Acceptability and Feasibility of Saliva-delivered PCR Coronavirus 2019 Tests for Young Children.

OBJECTIVES: Access to readily available, reliable, and easy-to-use coronavirus disease 2019 (COVID-19) tests remains critical, despite great vaccination progress. Universal back-to-school testing offered at early care and education ([ECE]; ie, preschool) sites to screen for positive cases may help preschoolers safely return to, and stay in, ECE. We examined the acceptability and feasibility of using a quantitative polymerase chain reaction COVID-19 saliva test for young children (n = 227, 54.0% girls: mean age = 52.3 ± 8.1 months) and their caregivers (n = 70 teachers: mean = 36.6 ± 14.7 years; n = 227 parents: mean = 35.5 ± 9.1 years) to mitigate the spread of COVID-19 and reduce days of school and work missed for households with children who test positive. METHODS: Participants were recruited at ECE sites serving low-income communities as part of the Rapid Acceleration of Diagnostic Testing-Underserved Populations Back to Early Care and Education Safely with Sustainability via Active Garden Education project (NCT05178290). RESULTS: Surveys in English or Spanish administered at testing events to children and caregivers at ECE sites showed child and adult acceptability and feasibility ratings were generally high. More favorable child and parent ratings were positively associated with child age and whether the child was able to produce a saliva sample. Language preference was not associated with any outcomes. CONCLUSIONS: Saliva sampling for COVID-19 at ECE sites is an acceptable strategy as an additional layer of protection for 4- and 5-year-olds; however, alternate testing strategies may be needed for younger children.

Qualitative Research on the Perceptions of Factors Influencing Diet and Eating Behaviors Among Primarily Latinx Seventh-Grade Students.

BACKGROUND: Latinx youth are a population of concern, at elevated risk for chronic diseases and with poor adherence to dietary recommendations. OBJECTIVES: To examine Latinx seventh-grade students' perceptions of the factors that influence their diet and eating behaviors. DESIGN: This qualitative research used focus groups and an inductive content analysis approach. PARTICIPANTS/SETTING: Five sex-stratified focus groups (three groups with females) with 35 primarily Latinx seventh-grade students were conducted at two local Title 1 public middle schools in a large metropolitan area of the Southwestern United States. MAIN OUTCOME MEASURES: The discussion protocol included questions about participants' food choices, the role of their parents in their diet, and healthy body-related concerns among their peers. ANALYSES: Verbatim transcripts were coded in NVivo 12 on the basis of specificity, extensiveness, and frequency. Themes emerged from group dialogue, detailed conversations, and predominant topics of discussion, and aligned with ecological systems theory. RESULTS: Participants referred to factors influencing Latinx seventh-grade students' eating behaviors at the individual, family, household, and school levels. At the individual level, participants described their eating as unhealthy and perceived it as determined by taste, convenience, ease of preparation, and home availability. Participants expressed concerns about diabetes because of their body weight and family history, and identified those concerns as reasons for acceptance of healthy foods and the desire for parents to model healthy eating behaviors. Family-level factors perceived as influencing dietary behaviors included the role of parents as providers of food and models of unhealthy eating, budget constraints, and availability (or lack thereof) of healthy foods at home. Similarly, the identified school-level factors aligned with availability and quality of foods in that environment. CONCLUSIONS: Family- and household-related factors emerged as important influences on seventh-grade students' dietary behaviors. Future diet interventions should incorporate strategies targeting these multiple-level factors that influence dietary intake for Latinx youth and that address the concerns related to disease risk.

Differences in health policies for drug availability in pulmonary arterial hypertension and chronic thromboembolic pulmonary hypertension across Latin America.

Treatment for pulmonary arterial hypertension and chronic thromboembolic pulmonary hypertension in Latin America differs between countries, with regard to disease etiology, health insurance coverage, and drug availability. A group of experts from Latin America, met to share regional experiences and propose possible lines of collaboration. The available evidence, regional clinical practice data, and the global context of the proceedings of the 6th World Symposium on Pulmonary Hypertension, held in Nice, France, in February 2018, were analyzed. Here, we discuss some priority concepts identified that could guide transnational interaction and research strategies in Latin America: (1) despite being evidence-based, the 6th World Symposium on Pulmonary Hypertension proceedings may not be applicable in Latin American countries; (2) proactive identification and diagnosis of patients in Latin America is needed; (3) education of physicians and standardization of appropriate treatment for pulmonary arterial hypertension and chronic thromboembolic pulmonary hypertension is vital; (4) our clinical experience for the treatment strategy for pulmonary arterial hypertension and chronic thromboembolic pulmonary hypertension is based on drug availability in Argentina, Brazil, Colombia and México; (5) there are difficulties inherent to the consultation of patients with pulmonary arterial hypertension and chronic thromboembolic pulmonary hypertension, and access to treatment; (6) the importance of data generation and research of Latin American-specific issues related to pulmonary arterial hypertension and chronic thromboembolic pulmonary hypertension is highlighted.

Riociguat in the Treatment of Pulmonary Arterial Hypertension.

Pulmonary arterial hypertension (PAH) is a severe clinical condition that significantly affects patients' quality of life and survival. Since the emergence of prostanoids 45 years ago, different drugs acting on vasoconstriction/vasodilation mechanisms have been developed for the treatment of PAH. Current evidence shows that better results occur when combined therapy is initiated up-front with periodic and systematized evaluations for escalation and switching. Among these strategies, riociguat has a relevant role, supported by the results of several clinical studies. This document issues recommendations by a panel of experts who analysed and discussed the indications and limitations for riociguat in PAH in different institutions of the Mexican health system.

Comparison of the retention of conventional dentures after the use of common adhesive brands on poor denture foundations: an in vitro study / Comparación de la retención de dentaduras convencionales con el uso de marcas comerciales de adhesivos en procesos alveolares deficientes: un estudio in vitro

There is no information about the possible impact in denture retention after the use of common denture adhesives (DAs) when poor denture foundations (PDF) are present. Moreover, there is a lack of information about which current formulation provides greater retention and for how long. Twelve models from edentulous patients with different ridge shape and border height were used and complete dentures were manufactured. Four different formulation brands of DAs were tested after 10 minutes and three, six, nine, and 12 hours of DA application using a universal testing machine. The Fittydent® and Fixodent® adhesives had the highest retention at 12 hours. The PDF group increased on average its retention by 400 %. However, the group presented lower retention compared to the good denture foundation group. In conclusion, DAs significantly increased denture retention. The PDF group were the most benefited with the application of DAs. The Fixodent® paste had the highest retention.

No existe información acerca del posible impacto en la retención de dentaduras después del uso de adhesivos dentales comunes (DAs) cuando existen rebordes alveolares deficientes (PDF). Más aun, existe una falta de información acerca de cuál formula actual provee mayor retención y por cuanto tiempo. Doce modelos de pacientes edentulos con diferentes formas y alturas en sus rebordes alveolares fueron usados, y dentaduras completas les fueron realizadas. Cuatro diferentes fórmulas y marcas de DAs fueron evaluadas después de 10 minutos, tres, seis, nueve y 12 horas de que se aplicó el DA usando una maquina universal de pruebas. Los adhesivos Fittydent® y Fixodent® presentaron la retención más alta a las 12 horas. El grupo con PDF incrementó su retención hasta en un 400 %. Sin embargo, el grupo presentó menor retención cuando se comparó con el grupo que posee adecuados procesos alveolares. Los DAs incrementaron significativamente la retención de las dentaduras. El grupo PDF fue el más beneficiado con la aplicación de DAs. La pasta Fixodent® provee la más alta retención.

Spare PRELI gene loci: failsafe chromosome insurance?

BACKGROUND: LEA (late embryogenesis abundant) proteins encode conserved N-terminal mitochondrial signal domains and C-terminal (A/TAEKAK) motif repeats, long-presumed to confer cell resistance to stress and death cues. This prompted the hypothesis that LEA proteins are central to mitochondria mechanisms that connect bioenergetics with cell responses to stress and death signaling. In support of this hypothesis, recent studies have demonstrated that mammalian LEA protein PRELI can act as a biochemical hub, which upholds mitochondria energy metabolism, while concomitantly promoting B cell resistance to stress and induced death. Hence, it is important to define in vivo the physiological relevance of PRELI expression. METHODS AND FINDINGS: Given the ubiquitous PRELI expression during mouse development, embryo lethality could be anticipated. Thus, conditional gene targeting was engineered by insertion of flanking loxP (flox)/Cre recognition sites on PRELI chromosome 13 (Chr 13) locus to abort its expression in a tissue-specific manner. After obtaining mouse lines with homozygous PRELI floxed alleles (PRELI(f/f)), the animals were crossed with CD19-driven Cre-recombinase transgenic mice to investigate whether PRELI inactivation could affect B-lymphocyte physiology and survival. Mice with homozygous B cell-specific PRELI deletion (CD19-Cre/Chr13 PRELI(-/-)) bred normally and did not show any signs of morbidity. Histopathology and flow cytometry analyses revealed that cell lineage identity, morphology, and viability were indistinguishable between wild type CD19-Cre/Chr13 PRELI(+/+) and CD19-Cre/Chr13 PRELI(-/-) deficient mice. Furthermore, B cell PRELI gene expression seemed unaffected by Chr13 PRELI gene targeting. However, identification of additional PRELI loci in mouse Chr1 and Chr5 provided an explanation for the paradox between LEA-dependent cytoprotection and the seemingly futile consequences of Chr 13 PRELI gene inactivation. Importantly, PRELI expression from spare gene loci appeared ample to surmount Chr 13 PRELI gene deficiency. CONCLUSIONS: These findings suggest that PRELI is a vital LEA B cell protein with failsafe genetics.

[Type 2 diabetes mellitus as a prognostic factor in patients with aneurysm clipping after subarachnoid hemorrhage]. / Diabetes mellitus tipo 2 como factor pronóstico en pacientes con clipaje de aneurisma por hemorragia subaracnoidea.

OBJECTIVE: To evaluate if type 2 diabetes mellitus (DM) constitutes a prognostic factor for death and severe disability in patients with aneurysm clipping after subarachnoid hemorrhage (ASH), in an Intensive Care Unit (ICU). MATERIAL AND METHODS: This is a cohort study in patients who were admitted to the ICU between December-2009 and June-2010; 20 with DM (exposed group) and 40 without DM (non-exposed group). Mortality was quantified during ICU stay. At ICU discharge, severe disability was measured through the Glasgow Outcome Scale (category 2); and Glasgow Coma Scale was used to estimate the difference in consciousness level between ICU arrival and discharge. Descriptive statistics and Kaplan Meier survival curves were performed. RESULTS: Mean age was similar between groups (55.8 +/- 11 and 55.6 +/- 15 years, respectively, p = 0.40). A vegetative state was present in one patient without DM. The Glasgow Coma Scale score at ICU entry was 14.1 +/- 1.4 and at discharge, 12.0 +/- 3.6 in the exposed group (p = 0.01); and 13.9 +/- 2.0 us. 13.5 +/- 2.6, in the non-exposed group, respectively (p = 0.45). There were 3 deaths in patients with DM and 5, in patients without DM (p > 0.05); survival time was 12 (95%CI 7, 16) and 10 days (95%CI 7, 13), respectively. Mean glucose remained higher in patients who died at the ICU (p < 0.001). Hydrocephaly was present in 6 exposed patients and 2, non-exposed (p = 0.007). Additionally, 7 and 5 with and without DM, respectively registered a positive blood culture (p = 0.04). CONCLUSIONS: DM was not associated with higher mortality in ICU patients, but hyperglycemia was; thus, it is essential that the intensive care provider watches closely the glycemic control.

Coordinate activation of inflammatory gene networks, alveolar destruction and neonatal death in AKNA deficient mice.

Gene expression can be regulated by chromatin modifiers, transcription factors and proteins that modulate DNA architecture. Among the latter, AT-hook transcription factors have emerged as multifaceted regulators that can activate or repress broad A/T-rich gene networks. Thus, alterations of AT-hook genes could affect the transcription of multiple genes causing global cell dysfunction. Here we report that targeted deletions of mouse AKNA, a hypothetical AT-hook-like transcription factor, sensitize mice to pathogen-induced inflammation and cause sudden neonatal death. Compared with wild-type littermates, AKNA KO mice appeared weak, failed to thrive and most died by postnatal day 10. Systemic inflammation, predominantly in the lungs, was accompanied by enhanced leukocyte infiltration and alveolar destruction. Cytologic, immunohistochemical and molecular analyses revealed CD11b(+)Gr1(+) neutrophils as major tissue infiltrators, neutrophilic granule protein, cathelin-related antimicrobial peptide and S100A8/9 as neutrophil-specific chemoattracting factors, interleukin-1ß and interferon-γ as proinflammatory mediators, and matrix metalloprotease 9 as a plausible proteolytic trigger of alveolar damage. AKNA KO bone marrow transplants in wild-type recipients reproduced the severe pathogen-induced reactions and confirmed the involvement of neutrophils in acute inflammation. Moreover, promoter/reporter experiments showed that AKNA could act as a gene repressor. Our results support the concept of coordinated pathway-specific gene regulation functions modulating the intensity of inflammatory responses, reveal neutrophils as prominent mediators of acute inflammation and suggest mechanisms underlying the triggering of acute and potentially fatal immune reactions.

HDAC11 plays an essential role in regulating OX40 ligand expression in Hodgkin lymphoma.

In Hodgkin lymphoma (HL), the malignant cells are surrounded by a large number of reactive infiltrating inflammatory cells, including OX40-expressing T cells and interleukin 10 (IL-10)-producing regulatory T (T-reg) cells. These T-reg cells can suppress the immune response and thus contribute to the maintenance of immune tolerance and to insufficient antitumor response. The engagement of OX40L with the OX40 receptor is essential for the generation of antigen-specific memory T cells and for the induction of host antitumor immunity. In the present study, we investigated whether histone deacetylase inhibitors (HDACis) may induce a favorable antitumor immune response by regulating the expression of OX40L in HL. We found that HDACis up-regulated OX40L surface expression in HL cell lines in a dose-dependent manner. Small interfering RNAs (siRNAs) that selectively inhibited HDAC11 expression, significantly up-regulated OX40L and induced apoptosis in HL cell lines, and silencing HDAC11 transcripts increased the production of tumor necrosis-α (TNF-α) and IL-17 in the supernatants of HL cells. Furthermore, HDACI-induced OX40L inhibited the generation of IL-10-producing type 1 T-reg cells. These results demonstrate for the first time that HDAC11 plays an essential role in regulating OX40L expression. Pharmacologic inhibition of HDAC11 may produce a favorable antitumor immune response in patients with HL.

Using community based participatory research to create a culturally grounded intervention for parents and youth to prevent risky behaviors.

The principal goal of this article is to contribute to the field of prevention science by providing a sequential description of how Community Based Participatory Research (CBPR) was used to develop a parent education curriculum aimed at preventing and decreasing adolescent drug use and risky sexual behaviors. CBPR principles are outlined, and information is provided on the unique contributions of researchers and community members who came together to develop this parent education program. Focus group information is presented as an exemplar to illustrate how thematic content from focus groups was used to inform the development of this parent education curriculum. A step by step description is given to facilitate replication of this process by other prevention researchers who are interested in applying this CBPR approach to develop a culturally responsive parent education intervention.

Enhanced airway inflammation and remodeling in adenosine deaminase-deficient mice lacking the A2B adenosine receptor.

Adenosine is a signaling nucleoside that is generated in response to cellular injury and orchestrates the balance between tissue protection and the progression to pathological tissue remodeling. Adenosine deaminase (ADA)-deficient mice develop progressive airway inflammation and remodeling in association with adenosine elevations, suggesting that adenosine can promote features of chronic lung disease. Furthermore, pharmacological studies in ADA-deficient mice demonstrate that A(2B)R antagonism can attenuate features of chronic lung disease, implicating this receptor in the progression of chronic lung disease. This study examines the contribution of A(2B)R signaling in this model by generating ADA/A(2B)R double-knockout mice. Our hypothesis was that genetic removal of the A(2B)R from ADA-deficient mice would lead to diminished pulmonary inflammation and damage. Unexpectedly, ADA/A(2B)R double-knockout mice exhibited enhanced pulmonary inflammation and airway destruction. Marked loss of pulmonary barrier function and excessive airway neutrophilia are thought to contribute to the enhanced tissue damage observed. These findings support an important protective role for A(2B)R signaling during acute stages of lung disease.

Inhibition of heat shock protein 90 function by 17-allylamino-17-demethoxy-geldanamycin in Hodgkin's lymphoma cells down-regulates Akt kinase, dephosphorylates extracellular signal-regulated kinase, and induces cell cycle arrest and cell death.

PURPOSE: Heat shock protein 90 (HSP90) is a chaperone for several client proteins involved in transcriptional regulation, signal transduction, and cell cycle control. HSP90 is abundantly expressed by a variety of tumor types and has been recently targeted for cancer therapy. The objective of this study was to determine the role of HSP90 in promoting growth and survival of Hodgkin's lymphoma and to determine the molecular consequences of inhibiting HSP90 function by the small-molecule 17-allylamino-17-demethoxy-geldanamycin (17-AAG) in Hodgkin's lymphoma. EXPERIMENTAL DESIGN: HSP90 expression in Hodgkin's lymphoma cell lines was determined by Western blot and in primary lymph node sections from patients with Hodgkin's lymphoma by immunohistochemistry. Cell viability was determined by the 3-(4,5-dimethyl-thiazol-2yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assay. Apoptosis and cell cycle fractions were determined by flow cytometry. Expression of intracellular proteins was determined by Western blot. RESULTS: HSP90 is overexpressed in primary and cultured Hodgkin's lymphoma cells. Inhibition of HSP90 function by 17-AAG showed a time- and dose-dependent growth inhibition of Hodgkin's lymphoma cell lines. 17-AAG induced cell cycle arrest and apoptosis, which were associated with a decrease in cyclin-dependent kinase (CDK) 4, CDK 6, and polo-like kinase 1 (PLK1), and induced apoptosis by caspase-dependent and caspase-independent mechanisms. Furthermore, 17-AAG depleted cellular contents of Akt, decreased extracellular signal-regulated kinase (ERK) phosphorylation, and reduced cellular FLICE-like inhibitory protein levels (FLIP), and thus enhanced the cytotoxic effect of doxorubicin and agonistic anti-tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) death receptor antibodies. CONCLUSION: Inhibition of HSP90 function induces cell death and enhances the activity of chemotherapy and anti-tumor necrosis factor-related apoptosis-inducing ligand death receptor antibodies, suggesting that targeting HSP90 function might be of therapeutic value in Hodgkin's lymphoma.

The kappa-like pre-B receptor: surplus biology or a missing link?

After the demonstration that surrogate JCkappa polypeptides could covalently bind mu heavy chain and upon the characterization of the Vkappa-like component of the kappa-like pre-B cell receptor, it became evident that germline transcription is not sterile. The present review discusses the concept of the alternative usage of kappa-like pre-B cell receptors and classical pre-B cell receptors utilizing the lambda-like surrogate light chain composed of lambda5 and VpreB. We propose that both kappa-like and lambda-like pre-B cell receptors work in concert in a fail-safe mechanism to promote light chain rearrangement, heavy chain allelic exclusion and B-lymphocyte maturation.

The human AKNA gene expresses multiple transcripts and protein isoforms as a result of alternative promoter usage, splicing, and polyadenylation.

We previously showed that the human AKNA gene encodes an AT-hook transcription factor that regulates the expression of costimulatory cell surface molecules on lymphocytes. However, AKNA cDNA probes hybridize with multiple transcripts, suggesting either the existence of other homologous genes or a complex regulation operating on a single gene. Here we report evidence for the latter, as we find that AKNA is encoded by a single gene that spans a 61-kb locus of 24 exons on the fragile FRA9E region of human chromosome 9q32. This gene gives rise to at least nine distinct transcripts, most of which are expressed in a tissue-specific manner in lymphoid organs. Many of the AKNA transcripts originate from alternative splicing; others appear to derive from differential polyadenylation and promoter usage. The alternative AKNA transcripts are predicted to encode overlapping protein isoforms, some of which (p70 and p100) are readily detectable using a polyclonal anti-AKNA antisera that we generated. We also find that AKNA PEST-dependent cleavage into p50 polypeptides is targeted to mature B cells and appears to be required for CD40 upregulation. The unusual capacity of the AKNA gene to generate multiple transcripts and proteins may reflect its functional diversity, and it may also provide a fail-safe mechanism that preserves AKNA expression.

Assembly of the kappa preB receptor requires a V kappa-like protein encoded by a germline transcript.

By confining germline transcription as a byproduct of the mechanisms inherent to genetic rearrangements, the translation of respective mRNAs and their biological relevance might have been overlooked. Here we report the identification, cloning, and biochemical characterization of a human Vkappa-like protein that is encoded by a germline transcript. This surrogate protein assembles with the immunoglobulin mu heavy chain at the surface of B cell progenitors and precursors to form a kappa-like antigen receptor. These findings support the notion that germline transcription is not futile and stress the flexibility in eukaryotic gene usage and expression. In addition, the present study confirms the co-existence of surrogate lambda and kappa receptors that are proposed to work in concert to promote B lymphocyte maturation.

Impaired germinal center maturation in adenosine deaminase deficiency.

Mice deficient in the enzyme adenosine deaminase (ADA) have small lymphoid organs that contain reduced numbers of peripheral lymphocytes, and they are immunodeficient. We investigated B cell deficiency in ADA-deficient mice and found that B cell development in the bone marrow was normal. However, spleens were markedly smaller, their architecture was dramatically altered, and splenic B lymphocytes showed defects in proliferation and activation. ADA-deficient B cells exhibited a higher propensity to undergo B cell receptor-mediated apoptosis than their wild-type counterparts, suggesting that ADA plays a role in the survival of cells during Ag-dependent responses. In keeping with this finding, IgM production by extrafollicular plasmablast cells was higher in ADA-deficient than in wild-type mice, thus indicating that activated B cells accumulate extrafollicularly as a result of a poor or nonexistent germinal center formation. This hypothesis was subsequently confirmed by the profound loss of germinal center architecture. A comparison of levels of the ADA substrates, adenosine and 2'-deoxyadenosine, as well resulting dATP levels and S-adenosylhomocysteine hydrolase inhibition in bone marrow and spleen suggested that dATP accumulation in ADA-deficient spleens may be responsible for impaired B cell development. The altered splenic environment and signaling abnormalities may concurrently contribute to a block in B cell Ag-dependent maturation in ADA-deficient mouse spleens.

In vivo expression of interleukin-8, and regulated on activation, normal, T-cell expressed, and secreted, by human germinal centre B lymphocytes.

T-cell homing within germinal centres (GCs) is required for humoral B-cell responses. However, the mechanisms implicated in the recruitment of T cells into the GC are not completely understood. Here we show, by immunohistology, and Northern and Western blots, that in vivo human GC B lymphocytes can express CxC and CC chemokines. Moreover, B-cell subset-specific experiments reveal that interleukin (IL)-8 and regulated on activation, normal, T-cell expressed, and secreted (RANTES) are predominantly expressed by GC centroblast and centrocytes, suggesting that chemokine expression is essential at stages in which B-lymphocytes engage in active antigen-dependent interactions with T lymphocytes. In keeping with this hypothesis, we show that the T cells recruited into the GC correlatively express the receptors for IL-8 and RANTES. We propose that chemokine expression is a key B-cell function that facilitates T-lymphocyte recruitment into the GCs and supports cognate B-cell : T-cell encounters. Moreover, our data are consistent with the impaired homing of T cells to secondary lymphoid organs in mice that are either deficient in CC and CxC chemokines or their receptors.

Life and death within germinal centres: a double-edged sword.

Within germinal centres, B lymphocytes are destined to die by apoptosis via Fas signalling, unless they are positively rescued by antigen and by signals initiated by CD40-CD154 interactions. Thus, while the germinal centre microenvironment can become a virtual graveyard for most B lymphocytes that fail to bind antigen with high affinity, it concomitantly provides the necessary stimuli for the survival of cells that successfully accomplish affinity maturation. Such dichotomy in the physiology of germinal centre reaction that results in survival of the functional B-cell repertoire and the elimination of abnormal cells, dictates the fate towards B-cell homeostasis or disease. Consequently, the death and survival-signalling arms within germinal centres predominantly reside on the timely and controlled expression of Fas and its ligand (FasL), and CD40 and CD154, respectively. In keeping with this notion, lymphoproliferation or deficient immunity are documented landmarks of inactivation of either the Fas/FasL or CD40/CD154 signalling pathways. The present review considers two different scenarios in the control of B-cell survival and death within germinal centres. The first is an idealistic scenario, in which a discriminatory and co-ordinate signalling initiated by the CD40/CD154 and Fas/FasL pairs, respectively, leads the rescue of the functional B-cell repertoire and the elimination of the abnormal phenotype. The second is a gloomy scenario in which both the lack and the hyperexpression of either receptor/ligand pairs, are seen as equally deleterious.

Population depletion activates autonomous CD154-dependent survival in biopsylike Burkitt lymphoma cells.

Population size is governed through cells reacting to a variety of intrinsic and extrinsic cues. Tumors, while liberated from many of the homeostatic constraints placed on physiologic counterparts, can nonetheless remain subject to both social and environmental control. Burkitt lymphoma cells faithful to the biopsy phenotype were used to model the reliance of the colony, if any, on an inbuilt population sensor. Below a normally suicidal threshold number of cells, low picomolar quantities of exogenous CD40 ligand (CD40L/CD154) were found to sustain the clone without the discernible shift in phenotype that accompanies high CD40L encounter. Although CD154 was undetectable in populous cultures, message was induced as numbers became limiting. Correspondingly, attempts to neutralize endogenous CD40L activity failed to perturb cells at optimal densities but resulted in their marked decline as the critical threshold was approached. These data reveal an auto-inducible survival mechanism seemingly regulated through the monitoring of population size, a process somewhat akin to that of "quorum sensing" among gram-negative bacteria in which diffusible molecules provide a means of communication to coordinate gene expression with population density. This process could be activated as cells discern depletions in their community or when deprived of signals otherwise furnished within an appropriate environmental niche.

Phorbol esters and cAMP differentially regulate the expression of CD4 and CD8 in human thymocytes.

BACKGROUND: Intrathymic development and selection of the T lymphocyte repertoire is restricted by the interactions of the T cell antigen receptor and CD4 or CD8 co-receptors with self major histocompatibility complex molecules. Positive or negative selection depends on a tight regulatory control of CD4 and CD8 expression. Determining the intracellular signals that differentially regulate the expression of CD4 and CD8 is important to understand the mechanisms that are implicated in selection of single positive CD4+CD8- or CD4-CD8+. RESULTS: The present study shows that stimulation of human thymocytes by phorbol esters or cAMP result in a differential regulation of CD4 and CD8 expression, both at the mRNA and cell surface glycoprotein level. CONCLUSIONS: The differential regulation of CD4 and CD8 gene expression suggests that the selective activation of protein kinase C (PKC) and cAMP-dependent protein kinases (PKA) may be required for the selection of single positive CD4+CD8- and CD4-CD8+ cells during Intrathymic differentiation.