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Biomedical subjects

A Singer

Publications and source records attributed to A Singer.

At least 55 records · Page 3Linked to original sources
PubMed2000

Basic residues of human group IIA phospholipase A2 are important for binding to factor Xa and prothrombinase inhibition comparison with other mammalian secreted phospholipases A2.

Human secreted group IIA phospholipase A2 (hGIIA) was reported to inhibit prothrombinase activity because of binding to factor Xa. This study further shows that hGIIA and its catalytically inactive H48Q mutant prolong the lag time of thrombin generation in human platelet-rich plasma with similar efficiency, indicating that hGIIA exerts an anticoagulant effect independently of phospholipid hydrolysis under ex vivo conditions. Charge reversal of basic residues on the interfacial binding surface (IBS) of hGIIA leads to decreased ability to inhibit prothrombinase activity, which correlates with a reduced affinity for factor Xa, as determined by surface plasmon resonance. Mutation of other surface-exposed basic residues, hydrophobic residues on the IBS, and His48, does not affect the ability of hGIIA to inhibit prothrombinase activity and bind to factor Xa. Other basic, but not neutral or acidic, mammalian secreted phospholipases A2 (sPLA2s) exert a phospholipid-independent inhibitory effect on prothrombinase activity, suggesting that these basic sPLA2s also bind to factor Xa. In conclusion, this study demonstrates that the anticoagulant effect of hGIIA is independent of phospholipid hydrolysis and is based on its interaction with factor Xa, leading to prothrombinase inhibition, even under ex vivo conditions. This study also shows that such an interaction involves basic residues located on the IBS of hGIIA, and suggests that other basic mammalian sPLA2s may also inhibit blood coagulation by a similar mechanism to that described for hGIIA.

Amino Acid Sequence↗
PubMed2000

Programming for cytotoxic effector function occurs concomitantly with CD4 extinction during CD8(+) T cell differentiation in the thymus.

CD4(+) T cells are generally specialized to function as helper cells and CD8(+) T cells are generally specialized to function as cytotoxic effector cells. To explain how such concordance is achieved between co-receptor expression and immune function, we considered two possibilities. In one case, immature CD4(+)CD8(+) thymocyte precursors might first down-regulate expression of one co-receptor molecule, with the remaining co-receptor molecule subsequently activating the appropriate helper or cytotoxic functional program. Alternatively, we considered that the same intrathymic signals that selectively extinguished expression of one or the other co-receptor molecule might simultaneously initiate the appropriate helper or cytotoxic functional program. In the present study, we attempted to distinguish between these alternatives by examining thymocyte precursors of CD8(+) T cells for expression of Cathepsin C and Cathepsin W, molecules important for cytotoxic effector function. We report in developing thymocytes that Cathepsin C and Cathepsin W are expressed coordinately with extinction of CD4 co-receptor expression. We conclude that CD4 extinction and initiation of the cytotoxic functional program occurs simultaneously during differentiation of CD8(+) T cells in the thymus.

Animals↗
PubMed2000

CD8 coreceptor extinction in signaled CD4(+)CD8(+) thymocytes: coordinate roles for both transcriptional and posttranscriptional regulatory mechanisms in developing thymocytes.

T-cell development in the thymus is characterized by changing expression patterns of CD4 and CD8 coreceptor molecules and by changes in CD4 and CD8 gene transcription. In response to T-cell receptor (TCR) signals, thymocytes progress through developmental transitions, such as conversion of CD4(+)CD8(+) (double-positive [DP]) thymocytes into intermediate CD4(+)CD8(-) thymocytes, that appear to require more-rapid changes in coreceptor expression than can be accomplished by transcriptional regulation alone. Consequently, we considered the possibility that TCR stimulation of DP thymocytes not only affects coreceptor gene transcription but also affects coreceptor RNA stability. Indeed, we found that TCR signals in DP thymocytes rapidly destabilized preexisting CD4 and CD8 coreceptor RNAs, resulting in their rapid elimination. Destabilization of coreceptor RNA was shown for CD8alpha to be dependent on target sequences in the noncoding region of the RNA. TCR signals also differentially affected coreceptor gene transcription in DP thymocytes, terminating CD8alpha gene transcription but only transiently reducing CD4 gene transcription. Thus, posttranscriptional and transcriptional regulatory mechanisms act coordinately in signaled DP thymocytes to promote the rapid conversion of these cells into intermediate CD4(+)CD8(-) thymocytes. We suggest that destabilization of preexisting coreceptor RNAs is a mechanism by which coreceptor expression in developing thymocytes is rapidly altered at critical points in the differentiation of these cells.

Animals↗
PubMed2000

Quantitative detection of oncogenic HPV DNA using hybrid capture to triage borderline and mildly dyskaryotic Papanicolaou smears.

OBJECTIVE: To investigate the use of hybrid capture to triage borderline and mildly abnormal PAP smears to either colposcopy or continued cytological surveillance. METHOD: A prospective cross-sectional study of 207 women with either mild or borderline dyskaryosis referred to the colposcopy clinic at the Whittington Hospital, London was done. Quantitative detection of oncogenic human papillomavirus deoxyribose nucleic acid was performed using the solution hybridization technique Hybrid Capture I (Digene Diagnostics). Positive or negative hybrid capture results were compared to colposcopically directed punch biopsy or loop excision of the transformation zone. RESULTS: Hybrid capture correctly predicted 1/1 micro-invasive cancers, 23/24 CIN 3 and 20/24 CIN 2, giving a sensitivity to detect significant disease of CIN 2 or above of 90%. For CIN 1, 37/66 were HPV positive making the sensitivity to detect all grades of CIN 70%. Of women with a normal cervix, 39/92 were HPV positive and in total 58% of the women were HPV positive and would have been referred to colposcopy. CONCLUSIONS: Hybrid capture was a simple solution hybridization method which provided a sensitive method of detecting CIN 2 and above lesions in women with minor PAP smear abnormalities. However, the sensitivity for CIN 1 and the specificity were low, meaning that further improvements in the technique are needed before it can be used as a triage strategy.

Adolescent↗
PubMed2000

Cervicography to triage women with borderline or mild dyskaryotic cervical PAP smears.

OBJECTIVE: To evaluate six years experience using cervicography to triage women with borderline or mildly dyskaryotic PAP smears to either immediate colposcopy or cytological surveillance. METHOD: Retrospective study of 1,436 women referred to the cervicography clinic of the Whittington Hospital, London. Women with suspicious cervigrams were examined colposcopically and biopsied. Women with normal appearances at cervicography were followed-up with cytology over a period of a least two years. RESULTS: Cervicography detected 281 out of 307 women with CIN 2/3 and 215 out of 264 women with CIN 1. The sensitivity of cervicography to detect CIN 1, 2 or 3 in women with minor PAP smear abnormalities was 92%. The specificity was 39% and 847 (59%) of the women were referred for colposcopy; 215 (15%) were lost to follow-up. CONCLUSIONS: Cervicography was a sensitive method to detect CIN in women with mild or borderline dyskaryosis on their PAP smears. However, the low specificity meant that a high proportion of the women were referred for colposcopy, and a significant proportion of women were lost to follow-up. Thus cervicography is not an efficient strategy for managing women with minor PAP smears abnormalities.

Adult↗
PubMed2000

[Testicular cancer--self-awareness and testicular self-examination in soldiers and physicians in the Israeli army].

Testicular cancer is the most common malignancy in young men. To evaluate knowledge and awareness of that cancer, and of the practice of testicular self-examination (TSE), we developed a questionnaire which was distributed to 717 male soldiers and 200 of their military physicians. 21% of the soldiers had received some explanation of the importance of TSE, but only 16% were actually instructed how to perform TSE, and only 2% practiced it regularly. 24% had never examined their testicles before, 185 only rarely, and 6% often. With increased age, TSE frequency increased, but previous education, type of military unit, and ethnic origin had no affect. 99% of military physicians had been taught how to examine breasts, but only 70% had been taught routine testicular examination. 22% performed it, but 27% never did. 84% had never taught their soldiers the importance of TSE, although 51% taught female soldiers breast self-examination. There was a significant lack of awareness of the importance of regular practice of TSE among both soldiers and their army physicians.

Adolescent↗
PubMed1999

Association of the adaptor molecule LAT with CD4 and CD8 coreceptors identifies a new coreceptor function in T cell receptor signal transduction.

Linker for activation of T cells (LAT) is an adaptor protein whose tyrosine phosphorylation is critical for transduction of the T cell receptor (TCR) signal. LAT phosphorylation is accomplished by the protein tyrosine kinase ZAP-70, but it is not at all clear how LAT (which is not associated with the TCR) encounters ZAP-70 (which is bound to the TCR). Here we show that LAT associates with surface CD4 and CD8 coreceptors and that its association is promoted by the same coreceptor cysteine motif that mediates Lck binding. In fact, LAT competes with Lck for binding to individual coreceptor molecules but differs from Lck in its preferential association with CD8 rather than CD4 in CD4(+)CD8(+) thymocytes. Importantly, as a consequence of LAT association with surface coreceptors, coengagement of the TCR with surface coreceptors induces LAT phosphorylation and the specific recruitment of downstream signaling mediators to coreceptor-associated LAT molecules. These results point to a new function for CD4 and CD8 coreceptors in TCR signal transduction, namely to promote LAT phosphorylation by ZAP-70 by recruiting LAT to major histocompatibility complex-engaged TCR complexes.

Adaptor Proteins, Signal Transducing↗
PubMed1999

ZAP-70 protein promotes tyrosine phosphorylation of T cell receptor signaling motifs (ITAMs) in immature CD4(+)8(+) thymocytes with limiting p56(lck).

As a result of interaction with epithelial cells in the thymic cortex, immature CD4(+)8(+) (double positive, DP) thymocytes express relatively few T cell receptors (TCRs) and contain diminished numbers of coreceptor-associated p56(lck) (lck) PTK molecules. As a result, TCR signal transduction in DP thymocytes is significantly impaired, despite its importance for repertoire selection. We report here that, in DP thymocytes, tyrosine phosphorylation of TCR signaling motifs (ITAMs) by lck, an early event in TCR signal transduction, is dependent upon ZAP-70 protein independent of ZAP-70's kinase activity. Furthermore, the dependence on ZAP-70 protein for ITAM phosphorylation diminishes as available lck increases. Importantly, ZAP-70's role in ITAM phosphorylation in DP thymocytes is not limited to protecting phosphorylated ITAMs from dephosphorylation. Rather, this study indicates that ZAP-70 protein augments ITAM phosphorylation in DP thymocytes and so compensates in part for the relative deficiency of coreceptor-associated lck.

Animals↗
PubMed1999

Odortypes: their origin and composition.

Odors that distinguish one individual from another member of the species and are determined by polymorphic genes are called odortypes. Odortypes and their considerable societal significance have been studied intimately only in mice and mainly with respect to the genes of the major histocompatibility complex. Further understanding and the matter of human relevance have been hampered by the apparent restriction of odortype expression to urine. The present finding that odorants comprising prerenal odortypes are already present in blood, albeit in masked form, affords the basis of a comprehensive view of odortypes. Accordingly, major histocompatibility complex and other polymorphic genes of antiquity are seen inter alia as agents of normal variation, which entails quantitative variation in output of odorant metabolites. Relatively few such normal variations should suffice for a vast range of compound odors whose specificity is determined by combinative assortment of the same set of individual volatile compounds.

Animals↗
PubMed1999

Signals involved in CD4/CD8 lineage commitment: current concepts and potential mechanisms.

A competent immune system requires that mature T cells express TCR and CD4/CD8 coreceptors with matching MHC specificities. Such matching of TCR and coreceptor specificity is induced in the thymus at the CD4(+)8(+)stage of development and is referred to as lineage commitment. The process by which immature CD4(+)8(+)thymocytes are signaled to undergo lineage commitment continues to be the subject of intense investigation and discussion. Here, we review the major models by which lineage commitment is thought to occur and discuss the experimental results on which they were based.

Animals↗
PubMed1999

Positive selection as a developmental progression initiated by alpha beta TCR signals that fix TCR specificity prior to lineage commitment.

During positive selection, immature thymocytes commit to either the CD4+ or CD8+ T cell lineage ("commitment") and convert from short-lived thymocytes into long-lived T cells ("rescue"). By formal precursor-progeny analysis, we now identify what is likely to be the initial positive selection step signaled by alpha beta TCR, which we have termed "induction". During induction, RAG mRNA expression is downregulated, but lineage commitment does not occur. Rather, lineage commitment (which depends upon the MHC class specificity of the alpha beta TCR) only occurs after downregulation of RAG expression and the consequent fixation of alpha beta TCR specificity. We propose that positive selection can be viewed as a sequence of increasingly selective developmental steps (induction-->commitment-->rescue) that are signaled by alpha beta TCR engagements of intrathymic ligands.

Animals↗
PubMed1999

The antigen-presenting environment in normal and human papillomavirus (HPV)-related premalignant cervical epithelium.

The activation of HPV-specific T cells within the cervical microenvironment is likely to play an important part in the natural history of cervical intraepithelial neoplasia (CIN). The extent and the type of T cell activation will depend critically on the expression of MHC, costimulatory cell surface molecules and cytokines by keratinocytes and Langerhans cells within the cervical lesion. Expression of MHC class II (HLA-A-DR and -DQ), costimulatory/adhesion molecules (CD11a/18, CD50, CD54, CD58 and CD86) and cytokines (tumour necrosis factor-alpha (TNF-alpha) and IL-10) was therefore investigated by immunohistochemistry in normal squamous epithelium (n = 12), low-grade (n = 23) and high-grade (n = 18) squamous intraepithelial lesions of the cervix. CIN progression was associated with de novo expression of HLA-DR and CD54, and increased expression of CD58 by keratinocytes. However, significantly, there was no expression of any adhesion/costimulation molecule by epithelial Langerhans cells in any cervical biopsy studied. Furthermore, TNF-alpha, a potent activator of Langerhans cells, was expressed constitutively by basal keratinocytes in normal cervix (12+/12). but expression of this cytokine was absent in a number of CIN samples (20+/23 for low-grade, 12+/18 for high-grade CIN). Conversely, the suppressive cytokine IL-10 was absent in normal epithelium (0+/12), but was up-regulated in a number of CIN lesions (12+/23 for low-grade; 8+/18 for high-grade CIN). The restricted expression of costimulation/adhesion molecules and the nature of the cytokine microenvironment within the epithelium may act to limit effective immune responses in some CIN lesions.

Antigen Presentation↗