A gene-based SNP linkage map for pacific white shrimp, Litopenaeus vannamei.

Pacific white shrimp (Litopenaeus vannamei) are of particular economic importance to the global shrimp aquaculture industry. However, limited genomics information is available for the penaeid species. We utilized the limited public information available, mainly single nucleotide polymorphisms (SNPs) and expressed sequence tags, to discover markers for the construction of the first SNP genetic map for Pacific white shrimp. In total, 1344 putative SNPs were discovered, and out of 825 SNPs genotyped, 418 SNP markers from 347 contigs were mapped onto 45 sex-averaged linkage groups, with approximate coverage of 2071 and 2130 cm for the female and male maps, respectively. The average-squared correlation coefficient (r(2)), a measure of linkage disequilibrium, for markers located more than 50 cm apart on the same linkage group, was 0.15. Levels of r(2) increased with decreasing inter-marker distance from approximately 80 cm, and increased more rapidly from approximately 30 cm. A QTL for shrimp gender was mapped on linkage group 13. Comparative mapping to model organisms, Daphnia pulex and Drosophila melanogaster, revealed extensive rearrangement of genome architecture for L. vannamei, and that L. vannamei was more related to Daphnia pulex. This SNP genetic map lays the foundation for future shrimp genomics studies, especially the identification of genetic markers or regions for economically important traits.

Genetic Differentiation of Colombian Populations of Anopheles darlingi Root (Diptera: Culicidae).

Anopheles darlingi Root is a primary vector of malaria in the neotropic region, a species not just highly anthropophilic but very efficient in transmitting Plasmodium species and considered the most important vector in the Amazon region. The main goal of this study was to determine the genetic structure of the A. darlingi populations using microsatellites (STR) in western and eastern regions of Colombia. DNA extraction was done with the cited protocol of band using the Genomic Prep™ cell and tissue isolation commercial kits. We used the STR reported by Conn et al (Mol Ecol Notes 1: 223-225, 2001). The analysis with STR proved there was a high genetic diversity and significant alterations of the Hardy-Weinberg equilibrium. The greatest genetic diversity was recorded in Mitu (Vaupes) (Na = 14, Ho = 0.520). The lowest was in Pueblo Nuevo (Cordoba) (Na = 12, Ho = 0.457). The eastern region and the Mitu (Vaupes) populations presented the highest number of primer alleles (Ap = 30; Ap = 13; Ap = 9), with variations between 0.010 and 0.097. The AMOVA revealed that the whole population underwent moderate genetic differentiation (F ST = 0.063, p < 0.05). The same differentiation was noticed (0.06 < F ST > 0.06, p < 0.05) with five of the six populations included in this job, and there was a low differentiation in the Las Margaritas (Santander) area (F ST = 0.02s3, p < 0.05). Our results suggest a slight positive correlation, which does not show a statistical significance between the geographic and genetic distances, probably suggesting that the moderate genetic differentiation found between pairs of populations does not need to be explained for the hypothesis of separation by distance.

COVID-19associated exfoliative shock syndrome / Síndrome de shock exfoliativo por covid-19

RESUMEN El síndrome de shock exfoliativo(SSE) asociado a COVID- 19 es una enfermedad recientemente descrita con características superpuestas de síndrome de shock tóxico (SST) y síndrome de la piel escaldada estafilocócica (SSSS, por sus siglas en inglés). Clínicamente se presenta con fiebre, hipotensión y erupción cutánea exfoliativa.Se expone un caso en donde las lesiones cutáneas por COVID-19 precedieron a las manifestaciones respiratorias.

ABSTRACT The exfoliative shock syndrome (ESS) associated with COVID-19 is a recently described disease with overlapping features of toxic shock syndrome (TSS) and staphylococcal scalded skin syndrome(SSSS). Clinically it presents with fever, hypotension, and exfoliative skin rash. A case is presented in which the skin lesions by COVID-19 preceded the respiratory manifestations.

Manejo anestésico de resección de quiste de vallécula en neonato. A propósito de un caso / Anesthetic management of vallecular cyst resection in neonate. A case report

Difficult airway management is one of the most important challenges an anesthesiologist faces. It is due to the high morbidity and mortality that it entails. The challenge is even greater if the patient is a newborn. For this reason, we should have different strategies that allow us to anticipate and treat possible complications derived from the procedure. In this case, we present a newborn with vallecular cyst and respiratory distress who is admitted for cyst resection. The gold-standard in anticipated difficult airway management is the fibrobronchoscope. We decided to perform an alternative management by means of orotracheal intubation with videolaryngoscope (Glydescope®) in spontaneous ventilation

El manejo de una vía aérea difícil es uno de los retos más importantes a los que puede enfrentarse un anestesiólogo debido a la elevada morbimortalidad que conlleva. El reto aún es mayor si el paciente es un neonato. Por este motivo, debemos contar con diferentes estrategias que permitan anticipar y poder tratar las posibles complicaciones derivadas del procedimiento. En este caso, presentamos un neonato con quiste de vallécula con clínica de trabajo respiratorio que es admitido para cirugía de exéresis del quiste. El gold standard en el manejo de una vía aérea difícil conocida es el fibrobroncoscopio. Nosotros decidimos realizar un manejo anestésico alternativo mediante intubación orotraqueal con videolaringoscopio (Glydescope®) en ventilación espontánea.

In vitro characterization of the hematopoietic system in pediatric patients with acute lymphoblastic leukemia.

Acute lymphoblastic leukemia (ALL) has been recognized as a hematologic neoplasia that originates at the level of a primitive lymphoid stem/progenitor cell. To date, however, the biology of the hematopoietic system in this disorder is still not fully understood. In the present study, we have determined the progenitor cell content (including myeloid, erythroid and multipotent progenitors) in 14 children with ALL and followed the proliferation kinetics of these cells in Dexter-type long-term marrow cultures. We have also characterized some aspects related to the composition and function of the hematopoietic microenvironment developed in vitro. All patients included in this study showed extremely reduced levels of progenitor cells (median of 6.2% of the levels found in normal marrow). Proliferation of these cells in long-term cultures was markedly deficient, since they showed very low numbers - compared to normal cultures - and reached undetectable levels after only a few weeks. Regarding the microenvironment developed in vitro, whereas normal marrow samples contained a median of 8 fibroblastic progenitors/10(5) marrow cells and the stromal cell layers developed in culture contained a median of 341000 adherent cells per well, ALL marrow samples showed no fibroblastic progenitors and the numbers of adherent cells were 21% of those in normal cultures. Interestingly, the levels of TNFalpha and IL-6 in ALL culture supernatants were significantly increased, compared to normal cultures. Bone marrow samples from all 14 children were also analyzed once they reached a complete clinical and hematological remission. Myeloid, erythroid and multipotent progenitor cell levels were significantly increased, compared to patients at diagnosis, and proliferation of myeloid progenitors in long-term cultures was also improved. In contrast, proliferation of erythroid progenitors showed no difference to that in cultures from patients at diagnosis. The numbers of fibroblastic progenitors and adherent cells were significantly increased, compared to patients at diagnosis, and TNFalpha and IL-6 levels returned to normal. In summary, in the present study, we have demonstrated significant in vitro alterations of the hematopoietic system, both in terms of its composition and function, in pediatric patients with ALL. Importantly, most of these alterations are corrected, at least partially, after chemotherapy.

An outbreak of plague including cases with probable pneumonic infection, Ecuador, 1998.

During February and March of 1998, 12 sudden deaths were reported among residents of a high-Andean community in Ecuador. All 12 fatalities were members of the same extended family and some had apparent exposure to sick guinea-pigs. Following an initial investigation by public health officials, an additional death was reported in a nearby community in April, also associated with exposure to sick guinea-pigs. Blood samples from humans, dogs, and a rodent were tested for antibody to the F1 antigen of Yersinia pestis by passive haemagglutination assay. Tissue from rodents was subjected to direct fluorescent antibody staining using fluorescein-labelled monoclonal antibody to Y. pestis F1 antigen. Formalin-fixed specimens from the 2 autopsies were evaluated using a 2-step alkaline phosphatase immunoassay with a monoclonal antibody to Y. pestis F1 antigen, and tissues that had not been embedded in paraffin were tested for the presence of DNA encoding the F1 structural antigen by polymerase chain reaction. Serological evaluation of close contacts of the fatalities revealed positive titres to F1 antigen of Y. pestis, the aetiological agent of plague, in 3 contacts from the first community and 1 from the second. Immunohistochemical staining of tissues collected from 2 of the fatalities provided evidence that both had pneumonic plague. Five of 14 dogs found in the communities were seropositive for plague antibody, providing evidence of a recent epizootic plague in the area.

[Polymorphism of the gene of vitamin D receptor and bone mineral density in postmenopausal women]. / Polimorfismo del gen del receptor de la vitamina D y densidad mineral ósea en mujeres posmenopáusicas.

BACKGROUND: Conflicting results have been reported on the association between restriction fragment length polymorphism at the vitamin D receptor (VDR) gene locus and bone mineral density (BMD). Population differences in environmental factors, such as calcium intake and calcidiol levels which have strong influence in BMD, may alter this association. PATIENTS AND METHODS: We analyzed the Bsml RFLP at the eight introm of the VDR gene in a population sample (n = 204) of postmenopausal Spanish women aged 50-65 years being seen clinically and studied calcium intake (dietetic questionnaire) and biochemical parameters (PTH and calcidiol). In parallel bone densitometry were measured in lumbar spine and proximal femur. RESULTS: We identified low BMD of the proximal femur in the BB group. This effect was not observed at other body locations. The calcium intake was lees than 500 mg/day in 60% of the studied population as calcidiol levels were lower than 10 ng/l in 36% of it. The total group population with normal calcium intake (> 1,000 mg/day) showed higher BMD (proximal femur and spine) than the group with low calcium intake, this variation not being observed in group BB alleles. Interestingly, we observed significant differences in BMD proximal femur between genotype groups BB versus Bb + bb when calcidiol levels were < 10 ng/l. Moreover, within the BB subgroup, those subjects with normal calcidiol levels have higher proximal femur BMD compared with those with low calcidiol levels. CONCLUSIONS: Our results indicate an effect of the VDR genotype on BMD proximal femur which is clearly influenced by calcium intake and calcidiol serum levels.

[Lawsuits against gynecologists-obstetricians in the National Commission of Medical Arbitration]. / Demandas contra ginecoobstetras en la Comisión Nacional de Arbitraje Médico.

UNLABELLED: The study of claims motives is relevant since Obstetrics and Gynecology (O&G) is one of the specialties that it is involved with greater frequency in demands in the Medical Arbitration National Commission (CONAMED). OBJECTIVE: In order to know the causes by those which the patients have attended to be complained of the attention provided by a Obstetrician/Gynecologist (OG). MATERIAL AND METHODS: Between June 1, 1996, and November 30, 1998, there were 635 demands reported to the CONAMED for obstetrical or gynecological care, 375 (60%) derived from obstetrical care; claims were grouped by motives and for stage of the attention in which they were originated. RESULTS: There were more than 17 different causes of claim, the most frequent were: complications (20%), care not opportune (16%), accidents (15%), improper actions (15%), diagnostic error (10%). Claims were derived from: Surgical procedures (45%), medical treatment (27%) and diagnosis (13%). 15 (2.4%) of claims were generated from vaginal delivery, but only 9 (1.4%) were obstetrician related. Obstetric surgical procedures account for 23% of claims. CONCLUSIONS: OG are more claimed because work harder, more than one million vaginal and more than 500,000 cesarean deliveries are performed yearly in Mexico. The rates of reported claims are low, one per 10,000 deliveries attended; one per 275,000 vaginal deliveries, one per 8,400 obstetric surgical procedures. It all points OG claims as a probabilistic problem, risk related.

[Puerperal infection. Analysis of 618 cases]. / Infección puerperal. Análisis de 618 casos.

From September 1993 to March 1995 a prospective, descriptive study was performed at Obstetrical Department of the General Hospital 2A the Mexican Institute of Social Security. An attempt to know the real puerperal infection incidence in our own hospital to be able to make hypothesis and take specific measures in puerperal infection control. Dairy account of interesting data of cases under inclusion criteria. Entering data in personal computer. Graphics and analysis were accomplished using Lotus 123, Statgraphics, EPI-6 of CDC and Freelance computational programs. Search of central tendency measures were performed, (media, median, mode, standard deviation). Odds ratio and relative risk were calculated, including hospitalization time and its temporary variation to data cross. X square and pi were including hospitalization time and its temporary variation to data cross. X square and pi were determined to statistic validates. The cumulated rate of general puerperal infection were 1.2%. By stratification, the cumulated rate of infection after cesarean section, vaginal delivery and miscarriage were 5.4%, 0.8% and 0.3%, respectively. There was predominance of infection after cesarean section, over infection after vaginal delivery and after miscarriage. (monthly media of 24.6, 7.3 and 0.47, respectively). The puerperal infection was present principally in primiparous and in patients with one previous cesarean section. The patients in which the termination of pregnancy was by cesarean section, (0.015 infection cumulated incidence), had an infection risk 5.76 and 18.66 times greater than the patients with vaginal delivery and miscarriage. (Relative risk of 6.76 and 19.66) The site of puerperal infection was implicated in combinations or isolated, under nine clinical situation. The five most frequent clinical situation, between these nine, in incidence order from major to minor were the following: Endometritis alone, Endometritis combined with wound abscess. Endometritis with urinary infection, complicated endometritis, (sub vesical abscess, parametritis, peritonitis, salpingitis), and wound abscess alone). The greater hospitalization time was present in cases of complicated endometritis followed by wound abscess alone or combined. Complicated endometritis, (incidence 0.0010), compel us to hysterectomy in 15 cases. No death was registered among the patients with puerperal infection studied.

[Evaluation of Mexican biomedical journals]. / La evaluación de las revistas biomédicas mexicanas.

We present the evaluation procedures of Biomedical Journals, performed by the Journal Committee of the Centro Nacional de Información y Documentación sobre Salud (CENIDS) for the preparation of CR-ROM ARTEMISA 2 (Edited health information articles in Mexico), which contains a database of the complete text of articles appearing in the journals of the highest quality published in Mexico.

[Proposal for Recertification of Medical Specialties in Colombia]. / Propuesta para la recertificación de las especialidades médicas en Colombia.

This article gives a brief overview of the aspects that justify implementing a recertification of doctors. After a description of this process in the countries where it has the most experience, the advantages of having a recertification process and the criticism of the system is also discussed. Finally, the creation of the Council on Accreditation and Recertification Colombian Medical Specialist professionals (CAMEC, in Spanish), as a product of the work of the Colombian Association of Scientific Societies, and also the draft decree of the national government is proposed in the creation of the Integrated System for Continuing Education and Continuing Professional Development in Health (SFCTHS, in Spanish).

[Comprehensive Assessment of Psychiatric Residents: An Addition to the Program Admission Process]. / Evaluación integral de residentes de psiquiatría: un complemento del proceso de admisión al programa.

The training of medical specialists is a long and complex process. Its purpose is to guarantee the society that they are the right professionals to meet the health needs of the population. The first step to ensure this objective is the admission process. In psychiatry this process, monitoring resident students and the criteria for each one are different in each country. Admission in Colombia is a heterogeneous process, not standardized, which varies greatly from one university to another, even between private and public universities. At the National University of Colombia, the admissions process is handled by the Admissions Office and includes: a written test for which you must obtain a minimum score, a resume rating and an interview. The Teaching Committee and the Department of Psychiatry considered the admission procedure in general to be good, but in need of refinement. Due to the experience of some teachers and given the current rules, a "comprehensive assessment" for master and doctoral students was required and in 1996 it was decided that this method of assessment for admission to a specialization in Psychiatry would serve to complement the admission process. The article describes the experience of the process and its outcomes, strengths and weaknesses.

Indicaciones, hallazgos broncoscópicos y mortalidad en pacientes pediátricos con traqueostomía en un hospital de México / Indications, bronchoscopic findings and mortality in pediatric patients with tracheostomy in a Mexican hospital

INTRODUCTION. Tracheostomy is an old surgical procedure, wich is currwently performed, in pediatric patients. Bronchoscopy is an effective procedure to follow these patients as it reveals data that can not be obtained with other methods. The aim of this study was to determine indications, bronchoscopic findings and mortality in patients with tracheostomy at the Hospital del Niño Morelense (HNM). in addiction, we sought to detail the role of bronchoscopy in patients follow-up. METHODS. Observational, descriptive and transversal study. We reviewed the records of the patients with tracheostomy during 5 years looking for bronchoscopic findings. RESULTS: The main indication for tracheostomy was prolonged ventilation (74.4 percent). The main bronchoscopic diagnoses were subglottic stenosis (20 percent), granulomas in the trachea (70 percent), and in bronchi abnormal secretions (70 percent) mortality was 32.5 percent. CONCLUSIONS: The main indication for tracheostomy is prolonged ventuilation. Mortality in children with tracheostomy depends mainly on the underlying pathology. Bronchospy is useful for monitoring the child with a tracheostomy

INTRODUCCIÓN. La traqueostomía es un procedimiento quirúrgico antiguo, que se realiza en pediatría cada vez con mayor frecuencia. La broncoscopía es un procedimiento efectivo para el seguimiento del paciente con traqueostomía ya que nos revela datos que no se pueden obtener con otros métodos. Se tuvo como objetios determinar indicaciones, hallazgos broncoscópicos y mortalidad en pacientes con traqueostomía, en el Hospital del Niño Morelense (HNM). MÉTODOS. Estudio observacional, descriptivo y transversal. Se revisaron los expedientes de los pacientes a quienes se les realizó traqueostomía durante 5 años buscando hallazgos broncoscópicos. RESULTADOS. La principal indicación de traqueostomía fue la ventilación prolongada (74 por ciento). Los principales diagnósticos broncoscópicos fueron: estenosis subglótica (20 por ciento), granulomas en tráquea (70 por ciento) y en bronquios secreciones anormales (70 por ciento). La mortalidad fue de 32.5 por ciento. CONCLUSIONES. la principal indicación para traqueostomía fue la ventilación prolongada. la mortalidad en niños con traqueostomía depende principalmente de la patología subyacente. La broncoscopía es útil para el seguimiento del niño con traqueostomía

Effects of genotype, level of supplementation, and organic chromium on growth performance, carcass, and meat traits grazing lambs.

The aim of the present study was to evaluate the effects of Suffolk×Dorper (SD) and Rambouillet (R) lamb genotypes, dietary supplementation, and organic chromium on growth performance, carcass, and meat traits in male lambs grazing ryegrass pasture. SD lambs had heavier cold carcass (HCW) and better carcass yield (CY) and rib eye area at 12th rib (RA) than R lambs; R had larger legs. Feed supplement increased average daily weight gain (ADG), slaughter live weight (SLW), hot carcass weight (HCW) and cold carcass weight (CCW), carcass yield, carcass length (CL), leg perimeter (LP), major thorax width (MTW), minor thorax width (MiTW), rib eye area and dorsal fat at 12th rib (DF12), and also decreased meat moisture. Organic chromium reduced dorsal fat at 12th rib and meat fat content.

Propuesta para la recertificación de las especialidades médicas en Colombia / Proposal for Recertification of Medical Specialties in Colombia

Este artículo hace una breve revisión de los aspectos que justifican implementar un proceso de recertificación de los médicos. Luego hace una descripción de este proceso en los países donde se cuenta con mayor experiencia y de las ventajas de tener un proceso de recertificación, así como de las críticas hacia el sistema. Finalmente, se presenta la creación del Consejo Colombiano de Acreditación y Recertificación Médica, de Especialistas y Profesionales Afines (CAMEC), como producto del trabajo de la Asociación Colombiana de Sociedades Científicas, y también el borrador del decreto del gobierno nacional en el que se propone la creación del Sistema Integrado para la Educación Continuada y el Desarrollo Profesional Continuo en Salud (SFCTHS).

This article gives a brief overview of the aspects that justify implementing a recertification of doctors. After a description of this process in the countries where it has the most experience, the advantages of having a recertification process and the criticism of the system is also discussed. Finally, the creation of the Council on Accreditation and Recertification Colombian Medical Specialist professionals (CAMEC, in Spanish), as a product of the work of the Colombian Association of Scientific Societies, and also the draft decree of the national government is proposed in the creation of the Integrated System for Continuing Education and Continuing Professional Development in Health (SFCTHS, in Spanish).

Evaluación integral de residentes de psiquiatría: un complemento del proceso de admisión al programa / Comprehensive Assessment of Psychiatric Residents: An Addition to the Program Admission Process

La formación de especialistas médicos es un proceso largo y complejo, cuyo objetivo primordial es garantizarle a la sociedad que sean profesionales idóneos para atender las necesidades de salud de la población. El primer paso para garantizar este objetivo es el proceso de admisión. En psiquiatría, como en otras especialidades, este proceso, el seguimiento a los residentes y los criterios utilizados para cada uno, son diferentes en cada país. En Colombia la admisión es un proceso heterogéneo, no estandarizado, que varía de manera significativa de una universidad a otra, incluso entre las mismas instituciones pertenecientes al sector público y entre aquellas de carácter privado. En la Universidad Nacional de Colombia el proceso de admisión está centralizado en la Oficina de Admisiones e incluye un examen escrito, en el que se debe obtener la puntuación estipulada como punto de corte o más, la calificación de la hoja de vida y una entrevista. El Comité Docente del Departamento de Psiquiatría consideraba que el procedimiento de admisión en general era bueno, pero, al igual que todo proceso de selección, imperfecto. Con base en esta consideración, la experiencia de algunos docentes y apoyados en la normatividad vigente que exigía una "evaluación integral" para los estudiantes de maestría y doctorado, se decidió, a partir de 1996, establecer esta modalidad de evaluación para los admitidos a la especialización en Psiquiatría, con el objeto de servir como complemento al proceso de admisión. El artículo describe la experiencia del proceso y sus resultados, fortalezas y debilidades.

The training of medical specialists is a long and complex process. Its purpose is to guarantee the society that they are the right professionals to meet the health needs of the population. The first step to ensure this objective is the admission process. In psychiatry this process, monitoring resident students and the criteria for each one are different in each country. Admission in Colombia is a heterogeneous process, not standardized, which varies greatly from one university to another, even between private and public universities. At the National University of Colombia, the admissions process is hand-led by the Admissions Office and includes: a written test for which you must obtain a minimum score, a resume rating and an interview. The Teaching Committee and the Department of Psychiatry considered the admission procedure in general to be good, but in need of refinement. Due to the experience of some teachers and given the current rules, a "comprehensive assessment" for master and doctoral students was required and in 1996 it was decided that this method of assessment for admission to a specialization in Psychiatry would serve to complement the admission process. The article describes the experience of the process and its outcomes, strengths and weaknesses.

Comparación de dos estrategias para la enseñanza de un módulo de entrevista clínica en estudiantes de pregrado de medicina / Comparison of two strategies for the teaching of a clinical interview module in undergraduate medical students

Introducción: Los cambios en la práctica médica limitan la disponibilidad de pacientes y han generado escenarios de enseñanza de la medicina cada vez más escasos. Por ello se ha hecho necesario desarrollar métodos multimedia en la educación médica. Materiales y métodos: Se diseñó un ensayo controlado, abierto, no aleatorizado para comparar dos métodos de enseñanza: clase magistral y una herramienta multimedia, dentro del proceso de enseñanza de un módulo de entrevista clínica en estudiantes de pregrado de medicina de una universidad pública y una privada. Resultados: 268 estudiantes, 156 que recibieron clase magistral y 112 que recibieron el material multimedia, participaron en el estudio. El promedio de las calificaciones obtenidas en la evaluación por los estudiantes que usaron el material multimedia fue significativamente más alto que quienes tomaron la clase magistral. Además, aprobar u obtener una calificación igual o mayor a 3,5 fue aproximadamente dos veces mayor en los que usaron la herramienta multimedia que en los que asistieron a clase. Conclusiones: La multimedia es una herramienta útil y eficiente para la enseñanza de la entrevista a estudiantes de medicina...

Introduction: Changes in medical practice have limited the availability of patients and scenarios for medical education, resulting in the need to develop multimedia tools for this purpose. Methods: This is a controlled, open, nonrandomized study comparing two teaching methods: Lecture vs. a multimedia tool, in the process of teaching a clinical interview module to undergraduate medical students from a public and a private universities. Results: 268 students participated in the study, 156 received a standard lecture and 112 multimedia material. The average scores on the examinations of students using the multimedia material were significantly higher than those who took the standard lecture. Approximately twice as many of the students using the multimedia tool obtained a passing score of 3.5 or higher when compared to those who attended the lecture. Conclusions: Multimedia is a useful and efficient tool for teaching the clinical interview to medical students...

Growth kinetics of progenitor cell-enriched hematopoietic cell populations in long-term liquid cultures under continuous removal of mature cells.

BACKGROUND: During long-term culture of primitive hematopoietic cells large numbers of mature cells are generated that, on the one hand, consume nutrients and cytokines present in the medium and, on the other hand, may produce or elicit the production of soluble factors that limit the growth of primitive cells. Thus it is possible that under standard culture conditions hematopoietic stem and progenitor cells are unable to display their true proliferation and expansion potentials. METHODS: Hematopoietic cell populations, enriched for CD34+ cells, were obtained from both umbilical cord blood (UCB) and mobilized peripheral blood (MPB), and cultured in cytokine-supplemented liquid culture, under continuous removal of mature cells by means of weekly re-selection of primitive, lineage-negative (Lin-) cells. Proliferation and expansion capacities of such cells were determined weekly for a 42-day culture period. RESULTS: As expected, based on our previous studies in standard liquid cultures, throughout the culture period there was a continuous decrease in the proportion of progenitor cells; however, after every re-selection on days 7, 14 and 21, there was a significant enrichment for both CD34+ cells and colony-forming cells (CFC). As a result of such an enrichment, the cumulative increase in the numbers of total cells and CFC in cultures with two, three or four selections was significantly higher than the increments observed in standard cultures, in which only a single selection was performed on day 0. Cultures of UCB cells showed consistently higher levels of both total cells and CFC than cultures of MPB cells. DISCUSSION: Taken together, these results indicate that continuous removal of mature cells from liquid cultures of primitive progenitors results in higher increments in the levels of both total cells and CFC.