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Biomedical subjects

D Dean

Publications and source records attributed to D Dean.

At least 91 records · Page 5Linked to original sources
PubMed1994

HPRT activity in embryos of a South American opossum Monodelphis domestica.

Marsupial females show preferential paternal X-inactivation. However, the time at which X-inactivation occurs in early development has not yet been determined. A double microassay which measures the activities of X-linked hypoxanthine phosphoribosyl transferase (HPRT) and the autosomally-coded adenine phosphoribosyl transferase (APRT) from the same sample was performed on a collection of embryos from a South American opossum Monodelphis domestica. The embryos ranged in age from the 2-cell stage to the bilaminar blastocyst stage. The results indicate that their embryonic HPRT and APRT are not expressed until just before the unilaminar blastocyst stage in M. domestica. This is at a later stage of development than that in the mouse where embryonic HPRT and APRT expression first occurs at the 4-8-cell stage. It is concluded that HPRT is an uniformative enzyme for assessing X chromosome activity in cleaving embryos of M. domestica. The widespread distribution of HPRT:APRT ratios after the unilaminar blastocyst stage also makes it difficult to draw conclusions about the state of X chromosome activity in early marsupial development.

Adenine Phosphoribosyltransferase↗
PubMed1994

Cantharidin-induced acantholysis: adhesion molecules, proteases, and related proteins.

Acantholysis is a feature of disorders such as Hailey-Hailey disease and Darier's disease. Immunocytochemical studies have shown internalization of desmosomal components after acantholysis. Basal cytokeratins show suprabasal expression in lesional Darier's disease. The exact mechanisms of acantholysis are still unclear. Cantharidin induces blistering, with suprabasal keratinocyte acantholysis, possibly by protease activation. Plasmin has been implicated in the pathogenesis of acantholysis in Darier's disease and Hailey-Hailey disease. We examined the distribution of desmosomal components, proteases and cytokeratins in cantharidin blisters, to compare them with those previously found in Darier's disease and Hailey-Hailey disease. Two drops of cantharidin collodion were applied to the skin of five normal volunteers. A 4-mm punch biopsy of the blister was taken, and snap frozen. Sections were stained with antibodies to desmosomal proteins (dp) 1/2, dp 3, desmosomal glycoproteins (dg) 1, 2/3, extracellular carbohydrate residues, using the lectins peanut agglutinin (PNA) and soybean agglutinin (SBA), proteases and cytokeratins. Acantholytic cells were stained diffusely with dp1/2; there was markedly reduced or absent peripheral staining for dp3, dg1, dg2/3, PNA and SBA. There was no clumping of stain. Plasminogen, fibrinogen and urokinase were expressed in some acantholytic cells. Basal keratin markers were expressed suprabasally in acantholytic cells. These results are similar to those previously obtained in Darier's disease, but different from the staining obtained in Hailey-Hailey disease. Extracellular glycosylated portions of adhesion molecules may be lost after acantholysis, perhaps as a result of conformational changes, internalization of extracellular domains, or proteolysis. The changes in the expression of plasminogen, fibrinogen, urokinase and cytokeratins in acantholytic cells in cantharidin-induced blisters are, as in Darier's disease and Hailey-Hailey disease, probably secondary to acantholysis, and changes in the shape of cells. We conclude that cantharidin blisters may be a useful model for the study of acantholysis in Darier's disease.

Acantholysis↗
PubMed1994

Cantharidin-induced acantholysis in Darier's disease: does acantholysis initiate dyskeratosis?

We have examined the action of cantharidin on the skin of patients with Darier's disease, and used immunohistological techniques to determine the distribution of desmosomal components, keratin intermediate filaments, and proteases in cantharidin-induced blisters. Cantharidin induced acantholysis, but the presence of acantholysis did not trigger the development of the characteristic warty, dyskeratotic papules in patients with Darier's disease. The distribution of desmosomal components, keratins and proteases within the acantholytic keratinocytes in the cantharidin-induced blisters was similar to that previously found in acantholytic cells within lesions of Darier's disease: peripheral staining for extracellular desmosomal components was reduced; some desmosomal components were detected diffusely in the acantholytic cells; basal cell keratin markers were expressed by some suprabasal acantholytic cells, and plasminogen was detected in association with acantholytic cells. Cleavage of desmosomes did not reveal the underlying abnormality in Darier's disease.

Acantholysis↗
PubMed1994

Keratinocyte differentiation in psoriatic scalp: morphology and expression of epithelial keratins.

The morphology of hair follicles was examined in psoriatic scalp biopsies and compared with normal scalp. In scalp psoriasis the lower outer root sheath and hair matrix were not affected by the psoriatic changes, although there was an irregular expansion in the proximal lower outer root sheath. This area has been characterized, by the presence of keratin K19-containing cells, as the putative stem cell region. In addition, marked shrinkage of the sebaceous glands was seen in the psoriatic scalp, as previously reported. A panel of monospecific monoclonal antibodies to individual epithelial keratins was used to analyse scalp specimens immunohistochemically. Keratin expression in scalp was generally unaffected by psoriasis, except for widespread expression of suprabasal keratins K16 and K17 in suprabasal interfollicular psoriatic scalp epidermis. Simple epithelial keratins K8 and K18 were not found in follicular epithelium from either normal or psoriatic scalp, using multiple monospecific antibodies. This study shows that keratin K17 is induced suprabasally during epidermal hyperproliferation, and cannot therefore be considered a hair follicle-specific keratin.

Adolescent↗
PubMed1994

Identification of individual genotypes of Chlamydia trachomatis from experimentally mixed serovars and mixed infections among trachoma patients.

Genetic polymorphisms in the major outer membrane protein gene (omp-1) of Chlamydia trachomatis B and Ba serovars have been demonstrated in Tunisian isolates. A total of 15 of 27 unique sequence signatures or omp-1 genotypes were identified. However, differentiation of unique signatures from sequences that reflect those of strains involved in a mixed infection is necessary to define the molecular epidemiology of chlamydial ocular infections. We devised a strategy for identifying mixed infections by characterizing their effects on omp-1 genotyping. Various ratios of elementary bodies from organisms of serovars A, B, Ba, and C that cause trachoma were amplified by PCR and were subjected to automated and manual sequencing. Serovar-specific primers were also designed so that each serovar could be individually amplified and its omp-1 genotype unequivocally determined. One of 27 Tunisian samples showed a mixed infection with sequences comparable to those of serovars B and D. The omp-1 genotypes of organisms involved in mixed infections can be accurately identified by automated sequencing and will be useful for molecular epidemiologic studies of populations worldwide who live where trachoma is endemic.

Bacterial Outer Membrane Proteins↗
PubMed1994

Chlamydia trachomatis infections.

Chlamydia trachomatis infections are the most common bacterial cause of sexually transmitted disease in the United States. Although precise incidence of infection is not known, it has been calculated that more than 4 million chlamydial infections occur each year. This article discusses the epidemiology of sexually transmitted chlamydial infections, the spectrum of clinical manifestations and their sequelae, the laboratory diagnosis of genital infections, and antibiotic treatment, emphasizing the significance of these issues for control efforts in the United States.

Adolescent↗
PubMed1993

An immunohistological study of desmosomal components in pemphigus.

Pemphigus vulgaris (PV) and pemphigus foliaceus (PF) are autoimmune diseases in which there is loss of cohesion between keratinocytes (acantholysis) and blistering within the epidermis. PV is characterized by acantholysis predominantly between the epidermal basal cells and suprabasal layers, whereas in PF intraepidermal cleavage is higher in the epidermis. Adhesion between keratinocytes is dependent on the function of transmembrane glycoproteins of the cadherin family present in specialized adhesion junctions, the desmosomes. The pathogenesis of acantholysis in pemphigus is uncertain, but the pemphigus autoantibodies bind to epithelial cadherins. We have used monoclonal antibodies to desmosomal components to investigate their distribution in different forms of pemphigus. Our results show that the localization of desmosomal components is abnormal in intact perilesional epidermis, intact epidermis above the blisters in PV and intact epidermis below the blisters in PF. We suggest that autoantibody binding may have a direct effect on the function of specific epithelial cadherins, but will only cause cell separation where the antigen is the principal adhesion molecule.

Acantholysis↗
PubMed1993

IgG subclasses in pemphigus in Indian and UK populations.

The autoimmune blistering disease pemphigus is more common in the Indian subcontinent than in the UK. This study of 19 patients from Oxford, UK and 39 patients from New Delhi, India demonstrates that the incidence of the disease subtypes is different in the two countries. In the UK the commonest subtypes are pemphigus vulgaris and foliaceus with equal prevalence (both eight of 19), but in India pemphigus vulgaris is the most frequent (31 of 39), while pemphigus foliaceus is uncommon (three of 39) and with equal prevalence to the other subtypes. These populations also differ with a younger age at onset in the Indian patients (36.9 India; 52.7 UK) though the sex distribution is the same. Study of the immunopathology shows that the antibodies produced by patients in the two countries do not differ significantly, and are predominantly of the IgG4 subclass. The antibody produced does not vary with the subtype of pemphigus or the age or sex of the patient. Although there are considerable differences between the two groups of patients this difference is not reflected by the subclass of auto-antibody response.

Adult↗
PubMed1992

Ionic interactions in the nitrogenase complex. Properties of Fe-protein containing substitutions for Arg-100.

A series of Azotobacter vinelandii strains have been constructed in which the nitrogenase Fe-protein (Av2) was altered by substitutions for Arg-100. This invariant residue is a likely partner in a salt bridge with the MoFe-protein and, in some species, is the site of reversible regulation by ADP-ribosylation (Pope, M. R., Murrell, S. A., and Ludden, P. W. (1985) Proc. Natl. Acad. Sci. U. S. A. 82, 3173-3177). Although we find that arginine is the optimum amino acid, other residues in this position could support diazotrophic growth. These results were surprising because Klebsiella pneumoniae Fe-protein substituted by His-100 had been reported to be inactive (Lowery, R. G., Chang, C. L., Davis, L. C., McKenna, M.-C., Stevens, P. J., and Ludden, P. W. (1989) Biochemistry 28, 1206-1212). Two altered Fe-proteins (Av2-R100Y, the tyrosyl form, and Av2-R100H, the histidyl form) were isolated and, in contrast to this earlier report, we found that both had some activity in acetylene reduction. However, both altered proteins exhibited a decreased maximum velocity (35 and 3% of wild type, respectively) and were strongly inhibited by excess MoFe-protein. These adverse activity parameters were also manifest in the increased sensitivity of the altered proteins to inhibition by salts. Indeed, the salt sensitivity of Av2-R100H is so significant that its activity is masked in the normal assay and is easily missed. In addition, for Av2-R100H, substrate reduction is substantially uncoupled from MgATP hydrolysis. These results suggest that substitutions for Arg-100 may decrease the affinity of the Fe-protein for the MoFe-protein prior to electron transfer but increase affinity after electron transfer. Hence, the role of Arg-100 may be to provide the optimum balance in stabilities of these two complexes for maximum efficiency in substrate reduction.

Acetylene↗
PubMed1992

The nifU, nifS and nifV gene products are required for activity of all three nitrogenases of Azotobacter vinelandii.

Strains with mutations in 23 of the 30 genes and open reading frames in the major nif gene cluster of A. vinelandii were tested for ability to grow on N-free medium with molybdenum (Nif phenotype), with vanadium (Vnf phenotype), or with neither metal present (Anf phenotype). As reported previously, nifE, nifN, nifU, nifS and nifV mutants were Nif- (failed to grow on molybdenum) while nifM mutants were Nif-, Vnf- and Anf-. nifV, nifS, and nifU mutants were found to be unable to grow on medium with or without vanadium, i.e. were Vnf- Anf-. Therefore neither vnf nor anf analogoues of nifU, nifS, nifV or nifM are expected to be present in A. vinelandii.

Azotobacter vinelandii↗
PubMed1992

Comparison of the major outer membrane protein variant sequence regions of B/Ba isolates: a molecular epidemiologic approach to Chlamydia trachomatis infections.

The molecular evaluation of the chlamydial major outer membrane protein (MOMP) gene (omp1) can facilitate epidemiologic investigations of this pathogen. Genotyping of omp1 provides a more precise characterization of Chlamydia trachomatis than do current immunotyping techniques. Genetic omp1 variants of serovars that are responsible for ocular disease in Tunisia were identified. Archival conjunctival samples collected during 1972 and 1975 from trachoma patients in Douz were sequenced by automation along with additional B and Ba trachoma and genital isolates. Over 90% of the nucleotide changes resulted in an amino acid substitution. Different amino acid sequence changes in variable segments 1, 2, and 4 were found in the specimens collected in 1975 from those collected in 1972. Determination of omp1 genotypes responsible for trachoma will be useful for prospective, epidemiologic studies to identify chlamydial reservoirs within the host, evaluate transmission patterns, and determine the antigenic variation of MOMP for rational vaccine development.

Amino Acid Sequence↗
PubMed1992

Scarring alopecia in discoid lupus erythematosus.

The clinicopathological features of the scarring alopecia of discoid lupus erythematosus (DLE) were studied. Scarring alopecia was present in 34% of 89 patients with DLE and was associated with a prolonged disease course. More than half these patients had scalp involvement at the onset of the disease. There was a significant reduction in size of sebaceous glands in affected scalp. Perifollicular lymphocytic inflammation was maximal around the mid-follicle at the level of the sebaceous gland, which seems to be an important functional level in the follicle. There are changes in the expression of the matrix molecules, the proteoglycans, in the connective tissue sheath and the keratin intermediate filaments in the outer root sheath cells at this level in normal scalp and in diseased scalp. Loss of a population of mid-follicular stem cells may be important in the pathogenesis of scarring alopecia in DLE.

Adolescent↗
PubMed1992

Absence of expression of class II major histocompatibility complex determinants on keratinocytes in bullous pemphigoid.

Aberrant expression of class II products of the major histocompatibility complex (HLA-D locus antigens) occurs on keratinocytes in several inflammatory dermatoses and on thyroid epithelial cells in autoimmune thyroiditis. The functional significance of aberrant HLA-D expression is unclear but it has been hypothesized that epithelial cells bearing these determinants may act as antigen-presenting cells for autoantigens. The aim of the present study was to investigate the pathogenesis of bullous pemphigoid using immunohistochemical methods to determine whether the HLA-D locus antigens are aberrantly expressed on keratinocytes in lesional and uninvolved skin. A panel of monoclonal antibodies to each of the HLA-D subregions (DR, DP and DQ) and to Langerhans cells was used. Epidermal expression of the HLA-D locus antigens was similar in patients and controls, and there was no significant increase in expression in lesional skin compared with uninvolved skin in six out of nine patients. In three out of nine patients slight enhancement of epidermal HLA-D expression in lesional epidermis corresponded to increased Langerhans cells rather than expression on keratinocytes. HLA-D locus antigens are absent from keratinocytes in bullous pemphigoid skin and aberrant expression of these determinants cannot therefore be implicated in antigen presentation.

HLA-D Antigens↗
PubMed1991

Pemphigus and the terminal hair follicle.

The scalp is frequently involved in the autoimmune skin disease pemphigus. This study demonstrates the distribution of pemphigus antigen in the scalp terminal hair follicle; as well as being found in the epidermis, it is distributed throughout the whole hair follicle outer root sheath and in the dermal bulb matrix cells. The increase in volume of target antigen offered by the follicular epithelium could be a factor determining scalp involvement in pemphigus.

Adult↗
PubMed1991

Direct sequence evaluation of the major outer membrane protein gene variant regions of Chlamydia trachomatis subtypes D', I', and L2'.

The nucleotide sequences of variable segments (VS) 1, 2, and 4 for the major outer membrane protein gene (omp1) of Chlamydia trachomatis were determined for serologically defined subtypes D', I', and L2'. Asymmetric DNA amplification was used to produce single-stranded DNA for direct sequencing. Amino acid substitutions were detected in VS1, VS2, and VS4 for I', in VS2 for L2', and in VS4 for D'. DNA sequencing of omp1 variant regions may be an important method for evaluating the molecular epidemiology of Chlamydia spp.

Amino Acid Sequence↗