 62E gene - a risk factor for coronary artery disease

The mutation of serine128 to arginine in the CD 62E gene is a risk factor for coronary artery disease (CAD). We designed a new method to detect this mutation based on the observation that it is due to a transversion of nucleotide A561 to C, which abolishes a PstI recognition site. Two alleles, A and C, are easily typed when genomic DNA is amplified by PCR, digested with PstI, and separated on agarose gels. Among 153 people who underwent an elective, diagnostic arteriography in Johns Hopkins Hospital, we found that the C allele accounts for 19.5% in angiographically documented CAD patients (n = 82). It is significantly higher than the 10.6% frequency observed in normal controls (n = 71, p < 0.05). It indicates that the C allele is associated with early-onset CAD. This new method should facilitate the screening of this mutant allele in large populations and contribute to the understanding of the molecular mechanism underlying the association of this mutation with CAD.

In vivo human knee joint dynamic properties as functions of muscle contraction and joint position

Information on the dynamic properties (joint stiffness, viscosity and limb inertia) of the human knee joint is scarce in the literature, especially for actively contracting knee musculature. A joint driving device was developed to apply small-amplitude random perturbations to the human knee at several flexion angles with the subject maintaining various levels of muscle contraction. It was found that joint stiffness and viscosity increased with muscle contraction substantially, while limb inertia was constant. Stiffness produced by the quadriceps was highest at 30 degrees flexion and decreased with increasing or decreasing flexion angle, while knee flexors produced highest stiffness at 90 degree flexion. When knee flexion was < 60 degrees, stiffness produced by the quadriceps was higher than that of the hamstrings and gastrocnemius at the same level of background muscle torque, while knee flexor muscles produced higher stiffnesses than the quadriceps at 90 degree flexion. Similar but less obvious trends were observed for joint viscosity. Passive joint stiffness at full knee extension was significantly higher than in more flexed positions. Surprisingly, as the knee joint musculature changed from relaxed to contracting at 50% MVC, system damping ratio remained at about 0.2. This outcome potentially simplifies neuromuscular control of the knee joint. In contrast, the natural undamped frequency increased more than twofold, potentially making the knee joint respond more quickly to the central nervous system commands. The approach described here provides us with a potentially valuable tool to quantify in vivo dynamic properties of normal and pathological human knee joints.

Simultaneous and nonlinear identification of mechanical and reflex properties of human elbow joint muscles

The naturally coexisting intrinsic mechanical and reflex properties of the human elbow joint were identified simultaneously using nonlinear, time-delay, continuous-time, and dynamic models. Angular random perturbations of small amplitude and low bandwidth were applied to the joint using a computer-controlled servomotor, while the subject maintained various levels of mean background muscle torque. Joint neuromuscular dynamics were identified from the measured elbow angle and torque. Stretch reflexes were modeled nonlinearly with both dynamic and static reflex gains. A continuous-time system identification method was developed to estimate parameters of the nonlinear models directly from sampled data while retaining realistic physical or physiological interpretations. Results from six subjects showed that dynamic stretch reflex gains, joint stiffness, and viscosity generally increased with mean background muscle torque; and that dynamic stretch reflex gain was higher during muscle stretch than that during muscle shortening. More importantly, the study provided realistic simultaneous estimates of the relative contributions of intrinsic mechanical and reflex actions to net joint torque. In particular, reflexively-mediated stiffness generated a significant portion of the total joint stiffness and the percentage varied systematically with background muscle torque.

A fibroblast cell line cultured from a hypertrophic scar displays selective downregulation of collagen gene expression: barely detectable messenger RNA levels of the pro alpha 1(III) chain of type III collagen

The present study was designed to investigate the expression of type I, III and VI collagens by a fibroblast cell line initiated from a hypertrophic scar. The same tissue has previously been demonstrated to display markedly elevated expression of type I and III collagen mRNAs in vivo. Unexpectedly, slot-blot and Northern hybridizations revealed a barely detectable steady-state level of pro alpha 1(III) collagen chain mRNA in cultured hypertrophic scar fibroblasts. The levels of pro alpha 1(I) and alpha 2(VI) collagen chain mRNAs were essentially the same in fibroblasts cultured from hypertrophic scar and in fibroblasts cultured from normal skin. However, Northern blot analyses indicated that the ratio of 5.8 kb to 4.8 kb species of pro alpha 1(I) collagen mRNA was slightly reduced in fibroblasts originating from the hypertrophic scar compared to that in normal fibroblasts. When normal fibroblasts were incubated in conditioned medium from hypertrophic scar cultures, the expression of pro alpha 1(III) collagen chain mRNA decreased to a markedly lower level. Our studies suggest that collagen synthesis by fibroblasts in hypertrophic scars is stimulated by humoral factors which are active only in vivo. Furthermore, the results suggest that fibroblasts cultured from hypertrophic scar display a selective downregulation of different collagen genes and that this downregulation is exerted through an autocrine mechanism.

The molecular epidemiology of human immunodeficiency virus type 1 in Edinburgh

Human immunodeficiency virus (HIV) type 1 sequences obtained from HIV-infected persons in different risk groups in Edinburgh were studied to determine the number and origin of virus variants and patterns of virus transmission. Phylogenetic analysis revealed that 12 of 14 hemophiliac patients who had been exposed to a single common batch of factor VIII had closely related gag gene sequences. Sequences from intravenous drug users and patients infected through heterosexual contact formed another distinct group, and 2 other hemophiliacs formed a third group. However, epidemiologic relationships inferred from analysis of the V3 region of the env gene were less conclusive, especially when the V3 loop was taken in isolation. This appears to be due to the length of time since infection and the action of selection, which has favored the independent appearance of similar V3 loop variants.

Normal and hypertrophic scars: quantification and localization of messenger RNAs for type I, III and VI collagens

The expression of type I, III and VI collagens was studied in nine normal and two hypertrophic scars using slot-blot and in situ hybridization techniques. Slot-blot hybridization indicated that the steady-state levels of pro alpha 1(I) and pro alpha 1(III) collagen chain mRNAs were moderately elevated in two of the nine normal scars, whereas the two hypertrophic scars analysed displayed markedly elevated mRNA levels when compared with normal skin. The mRNA levels of alpha 2(VI) collagen chain were only slightly elevated in both types of scars studied. In situ hybridization was most informative when applied to hypertrophic scars. These lesions were characterized by the presence of intense hybridization signals for type I and III collagen mRNAs, and a moderate signal for type VI collagen mRNA, in nodules which were located in the upper dermis on each side of the original wound. This may explain, in part, why hypertrophic scars rise above the level of the surrounding skin. The results of the present study are in marked contrast to our previous findings on collagen gene expression in keloids and neurofibromas, in which the steady-state levels of type VI and I collagen mRNAs in particular were shown to be elevated. Thus, our results emphasize that distinct molecular mechanisms are operative in the development of clinically different dermal fibrotic conditions, such as normal and hypertrophic scars, keloids and neurofibromas.

Expression of type I, III, and VI collagen mRNAs in experimentally injured porcine intervertebral disc

Young domestic pigs were incised with a scalpel blade into the anterior part of annulus fibrosus of lumbar discs in order to study the reparative processes in the annulus fibrosus and the secondary reactions in the nucleus pulposus. Northern and slot-blot hybridizations were used to investigate type I, III, and VI collagen gene expression in the disc tissue. For this purpose a method for RNA isolation was modified so as to be applicable to the intervertebral disc, which has a low cell density and a high proteoglycan content in its extracellular matrix. The amount of total RNA was found to be very low, particularly in the nucleus pulposus. Intact RNA could be isolated from most parts of the injured discs, but only from the outer annulus of the control discs. Hybridizations showed that healing of the wound in the annulus fibrosus involves an increase in the synthesis of particularly type I and type III collagens. However, no changes in the collagen gene expression were detectable in the nucleus pulposus two weeks after the injury.

Establishment of cell lines from B-cell precursor acute lymphoblastic leukemia

In an attempt to establish permanent cell lines from children with B-cell precursor acute lymphoblastic leukemia (BCP-ALL), 123 clinical samples from 117 patients were cultured in vitro. Using a method which was successful for the growth of ALL with T-cell phenotype, 3% (2/74) of BCP-ALL samples from patients at diagnosis and 31% (9/29) of BCP-ALL samples from patients at relapse were established as cell lines. However, in most cultures, leukemic cells survived for only a few weeks and the majority of viable cells present after 28 days of culture were esterase-positive mononuclear cells. Based on the hypothesis that mononuclear cells inhibited leukemic cell growth, we evaluated the effect of a monocyte toxin, L-leucine methyl ester (Leu-OMe), on the growth of four frozen BCP-ALL samples. Thawed leukemic cells treated with Leu-OMe, but not untreated control cells, proliferated in three samples and one new cell line was established. Subsequently, when Leu-OMe was added to fresh leukemia cells in culture, leukemic cell lines were grown from 29% (4/14) of samples at diagnosis and 66% (4/6) of relapse samples. Overall, 20 BCP-ALL cell lines were established, all were Epstein-Barr virus (EBV)-negative, and authenticity of each cell line was verified by a direct comparison of the immunophenotype, karyotype, and genotype with the patient's tumor cells. This improved method of cell culture permits a higher success rate of cell line establishment from patients with BCP-ALL thereby aiding in analysis of B-lymphocyte transformation and neoplasia.

The effect of mangxiao (natrii sulphas) in the relief of stasis and swelling after implantation of cardiac pacer

Sixteen patients with local stasis and swelling after implanting cardiac pacemaker were treated with Mangxiao (Natrii Sulphas) on the implanted local surface for 4-14 days. The effect was satisfactory. Reopening of the skin for the cleaning of the stasis and swelling and removal of the pacemakers could thus be avoided in these patients. The mechanism of action of Mangxiao in relieving stasis and swelling was studied preliminarily.

Characterization of a CD34+ cell line established from a child with large cell cutaneous lymphoma

BACKGROUND

Lymphoma presenting with skin involvement has heterogeneous morphology and rarely is seen in children. To study the pathogenesis of this disease, lymphoma cells from a child with B-cell large cell lymphoma of the skin were cultured in vitro.

METHODS

Lymphoma cells cultured on a feeder layer under hypoxic conditions grew in vitro after a latency period of 2 weeks. Since interleukin-6 (IL-6) induces final differentiation of activated B-lymphocytes, the cell line was evaluated for the presence of IL-6 receptors and biologic response to IL-6.

RESULTS

An Epstein-Barr virus (EBV)-negative cell line (UoC-B2) was established which expressed CD34, CD45, HLA-DR, CD19, CD20, sIgM, sIgD, and lambda light chain. Good general concordance was observed between the patient's lymphoma and the cell line by comparing the immunophenotype, genotype, and karyotype. The UoC-B2 cells expressed surface IgM but did not secrete IgM into the culture media even in the presence of supplemental IL-6.

CONCLUSIONS

A B-lymphoid cell line (UoC-B2) was established from a child with primary cutaneous lymphoma. The cells expressed cell surface IgM and receptors for IL-6 but supplemental IL-6 had no effect on IgM production or cell proliferation.

Selection for specific sequences in the external envelope protein of human immunodeficiency virus type 1 upon primary infection

Viral RNA was extracted from plasma samples collected from five individuals during the period of viremia before seroconversion in primary infection with human immunodeficiency virus type 1 (HIV-1) and amplified by polymerase chain reaction. Nucleotide sequence analysis of amplified DNA from the V3 and V4 hypervariable regions indicated that the initial virus population of each acutely infected individual was completely homogeneous in sequence. No intrasample variability was found among the 44,090 nucleotides sequenced in this region of env, contrasting with the high degree of variability normally found in seropositive individuals. Paradoxically, substantial sequence variability was found in the normally high conserved gag gene (encoding p17) in most of the preseroconversion samples. The diversity of p17 sequences in samples that were homogeneous in V3 and V4 can most readily be explained by the existence of strong selection for specific env sequences either upon transmission or in the interval between exposure and seroconversion in the exposed individual. Evidence that localizes the selected region upon transmission to V3 is provided by the similarity or identity of V3 loop sequences in five individuals with epidemiologically unrelated HIV-1 infections, while regions flanking the V3 loop and the V4 hypervariable region were highly divergent. The actual V3 sequences were similar to those associated with macrophage tropism in primary isolates of HIV, irrespective of whether infection was acquired by sexual contact or parenterally through transfusion of contaminated factor VIII. Proviral DNA sequences in peripheral blood mononuclear cells remained homogeneous in the V3 and V4 regions (and variable in p17gag) for several months after seroconversion. The persistence of HIV sequences in peripheral blood mononuclear cells identical to those found at primary infection in the absence of continued virus expression provides an explanation for the previously observed differences in the composition of circulating DNA and RNA populations in sequential samples from seropositive individuals.

Molecular investigation of human immunodeficiency virus (HIV) infection in a patient of an HIV-infected surgeon

Recall of patients who had been treated by a human immunodeficiency virus (HIV)-infected surgeon uncovered 1 previously unknown HIV-seropositive person. Nucleotide sequencing of the gag gene and maximum likelihood phylogenetic analysis were used to investigate the relationships among sequences from the surgeon, the patient, and an anonymous blood donor from whom the patient had received blood products. The likelihoods of all possible pathways of transmission linking these persons were estimated. On these data, transmission from the surgeon to the patient was significantly less likely than from the blood donor to the patient. It is concluded that none of the recalled patients were infected by the surgeon.

Investigation of potential HIV transmission to the patients of an HIV-infected surgeon

OBJECTIVE

To ascertain if a surgeon infected with the human immunodeficiency virus (HIV) transmitted HIV to patients during invasive surgical procedures.

DESIGN

Survey of patients and acquired immunodeficiency syndrome (AIDS) case registries, and laboratory analysis of nucleotide sequence data.

SETTING

One surgeon's private and institutional practices within one academic referral hospital.

PATIENTS

A total of 1131 persons identified in hospital databases who underwent invasive surgical procedures from 1984 through 1990 and for whom the surgeon was listed as the admitting or operating surgeon.

MEASUREMENT

Patients presumed to be living were surveyed by mailed questionnaire. The AIDS case registries were reviewed for all patients having undergone invasive procedures and death certificates were obtained. Person-hours of surgery during which exposure might have occurred were calculated for surgical procedures.

RESULTS

Of 1131 patients, 101 were dead, 119 had no address, 413 had test results known, and 498 did not respond to the questionnaire. No study patient name was found in reported AIDS case registries. One newly detected, HIV-seropositive patient was determined (through nucleotide sequencing) to have been most probably infected in 1985 during a transfusion. There was no HIV transmission in 369 person-hours of surgical exposure, indicating that HIV transmission to patients is unlikely to occur more frequently than once per 1000 person-hours of surgical exposure.

CONCLUSIONS

If study validity and resources permit, investigation of publicly disclosed, HIV-infected health care workers whose practices involve invasive procedures should be pursued. The risk of HIV transmission during surgery may be so small that it will be quantified only by pooling data from multiple, methodologically similar investigations.

Convergent and divergent sequence evolution in the surface envelope glycoprotein of human immunodeficiency virus type 1 within a single infected patient

In an investigation of the evolution of the third hypervariable loop of gp120 (V3), the principal neutralization determinant of human immunodeficiency virus type 1, we have analyzed 89 V3 sequences of plasma viral RNA purified from peripheral blood samples donated over 7 years by an infected hemophiliac. Considerable sequence diversity in the V3 region was found at all time points after seroconversion. Phylogenetic analysis revealed that an important diversification had occurred by 3 years postinfection and that, subsequently, most sequences could be allocated to either one of two major lineages that persisted throughout the remainder of the infection. Rapid changes in frequency of the most common sequences and the observation that the same hexapeptide motif (GPGSAV) at the crown of the V3 loop has evolved convergently provide strong evidence that selective processes determine the evolutionary fate of sequence variants in this region.

Hepatitis C viraemia in United Kingdom blood donors. A multicentre study

Of 10,633 blood donations tested in three regional blood transfusion centres with two commercial first generation screening assays for antibodies to the hepatitis C virus (HCV), 65 (0.61%) were found to be repeatedly reactive in one or both assays. Five of the 65 were confirmed positive by recombinant immunoblot assay (Ortho RIBA-2) and a further 4 were judged indeterminate. All 5 RIBA-2 positive donations and 1 of the 4 RIBA-2 indeterminates were shown to be viraemic by HCV-RNA polymerase chain reaction (PCR) assays performed at three independent reference laboratories. The remaining 56 screen test reactive donations proved negative by RIBA-2 and, with 1 exception, negative by PCR. We conclude that while first generation anti-HCV screening assays generate a high proportion of false reactions when screening low prevalence populations, results of the RIBA-2 confirmatory test correlate well with PCR findings and thus indirectly with both hepatitis C viraemia and infectivity.

Use of several second generation serological assays to determine the true prevalence of hepatitis C virus infection in haemophiliacs treated with non-virus inactivated factor VIII and IX concentrates

To investigate the prevalence of hepatitis C virus infection in two risk groups, stored serum samples from treated haemophiliacs and intravenous drug users were tested for anti-HCV by both anti-C-100 based and second generation ELISAs (Abbott and Ortho) followed by testing in two confirmatory immunoblot assays that incorporate core as well as other non-structural antigens (Innogenetics LIA and Chiron RIBA-HCV test). Clear evidence of HCV infection was found in all but one of 78 haemophiliacs treated with non-virus inactivated clotting factor concentrates, but in none exposed only to super dry heat-treated concentrates. Only four samples gave rise to conflicting serological results between the four tests, two of these occurred in patients with advanced HIV related disease and almost certainly reflected loss of humoral immunity associated with disease progression, and the others occurred in the only two patients tested who were chronic carriers of hepatitis B infection and may reflect an interaction between the two viruses. Comparison of anti-C-100 versus second generation tests in immunocompetent drug users revealed a false negative rate of 20% using C-100 alone, indicating the advantage of using second generation assays for detection of past or current HCV infection. Of all of the antigens used in the confirmatory assay, positive sera showed strongest and most frequent reactivity with the C22 and C33c proteins (Ortho RIBA).

Pattern analysis of electromyographic linear envelopes exhibited by subjects with uninjured and injured knees during free and fast speed walking

We wished to determine whether anterior cruciate ligament (ACL) injury caused changes in patterns of activity of individual or groups of muscles that control the knee joint. The electromyographic (EMG) patterns of six muscles in 26 individuals with uninjured knees and 20 individuals with ruptured ACL were studied during free and fast speed walking. A previously developed clustering technique was used for analysis. This technique involves making the Fourier transform of the average linear envelope (LE) of each muscle for each subject and using the amplitude and phase angles of the lower frequency harmonics as features to describe a pattern. These features are then grouped to subdivide the population of EMG patterns into different types. The results of analyses on single muscles showed that there exists a typical or "normal" pattern for each muscle which most uninjured and some injured subjects exhibit as well as several atypical patterns which mostly injured subjects exhibit, and that the atypical patterns are much more evident at fast walking speed. The characteristics of atypical patterns with respect to normal include time shifts in the peak of major phases of activity, the absence of a second phase of activity, and the existence of additional phases of activity. Synergy analysis showed that if one muscle has an atypical pattern, then several do; i.e., ACL injury induces major changes in the control strategy of the knee. The implications are that for rehabilitation programs one must focus on the training and strengthening of more than one muscle, and that for reconstructive procedures the changes in mechanics of the joint can possibly induce a significant change in its control strategy.

A quantitative and qualitative description of electromyographic linear envelopes for synergy analysis

The muscular synergy patterns of human locomotion can be described by the phasic activity of electromyographic linear envelopes (LE) and the interphasic spatio-temporal relations. To represent the phasic activity, the LE is modeled as the summation of Gaussian pulses of various lengths. The parameters of interest are the temporal features: time, duration, and amplitude of the phases of activity. A maximum likelihood approach to the parameter estimation for a mixture of normal distributions is adopted for extracting the temporal features. Based on the derived temporal features, a set of relational descriptors can be defined to describe the spatio-temporal relations between the multichannel phasic activities. The strength of this approach is not only that the phasic activity of LE can be quantitatively represented accurately, but also that the resulting synergy patterns can be easily interpreted by observers.

Discontinuous sequence change of human immunodeficiency virus (HIV) type 1 env sequences in plasma viral and lymphocyte-associated proviral populations in vivo: implications for models of HIV pathogenesis

Sequence change in different hypervariable regions of the external membrane glycoprotein (gp120) of human immunodeficiency virus type 1 (HIV-1) was studied. Viral RNA associated with cell-free virus particles circulating in plasma and proviral DNA present in HIV-infected peripheral blood mononuclear cells (PBMCs) were extracted from blood samples of two currently asymptomatic hemophiliac patients over a 5-year period. HIV sequences were amplified by polymerase chain reaction to allow analysis in the V3, V4, and V5 hypervariable regions of gp120. Rapid sequence change, consisting of regular replacements by a succession of distinct viral populations, was found in both plasma virus and PBMC provirus populations. Significant differences between the frequencies of sequence variants in DNA and RNA populations within the same sample were observed, indicating that at any one time point, the predominant plasma virus variants were antigenically distinct from viruses encoded by HIV DNA sequences in PBMCs. How these findings contribute to current models of HIV pathogenesis is discussed.

Tumor necrosis factor-alpha, interleukin 1, and phorbol myristate acetate are independent activators of NF-kappa B which differentially activate T cells

Gene expression in eukaryotic cells can be altered in different ways by extracellular agents, including mitogens and cytokines. Such differential gene expression is mediated in part through the effects of these stimuli on distinct sets of cellular transcription factors. In this report, the effects of phorbol myristate acetate, tumor necrosis factor-alpha (TNF-alpha), and interleukin 1 (IL-1) on differential gene expression in the LBRM mouse T-lymphoma cell line are examined. Although these three different stimuli produce similar levels of induction of the NF-kappa B transcription factor, it is reported that they cause differential expression of other cellular activation genes, including c-fos and IL-2. The roles of IL-1 and TNF-alpha were also analyzed in EL-4 cells in the presence of a second activator, ionomycin. IL-1, but not TNF-alpha, was found to stimulate the IL-2 enhancer in the presence of this costimulator. These findings suggest that one transcription factor can be the target of cellular activators that exert otherwise different effects on gene expression. Cellular activation pathways can therefore be defined by the set of transcription factors stimulated within a cell. This approach may allow a more precise definition of the requirements for differential gene activation in different cell types and thereby provide a basis for the selective manipulation of gene expression in cytokine-responsive cells.

Clustering analysis and pattern discrimination of EMG linear envelopes

A technique has been developed for performing pattern analysis of EMG activities generated during locomotion. In this development it was found that the shapes of the EMG linear envelopes (LE) are mainly determined by their phase spectra; their magnitude spectra are much less important. Autoregressive (AR) parametric models and discrete Fourier transform (DFT) approaches were tested and compared. The latter was proved to be a better way to describe the EMG LE's. Feature extraction and clustering were performed by doing DFT of EMG LE's, extracting part of the phase and magnitude spectra (in less important degree) as features, and using the percent powers to weigh the corresponding harmonics. The approach was applied to the clustering analysis of EMG LE's of normal and anterior cruciate ligament (ACL) injured subjects during walking.

Detection, quantification and sequencing of HIV-1 from the plasma of seropositive individuals and from factor VIII concentrates

A highly sensitive and reliable RNA polymerase chain reaction method has been developed which has been used to detect, quantify and sequence cell-free HIV RNA directly from the plasma of seropositive individuals. Plasma from 10 out of 12 haemophiliacs tested was found to contain detectable levels of HIV-1 RNA [log mean value: 1.2 x 10(3) copies for Centers for Disease Control (CDC) group II patients, 5.5 x 10(3) copies for CDC group IV patients]. The presence of cell-free circulating virus in both symptomatic and asymptomatic individuals suggests that viral replication continues throughout the course of infection. The same procedure has been used to detect and sequence HIV-1 RNA in two batches of unheated commercial factor VIII concentrate distributed in 1981 and 1983. The sequences obtained revealed a closer relationship to North American than to African strains of HIV-1.

Decreases in the relative concentrations of specific hepatocyte plasma membrane proteins during liver regeneration: down-regulation or dilution?

Antibodies were used to quantify seven domain-specific integral proteins of the rat hepatocyte plasma membrane during rat liver regeneration in response to two-thirds hepatectomy. Quantitative immunoblotting revealed that a subset of the plasma membrane proteins exhibited transient 30-70% decreases in relative concentration during the period of hepatocyte proliferation. The list of affected proteins included at least one representative from each of the plasma membrane domains: the apical protein HA 4, the lateral protein HA 321, and the basolateral receptors for epidermal growth factor and asialoglycoproteins. In contrast, the relative concentrations of three other plasma membrane proteins, the basolateral protein CE 9 and the two apical proteins dipeptidylpeptidase IV and aminopeptidase N, remained unchanged throughout liver regeneration. The decreases in the relative concentrations of the plasma membrane proteins were observed even when the synthesis of hepatocyte DNA was blocked by hydroxyurea, suggesting that the signalling for these two delayed consequences of two-thirds hepatectomy occurred along parallel, dependent pathways. Pulse and pulse-chase metabolic radiolabeling studies revealed that the decreases in the concentrations of the PM proteins were accomplished through protein-selective decreases in the rates of synthesis of the high-mannose precursors of the affected proteins, but not through the accelerated degradation of the mature plasma membrane proteins.