An experimental inter-expert telepathology network using static imaging.

AIMS: To set up a network for remote consultation using static imaging telepathology via Internet connection between pathologists in different European countries, and to collect some numerical and subjective impressions on the usefulness of this form of telepathology. METHODS: A static image remote consultation network between 11 pathologists in nine European countries was set up; all pathologists were equipped with the same telepathology system. The pathologists formed three subject oriented subgroups concerned with prostate, melanoma, and soft tissue sarcoma pathology. Each pathologist sent and received a small number of cases, and data on each case were collected and analysed. The whole experiment was controlled through a World Wide Web site. RESULTS: A total of 56 case consultations on 34 different cases were exchanged. The average case document contained seven images, and contained 1.97 Mbytes of data. For cases in which data were recorded, average case preparation and remote consultation time was 55 minutes and 9.2 minutes, respectively. Transmission times averaged 3.9 minutes. In subjective impressions, reservations were expressed in several cases regarding the confidence that could be given to the diagnosis from the images presented. CONCLUSIONS: Remote consultation by telepathology via the Internet is now technically feasible and reasonably user friendly, but is only suitable as a method of disease diagnosis in some cases.

Quantitation of AgNORs by flow versus image cytometry.

AgNORs are nucleolar proteins that interact specifically with silver salts. The size of silver precipitates measured by image analysis (ICM) in cycling cells proved to be inversely proportional to the cell cycle time and provided a significant correlation with prognosis for a large spectrum of cancers. Because ICM is time-consuming and poorly reproducible among laboratories using different imaging settings, this article presents a new approach to AgNOR quantitation based on flow cytometry (FCM). We report that silver precipitates caused a great decrease in the forward scattered light and that this effect was correlated with the AgNOR's relative area as measured by ICM. These results were confirmed by measuring cell lines having different cell cycle durations. Moreover, double staining using APase-Fast red fluorescence to reveal the Ki-67/MIB 1 antigen of cycling cells and silver nitrate to stain the AgNORs was successfully analyzed by FCM. The procedure makes it possible, for the first time, to validly and rapidly compare the growth fraction and cycling speed of partially proliferating cell populations, such as tumors.

Correlation between silver-stained nucleolar organizer region area and cell cycle time.

BACKGROUND: The relationship between the population doubling time and the quantity of silver-stained nucleolar organizer region (AgNOR) interphase proteins was studied in cell culture at three different temperatures used to modulate the cell cycle duration. METHODS: After MIB 1 and AgNOR combined staining, the quantity of AgNOR proteins was measured in cycling cells by image cytometry. RESULTS: Among the several parameters calculated, the AgNOR relative area showed a strong correlation with the changes of the population doubling time induced by different temperatures. CONCLUSIONS: The results support the hypothesis that the cell cycle time and the size of the ribogenesis machinery are coregulated and that measurements of AgNORs can thus be used as a static evaluation of the cell cycle duration in arbitrary units.

A proliferation control network model: the simulation of two-dimensional epithelial homeostasis.

Despite the recent progress in the description of the molecular mechanisms of proliferation and differentiation controls in vitro, the regulation of the homeostasis of normal stratified epithelia remains unclear in vivo. Computer simulation represents a powerful tool to investigate the complex field of cell proliferation regulation networks. It provides huge computation capabilities to test, in a dynamic in silico context, hypotheses about the many pathways and feedback loops involved in cell growth and proliferation controls. Our approach combines a model of cell proliferation and a spatial representation of cells in 2D using the Voronoi graph. The cell proliferation model includes intracellular (cyclins, Cyclin Dependent Kinases - CDKs. Retinoblastoma protein - Rb, CDK inhibitors) and extracellular controls (growth and differentiation factors, integrins). The Voronoi graph associates a polygon with every cell and the set of these polygons defines the tissue architecture. Thus, the model provides a quantitative model of extracellular signals and cell motility as a function of the neighborhood during time dependent simulations. The 2D simulations illustrate the influence of the microenvironment on cell proliferation in basal layers of stratified epithelia and of differential adherence in keratinocytes differentiation and related upward migration. Our results particularly show the role of CDK inhibitors (mainly the protein p27) in the Rb dependent control pathway of the transition from the G1 to S phase of the cell cycle.

Regional and international integrated telemedicine network for organ transplant (HC 4028 & IN 4028 European Commission DGXIII).

A substantial portion of future medical practice will depend greatly on improved collaboration between the providers throughout the healthcare sector, and effective sharing of data and expertise by different healthcare professionals. In organ transplant it is a rule, donor organs are matched to recipients via national or multinational organ-sharing organizations. Only through close co-operation between transplant surgeons, immunologists, nephrologists, pathologists, radiologists and other physicians could one increase the efficiency of organ transplantation. Information technology (IT) has become an inevitable and inherent part of transplantation medicine. The RETRANSPLANT project interfaces and integrates IT from the European Union Fourth Framework projects to support the development of regional organ transplant information networks in Central Europe.

Improving accuracy in the grading of renal cell carcinoma by combining the quantitative description of chromatin pattern with the quantitative determination of cell kinetic parameters.

The determination of grade and stage in renal cell carcinomas (RCCs) often fails to predict the actual clinical outcome for individual patients. The aim of the present work was to investigate whether it is possible to significantly improve the prognostic accuracy of the grading system by using the combination of two independent computer-assisted microscopy techniques. The first technique relates to the quantitative description of morphonuclear and nuclear DNA content features by means of the image analysis of Feulgen-stained cell nuclei, and the second quantitatively characterizes tumor growth by means of different cell kinetic parameters. These parameters consist of a duplication of a time-related parameter determined by means of the technique of using silver-stained proteins in interphase nucleolar organizer regions (AgNOR), a proliferation index determined by means of MIB-1 immunohistochemistry, and an apoptotic index determined by means of the terminal dUTP nick end labeling technique. The prognostic value of these quantitative features was investigated in a series of 60 RCCs. The quantitative analysis of Feulgen-stained nuclei made it possible to identify subgroups of patients with significantly different prognoses in both grade II and grade III RCCs. We labeled the RCCs associated with the most favorable prognoses as grade II- and III- and those with the least favorable ones as grade II+ and III+. The two most important kinetic variables to identify patients with different clinical outcomes were the MIB-1 index and the mean AgNOR area in the MIB-1-positive cells. Three significantly different survival curves were obtained for the 53 grade II and III RCC patients. Our results show that conventional RCC grading can be significantly improved by the quantitative analysis of Feulgen-stained nuclei, by cell kinetic parameter determination, and, more importantly, by combining the proliferation index with the mean AgNOR area parameter.

External quality assessment of trans-European multicentre antigen determinations (enzyme-linked immunosorbent assay) of urokinase-type plasminogen activator (uPA) and its type 1 inhibitor (PAI-1) in human breast cancer tissue extracts.

High levels of urokinase-type plasminogen activator (uPA) and plasminogen activator inhibitor type 1 (PAI-1) in breast cancer tissue extracts have been associated with rapid disease progression. In these studies, different enzyme-linked immunosorbent assay (ELISA) kits have been applied for the quantification, and consequently the ranges of uPA and PAI-1 levels reported differ considerably. Therefore, the Receptor and Biomarker Study Group (RBSG) of the European Organization for Research and Treatment of Cancer (EORTC) and a consortium of the BIOMED-1 project 'Clinical Relevance of Proteases in Tumor Invasion and Metastasis' initiated three collaborative between-laboratory assessment trials aimed at controlling uPA and PAI-1 antigen analyses. For this purpose, two control preparations were produced from different sources: pooled human breast cancer specimens (QC-240893) and human breast cancer xenografts raised in nude mice (QC-101094). The lyophilized preparations were stable for prolonged times (at least 3 and 27 months respectively) at 4 degrees C. Furthermore, a good parallelism following dilution was found for uPA and PAI-1. The data from QC trial no. 1 clearly indicated that acceptable between-laboratory coefficients of variation (CVs) for uPA (<8.2%) and PAI-1 (<16.6%) in QC-240893 could be achieved when the same type of ELISA kit (American Diagnostica) was used. From the second trial, in which ten EORTC laboratories each received five identical lyophilized QC-101094 samples, it appeared that the within-laboratory variations for uPA and PAI-1 determinations obtained by 'experienced' laboratories were lower (<12.9%) than those from non-experienced laboratories (<36.4%). In a third QC trial, five BIOMED-1 laboratories, all of which employed ELISA procedures for uPA and PAI-1, participated in six subsequent quality assessment rounds receiving five samples of QC-101094. Although for each laboratory the within-run CVs for uPA as well as for PAI-1 were low (<7.8%), the between-run CVs were found to be considerably higher (up to 56.2% for uPA and to 27.6% for PAI-1). Consequently, because of the different ELISA formats used, the absolute analyte values measured in the different laboratories varied substantially. The use of 'common external standards' in the different ELISAs resulted in a significant reduction of the between-laboratory CVs from 61.3% to 15.7% (uPA) and from 42.1% to 19.1% (PAI-1). The present data demonstrate that in multicentre studies the same ELISA kit should be used, and that external quality assurance (QA) is mandatory. Furthermore, it appears from the present study that standardization of the protein assay as a tissular parameter is imperative.

Digital imagery/telecytology. International Academy of Cytology Task Force summary. Diagnostic Cytology Towards the 21st Century: An International Expert Conference and Tutorial.

ISSUES: Optical digital imaging and its related technologies have applications in cytopathology that encompass training and education, image analysis, diagnosis, report documentation and archiving, and telecommunications. Telecytology involves the use of telecommunications to transmit cytology images for the purposes of diagnosis, consultation or education. This working paper provides a mainly informational overview of optical digital imaging and summarizes current technologic resources and applications and some of the ethical and legal implications of the use of these new technologies in cytopathology. CONSENSUS POSITION: Computer hardware standards for optical digital imagery will continue to be driven mainly by commercial interests and nonmedical imperatives, but professional organizations can play a valuable role in developing recommendations or standards for digital image sampling, documentation, archiving, authenticity safeguards and teleconsultation protocols; in addressing patient confidentiality and ethical, legal and informed consent issues; and in providing support for quality assurance and standardization of digital image-based testing. There is some evidence that high levels of accuracy for telepathology diagnosis can be achieved using existing dynamic systems, which may also be applicable to telecytology consultation. Static systems for both telepathology and telecytology, which have the advantage of considerably lower cost, appear to have lower levels of accuracy. Laboratories that maintain digital image databases should adopt practices and protocols that ensure patient confidentiality. Individuals participating in telecommunication of digital images for diagnosis should be properly qualified, meet licensing requirements and use procedures that protect patient confidentiality. Such individuals should be cognizant of the limitations of the technology and employ quality assurance practices that ensure the validity and accuracy of each consultation. Even in an informal teleconsultation setting one should define the extent of participation and be mindful of potential malpractice liability. ONGOING ISSUES: Digital imagery applications will continue to present new opportunities and challenges. Position papers such as this are directed toward assisting the profession to stay informed and in control of these applications in the laboratory. Telecytology is an area in particular need of studies of good quality to provide data on factors affecting accuracy. New technologic approaches to addressing the issue of selective sampling in static image consultation are needed. The use of artificial intelligence software as an adjunct to enhance the accuracy and reproducibility of cytologic diagnosis of digital images in routine and consultation settings deserves to be pursued. Other telecytology-related issues that require clarification and the adoption of workable guidelines include interstate licensure and protocols to define malpractice liability.

Identifying cytologic characteristics and grading endocervical columnar cell abnormalities. A study aided by high-definition television.

OBJECTIVE: To test the ability of cytotechnologists to recognize and accurately interpret selected architectural, cellular and nuclear features presented on a high-definition television (HDTV) and to make a reliable diagnosis with HDTV. STUDY DESIGN: A total of 1,122 features considered diagnostic of different endocervical columnar cell abnormalities were selected from 50 smears from 48 women with the help of a motor-driven-stage microscope by five observers who had knowledge of the final diagnosis. The selected and stored features were presented on an HDTV and evaluated in five successive sessions without knowledge of the final diagnosis. RESULTS: Specific types of features were correctly identified in a high number of cases. Considerable interobserver variability was demonstrated in the scoring of grades of expression of features. Overrated and under-rated monitor diagnoses were related to overvalued and undervalued features. From a group of 437 images that were correctly diagnosed by four or five observers, five features proved to be highly related to the correct diagnosis. CONCLUSION: Observers were capable of making a reliable diagnosis on features, selected by other observers, when presented on an HDTV. An overall correct diagnosis was made in 93% of cases.

An evaluation of 'rapid review' as a method of quality control of cervical smears using the AxioHOME microscope.

One method of quality control which has recently been recommended by professional bodies in the UK is the 'rapid review' method. This involves the microscopic 30 s review of all negative cervical smears with the intention of flagging potential missed abnormalities. Although it has been suggested that rapid review is better than 10% random rescreening of negative smears, the efficiency and efficacy of this method of quality control have not been thoroughly evaluated. We have used the AxioHOME system, which can record the area of a slide covered and the screening time, to investigate slide coverage during rapid review quality control, as performed by 15 cytoscreeners and MLSOs reviewing a test set of 22 slides each. The test set comprised 18 negative slides, three positive slides, and one unsatisfactory slide. We have recorded two distinct methods of rapid review in use amongst cytotechnologists, the step method and the whole slide method. The data show that rapid review takes longer on average than the recommended 30 s, the mean screening times being 76 s and 82 s for the step and whole slide methods, respectively. Abnormal smears were missed on three of 15 occasions by the step method (sensitivity 80%, positive predictive value 85%), and on seven of 30 occasions by the whole slide method (sensitivity 76.6%, positive predictive value 45%). However, the 95% confidence intervals were wide (57.7-90.7% for the step method, and 51.9-95.7% for the whole slide method). Analysis of scanning tracks and screening rates shows significant flaws in the methodology of rapid review. Abnormal cells were not identified, although dyskaryotic cells were included in the scanning track on nine occasions, seven using the whole slide method and two using the step method. On one occasion (using the step method) abnormal cells were not identified because they were not included in the scanning track. Further research is in progress to determine optimal methods of rapid review, and whether the rapid review technique is as effective as automated screening systems for quality assurance in cytology.

Assessing slide coverage by cytoscreeners during the primary screening of cervical smears, using the AxioHOME Microscope system.

We have used the HOME Microscope system to examine the screening patterns of cytotechnologists who undertake the primary screening of cervical smears, in order to measure accuracy of screening against screening time, slide coverage, and mean screening rate. Twelve cytotechnologists engaged routinely on cervical screening volunteered for this study. They were asked to perform primary screening of 10 test slides under normal laboratory conditions in the normal way. Slide coverage and screening time were recorded on the HOME system. Slide maps were prepared and the results analysed. The exercise demonstrated that all primary screeners fail at some point to scan the whole of the slide during primary screening. The maps produced by the HOME system clearly demonstrated that 5 different types of error can occur that lead to incomplete coverage of the slide. Mean slide coverage was 84%, and some individuals averaged only 66% coverage. The results show that there is a major problem in the education of some individual cytotechnologists in slide coverage. This could be rectified by the incorporation of a HOME system into every training centre, and the establishment of a protocol for assessment of slide coverage in competence examinations. Furthermore, the exercise has shown that even those individuals who normally attain a good standard of slide coverage would be able to improve slide coverage given access to the daily use of a HOME Microscope, or a system with equivalent screening/reviewing functionality.

Interest of targeting AgNORs measurement in cycling cells: in vivo cell kinetic evaluation of non-small cell lung cancer.

This study investigated the actual growth rate of 30 low stage operable non-small cell lung carcinomas, including disease-free surviving and deceased patients. The actual growth rate was defined as the cell production rate and was calculated from the growth fraction and the cell cycle time of each tumor at the time of surgical resection. The growth fraction was assessed by the Ki67 index while the cell cycle time was assumed to be reflected by the AgNORs content in the cells positive for Ki67. AgNORs content was evaluated by means of image analysis of double-stained AgNOR-Ki67 tissue section. The actual growth rate did not discriminate between the disease-free surviving and deceased patients but the AgNORs content in Ki67 cells correlated with the survival time of those patients who died of the tumor. Patients expressing a small AgNORs content, which might indicate a long cell cycle, may die but later; patients with a high AgNORs content, which might indicate a short cell cycle, die early or will survive. A twilight curve was derived from this data and might provide new prognostic indicators.

Individual use of cytomorphologic characteristics in the diagnosis of endocervical columnar cell abnormalities: selection of preferred features with help of the 'Navigator' microscope.

In our previous interobserver studies on endocervical columnar cell abnormalities, we studied architectural, cellular and nuclear features in cervical smears of women known to have columnar cell atypias of variable severity, to determine cytomorphologic criteria, discriminating between mild, moderate and severe intraepithelial columnar cell lesions and adenocarcinoma. The results of these studies revealed a number of architectural, cellular and nuclear characteristics in different grades of expression, which were of importance for the primary diagnosis of: no abnormalities, different grades of intraepithelial endocervical columnar cell lesions and adenocarcinoma. Furthermore we concluded that observers used different characteristics and different grades of expression of these characteristics for comparable diagnoses. The present study was undertaken to determine those features, which were considered discriminating by each individual for the diagnosis of mild, moderate and severe atypia, adenocarcinoma in situ and adenocarcinoma. Features selected by five observers with knowledge of the final diagnosis, were stored and reviewed with help of a motor driven stage ('Navigator')-microscope and a high definition television-monitor. The results confirmed individual observer variability in the number and type of features used in the diagnosis of endocervical columnar cell abnormalities. Features such as 'variation in nuclear size and shape', 'irregular chromatin distribution' and 'coarsely granular chromatin' were selected preferentially by all observers in the diagnosis of endocervical columnar cell lesions, conversely striking differences were observed in the application of 'architectural'-and, especially in cases of 'adenocarcinoma', 'nucleolar' characteristics.

Cellular sociology applied to neuroendocrine tumors of the lung: quantitative model of neoplastic architecture.

This paper reports on cellular sociology, which consists of modeling tissular architecture based on graph theory. Voronoi's diagram was chosen to build the models. This diagram derives from a cell neighborhood concept and generates parameters which objectively represent tissue architecture. Minimal spanning tree (MST) is probably the more frequently used among graphs and successfully discriminates different grades of pathological process. However, Voronoi's diagram is more comprehensive and a more complete representation of architecture with the advantage of stability. The lung neuroendocrine tumor classification is far from being consensual, especially for lesions which don't fall in with typical carcinoid and small cell carcinoma groups. By comparing architectural models of 20 neuroendocrine tumors of the lung, this work supports the morphologic spectrum concept of these tumors and also supports the recently proposed concept of large-cell neuroendocrine tumors of the lung. Finally, architectural parameters separate small-cell-lung carcinomas from neuroendocrine non-small-cell lung carcinomas.

Endocervical columnar cell intraepithelial neoplasia (ECCIN). 3. Interobserver variability in feature use.

In our previous studies on endocervical columnar cell abnormalities, the ability of 5 cytotechnicians was tested to distinguish between cases of: no abnormalities, different grades of intraepithelial endocervical columnar cell atypias and invasive adenocarcinoma. On the basis of stepwise multiple regression analysis, nuclear chromatin distribution, variation in cellular and nuclear size, cytoplasmic eosinophilia and architectural features such as cell-crowding, cluster formation, formation of gland-like structures and pseudostratification appeared to be of primary diagnostic importance to discriminate between no abnormalities, different grades of cervical columnar cell atypias, adenocarcinoma in situ and adenocarcinoma. The present paper reports the results of a study which was designed to assess the individual performance in feature use and classification of endocervical lesions. The results of this study indicate that observers use different characteristics and different grading for the level of expression of these characteristics. However, all observers illustrated a strong relationship between the presence and the expression grade of a certain feature and the degree of endocervical columnar cell atypia. With acceptance of one grade of difference in grades of severity, an overall correct diagnosis was made in 87.6% of cases (range 80-98.2%).

Quantitative microscopy and tumour cell proliferation.

The number of cell probes is rapidly increasing. During the last few years it has become possible to label total nuclear DNA (Feulgen), synthesized DNA (BrdU), specific A/T versus G/C rich DNA, cell cycle proteins (PCNA, Ki67), hormonal receptors (ER, PR, EGF), cdc genes and gene primary transcripts, etc. Taking advantage of this roster of cellular probes to assess cell kinetics in normal and malignant tissues implies not only quantitating their amount per cell but also analysing their intra-cellular respective distribution and inter-cellular variation. Image cytometry is the tool of choice for this purpose provided the quantitative results are properly interpreted. Confusions are often made between the respective meaning of i) reduced cell cycle speed (cell cycle duration), ii) increased proportion of proliferative cells (growth fraction), and iii) fraction of cells in S phase (SPF) and mitotic index (proportion of mitoses) which all tune the cell proliferative activity. The contribution of these biological cell population features to tumour growth is illustrated. Examples based on image cytometry are presented to define the individual tumour cell proliferation profile and tumour heterogeneity for proliferation profiles. It will be finely demonstrated how quantitative microscopy can turn the 'conventional static histological picture' of a tumour into a 'functional picture' that might support decision for therapeutic strategies.

Endocervical columnar cell intraepithelial neoplasia. II. Grades of expression of cytomorphologic criteria.

OBJECTIVE: To determine the relationship between the grade of expression of discriminating cytomorphologic architectural, cellular and nuclear features and the degree of endocervical columnar cell atypia. STUDY DESIGN: The study group consisted of 55 smears from 53 women known to have endocervical columnar cell atypias of variable severity. The smears were reviewed by five observers by means of 46 architectural, cellular and nuclear features. Seventeen of the 46 evaluated features were scored as revealing three grades of expression: slight, moderate and marked. RESULTS: Grades of expression of cellular and nuclear characteristics used in the evaluation of endocervical columnar cell abnormalities were identical to the characteristics used in the diagnosis of squamous (metaplastic) lesions. As such the features were extremely useful, with the exception of hyperchromasia, which was less prominently expressed. Furthermore, the results on architectural features revealed that the expression grades slight and moderate were indicative of mild and moderate endocervical columnar cell atypia, whereas the marked expression grade was strongly related to the severe intraepithelial lesions and adenocarcinoma. CONCLUSION: Characteristic cytomorphologic features at different grades of expression proved to be reliable light microscopic parameters in the diagnosis of different grades of endocervical columnar cell abnormalities. The accuracy of diagnosis at least equaled that of detecting squamous (metaplastic) lesions.

Endocervical columnar cell intraepithelial neoplasia. I. Discriminating cytomorphologic criteria.

OBJECTIVE: To identify specific cytomorphologic characteristics of mild, moderate and severe atypia of endocervical columnar cell lesions. STUDY DESIGN: The study group consisted of 55 smears from 53 women known to have columnar cell atypias of variable severity. The smears were reviewed by five observers in terms of 46 architectural, cellular and nuclear features. Review diagnoses were given together with the scoring for a large number of cellular characteristics. RESULTS: Nuclear chromatin distribution, variation in cellular and nuclear size, cytoplasmic eosinophilia and such architectural features as cell crowding, cluster formation, formation of gland-like structures and pseudostratification appeared to be of primary diagnostic importance for discriminating between no abnormalities, different grades of severity of endocervical intraepithelial neoplasia and adenocarcinoma. With acceptance of one grade of difference in grades of severity, a correct diagnosis was made in 87.6% of cases. CONCLUSION: With the application of specific architectural, cellular and nuclear features, the cytologic detection of different grades of endocervical intraepithelial neoplasia and of adenocarcinoma proved to be dependable and reproducible, with accuracy that at least equaled that of detecting squamous (metaplastic) lesions.

Fluorescence image analysis of the MCF-7 cycle related changes in chromatin texture. Differences between AT- and GC-rich chromatin.

This paper reports on quantitative in situ changes in chromatin structure that occur throughout the cell cycle of the human breast cancer epithelial cell line, MCF-7. Texture parameters were measured by image cytometry on nuclei stained by DNA specific fluorochromes. These parameters calculated from the co-occurrence and run length matrices of grey level images were previously shown to be related to condensation, organization and distribution of DNA. In some experiments, cells were triple stained for DNA/Ki-67/PCNA, and compartmentalization in the cycle was ascertained from the Ki-67/PCNA pattern expression. In these experiments, Hoechst dye was used to stain DNA. Chromatin of cells traversing G1 phase progressively decondensed and became homogeneously distributed. In addition, these G1 cells had more condensed chromatin than cells in G0 phase (as determined by Ki-67 negative staining). During the S and G2 phases, chromatin condensation took place and an increasing reticulated organization was quantified. Similar profile of changes in chromatin texture was found in experiments done with cells double stained by AT-specific Hoechst dye and the GC-specific mithramycin dye. GC-rich chromatin texture-associated parameters greatly varied comparing to those of AT-rich chromatin during the G0/G1 phase as well as in the first mid-S phase. Conversely, variation of the AT-associated parameters was much greater in the second half of S phase as compared to the GC-associated parameters that barely varied during this period. This study well establishes the correlation between in situ chromatin texture and proliferation state because the latter is assessed by proliferation-associated antigens. Moreover, changes in chromatin texture are independently ascribed to the AT- and GC-rich regions suggesting that these 2 types of chromatin are involved to different extents in transcriptional and replicational tasks.