Intracellular signaling pathways involved in the induction of apoptosis in immature thymic T lymphocytes

We describe a novel technique for studying the signaling pathways that control thymocyte negative selection which maintains the essential interactions between thymocytes and thymic stromal cells. Bisected lobes from newborn mouse thymus are maintained in organ culture for up to 36 h, and the thymocytes analyzed by flow cytometry. Inclusion of [3H]inositol during culture allows measurements of phosphatidylinositol 4,5-biphosphate (PtdIns(4,5)P2) hydrolysis and inositol phosphate accumulation. Using this technique we have compared the thymocyte responses induced by anti-CD3, anti-Fas, Con A, and beta-adrenergic stimulation. We show that PtdIns(4,5)P2 hydrolysis precedes anti-CD3-induced thymocyte apoptosis, but not the apoptosis induced by anti-Fas. In contrast, Con A stimulates PtdIns(4,5)P2 hydrolysis, but does not induce thymocyte apoptosis. Anti-CD3, anti-Fas, and Con A all fail to change thymic cAMP levels, but beta-adrenergic stimulation causes a large increase in intracellular cAMP, and agents that elevate cAMP induce thymocyte apoptosis. Inhibition of protein synthesis (with cycloheximide or emetine) prevents the apoptosis induced by anti-CD3 and elevated cAMP, but not that induced by anti-Fas, whereas protease inhibition (with 3,4-dichloroisocoumarin or N(alpha)-tosyl-phenylalanine chloromethyl ketone) prevents the apoptosis caused by all of the effective stimuli. These results offer three important conclusions. First, activation of a variety of different signaling pathways can bring about thymocyte apoptosis. Second, ligation of the thymocyte TCR/CD3 complex provokes PtdIns(4,5)P2 hydrolysis, but signaling through this pathway alone does not necessarily lead to apoptosis. Third, by whichever signaling pathway the response is initiated, the activity of one or more protease enzymes appears to form an essential component in the final common pathway leading to apoptosis.

Intracellular signaling pathways involved in the induction of apoptosis in immature thymic T lymphocytes

We describe a novel technique for studying the signaling pathways that control thymocyte negative selection which maintains the essential interactions between thymocytes and thymic stromal cells. Bisected lobes from newborn mouse thymus are maintained in organ culture for up to 36 h, and the thymocytes analyzed by flow cytometry. Inclusion of [3H]inositol during culture allows measurements of phosphatidylinositol 4,5-biphosphate (PtdIns(4,5)P2) hydrolysis and inositol phosphate accumulation. Using this technique we have compared the thymocyte responses induced by anti-CD3, anti-Fas, Con A, and beta-adrenergic stimulation. We show that PtdIns(4,5)P2 hydrolysis precedes anti-CD3-induced thymocyte apoptosis, but not the apoptosis induced by anti-Fas. In contrast, Con A stimulates PtdIns(4,5)P2 hydrolysis, but does not induce thymocyte apoptosis. Anti-CD3, anti-Fas, and Con A all fail to change thymic cAMP levels, but beta-adrenergic stimulation causes a large increase in intracellular cAMP, and agents that elevate cAMP induce thymocyte apoptosis. Inhibition of protein synthesis (with cycloheximide or emetine) prevents the apoptosis induced by anti-CD3 and elevated cAMP, but not that induced by anti-Fas, whereas protease inhibition (with 3,4-dichloroisocoumarin or N(alpha)-tosyl-phenylalanine chloromethyl ketone) prevents the apoptosis caused by all of the effective stimuli. These results offer three important conclusions. First, activation of a variety of different signaling pathways can bring about thymocyte apoptosis. Second, ligation of the thymocyte TCR/CD3 complex provokes PtdIns(4,5)P2 hydrolysis, but signaling through this pathway alone does not necessarily lead to apoptosis. Third, by whichever signaling pathway the response is initiated, the activity of one or more protease enzymes appears to form an essential component in the final common pathway leading to apoptosis.

Parental presence during induction of anesthesia. A randomized controlled trial

BACKGROUND

To determine whether parental presence during induction of anesthesia is an effective preoperative behavioral intervention, a randomized controlled trial with children undergoing outpatient surgery was conducted.

METHODS

Eighty-four children were randomly assigned to a parent-present or parent-absent group. Using multiple behavioral and physiologic measures of anxiety, the effect of the intervention on the children and their parents was assessed. Predictors for the response to the intervention were examined using multivariate linear regression analysis.

RESULTS

When the intervention group (parent-present) was compared to the control group (parent-absent), overall there were no significant differences in any of the behavioral or physiologic measures of anxiety tested during induction of anesthesia. Using the child's serum cortisol concentration as the outcome, parental presence, the child's age and baseline temperament, and trait anxiety of the parent, were identified as predictors of the child's anxiety during induction. Analysis of variance demonstrated that three groups showed diminished cortisol concentrations with parental presence: children older than 4 yr (P = 0.001), children whose parent had a low trait anxiety (P = 0.02), and children who had a low baseline level of activity as assessed by temperament (P = 0.05).

CONCLUSIONS

Children who were older than 4 yr or those with a parent with a low trait anxiety or who had a low baseline level of activity/temperament benefited from parental presence during induction.

Elevated cerebrospinal fluid corticotropin-releasing factor in Tourette's syndrome: comparison to obsessive compulsive disorder and normal controls

Stress- and anxiety-related fluctuations in tic severity are cardinal features of Tourette's syndrome (TS), and there is evidence for involvement of noradrenergic mechanisms in the pathophysiology and treatment of the disorder. To examine further the pathobiology of this enhanced vulnerability to stress and anxiety, we measured central activity of corticotropin-releasing factor (CRF) in patients with TS and the related condition, obsessive compulsive disorder (OCD). Lumbar cerebrospinal fluid (CSF) was obtained in a standardized fashion for measurement of CRF from 21 medication-free outpatients with TS, 20 with OCD, and 29 healthy controls. The TS patients had significantly higher levels of CSF CRF than both the normal controls and the OCD patients. However, there was no difference in CSF CRF between the OCD patients and the normal controls. Group differences in CSF CRF were unrelated to current clinical ratings of depression, anxiety, tics, and obsessive compulsive behaviors. Although the functional significance of this finding remains to be elucidated, these results are consistent with the hypothesis that stress-related neurobiological mechanisms may play a role in the pathobiology of TS.

Cellular interactions in thymocyte development

Interactions between stromal cells and thymocytes play a crucial role in T cell development. The thymic stroma is complex and consists of epithelial cells derived from the pharyngeal region during development, together with macrophages and dendritic cells of bone marrow origin. In addition, fibroblasts and matrix molecules permeate the whole framework. It is now apparent that these individual stromal components play specialized roles at different stages of T cell differentiation. Thus, at the early CD4-8- stage of development, T cell precursors require fibroblast as well as epithelial cell interactions. Later, at the CD4+8+ stage, as well as providing low avidity TCR/MHC-peptide interactions, thymic epithelial cells have been shown to possess unique properties essential for positive selection. Dendritic cells, on the other hand, are probably efficient mediators of negative selection, but they may not be solely responsible for this activity. Alongside the functional roles of stromal cells, considerable progress is being made in unraveling the nature of the signaling pathways involved in T cell development. Identification of the pre-T cell receptor (pre-TCR) and associated signaling molecules marks an important advance in understanding the mechanisms that control gene rearrangement and allelic exclusion. In addition, a better understanding of the signaling pathways that lead to positive selection on the one hand and negative selection on the other is beginning to emerge. Many issues remain unresolved, and some are discussed in this review. What, for example, is the nature of the chemotactic factor(s) that attract stem cells to the thymus? What is the molecular basis of the essential interactions between early thymocytes and fibroblasts, and early thymocytes and epithelial cells? What is special about cortical epithelial cells in supporting positive selection? These and other issues are ripe for analysis and can now be approached using a combination of modern molecular and cellular techniques.

Involvement of LFA-1/ICAM-2 adhesive interactions and PKC in activation-induced cell death following SEB rechallenge

Ligation of T-cell receptor (TCR) causes mature T cells to proliferate or, on re-exposure to antigen, can cause them to die by activation-induced cell death (AICD). In proliferative responses, costimulatory and adhesive interactions are required and activation of protein kinase C (PKC) has been shown to be essential. Whether or not interactions involving costimulatory signals and PKC have a role in facilitating AICD remains unclear. Here we have examined the role of CD28/B7 and leucocyte function associated antigen-1 (LFA-1)/intracellular adhesion molecule (ICAM) mediated interactions in AICD triggered by staphylococcal enterotoxin B (SEB) in murine lymph node T cells. We show that, after a primary proliferative response to SEB, LFA-1/ICAM-2 adhesive interactions can play a part in AICD following SEB rechallenge, while B7 and ICAM-1 mediated interactions are not essential for this process. In addition, using a highly selective PKC inhibitor, Ro31.8425, we show that PKC activation is essential for the regulation of AICD by SEB rechallenge.

Trends in the utilization of noninvasive cardiac diagnostic tests in Ontario from fiscal year 1989/90 to 1992/93

OBJECTIVE

To describe pattern of utilization of noninvasive cardiac diagnostic test in Ontario.

DESIGN

Retrospective analysis using Ontario Health Insurance Plan (OHIP) administrative data.

SETTING

Ambulatory care settings in Ontario.

MAIN OUTCOME MEASURES

First, the volume of services and expenditures on electrocardiograms (ECG), ambulatory ECG, radionuclide angiocardiograms (RNA), echocardiograms, exercise stress tests (EST), and myocardial perfusion scintigrams from 1989/90 to 1992/93; second, the number and specialty of physicians performing these tests.

MAIN RESULTS

Ontario spent $119 million on noninvasive diagnostic cardiology test in 1992/93, representing 2.67% of total OHIP expenditures. Expenditures on these procedures grew by 49.3 % over the four-year period, exceeding the overall OHIP growth rate, and was most rapid for nuclear cardiology and echocardiography. Changing demographics accounted fpr only a minor portion of expenditure growth. Second, age-adjusted utilization rates for EST, myocardial perfusion scintigraphy and RNA were higher for men, but sex differences tended to diminish over time. Third, utilization rates differed markedly by geographic region, and variations were greatest for nuclear medicine studies. Geographic variations tended to be attenuated over time. There was also wide variation in the frequency with which physicians performed Doppler studies with two-dimensional echocardiography.

CONCLUSIONS

The use of noninvasive cardiac diagnostic test has grown rapidly in recent years. This growth may have been influenced by practice guidelines, by greater diffusion of, and access to, newer technology and by more testing in women. Wide regional variations suggest that clearer practice guidelines are needed concerning the appropriate use of noninvasive cardiac diagnostic investigations.

Childhood physical and sexual abuse in patients with anxiety disorders and in a community sample

OBJECTIVE

The authors investigated whether histories of childhood physical or sexual abuse were reported more frequently in a clinical sample of patients with anxiety disorders than in a matched community comparison sample.

METHOD

A standardized interview with an extensive series of trauma probes was administered to 125 patients with DSM-IV anxiety disorders (panic disorder, social phobia, or obsessive-compulsive disorder) and to 125 age- and gender-matched subjects drawn from a random community sample.

RESULTS

Childhood physical abuse was higher among both men (15.5%) and women (33.3%) with anxiety disorders than among comparison subjects (8.1%). Childhood sexual abuse was higher among women with anxiety disorders (45.1%) than among comparison women (15.4%) and was higher among women with panic disorder (60.0%) than among women with other anxiety disorders (30.8%).

CONCLUSIONS

These findings confirm the association between anxiety disorders and reported childhood physical and sexual abuse and extend earlier findings by pointing to a particular association between sexual abuse and panic disorder in women.

Evaluation of a hospital-based utilization management program

The objective of this study was to evaluate the impact of a utilization management (UM) program designed to decrease inappropriate use of acute care hospital beds while maintaining quality of care. The measure used to define appropriateness was the ISD-A, a diagnosis-independent measurement tool which relies on severity of illness and intensity of service criteria. The outcome measures for the study included appropriate admission to hospital and continued days of stay in hospital, 30-day readmission rates and physician perceptions of the impact of the intervention on quality of care, access to services and patient discharge patterns. The sample frame for the study included two control and two intervention community hospitals, involving 1,800 patient charts. Readmission rates were determined by analyzing all separations from medical services (N = 42,014) in the two experimental and two control hospitals. All physicians with admitting privileges (N = 312) at the intervention hospitals were surveyed; obstetricians, pediatricians, and psychiatrists were excluded from the survey. The results of the study demonstrated that the proportion of inappropriate admissions did not decrease significantly in any of the hospitals, but there were significant decreases in inappropriate continued stay in the intervention hospitals (p < 0.05). Both intervention and one of the control hospitals had lower 30-day readmission rates in the "after" period than in the "before" period (p < 0.05). Eighty-six percent believed that there had been no adverse impact on access to care and, although 25% thought the program may have led to premature discharge, this was not supported by the readmission data.

Protecting children with chronic illness in a competitive marketplace

Health care for children with chronic illnesses is significantly more expensive than for the average child. Children with chronic illnesses are especially vulnerable in a competitive health care environment because of the higher ongoing cost associated with treating their illnesses and the inherent pressures to reduce services to manage within the capitated rate. To minimize the adverse impact a competitive market could have on these children, a "carve-out" for specific medical conditions is discussed. A capitation pricing system that reflects their higher costs is proposed, as well as a delivery system that is focused on their needs.

Positive selection of thymocytes involves sustained interactions with the thymic microenvironment

CD4+8+ cortical thymocytes are critically dependent upon interaction with the thymic epithelium to undergo positive selection and maturation into single-positive CD4+ or CD8+ cells. Here we investigate further the nature of this interaction and provide evidence that positive selection requires sustained, rather than "single hit," interaction with thymic stromal cells. We also show that calcineurin-mediated signaling in thymocytes is required for the initial stages of positive selection, but is not essential throughout the period of thymocyte dependence on stromal cell contact during positive selection. In addition, we show that double-positive thymocytes that have initiated positive selection (CD69+4+8+) and newly generated single-positive (CD69+4+) cells differ markedly in response to the same stimulus through the TCR. The former undergo deletion, whereas the latter proliferate, indicating that a critical change in response to TCR ligation occurs within the narrow developmental window between these two stages.

Positive selection of thymocytes involves sustained interactions with the thymic microenvironment

CD4+8+ cortical thymocytes are critically dependent upon interaction with the thymic epithelium to undergo positive selection and maturation into single-positive CD4+ or CD8+ cells. Here we investigate further the nature of this interaction and provide evidence that positive selection requires sustained, rather than "single hit," interaction with thymic stromal cells. We also show that calcineurin-mediated signaling in thymocytes is required for the initial stages of positive selection, but is not essential throughout the period of thymocyte dependence on stromal cell contact during positive selection. In addition, we show that double-positive thymocytes that have initiated positive selection (CD69+4+8+) and newly generated single-positive (CD69+4+) cells differ markedly in response to the same stimulus through the TCR. The former undergo deletion, whereas the latter proliferate, indicating that a critical change in response to TCR ligation occurs within the narrow developmental window between these two stages.

Stimulation of thymocytes before and after positive selection results in the induction of different NF-kappa B/Rel protein complexes

Positive selection triggers the differentiation of immature CD4+8+TCRlow thymocytes into TCRhigh single-positive CD4+ or CD8+ cells and is associated with major changes in gene expression. However, little is known about the DNA binding factors controlling these fundamental changes. Here we have examined NF-kappa B/Rel subunit expression and DNA-binding activity in developing thymocytes before and after the induction of positive selection. We show that positive selection is accompanied by the strong up-regulation of c-rel mRNA expression and the constitutive activation of p50/p65 and p50/c-Rel NF-kappa B/Rel complexes, confirming the activation-like status of cells undergoing positive selection. Moreover, CD69+ cells that have initiated positive selection (but not their preselection CD4+8+TCR- precursors) respond to stimulation by the preferential activation of c-Rel-containing DNA-binding complexes. Because the different NF-kappa B/Rel dimers have distinct transcriptional activities and binding site preferences, this preferential activation of c-Rel-containing DNA-binding complexes may well have implications for the changes in gene expression and functional response associated with positive selection.

Stimulation of thymocytes before and after positive selection results in the induction of different NF-kappa B/Rel protein complexes

Positive selection triggers the differentiation of immature CD4+8+TCRlow thymocytes into TCRhigh single-positive CD4+ or CD8+ cells and is associated with major changes in gene expression. However, little is known about the DNA binding factors controlling these fundamental changes. Here we have examined NF-kappa B/Rel subunit expression and DNA-binding activity in developing thymocytes before and after the induction of positive selection. We show that positive selection is accompanied by the strong up-regulation of c-rel mRNA expression and the constitutive activation of p50/p65 and p50/c-Rel NF-kappa B/Rel complexes, confirming the activation-like status of cells undergoing positive selection. Moreover, CD69+ cells that have initiated positive selection (but not their preselection CD4+8+TCR- precursors) respond to stimulation by the preferential activation of c-Rel-containing DNA-binding complexes. Because the different NF-kappa B/Rel dimers have distinct transcriptional activities and binding site preferences, this preferential activation of c-Rel-containing DNA-binding complexes may well have implications for the changes in gene expression and functional response associated with positive selection.

Induction of thrombosis in a mouse model by IgG, IgM and IgA immunoglobulins from patients with the antiphospholipid syndrome

Antiphospholipid syndrome is a disorder of recurrent thrombosis and pregnancy losses associated with production of anticardiolipin antibodies and lupus anticoagulant positivity. Recently, we have adapted a mouse model of induced venous thrombosis to study the role of autoantibodies in thrombus formation. To determine whether immunoglobulins from patients with the antiphospholipid syndrome play a role in thrombosis, we injected groups of CDI mice either with immunoglobulins purified from seven patients with the antiphospholipid syndrome (nine preparations studied: four IgG, three IgM and two IgA) or with immunoglobulins of the same isotype from healthy controls. Seventy-two h after injection, a non-occlusive thrombus was induced in the femoral veins of experimental mice by a pinch injury; the thrombus areas as well as times of formation and disappearance of the thrombi were measured. Eight of the nine antiphospholipid syndrome immunoglobulin preparations caused a significant increase in mean thrombus area and a significant delay in mean thrombus disappearance time as compared with normal controls. To determine whether anticardiolipin antibodies might be involved, separate groups of mice were injected with affinity-purified IgG (n = 2) or IgM (n = 2) anticardiolipin antibodies or with normal immunoglobulins of the same isotype, and the effects on thrombus formation compared. Mean thrombus area and mean disappearance times were again significantly increased in all four groups injected with affinity-purified antibodies. This is the first study to show that anticardiolipin antibodies of IgG, IgM and IgA isotypes may play a role in thrombosis in vivo.

A decrease from 8 to 6 weeks in obstetrics and gynecology clerkship: effect on medical students' cognitive knowledge

We undertook this study to determine whether a decrease in the amount of time a third-year medical student spent in an obstetrics and gynecology clerkship would cause a decrease in the knowledge of the subject. We compared National Board of Medical Examiners (NBME) obstetrics and gynecology subject examination scores of 168 students at the University of Texas Medical Branch at Galveston completing an 8-week obstetrics and gynecology rotation or the 1989-1990 academic year to scores of 187 University of Texas Medical Branch students competing a 6-week rotation during 1990-1991. No significant change in the total mean NBME subject examination score in obstetrics and gynecology was noted after the decrease in rotation length. Passing scores were those greater than 445 points. The failure rate for those students who completed the 8-week rotation was consistent throughout the 1989-1990 academic year. In contrast, those students who rotated through obstetrics and gynecology during the 6-week clerkship in the first half of the academic year had a failure rate that was statistically higher than those taking the clerkship in the last half of the year. The length of the obstetrics and gynecology clerkship was shortened to 6 weeks without significantly affecting students' overall performance on the NBME obstetrics and gynecology subject examination. However, a greater percentage of students who completed the rotation during the first half of the year scored low on the NBME obstetrics and gynecology subject examination than did those taking the rotation and thus the NBME subject examination in the second half of the year.

Community organization to promote breast cancer screening among women ages 50-75

BACKGROUND

To reduce breast cancer mortality, ways to promote the use of mammography screening among women age 50 and above are needed. Community organization may be a useful approach.

METHODS

The Washington State Community Breast Cancer Screening Project involved implementation of promotional activities initiated by physician and lay community boards in two communities. Two comparable communities served as controls for evaluation purposes. Random-digit-dial telephone interviews were used to assess recent use of mammography at baseline and follow-up in independent samples of women ages 50 to 75 from the four communities. The extent of exposure to intervention activities and the relationship between exposure to intervention activities and mammography use were estimated from data collected at follow-up.

RESULTS

Exposure to patient reminders from physicians, wallet reminder cards, and newspaper advertisements were consistently related to mammography use. Physician office staff encouragement and a display board were significantly related to mammography use only in Intervention Communities A and B, respectively. Neither exposure to promotional activities nor the change in prevalence of mammography use was significantly higher in the intervention communities than in the comparison communities at follow-up.

CONCLUSIONS

Although several activities were useful in promoting mammography use, organization of the community did not enhance efforts undertaken spontaneously by comparable communities.

A peptide from the caudal neurosecretory system of the dogfish Scyliorhinus canicula that is structurally related to urotensin I

Using reversed-phase HPLC in combination with a radioimmunoassay for ovine corticotropin-releasing hormone (CRH), a peptide with CRH-like immunoreactivity was isolated in pure form from an extract of the caudal spinal cord region of the spotted dogfish, Scyliorhinus canicula. The primary structure of the peptide was established as Pro-Ala-Glu-Thr-Pro-Asn-Ser-Leu10-Asp-Leu-Thr-Phe-His-Leu-Leu-Arg- Glu-Met-Ile- Glu20-Ile-Ala-Lys-His-Glu-Asn-Gln-Gln-Met-Gln30-Ala-Asp-Ser- Asn-Arg-Arg-Ile-Met - Asp-Thr40-Ile.NH2. This amino acid sequence shows moderate structural similarity to Catostomus urotensin I (51%) and to human CRH (56%). The data provide, therefore, chemical evidence to support the conclusions of earlier immunohistochemical studies that the diffuse caudal neurosecretory system of elasmobranchs produces a peptide that is immunochemically related to teleost urotensin I peptides. However, the primary structure of urotensin I has been poorly conserved during evolution.

A retrospective analysis of the long-term effect of splenectomy on late infections, graft-versus-host disease, relapse, and survival after allogeneic marrow transplantation for chronic myelogenous leukemia

The present study was performed as a retrospective analysis of the role of pretransplant splenectomy to determine the incidence of late bacterial infections, acute and chronic graft-versus-host disease (GVHD), relapse, and survival among 358 patients receiving HLA-identical marrow grafts for chronic myelogenous leukemia. Sixty-eight (19%) of the 358 patients had undergone splenectomy before transplantation. There was a trend towards more grade II-IV acute GVHD among splenectomized patients, but this was not significant in the multivariate analysis. The incidence of chronic GVHD was similar for splenectomized and nonsplenectomized patients. Late infectious complications did not significantly differ between splenectomized and control patients (rates per patient year were 0.16 and 0.14, respectively). The overall risk of leukemic relapse was significantly increased for splenectomized patients (56% v 32% for controls, P = .001) and control patients with splenomegaly (P < .0001). Splenectomy and splenomegaly remained significant and independent hazards for relapse in the multivariate analysis (hazard ratio [HR], 1.82, P = .029; and HR, 1.49, P = .002; respectively). Relapse was also increased in patients with advanced disease (HR, 2.95; P = .0001), in patients with T-cell-depleted marrow (HR, 4.51; P = .0001), and in the female donor and male recipient combination (HR, 1.74; P = .044). Patients with splenectomy had an increased overall mortality (HR, 1.18), but this was not statistically significant in the multivariate analysis. In summary, our study showed no significant influence of splenectomy on late posttransplant infections, acute or chronic GVHD, or overall survival. There was no evidence that splenectomy decreased recurrence of chronic myelogenous leukemia.

Correlation of cell surface fluorescence with conventional PAP analysis of cells of cytological interest obtained from cervical scrapes

Archival PAP stained cervical smears were destained and treated with a fluorescent probe for a cell surface enzyme (GB). Cells which exhibited cell surface fluorescence were demonstrated to be cells of cytological interest in the analysis of cervical smears. These cells could be directly related to PAP and reclassified by subsequent restaining with PAP. Fluorescent cell surface technology was shown to be compatible with conventional PAP staining.

The role of the thymus during T-lymphocyte development in vitro

To date, fetal thymic organ culture is the only in-vitro system capable of supporting a complete programme of T-lymphocyte development in a manner comparable to that seen in vivo. In this review, we will summarise recent studies in which thymic organ cultures have been used to investigate the regulatory mechanisms of particular stages of thymocyte development. In addition, the use of other culture systems of T-cell maturation will be discussed in an attempt to define the optimal conditions for T-cell development in vitro.

Exfoliative cytology and electron microscopy in the diagnosis of hairy leukoplakia

The diagnosis of lesions clinically suggestive of hairy leukoplakia was assessed by light and electron microscopic examination of cytologic smears. We found exfoliative cytology to be a simple and noninvasive technique that can confirm the clinical diagnosis of hairy leukoplakia. Our results suggest that electron microscopy may be more sensitive and reliable than light microscopy in confirming the clinical diagnosis of hairy leukoplakia.

Intracellular signaling events during positive and negative selection of CD4+CD8+ thymocytes in vitro

We have used in vitro models of thymocyte positive and negative selection in conjunction with selective inhibitors of the TCR-mediated signaling cascade to investigate the intracellular signaling events that mediate these processes. We report that Ro 31.8425, a potent and selective inhibitor of protein kinase C, which blocks the activation of mature T cells in a dose-dependent fashion, has no effect on either positive or negative selection of CD4+8+ thymocytes. In contrast, cyclosporin A fails to prevent negative selection, but inhibits positive selection through a direct effect on developing thymocytes, rather than through the perturbation of stromal cell support. Thus, our data suggest that positive and negative selection may operate via distinct intracellular signaling pathways.