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Biomedical subjects

M A Keller

Publications and source records attributed to M A Keller.

At least 19 recordsLinked to original sources
PubMed2006

Transcriptional regulatory network analysis of developing human erythroid progenitors reveals patterns of coregulation and potential transcriptional regulators.

Deciphering the molecular basis for human erythropoiesis should yield information benefiting studies of the hemoglobinopathies and other erythroid disorders. We used an in vitro erythroid differentiation system to study the developing red blood cell transcriptome derived from adult CD34+ hematopoietic progenitor cells. mRNA expression profiling was used to characterize developing erythroid cells at six time points during differentiation (days 1, 3, 5, 7, 9, and 11). Eleven thousand seven hundred sixty-three genes (20,963 Affymetrix probe sets) were expressed on day 1, and 1,504 genes, represented by 1,953 probe sets, were differentially expressed (DE) with 537 upregulated and 969 downregulated. A subset of the DE genes was validated using real-time RT-PCR. The DE probe sets were subjected to a cluster metric and could be divided into two, three, four, five, or six clusters of genes with different expression patterns in each cluster. Genes in these clusters were examined for shared transcription factor binding sites (TFBS) in their promoters by comparing enrichment of each TFBS relative to a reference set using transcriptional regulatory network analysis. The sets of TFBS enriched in genes up- and downregulated during erythropoiesis were distinct. This analysis identified transcriptional regulators critical to erythroid development, factors recently found to play a role, as well as a new list of potential candidates, including Evi-1, a potential silencer of genes upregulated during erythropoiesis. Thus this transcriptional regulatory network analysis has yielded a focused set of factors and their target genes whose role in differentiation of the hematopoietic stem cell into distinct blood cell lineages can be elucidated.

Antigens, CD34↗
PubMed2006

Cerebral metabolites in HIV-infected children followed for 10 months with 1H-MRS.

BACKGROUND: Previous studies have shown that HIV-infected children have abnormal cerebral metabolites, measured by proton MR spectroscopy (1H MRS), but the stability of these measurements over time has not been described in HIV-infected children. The authors recently reported a study of cerebral metabolites in 20 HIV-infected children (6 to 16 years of age); the current study followed 12 of these children (10.0 years +/- 3.7 years) and repeated the MR spectroscopy at 24.1 +/- 3.7 weeks and 42.2 +/- 3.5 weeks following the entry time with repeated neuropsychological testing. METHODS: 1H MR spectra were acquired at 1.5 T (GE Signa, PRESS localization, repetition time = 3,000 msec, echo time = 30 msec). Five brain regions were studied: right frontal white matter, left frontal white matter, right basal ganglia, right hippocampus, and midfrontal gray matter. The concentrations of N-acetylaspartate (NAA), choline (CHO), creatine (CR), and myo-inositol (mI) and the ratio of each metabolite to CR were determined. RESULTS: There were no changes in the metabolite concentrations or metabolite/CR ratios at the three time periods. Similarly, during this follow-up period, HIV-positive children showed no changes in clinical signs, HIV viral loads, CD4%, or CD4 counts, except for improved spatial memory with repeat testing. CONCLUSION: In a clinically and neurologically stable group of HIV-infected children, cerebral metabolites were stable over a 10-month time period, suggesting that it is possible to assess changes in cerebral metabolites as a measure of cerebral health, but longer follow-up in a larger sample is needed.

Adolescent↗
PubMed2005

The ComPact UniLock 2.0/2.4 system and its clinical application in small animal orthopedics.

This study describes the titanium ComPact UniLock 2.0/2.4 locking plate system (Stratec Medical, Oberdorf, Switzerland) and reports its application in nine selected clinical cases. The system was found useful for a variety of indications. Three categories of clinical applications are illustrated. They include (a) long bone fractures, (b) cervical spinal fractures and instabilities and (c) joint instabilities and luxations. A brief introduction to the system has already been published

Animals↗
PubMed2004

Altered neurometabolite development in HIV-infected children: correlation with neuropsychological tests.

BACKGROUND: HIV-infected children have abnormal cerebral metabolites, measured by proton MR spectroscopy ((1)H-MRS), but how these abnormalities relate to brain function is unclear. METHODS: Metabolite concentrations in five brain regions of 20 HIV-infected and 13 control children were measured, and these findings were correlated with age, log(10) plasma viral load, CD4 count, and neuropsychological scores. RESULTS: Compared with control subjects, HIV patients had decreased choline concentration [Cho] in left frontal white matter (LFW) (-12%; p = 0.04); those with high viral load (>5,000 HIV RNA copies/mL) had decreased right basal ganglia (RBG) [Cho] (-15%; p = 0.005), and [Cr] (-13%; p = 0.02). Patients with high viral load also had higher [Cho] in the midfrontal gray matter (MFG) (+25%; p = 0.002) and lower myo-inositol [Ins] in the RBG (-18%; p = 0.04) than patients with low HIV viral load. N-Acetyl aspartate concentration ([NAA]) correlated with age in right frontal white matter (RFW) (r = 0.59, p = 0.04), LFW (r = 0.66, p = 0.02), and right hippocampus (RHIP) (r = 0.69, p = 0.02) only in control subjects. In contrast, [Ins] correlated with age in both RFW and LFW (r = 0.71, p = 0.0006; r = 0.65, p = 0.006) only in the HIV patients. Log(10) plasma viral load correlated positively with [Ins] in RFW (r = 0.54, p = 0.02) and [Cho] in MFG (r = 0.49, p = 0.04). Compared with control subjects, HIV patients had poorer spatial memory (p = 0.045) and delayed spatial memory correlated with [Cho] in RHIP (r = 0.68, p = 0.02). CONCLUSIONS: These data suggest that normal brain development may be affected in children infected with HIV at birth, particularly evidenced by the lack of age-related increases in the neuronal marker [NAA]. Early, aggressive treatment of infants with HIV before development of encephalopathy is warranted.

Adolescent↗
PubMed2001

Breast milk transmission of viral disease.

Breast milk transmission of maternal viral infection is well established for CMV and HIV-1. In the case of CMV, this usually does not pose a risk to the infant since serious disease is prevented by placentally transferred maternal antibody. However, in HIV infection, breast-feeding increases the risk of maternal-fetal transmission by about 25% with late breast-feeding (after six months of age) constituting a particular risk. In other maternal viral diseases, e.g., other herpes viruses, parvovirus, hepatitis A, B and C, and rubella, the virus is often demonstrated in the breast milk, but transmission is very rare. The highest risk is during an acute viral infection at the time of birth, since the breast milk has a high titer of virus, and a lack of antibody to neutralize the organism.

Breast Feeding↗
PubMed2001

Trophic barriers to fertilizer Cd bioaccumulation through the food chain: a case study using a plant--insect predator pathway.

The objective of this study was to assess the uptake and subsequent transfer of Cd and Zn from a soil amended with a single application (150 kg P ha(-1)) of triple super phosphate fertilizer to wheat plants, aphids, and a predator and biocontrol agent of aphids, lacewings. The fertilizer amended soil and wheat plants grown on this soil had elevated concentrations of Cd compared to the controls, but similar concentrations of Zn. Aphids feeding on wheat plants on the fertilized soil had between three and seven times the concentrations of Cd and Zn observed in aphids feeding on the control plants. However, the lacewings showed no significant accumulation of Cd or Zn, and no differences in larval performance were recorded. Changes in the availability of Cd and Zn in the soils and the transfer through the plant-insect pathway were monitored using isotope dilution, by labeling the soils with carrier-free (109)Cd and (65)Zn. Decreases in the specific activities for Cd in the plants and aphids were observed for the fertilized soils compared to the controls, suggesting an increase in bioavailable Cd. On the fertilized soils the Cd:Zn ratio of the phloem-feeding aphids (0.008) was significantly less than the host plants (0.025), indicating a reduced relative uptake of Cd and a possible barrier for Cd along the soil--plant--herbivorous insect pathway--reducing uptake by phloem feeders and subsequently their predators.

Animals↗
PubMed2001

RNA replication from the simian virus 5 antigenomic promoter requires three sequence-dependent elements separated by sequence-independent spacer regions.

We have previously shown for the paramyxovirus simian virus 5 (SV5) that a functional promoter for RNA replication requires proper spacing between two discontinuous elements: a 19-base segment at the 3' terminus (conserved region I [CRI]) and an 18-base internal region (CRII) that is contained within the coding region of the L protein gene. In the work described here, we have used a reverse-genetics system to determine if the 53-base segment between CRI and CRII contains additional sequence-specific signals required for optimal replication or if this segment functions solely as a sequence-independent spacer region. A series of copyback defective interfering minigenome analogs were constructed to contain substitutions of nonviral sequences in place of bases 21 to 72 of the antigenomic promoter, and the relative level of RNA replication was measured by Northern blot analysis. The results from our mutational analysis indicate that in addition to CRI and CRII, optimal replication from the SV5 antigenomic promoter requires a third sequence-dependent element located 51 to 66 bases from the 3' end of the RNA. Minigenome RNA replication was not affected by changes in the either the position of this element in relation to CRI and CRII or the predicted hexamer phase of NP encapsidation. Thus, optimal RNA replication from the SV5 antigenomic promoter requires three sequence-dependent elements, CRI, CRII and bases 51 to 66.

Base Sequence↗
PubMed2000

The genetic contribution of single male immigrants to small, inbred populations: a laboratory study using Drosophila melanogaster.

This study examined the genetic contribution of single male immigrants to small, inbred laboratory populations of Drosophila melanogaster. Genetic contribution was assessed by measuring the relative frequency of immigrant marker alleles in the first and second generations after immigration, while controlling for any selection effects at the marker locus, and for the experience of male immigrants. When immigrants were outbred, the mean frequency of the immigrant allele was significantly higher than its initial frequency, in both the first and second generations after immigration. There was no significant change in allele frequency for populations receiving inbred immigrants. The increase in allele frequency for outbred immigrants was attributed to an initial outbred vigour fitness advantage of immigrant males over resident males experiencing inbreeding depression. Hybrid vigour of immigrant progeny and the rare-male effect did not have a statistically significant role in the fitness advantage of the immigrant allele. The results suggest that inbreeding may have a considerable impact on the contribution of immigrants to the genetic diversity of populations.

Alleles↗
PubMed2000

Passive immunity in prevention and treatment of infectious diseases.

Antibodies have been used for over a century in the prevention and treatment of infectious disease. They are used most commonly for the prevention of measles, hepatitis A, hepatitis B, tetanus, varicella, rabies, and vaccinia. Although their use in the treatment of bacterial infection has largely been supplanted by antibiotics, antibodies remain a critical component of the treatment of diptheria, tetanus, and botulism. High-dose intravenous immunoglobulin can be used to treat certain viral infections in immunocompromised patients (e.g., cytomegalovirus, parvovirus B19, and enterovirus infections). Antibodies may also be of value in toxic shock syndrome, Ebola virus, and refractory staphylococcal infections. Palivizumab, the first monoclonal antibody licensed (in 1998) for an infectious disease, can prevent respiratory syncytial virus infection in high-risk infants. The development and use of additional monoclonal antibodies to key epitopes of microbial pathogens may further define protective humoral responses and lead to new approaches for the prevention and treatment of infectious diseases.

Animals↗
PubMed1999

Inhibition of the anti-V3 loop response to a recombinant gp120SF2 vaccine by preexisting monoclonal antibody.

Our previous studies have shown that maternally transferred MAb 83.1 (Repligen), which recognizes the V3 loop of HIV-1SF2, inhibited the anti-V3 IgG response of offspring BALB/c mice immunized with rgp120SF2 (Chiron). To determine the mechanism of this epitope-specific inhibition, MAb 83.1 was directly administered intraperitoneally to 19-day-old BALB/c mice, followed by immunization with rgp120SF2 in Freund's complete adjuvant at 21 days of age. The total serum anti-rgp120SF2 IgG response was not inhibited by preexisting MAb 83.1, but the anti-V3 IgG response was significantly inhibited (p < 0.03) 12 weeks after immunization. These results confirm epitope-specific inhibition of the immunodominant V3 loop and are consistent with epitope masking by preexisting antibody. Idiotypic dysregulation is unlikely since MAb 83.1 exposure was not required during the period of repertoire development in neonatal mice. Treatment with MAb prior to immunization may redirect the epitope specificity of an HIV vaccine response.

AIDS Vaccines↗
PubMed1999

A prospective, blinded comparison of clinical examination and computed tomography in deep neck infections.

OBJECTIVES/HYPOTHESIS: To determine whether there is a scientific basis for the routine use of contrast-enhanced computed tomography (CECT) in the evaluation of suspected deep neck infection (DNI). STUDY DESIGN: We conducted a prospective, blinded comparison of clinical examination and CECT in DNI. METHODS: Thirty-five consecutive patients with suspected DNI were prospectively assessed by clinical examination and CECT for the presence and extent of surgically drainable purulent collections. Before CECT a surgeon recorded clinical data and predicted the extent of infection. A head and neck neuroradiologist, blinded to the clinical evaluation, predicted the extent of infection based on CECT. Final outcome (the presence of a purulent collection) was determined at surgery or in long-term follow-up. The clinical and CECT findings were compared with the final outcome to determine the sensitivity, specificity, and accuracy of each modality. RESULTS: Twenty patients had purulent drainable collections. The accuracy of clinical examination alone in identifying a drainable collection was 63%, the sensitivity was 55%, and the specificity was 73%. The accuracy of CECT alone was 77%, the sensitivity was 95%, and the specificity 53%. When CECT and clinical examination were combined, the accuracy in identifying a drainable collection was 89%, the sensitivity was 95%, and the specificity 80%. If fluid collections with volumes of 2 mL or greater on CECT were considered, the accuracy of CECT would have been 85%, the sensitivity 89%, and the specificity 80%. CONCLUSION: CECT and clinical examination are both critical components in the evaluation of suspected DNI.

Adolescent↗
PubMed1998

Reoperative parathyroidectomy in the era of localization technology.

BACKGROUND: Recurrent and/or persistent hyperparathyroidism (HPT) is an uncommon disease. Relatively few cases are seen by any one center or surgeon. Most of the prior reviews of this problem were done in the era prior to potentially accurate magnetic resonsance imaging (MRI) and sestimibi scan localization and do not reflect current preoperative localization technology. METHODS: All cases of recurrent or persistent parathyroidectomy seen in our institution between 1992 and 1996 were reviewed retrospectively to assess the predictive value of preoperative MRI, selective venous sampling, sestimibi scanning, ultrasound examination, and computerized tomography (CT) scanning. The preoperative localization studies were compared with the findings at operation, the pathology report, and the patient's long-term calcium status. RESULTS: Twenty-eight patients were operated upon at our institution for recurrent or persistent HPT during this time interval. The final pathology turned out to be: adenoma, 24; hyperplasia, 2; carcinoma, 2. The site at which the reoperative pathology was found was in the neck in 22 patients and intrathoracic requiring sternotomy in 6. The long-term outcome, i.e., serum calcium level at > 6 months postoperatively, was normocalcemia in 22 of 28 (85%), persistent hypocalcemia in 2 of 28, and persistent hypercalcemia in 2 of 28. Some combination of MRI, sestimibi, selective venous sampling, ultrasound, and CT scan was performed on all patients preoperatively. Preoperative MRI scans were performed on 26 of 28 patients. They correctly localized the side and site of the pathology in only 12, yielding a sensitivity of 66%. There were, however, no false positives; therefore, the positive predictive value of this test was 100%. Selective venous sampling was carried out on 26 of 28 patients and correctly localized in only 8 (sensitivity, 50%). Again, there were no false positives, yielding a positive predictive value of 100%. Sestimibi scanning was performed in 16 of 28, localizing in 8 (sensitivity, 50%). The positive predictive value of this test was 80%. Ultrasound was performed in 26 of 28 patients and localized in only 3, yielding a sensitivity of 17%, with a positive predictive value of 75%. Computerized tomographic scan was performed preoperatively only when all other investigations turned out to have been nonlocalizing and was therefore done in only four patients, one of whom had a positive CT scan showing an intrathoracic, intrapericardial adenoma. CONCLUSIONS: These data demonstrate that despite the availability of what are putatively accurate preoperative localizing tests for previously unoperated cases, no one localizing test is particularly sensitive in reoperative parathyroid surgery. Magnetic resonance imaging and selective venous sampling, however, are complementary and when positive do accurately predict the site of the persistent/recurrent parathyroid pathology. Use of these preoperative localizing studies resulted in a successful outcome, i.e., normocalcemia or hypocalcemia in 93% of patients operated on.

Adult↗
PubMed1998

HIV hyperimmune globulin or intravenous immune globulin inhibits response to an HIV vaccine.

The murine model was developed to assess the effects of maternally transferred HIV hyperimmune globulin or human intravenous immune globulin on the immunization of the offspring at 18-21 days of age with rgp 120SF2-complete Freund's adjuvant. Either HIV hyperimmune globulin or intravenous immune globulin was administered intraperitoneally to post-partum BALB/c mice and was transferred via milk to the offspring. Both HIV hyperimmune globulin and intravenous immune globulin inhibited the offspring anti-rgp 120SF2 IgG response to the vaccine. The HIV hyperimmune globulin inhibition persisted for 28 days after immunization while the intravenous immune globulin inhibition was still present at 63 days after immunization. In addition, the intravenous immune globulin had a more generalized immunosuppressive effect, inhibiting the IgG response to both rpg 120SF2 and an additional protein antigen, hen egg-white lysozyme. Effects of maternal or exogenously administered pre-existing antibody, including control antibodies (intravenous immune globulin), on the newborn response to HIV and other vaccines must be carefully evaluated when vaccine studies proceed in newborns.

AIDS Vaccines↗
PubMed1996

Maternal monoclonal antibody to the V3 loop alters specificity of the response to a human immunodeficiency virus vaccine.

The effect of maternally transferred monoclonal antibody (MAb) on the offspring antibody response to rgp120SF2 was examined in a murine model. Two MAbs were studied: MAb 83.1, which recognizes a determinant in the V3 loop of gp120 from human immunodeficiency virus-1 (HIV-1) SF2, and MAb 26.2D3, which recognizes a conserved N-terminal region of gp120 from HIV-1SF2. Offspring were immunized at 18-21 days of age with 100 micrograms of rgp120SF2 in complete Freund's adjuvant. Offspring immunized in the presence of preexisting MAb 83.1 but not MAb 26.2D3 demonstrated inhibition of the IgG anti-V3 response. The total IgG anti-rgp120SF2 response was not affected by preexisting MAb. Since newborns at risk for HIV may be immunized in the presence of maternal or administered anti-HIV antibody, alternative strategies may be required to circumvent inhibition of the infant's epitope-specific response to HIV immunization by preexisting antibody.

AIDS Vaccines↗
PubMed1995

Inhibition of the offspring anti-recombinant gp120 antibody response to a human immunodeficiency virus vaccine by maternal immunization in a murine model.

A murine model was developed for assessing the effects of passively transferred polyclonal maternal anti-gp120 antibodies on the subsequent immunization of the offspring with recombinant gp120SF2 in complete Freund's adjuvant (rgp120SF2-CFA). Adult female BALB/c mice were immunized with rgp120SF2-CFA 6 weeks before mating. The 3-week-old offspring were subsequently immunized with the same vaccine and followed for 9 weeks. Both the total IgG anti-rgp120SF2 and the anti-V3 IgG antibody response to vaccine were inhibited in the experimental animals. The total IgG anti-rgp120SF2 response was < 20% of the control response (P < .001) 9 weeks after immunization. Anti-V3 antibody was also decreased. As vaccine studies begin in infants, the effects of preexisting antibody on the infant response to human immunodeficiency virus vaccines must be considered.

AIDS Vaccines↗
PubMed1995

Lineage-specific alternative splicing of the human Fc gamma RIIA transmembrane exon requires sequences near the 3' splice site.

The human Fc gamma RIIA gene produces multiple transcripts, including those with (Fc gamma RIIa1) and without (Fc gamma RIIa2) the single exon encoding the transmembrane domain (TM). Previously, a fluorescence-based RT-PCR assay showed lineage-specific differences in Fc gamma RIIA transcript ratios (Fc gamma RIIa2/Fc gamma RIIa1). The mechanism of this lineage-specific expression was investigated in this study. Differential transcript stability does not play a major role, because transcript ratios remained constant in cells with both low (K562) and high (Dami) ratios following actinomycin D treatment. Transient expression studies in K562 and Dami cells using a minigene construct containing a 5.0 kb genomic fragment including the TM exon and adjacent intron and exon sequences showed recapitulation of endogenous transcript ratios. The TM exon was efficiently spliced in by the constitutive splicing machinery in HeLa cells, an Fc gamma RIIA-negative cell line. Lineage-specific TM exon skipping was markedly diminished by two independent minigene mutations: a point mutation of the first nucleotide of the TM exon, and a five basepair intronic deletion near a putative branchpoint. These data demonstrate that cis-acting sequences in or near the TM exon 3' splice acceptor site contribute to lineage-specific differences in Fc gamma RIIA transcript ratios.

Alternative Splicing↗