PubMed Health⌕ Search

Biomedical subjects

K M Sheehan

Publications and source records attributed to K M Sheehan.

26 records · Page 2Linked to original sources
PubMed1993

The utilization of individual VH exons in the primary repertoire of adult BALB/c mice.

The utilization of VH gene families is severely biased during fetal development, such that D-region proximal VH genes are overrepresented. After birth the VH repertoire becomes more equally representative of the total inherited set of functional VH genes. To investigate the extent of this normalization process, we have determined the relative utilization of individual VH exons in the pre-immune repertoire of adult BALB/c spleen cells. Large samples of IgM heavy chain transcripts from polyclonally activated B cells were captured in a cDNA phage library and screened by hybridization using highly specific oligonucleotide probes. These studies revealed that the utilization of particular VH exons can differ by an order of magnitude. Significantly, the VH genes most under-represented in the pre-immune repertoire are located in the region of the Igh locus most distal to the DjhCh region. We suggest that the chromosomal position of a particular VH gene may influence its utilization and that the normalization of the adult repertoire is incomplete.

Animals↗
PubMed1993

Junctional diversification in the generation of the precursor of a discrete immune response.

Phosphocholine (PC)-specific antibodies that arise in the mouse in response to Proteus morganii (PM) and use V1-DFL16.1-JH1 are characterized by a number of recurring mutations. Most striking is an invariant A for G substitution in codon 95 of VH which results in an asparagine instead of aspartate at that position. Because of the apparent importance of this substitution in an anti-PC(PM) response, we wanted to determine the molecular basis for this base change. A cDNA library derived from pre-immune splenic B cells was examined for the frequency of VDJ containing the A substitution at 95 and the presence of additional point mutations in these sequences. Six different cDNA were isolated which contained an A substitution at the VD junction (frequency 0.00009); a seventh positive cDNA could not be examined. The V segments of four of these cDNA matched known germline genes and were, therefore, unmutated. Two others closely matched V in families whose members have not all been characterized, hence, it is not known whether the mutations observed are somatic or germline in origin. Sequences of 35 cDNA clones, containing the same V segment but differing in D, J and junctional nucleotides, revealed no mutations. These results indicate that the A substitution generated at codon 95 is most likely a product of V-DJ joining.

Animals↗
PubMed1993

V(D)J recombination: signal and coding joint resolution are uncoupled and depend on parallel synapsis of the sites.

V(D)J recombination in lymphoid cells is a site-specific process in which the activity of the recombinase enzyme is targeted to signal sequences flanking the coding elements of antigen receptor genes. The order of the steps in this reaction and their mechanistic interdependence are important to the understanding of how the reaction fails and thereby contributes to genomic instability in lymphoid cells. The products of the normal reaction are recombinant joints linking the coding sequences of the receptor genes and, reciprocally, the signal ends. Extrachromosomal substrate molecules were modified to inhibit the physical synapsis of the recombination signals. In this way, it has been possible to assess how inhibiting the formation of one joint affects the resolution efficiency of the other. Our results indicate that signal joint and coding joint formation are resolved independently in that they can be uncoupled from each other. We also find that signal synapsis is critical for the generation of recombinant products, which greatly restricts the degree of potential single-site cutting that might otherwise occur in the genome. Finally, inversion substrates manifest synaptic inhibition at much longer distances than do deletion substrates, suggesting that a parallel rather than an antiparallel alignment of the signals is required during synapsis. These observations are important for understanding the interaction of V(D)J signals with the recombinase. Moreover, the role of signal synapsis in regulating recombinase activity has significant implications for genome stability regarding the frequency of recombinase-mediated chromosomal translocations.

Animals↗
PubMed1989

Organization and expression of VH gene families preferentially expressed by Ly-1+ (CD5) B cells.

Previously we have shown that a high proportion (5%-15%) of peritoneal Ly-1+ B cells that bind the common membrane phospholipid, phosphatidylcholine, express either of two VH genes. One of these genes, CH34VH, belongs to the recently described VH11 family, whereas the other VH gene, CH27VH, is reported here to belong to a new, single-member family which we designate VH12. We have characterized these new VH families in terms of strain polymorphism, map position relative to nine other VH gene families, and frequency of expression in polyclonally stimulated splenic B cell populations. We find that VH11 and VH12 genes are expressed at frequencies similar to the VH genes of other families in the spleen, and that these genes are not located among the J-proximal VH segments which are preferentially expressed during early development. These results suggest that the VH11 and VH12 genes are not preferentially rearranged, and support our earlier studies which suggested that the high frequency of VH11 and VH12 expression among peritoneal Ly-1 B cells is due to antigen selection.

Animals↗
PubMed1989

Molecular cloning of the primary IgH repertoire: a quantitative analysis of VH gene usage in adult mice.

The generation of the primary antibody repertoire requires the somatic rearrangement of germline gene segments. It is not known, however, whether all functional V and J gene segments have an equal probability of contributing to this initial set of antibody specificities. To address this issue, we have examined the relative utilization of VH and JH gene segments of the mouse. We have constructed VH cDNA phage libraries from C mu transcripts obtained from polyclonally activated spleen cells of the BALB/c and C57BL/6 strains. We show that probes specific for either one, two or three functional VH gene segments hybridize to cDNAs at frequencies directly proportional to the number of functional germline VH genes detected by each probe. In contrast, the representation of 10 VH gene families within each library indicates that certain families are under-represented relative to their estimated germline gene number. These families must either have extraordinary proportions of nonfunctional genes or are influenced by as yet unidentified regulatory mechanisms or constraints on rearrangement.

Animals↗
PubMedDate not supplied

Laparoscopic colorectal resection: initial experience in a specialist unit.

The adoption of the laparoscopic approach to colorectal resection has been slow amongst colorectal surgeons principally due to concerns regarding oncological safety. Recent randomized controlled trials have confirmed both the safe and some advantage of this procedure have been performing laparoscopic assisted colorectal resection since 2002 and have now performed over 100 cases on non consecutive and selected patients. We have reviewed our experience with the introduction of this technique. 61 patients were operated on for cancer and 39 for benign disease mainly Crohn's and diverticular disease. Operative time was a median of 128 minutes over the course of study. Conversion rate was 5%. Pathological analysis of the resected specimens in the cancer cases revealed adequate lymph node harvest and margins. No patient had a positive margin and no port site metastasis have been seen. Duration of ileus and length of stay were a median of 0 and 6 days. Post operative morbidity and mortality were comparable to open colorectal surgery with the exception of port site herniation which occurred in 4% of patients. This study suggests that a laparoscopic approach to colorectal resection can be successfully introduced in an Irish hospital setting. The challenge facing Irish surgery is to disseminate this technique in a controlled and safe manner for Irish patients.

Adult↗
PubMedDate not supplied

Prospective evaluation of the utilization of aspirin and non-steroidal anti-inflammatory drugs in acute medical admissions.

The aim of this study was to analyse the frequency of aspirin and NSAID usage in 400 unselected patients admitted to the general medical wards through the Accident and Emergency Department. One hundred and twenty patients (30%) reported using NSAIDs (n = 27) or aspirin (n = 99) prior to admission. The median age was 70.5 years (IQR 54-80). Most aspirin use was low dose for cardiovascular prophylaxis and headache. The reported indications for NSAID use were osteoarthritis (n = 12), rheumatoid arthritis (n = 9), gout (n = 3) and psoriatic arthritis (n = 2) and headache (n = 1). Only 23 (19%) patients were aware of the potential side effects of these agents. Co-prescribing with an H2 antagonist (n = 10), proton pump inhibitor (n = 11) or misoprostol (n = 5) was noted in 21.6%. Approximately one third of patients admitted to general medical wards in this study were receiving NSAIDs or Aspirin. The indications for prescribing were appropriate for aspirin. NSAID use was more symptom based and may have been better managed using an analgesic in some cases. Despite the high prevalence of upper gastrointestinal symptoms, co-prescribing of ulcer healing drugs was relatively uncommon.

Aged↗