Biomedical subjects

R G Miller

Publications and source records attributed to R G Miller.

At least 127 records · Page 7Linked to original sources

PubMed1994

Correlation between lymphocyte-induced donor-specific tolerance and donor cell recirculation. Role of class I and class II major histocompatibility complex.

Intravenous infusion of mice with viable allogeneic lymphocytes can produce donor-specific enhancement of skin graft survival, but only if the injected lymphocytes can persist in the host's recirculating lymphocyte pool for at least 3 days. We have investigated the relative roles of class I and class II MHC for C57BL/6 mice infused with lymphoid cells from co-isogenic strains mutated at class I MHC (bm1) or class II MHC (bm12), and for A.TH lymphoid cells infused into C3H (class I different, class II identical) or A.TH (class II different, class I identical). Injected cells differing from the host at class I MHC, but not at class II MHC, can be rapidly removed by host natural immune mechanisms (probably NK cells). Persistence is favored if the injected cells also carry host class I MHC, i.e., tolerance is more readily induced by injecting F1 (A x B) into A rather than B into A, consistent with the "missing self" hypothesis of NK recognition, with class I MHC being the relevant self-marker. Injected cells differing from the host at class II MHC but not at class I MHC always persist for at least 3 days, even when class I-different cells are being actively removed.

Animals↗

PubMed1994

Role of infused CD8+ cells in the induction of peripheral tolerance.

The CD8 molecule when present on a cell recognized by a mature T cell has been shown to have an inhibitory effect on the development of an in vitro immune response by that T cell. To test whether CD8 has a role in the induction of peripheral tolerance in vivo, we have studied tolerance induction in B6 female mice carrying a transgenic TCR specific to male H-Y Ag. Previous studies have shown that male Ag reactive cells are inactivated in these mice after the i.v. injection of viable male lymphoid cells. Here, B6 female transgenic mice were injected with B6 male lymph node cells from CD4 or CD8 gene knockout mice, and the fate of male Ag-specific T cells was followed in vivo. Our results indicate that injection of male CD4 knockout (express CD8) lymphoid cells but not CD8 knockout (do not express CD8) lymphoid cells induced a significant reduction of male H-Y Ag reactive cells in the periphery, suggesting that CD8 plays an important role in the induction of peripheral tolerance of class I-restricted T cells. These results imply that peripheral tolerance can be induced not just by absence of signals required for activation but by the presence of additional signals.

Animals↗

PubMed1994

Reduction of CTL antipeptide response mediated by CD8+ cells whose class I MHC can bind the peptide.

Primary CTL responses can be generated in vitro against defined peptides in association with class I MHC molecules. We show here that if cells obtained from a 5-day MLR are also included in the cultures, the response is greatly reduced if the added cells both carry CD8 and can bind the peptide. Our interpretation is that the added MLR cells are acting as deletional APC or veto cells. Peptide-specific CTL precursors recognize the peptide on the class I MHC of the CD8+ MLR cells and then receive a negative signal via CD8 on these cells. In support of this, when MLR cells carrying the Lyt-2.1 allele of CD8 were used to down-regulate the response of Ly-2.2+ responder cells, inclusion of anti-Ly-2.1 mAb in the cultures partially reversed the response reduction. Similar signaling may occur in vivo. When mice were injected i.v. with syngeneic lymphoid cells incubated with a peptide which they could bind, the response against that peptide was specifically reduced in a subsequent in vitro assay.

Amino Acid Sequence↗

PubMed1994

Postexercise phosphocreatine resynthesis is slowed in multiple sclerosis.

To determine whether skeletal muscle oxidative metabolism is impaired in multiple sclerosis (MS), phosphorus magnetic resonance spectroscopy was used to measure the rate of intramuscular phosphocreatine (PCr) resynthesis following exercise in MS and controls. Thirteen MS patients underwent intermittent isometric tetanic contractions of the dorsiflexor muscles elicited by stimulation of the peroneal nerve. Eight healthy control subjects performed voluntary isometric exercise of the same muscles. During exercise, there were no differences between groups in the fall of either PCr or pH. However, the half-time (T1/2) of PCr recovery following exercise was significantly longer in MS (2.3 +/- 0.3 min) compared to controls (1.2 +/- 0.1 min, P < 0.02). These data provide evidence of slowed PCr resynthesis following exercise in MS, which indicates impaired oxidative capacity in the skeletal muscle of this group. This finding suggests that intramuscular changes consistent with deconditioning may be important in the altered muscle function of persons with MS.

Adult↗

PubMed1994

Metabolic and nonmetabolic components of fatigue monitored with 31P-NMR.

The goal of this study was to determine the roles of metabolic and nonmetabolic factors in muscle fatigue. Rat gastrocnemius muscles were fatigued by stimulation of the nerve (n = 6) or muscle (n = 4, after 2 days of denervation). 31Phosphorus nuclear magnetic resonance spectroscopy was used to measure levels of intracellular inorganic phosphate (Pi) and hydrogen ions (H+) (which are thought to inhibit contraction) and the high-energy phosphates, phosphocreatine (PCr), and ATP. For both indirect and direct stimulation, with fatigue to approximately 60% initial tetanic force, [Pi] increased from approximately 3.5 mmol/L to approximately 20 mmol/L and [PCr] decreased from approximately 27 mmol/L to approximately 9 mmol/L. However, with continued fatigue to 25-35% initial tetanic force, neither [Pi] or [PCr] changed further. [ATP] and pH changed only slightly during fatigue. The results are consistent with early fatigue arising from metabolic inhibition of contraction; but later fatigue arising independent of metabolites, due to impaired activation beyond the neuromuscular junction.

Adenosine Triphosphate↗

PubMed1994

Effects of exercise on muscle activation and metabolism in multiple sclerosis.

We investigated the role of metabolism in muscle fatigue during voluntary exercise in persons with mild multiple sclerosis (MS). Six MS and 8 healthy control subjects performed intermittent, progressive, isometric contractions of the ankle dorsiflexors, during which we measured maximum voluntary force (MVC), inorganic phosphate (Pi), phosphocreatine (PCr), and pH. During exercise, MVC fell sooner in MS, but by the end of exercise the relative decrease in MVC was similar in both groups. In contrast, at the end of exercise Pi/PCr increased to 1.86 +/- 0.22 in controls but to only 0.66 +/- 0.04 in MS (P < 0.01); likewise, pH was 6.75 +/- 0.04 in controls and unchanged (7.06 +/- 0.04) in MS (P < 0.01). The smaller metabolic change at the same relative exercise intensity suggests a failure of muscle activation that is present even in mild MS. Neurophysiologic measures of activation indicated some central activation failure and no neuromuscular junction impairment in MS, and suggested that activation failure beyond the muscle membrane (excitation-contraction coupling) may be important in MS. We conclude that metabolic factors do not play a significant role in the development of muscle fatigue during voluntary exercise in mild MS.

Adult↗

PubMed1994

Treatment of ALS with high dose pulse cyclophosphamide.

Autoimmune abnormalities have been described in sporadically acquired amyotrophic lateral sclerosis (ALS), but ALS patients do not benefit from conventional immunosuppressive therapy. Because Multifocal Motor Neuropathy causes a syndrome mimicking the lower motor neuron involvement in ALS and responds to high dose cyclophosphamide, we tested whether ALS patients would respond to the same treatment. Eighteen patients with classical ALS initially received a high loading dose of intravenous cyclophosphamide (3 g/m2) followed by 6-monthly injections of 750-1000 mg/m2. We monitored isometric strength, fine motor coordination and pulmonary function monthly for 3 months prior to the study, during the treatment phase, and for 6 months after treatment. Treatment subjects were matched to control subjects from the WALS natural history data base and compared on the basis of decline rate (megaslopes). Treatment did not alter the course of ALS.

Adult↗

PubMed1994

Proteolytic activity and fatal gram-negative sepsis in burned mice: effect of exogenous proteinase inhibition.

Circulating proteolytic activity (PA) increases following burn or surgical trauma. Challenging traumatized mice with the yeast Candida albicans further increases PA. Once a PA threshold has been passed, mortality increases as PA increases. The purposes of this study were to determine (i) if gram-negative bacterial challenge affects circulating PA and mortality as Candida challenge does and (ii) if proteinase inhibitor treatment with aprotinin, antithrombin III, and alpha 1-proteinase inhibitor decreases circulating PA and increases the survival of burned mice infected with a bacterium. For all bacteria tested (Proteus mirabilis, Pseudomonas aeruginosa, and Klebsiella pneumoniae), burn plus challenge significantly elevated PA and mortality above levels in mice that were only burned or only challenged. Quantitative culture counts indicated that the mice died of sepsis. Proteinase inhibitor treatment of mice burned and challenged with K. pneumoniae significantly decreased circulating PA, decreased the hepatic microbial load, and increased survival. Hence, in traumatized mice challenged with either C. albicans or gram-negative bacteria, a relationship exists between proteolytic load and subsequent septic death. Parallels between these animal studies and human studies are discussed.

Animals↗

PubMed1994

Energy use by contractile and noncontractile processes in skeletal muscle estimated by 31P-NMR.

The goal of this study was to separately determine ATP use by contractile and noncontractile processes in stimulated skeletal muscle. ATP use by tetanically stimulated bullfrog semitendinosus muscle was monitored at room temperature with in vivo 31P-nuclear magnetic resonance. Oxidative phosphorylation was inhibited by cyanide, and ATP use could therefore be calculated by accounting for ATP derived from the creatine kinase (CK) reaction (measured from decreases in phosphocreatine) and from glycolysis (estimated from decreases of intracellular pH). In unfatigued muscles stimulated at optimal length for force production, total ATP utilization (representing both contractile and noncontractile processes) was 2.5 +/- 0.09 (SE) mM/s (n = 6; 53% ATP from glycolysis, 47% from CK). In separate experiments, cross-bridge interactions between actin and myosin filaments were eliminated by increasing sarcomere length; therefore, with stimulation, residual ATP use reflected only noncontractile processes. In stimulated stretched muscles, ATP utilization was reduced compared with unstretched muscles to 1.07 +/- 0.08 mM/s (61% ATP from glycolysis, 39% from CK). These findings suggest that, during contraction near optimum length, a large proportion (approximately 43%) of ATP is used by noncontractile processes, with more ATP derived from glycolysis than from CK.

Adenosine Triphosphate↗

PubMed1994

The effects of ion sputtering on dentin and its relation to depth profiling.

Characterization of the dentin surface and the dentin/adhesive interface is fundamental to investigations concerning adhesive bonding to dentin. It has been shown that good adhesive bonding depends on both the structure and composition of the dentin surface. A combination of ion sputter etching and Auger electron spectroscopy can be used to obtain surface composition and elemental depth profiles at interfaces. This investigation was conducted to examine the changes induced in human dentin by ion sputtering under conditions commonly encountered during depth profiling. The sputtering was conducted with argon ions at 7.5 keV and an ion flux ranging from 10(18)-10(19) ions/m2s. The amount of material sputtered was calculated from profilometer measurements of the sample surface. The surface composition was monitored by Auger electron spectroscopy. The results indicate that, under these conditions, collagen was removed at a much faster rate than hydroxyapatite, causing the surface composition of dentin to change during the sputtering process. The sputter yields for hydroxyapatite and collagen were found to be 5 and 28 atoms/ion, respectively, at a sputter angle of 45 degrees. At a sputter angle of 29 degrees, the yields were 2 and 25 atoms/ion, respectively. Both the changes in composition of dentin and the measured sputter rates are in agreement with the behavior predicted by a theoretical model for two phase materials (Blaise, 1978; Blaise et al., 1978).

Acid Etching, Dental↗

PubMed1994

Excessive muscular fatigue in the postpoliomyelitis syndrome.

To investigate anterior tibial muscle fatigability and metabolism in postpoliomyelitis syndrome patients and controls, we performed measurements of force and relaxation time, as well as 31P magnetic resonance spectroscopy, during intermittent, low-intensity, isometric, voluntary exercise. Both maximum voluntary contraction and tetanic force declined significantly more during exercise and subsequently recovered less in patients compared with controls, indicating greater fatigue in patients. However, intracellular pH and phosphocreatine were not different in the two groups at rest or during exercise or recovery, suggesting that the greater fatigue of the patients was not due to an excessive change of metabolites. Moreover, the pre-exercise half-relaxation time of the tetanus was significantly prolonged in patients compared with controls, and the decline in tetanic force during exercise was linearly related to the half-relaxation time of tetanus, suggesting impaired calcium kinetics. Taken together, the findings of increased fatigability, delayed recovery, and prolonged half-relaxation time, without differences in metabolites, suggest that the fatigue in postpoliomyelitis syndrome may be due to impaired activation beyond the muscle membrane.

Action Potentials↗

PubMed1994

Molecular diagnosis and modern management of Duchenne muscular dystrophy.

The increased understanding of the genetic basis for DMD and the pathophysiology of the disease have produced improved techniques of patient and carrier diagnosis, genetic counseling, and new approaches to searching for a treatment. The present level of experimentation with both myoblast implantation and gene therapy may make treatment of this inherited, relentlessly progressive muscle disease possible within the next several years.

Adult↗

PubMed1994

Neuromuscular complications of human immunodeficiency virus infection and antiretroviral therapy.

At least 4 distinct peripheral neuropathy syndromes occur in patients infected with the human immunodeficiency virus. The most common, painful sensory neuropathy, may be related to the viral infection or may be medication induced and is treated symptomatically. The other 3, chronic inflammatory demyelinating polyradiculoneuropathy, mononeuropathy multiplex (some patients), and the progressive polyradiculopathies related to the acquired immunodeficiency syndrome, may all respond to appropriate therapy. Both inflammatory myopathy and zidovudine myopathy also abate with early diagnosis and treatment.

Acquired Immunodeficiency Syndrome↗

PubMed1994

Magnetic resonance spectroscopy studies of human muscle.

The use of MRS has become more widespread as cost and availability have improved. It has been demonstrated that MRS of human skeletal muscle can play a significant role in (1) understanding healthy muscle metabolism and the mechanisms of muscle fatigue, (2) understanding the effects of disease on muscle metabolism and function, (3) monitoring the efficacy of therapeutic intervention, and (4) the confirmation of disease diagnoses. The results of the 31P MRS studies of disease are summarized in the Table 1. A few conditions (McArdle's, PFK deficiency) are associated with failure to develop acidosis during exercise. This response appears to be relatively specific to these metabolic myopathies. For most of the conditions reviewed here, however, the metabolic findings of reduced PCr/Pi and greater acidosis during exercise with impaired recovery of PCr/Pi and pH are very similar. The nonspecificity of the MRS results suggests the possibility that a common mechanism may be at work in all of these diseases. A major question to arise from clinical studies using MRS concerns the extent to which deconditioning may have played a role in some of these findings. This is because conditions associated with muscle weakness, rapid fatiguability, and muscle pain during or following vigorous physical activity may also be those that lead to deconditioning. In virtually all studies reviewed here, healthy, active subjects were used as controls. There are no examples in which controls were appropriately matched to the subjects for their level of conditioning. Conditioning could be assessed by questionnaire, activity logs, activity monitoring devices, or measurements of conditioning effects such as maximal oxygen consumption. The role of deconditioning in the decreased quality of life of persons with chronic diseases has not been fully explored. Future studies of chronic disease using MRS should combine MRS with other techniques to further probe the mechanisms of muscle metabolism under various conditions, and the extent to which these mechanisms are sensitive to the level of physical conditioning.

Humans↗

PubMed1993

Gamma delta T cells differentiate into a functional but nonproliferative state during a normal immune response.

To obtain a homogeneous population of gamma delta T cells to investigate their role in an immune response, we have made a scid mouse doubly transgenic for rearranged gamma and delta genes. The receptor (KN6) encoded by these genes is specific for the major histocompatibility complex class I protein encoded by the T22b gene. This mouse contains high levels of transgenic gamma delta T cells in the spleen and thymus and no other T lymphocytes. Immunization of these KN6-scid (H-2d, TLd) mice with 10(7) C57BL/6J (abbreviated B6) (H-2b, TLb) spleen cells resulted in proliferation and activation of the gamma delta T cells in spleen and clearing of the allogeneic B6 lymphocytes. Subsequently, the majority of activated cells died by apoptosis and the remaining cells were anergic with regard to proliferation. The anergic cells did not respond to restimulation by B6 spleen cells in vitro or in vivo, and addition of exogenous interleukin 2 failed to restore the response to B6 cells. Cytotoxicity, a property of KN6+ cells during a primary stimulation, was no longer detectable in the proliferatively anergic cells. However, B6 spleen cells injected into mice primed 12 days previously were cleared with a much greater efficiency than on primary challenge and in an antigen-specific manner. We conclude that after exposure to antigen, gamma delta T cells rapidly proliferate into blasts; the majority of the blasts rapidly die, with the nonproliferating cells remaining in a highly active state for several weeks and able to initiate elimination of lymphoid cells bearing the TLb epitope.

Animals↗

PubMed1993

Religation of the T cell receptor after primary activation of mature T cells inhibits proliferation and induces apoptotic cell death.

The proliferative response of murine splenic T cells, initially activated by cross-linking the TCR complex with either antibodies, mitogenic lectin, or alloantigen was severely inhibited when the activated cells were recovered and given an additional activation signal by recross-linking the TCR complex, or by adding Ca2+ ionophore and phorbol ester. Under the same conditions, cross-linking other T cell surface determinants such as CD4, CD8, or class I MHC on preactivated T cells had no effect. Assessment of cell viability using vital dye exclusion together with the detection of DNA fragmentation revealed that the reduction of the proliferative responses was associated with an induction of apoptotic-like cell death in the activated T cell population and not due to a blockade of cell division. Accumulation of eosin stained (dead) cells did not occur immediately upon replating the activated cells, but began after a lag period during which at least two cell divisions occurred. In addition, perturbation of T cell proliferation after activation depended on how the cells were initially activated. Only T cells activated in the presence of additional cells found in spleen and lymph node were susceptible to inhibition; T cells activated after nylon wool purification were not susceptible. These results have potential implications for understanding self-tolerance and immunoregulation.

Animals↗

PubMed1993

Multifocal motor neuropathy: response to human immune globulin.

Multifocal motor neuropathy (MMN) is a progressive disorder producing asymmetrical weakness and muscle wasting. Case reports suggest that patients with MMN improve after cyclophosphamide therapy, but not after prednisone or plasmapheresis. Because MMN is likely to be immune mediated, we investigated the therapeutic response to human immune globulin (HIG) in an open, uncontrolled trial. Nine patients, ages 28 to 58 years, had chronic, progressive, asymmetrical, predominantly distal, limb weakness for 5 to 18 years. Sensation was normal, and reflexes were reduced asymmetrically. All had physiological evidence of multifocal motor demyelination with partial motor conduction block, and 7 had elevated serum titers of anti-GM1 IgM antibody. All patients were treated with HIG, 1.6 to 2.4 gm/kg, given intravenously over 3 to 5 days. Strength improved in all patients 3 to 10 days after treatment, with improvement peaking at 2 weeks and lasting for an average of 2 months. The range of functional improvement varied from dramatic to mild. The degree of partial motor conduction block was reduced, at least partially, in 7 of 8 patients. The serum anti-GM1 antibody titers did not change. Repeated courses of HIG resulted in similar improvements. We conclude that HIG may be an effective therapy for patients with MMN.

Adult↗

PubMed1993

Alloreactive cytotoxic T cells can develop and function in mice lacking both CD4 and CD8.

Using the technique of homologous recombination in embryonic stem cells, a mouse strain without functional CD4 and CD8 genes has been generated. Surprisingly, these mice contain significant numbers of alpha beta T cells. Although mice deficient for CD8 only do not show any cytotoxic response when their T cells are stimulated with either alloantigen or viral antigen, the CD4-8- mice do generate alloreactive cytotoxic T cells. These cytotoxic T cells bear the alpha beta T cell receptor and recognize major histocompatibility complex class I antigens. In addition fully allogeneic skin transplants were rejected but skin transplants expressing only minor transplantation antigens were not. Virus-specific cytotoxic T lymphocytes were also not detected. It seems that alloreactive cytotoxic T cells can be induced and exert their effector function in vitro and in vivo in the absence of CD8, and that they can develop and mature in vivo without the CD8 molecule or the signals it might provide.

Animals↗