CD30 (Ber-H2) expression by thymocytes and thymic epithelial cells during the late first and second trimester of gestation: an immunohistochemical and in situ hybridization (ISH) study.

BACKGROUND: The exact biological function of CD30 in the thymus during development has been only partially elucidated, although data indicate it may be involved in negative selection. This study was prompted by the observation of a positive reaction of thymic epithelial cells (TECs), Hassall's corpuscles, and thymocytes with the monoclonal antibody CD30 during the late first and second trimester. MATERIAL/METHODS: Twenty paraffin-embedded fetal thymus specimens at the late first and second trimester were investigated by conventional histology and immunohistology for CD30 expression. To provide additional information on the nature and localization of CD30+ thymocytes and CD30+ TECs, in situ hybridization (ISH) was performed on the specimens. RESULTS: 1) In the medulla, a statistically significant difference between CD30+ thymocytes from the late first trimester and those from the second trimester (p<0.0001, t-test) was demonstrated. No significant difference was found concerning CD30+ thymocytes in the cortex. 2) Many medullary TECs and Hassall's corpuscles showed high expression of CD30 during the second trimester, whereas small numbers of CD30+ TECs were found during the late first trimester. No statistically significant difference was found concerning CD30+ TECs in the cortex. CD30 was expressed by ISH in many cells in the medulla and along the septa, whereas the cortex showed little if any expression. Accordingly, a higher CD30 expression was found in medullary than in cortical thymocytes. CONCLUSIONS: Comparison of CD30 expression by TECs and thymocytes during the late first trimester and second trimester suggests an important role for CD30 in thymic selection.

Jaw bone metastases: four cases.

OBJECTIVE: Metastatic tumors make up approximately one percent of all oral malignancies. Such tumors may present in the jaw bones and oral soft tissues. The commonest oral site is the mandible. PATIENTS AND METHODS: This is a retrospective study of four cases of metastatic tumors of the jaws seen at the Oral-Maxillofacial Department, General University Hospital of Alexandroupolis, Thrace, Greece from 1989 to 2005, representing 1% of all histologically confirmed malignant tumors at the hospital. RESULTS: Two cases originated from the thyroid gland, one was from the esophagus, and one from the liver. Three metastases occurred in the mandible and one in the maxilla. The oral symptoms were similar to odontogenic infections or to benign neoplasms. CONCLUSIONS: In view of the resemblance in the presentation of metastases and other tumors affecting the jaws, a high index of clinical suspicion is advocated to ensure early, multidisciplinary care of hosts.

Cytoplasmic expression of c-erb-B2 in endometrial carcinomas.

BACKGROUND: The aim of this study was to investigate the expression of c-erb-B2 in endometrial cancer with attention to both membranous and cytoplasmic staining, and to elucidate the significance of cytoplasmic signaling. MATERIALS AND METHODS: c-erb-B2 reactivity was assessed by immunohistochemistry in 110 patients using a polyclonal antibody, and evaluated semiquantitatively according to the percentage of cells demonstrating membranous or diffuse cytoplasmic staining. Correlation was made with tumor stage, grade, myometrial invasion, histologic type, and disease outcome. RESULTS: c-erb-B2 overexpression, indicated by membranous and cytoplasmic staining of at least 10% of the tumor cells, was found in 47 (42.7%) cases. Cytoplasmic expression of c-erb-B2 was observed more frequently than membranous (69.1 vs. 5.5%). Synchronous cytoplasmic and membranous signaling was noticed in 7.9% of cases. Interestingly, patients with cytoplasmic c-erb-B2-positive tumors had a significantly shorter survival (p = 0.047). CONCLUSIONS: These results indicate that c-erb-B2 is a specific marker of endometrial cancer. It is also an independent prognostic indicator of poor outcome. Cytoplasmic staining is as important as membranous staining, and is also a specific finding.

Intraoperative touch imprint cytological analysis of sentinel lymph nodes for the presence of metastases in breast cancer.

BACKGROUND: Imprint cytology may provide a fast and accurate method for intraoperative screening of sentinel lymph nodes, so a decision can be made regarding whether to perform axillary clearance during primary surgery. If the findings are negative, in many cases axillary dissection can be omitted. PATIENTS AND METHODS: 128 sentinel nodes from a cohort of 87 patients that had been identified using technetium-99m nanocolloid as a radioactive tracer and Patent blue dye were dissected for rapid Diff-Quick stained touch preparations. Intraoperative evaluation of sentinel node status by imprint cytology was correlated with histopathological results of permanent sections. Tumor-negative nodes in routine paraffin sections were further investigated with the employment of an anti-cytokeratin antibody. RESULTS: 36 of all sentinel nodes harbored metastases in the paraffin sections, of which 32 were identified by imprint cytology (sensitivity 88.8%). 3 sentinel nodes were positive by imprint cytology and negative by histopathology of the paraffin sections. Comparison of the results of the touch preparations with the final histopathology (hematoxylin-eosin and anticytokeratin antibody stains) demonstrated a sensitivity of 83.3% and a negative predictive value of 92.5%. The specificity and positive predictive value were 100% each. CONCLUSIONS: Touch imprint cytology is potentially useful for intraoperative evaluation of sentinel lymph nodes in breast cancer patients.

Papillary thyroid carcinoma metastasis most probably due to fine needle aspiration biopsy. A case report.

Implantation of cancer cells from needle biopsy has been reported in a wide range of malignancies. Fine needle aspiration biopsy has become an accepted method for assessment of thyroid nodules. Local reappearance of thyroid cancer from needle track dissemination is a rare complication of thyroid aspiration. A 45-year-old female developed local recurrence of papillary thyroid carcinoma four years after aspiration biopsy and thyroidectomy. Metastatic deposits appeared in the skin and the sternocleidomastoid muscle. The linear array and the site of metastases implied that seeding most probably resulted from the needle biopsy.

CD30 (Ki-1) molecule expression in human embryonal epithelial cells of the basal layer of the developing epidermis and epidermal buds and its potential significance for embryogenesis.

OBJECTIVE: CD30 antigen has long been considered to be restricted to tumour cells of Hodgkin's disease, of anaplastic large cell lymphoma and T and B activated lymphocytes. Expression of CD30 antigen has been reported in the decidual stroma, cultivated macrophages, lipoblasts, myoepithelial cells, reactive and neoplastic vascular lesions, mesotheliomas, embryonal carcinoma and seminoma cells. The fact that the CD30 molecule can mediate signals for cell proliferation or apoptosis prompted us to perform a systematic investigation of CD30 antigen expression in embryonal tissues during the proliferation and differentiation stages. We first targeted foetal human intestinal cryptae cells with positive results. The epidermis is a dynamic epithelium that is constantly renewed throughout life. Its turnover is estimated at about 7 days in mice and about 60 days in humans. This rapid replacement demands, as with other epithelial tissues, that an adult has stem cells capable of supplying differentiated cells throughout life. The most basic and widely accepted criteria for these stem cells are that they have a high capacity for self-renewal and the ability to generate daughter cells that undergo terminal differentiation. Not all of the proliferative cells in the basal layer are stem cells and we were intrigued to find out if stem or other cells in the basal layer can express the CD30 antigen. MATERIALS AND METHODS: We investigated the immunohistochemical expression of CD30 antigen in 15 paraffin-embedded tissue samples representing epidermis and epidermal buds from foetuses after spontaneous abortion in 8th, 10th, and 12th week of gestation, respectively, using the monoclonal antibody Ki-1. RESULTS: The results showed that the epithelial cells of the epidermis in the developing skin express the CD30 antigen and CD30 expression in these epithelial cells is higher in cases of hormonal administration than in normal gestation. A similar positive reaction was observed in the epidermal buds associated with the development of the skin appendages.

An unusual case of posttransplant peritoneal primary effusion lymphoma with T-cell phenotype in a HIV-negative female, not associated with HHV-8.

Primary effusion lymphoma (PEL) is a recently individualized form of non-Hodgkin's lymphoma (WHO classification) that mainly develops in HIV infected males, more frequently in homosexuals and advanced stages of the disease (total CD4+ lymphocyte count below 100-200/microL). Occasionally, it appears in other immunodepressive states (such as solid organs transplant period) and even, although very rarely, in immunocompetent patients. From a pathogenetic point of view, PEL has been related to Kaposi's sarcoma associated herpes virus (also named human herpesvirus 8, HHV-8), an etiological factor of Kaposi's sarcoma. The relative infrequency of this disease, the absence of wide casuistics allowing a better characterization, and its unfavorable outcome support the need of a deeper knowledge. We present here the clinical-biological findings of a patient, HIV seronegative, who was diagnosed with peritoneal PEL of T-cell origin, and not HHV-8-associated, five years after renal transplantation.

Metachronous extranodal marginal zone B-cell lymphoma of mucosa-associated lymphoid tissue (MALT lymphoma) and peripheral T-cell lymphoma unspecified: histologic, immunophenotypic, and molecular documentation.

BACKGROUND: Coexistence of B- and T-cell lymphoid malignancies has been reported sporadically. CASE REPORT: A 68-year-old woman developed a lymphoid neoplasm in the large intestine and a second lymphoid neoplasm in the esophagus, 24 months after the diagnosis of the first lymphoma. Immunophenotypic analyses were consistent with extranodal marginal zone B-cell mucosa-associated lymphoid tissue type (MALT type) and peripheral T-cell unspecified lymphomas in the large intestine and the esophagus, respectively. The molecular analysis confirmed the B-clonal genotype of the first lymphoma, and disclosed a biclonal genotype of the second one (composite T- and B-cell lymphoma). No evidence of Epstein-Barr virus (EBV) association was shown in either tumor. CONCLUSION: B- and T-cell neoplasms represent two distinct malignancies rather than progression of the same neoplastic clone.

ALK-positive neutrophil-rich variant of anaplastic large cell lymphoma diagnosed after head trauma.

BACKGROUND: Anaplastic lymphoma kinase (ALK) expression has not been described in neutrophil-rich anaplastic large cell lymphoma (NR-ALCL). CASE REPORT: A 12-year old female with a 4-weeks history of a non-resolving bump over the forehead resulting from injury, was diagnosed of stage IE cutaneous T-cell lymphoma, and radiation was employed. Shortly after completion of therapy, there was progress of the disease on the soft tissue of the right hand, and bone marrow involvement was also found. A fine-needle aspiration of the hand mass was performed, and a diagnosis of CD30+/ALK+ NR-ALCL, was rendered. METHODS: We studied the morphological characteristics of CD30+/ALK+ NR-ALCL using histological methods. A panel of antibodies were used to establish diagnosis and subtyping. In addition EBV status and molecular cytogenetics were determined. CONCLUSIONS: ALK-ALCL arising in the skin represents a single disease with a broad spectrum of morphology; clinicians and pathologists should be aware of this neutrophil-rich (NR) variant with aggressive clinical presentation.

Fine needle aspiration cytology diagnosis of gastrointestinal stromal tumors utilizing scanning electron microscopy.

BACKGROUND: Digestive stromal neoplasms are the most frequent undifferentiated mesenchymal tumors. The outcome of these malignancies is difficult to predict and the histogenesis is still controversial. However, the frequent and specific expression of CD117 (c-kit) by these tumors could imply an origin from interstitial cells of Cajal. Our objective was to analyze the role of fine needle aspiration cytology, cell block preparation, and immunocytochemistry in the interpretation of gastrointestinal stromal tumors, and to establish scanning electron microscopy as a useful research aid for pathologic changes of the surface cells of gastrointestinal stromal tumors, not totally appreciated by light microscopy. MATERIAL AND METHODS: Twelve cases of gastrointestinal stromal tumors were included in this study, in which fine needle aspiration cytology was performed. RESULTS: On aspirated material, the tumor cells formed closely packed cohesive tissue fragments with high cellular density often in bloody background, or fascicles with parallel side-by-side arrangements of the nuclei. On cell block biopsy material, gastrointestinal stromal tumors were highly cellular spindle or epithelioid tumors with basophilic appearance. Immunocytochemically, they were CD117 positive in all twelve cases, CD34 positive in nine, weakly smooth muscle actin-positive in five, and S-100 and GFAP-negative in all cases. The scanning electron microscopy study showed a strong correlation with the cytomorphological profile. CONCLUSIONS: Gastrointestinal stromal tumors show a broad morphologic variety, but nuclear pleomorphism by cytology alone, rarely correlates with malignant potential. In the appropriate clinical and radiological setting, a confident diagnosis of gastrointestinal stromal tumors can be documented by fine needle aspiration cytology, cell block, immunocytochemical, and scanning electron microscopy results.

Human embryonal epithelial cells of the developing small intestinal crypts can express the Hodgkin-cell associated antigen Ki-1 (CD30) in spontaneous abortions during the first trimester of gestation.

BACKGROUND: Ki-1 (CD30) antigen expression is not found on peripheral blood cells but its expression can be induced in vitro on T and B lymphocytes by viruses and lectins. Expression of CD30 in normal tissues is very limited, being restricted mainly to a subpopulation of large lymphoid cells; in particular, cells of the recently described anaplastic large cell lymphoma (ALCL), the Reed-Sternberg (RS) cells of Hodgkin's lymphoma and scattered large parafollicular cells in normal lymphoid tissues. More recent reports have described CD30 expression in non-hematopoietic and malignant cells such as cultured human macrophages, human decidual cells, histiocytic neoplastic cells, mesothelioma cells, embryonal carcinoma and seminoma cells. RESULTS: We investigated the immunohistochemical expression of CD30 antigen in 15 paraffin-embedded tissue samples representing small intestines from fetuses after spontaneous abortion in the 8th, 10th and 12th weeks using the monoclonal antibody Ki-1. Hormones had been administered to all our pregnant women to support gestation. In addition, a panel of monoclonal antibodies was used to identify leukocytes (CD45/LCA), B-lymphocytes (CD20/L-26) and T-lymphocytes (CD3). Our findings were correlated with those obtained simultaneously from intestinal tissue samples obtained from 15 fetuses after therapeutic or voluntary abortions. CONCLUSIONS: The results showed that: (1) epithelial cells in the developing intestinal crypts express the CD30 (Ki-1) antigen; (2) CD30 expression in these epithelial cells is higher in cases of hormonal administration than in normal gestation. In the former cases (hormonal support of gestation) a mild mononuclear intraepithelial infiltrate composed of CD3 (T-marker)-positive cells accompanies the CD30-positive cells.

Human decidual cells activity in women with spontaneous abortions of probable CMV aetiology during the first trimester of gestation. An immunohistochemical study with CMV-associated antigen.

AIM: To determine the expression of CMV-associated antigen in the human decidual endometrial stromal cells in spontaneous abortions with no evidence of maternal relapse during the first trimester of gestation. EXPERIMENTAL DESIGN: We examined 15 placentas resulting from intrauterine fetal death after spontaneous abortion during the 8th, 10th, and 12th week of gestation respectively, and in which CMV reactivation was ruled out from serological evaluation of the pregnant women at admission, versus equal controls after voluntary abortion following well-documented maternal viral recurrence. In addition, a panel of monoclonal antibodies for the identification of leukocytes (CD45/LCA), B-lymphocytes (CD20/L-26), and T-lymphocytes (CD45RO/UCHL1), was performed. All women received hormonal medication to support gestation, in the cases of spontaneous abortions. RESULTS: Immunohistochemical examination using a specific antibody against cytomegalovirus showed large multinucleated infected cells with intranuclear inclusions, located primarily in the decidual stroma within a lymphoplasmacytic infiltrate in the cases of spontaneous abortions. No evidence of infection was observed in the chorionic villi. In the cases of voluntary abortions same findings were observed in the relevant areas, and a strong evidence of infection was observed in the chorionic villi. CONCLUSION: This study demonstrates 1) that the decidual endometrial stromal cells can express the CMV-associated antigen prior to serological manifestation of the viral replication, 2) the expression of the antigen is higher in cases of hormonal administration to support gestation. In these cases a mild mononuclear infiltrate of UCHL1 (T marker) positive cells, accompanies the CMV-associated antigen positive cells.

Does neoplastic cholecystokinin expression reflect the embryonal pattern of the protein? A study in human pancreas.

AIM: To determine the immunoreactivity of cholecystokinin (CCK) during the development of the human fetal pancreas and pancreatic adenocarcinoma, given that, CCK positive cells were demonstrated either in its embryonic anlage or in pancreatic cancer. In order to obtain possible parallels in the expression pattern of neoplastic cells in adults (well--moderately--poorly differentiated), we investigated the pattern of CCK expression in the pancreatic tissue during the various stages of development and compared these with the proliferation of tissue assessed by proliferating cell nuclear antigen (PCNA) immunohistochemistry. EXPERIMENTAL DESIGN: Tissue sections from 15 pancreatic fetal specimens, and equal number of ductal adenocarcinoma specimens, were assessed using immunohistochemical methods for CCK. RESULTS: The density of positive cells in the primitive exocrine ductal walls and outgrowing buds was significantly higher than the relevant density in the neoplastic pancreatic tissue of mixed (ductal-endocrine) and pure ductal type (p1=0.004, p2 < 0.0005, p3 < 0.0005 and p4=0.023 respectively). The above values were estimated from 20th to 22nd weeks of gestation. There was no significant difference in the density of positive cells in the islet cell epithelium from 25-30 weeks, and the neoplastic tissue of mixed (p5=0.10) and pure ductal type (p6=0.15). CONCLUSIONS: The immunostaining for CCK identifies a sub-group of pancreatic ductal adenocarcinomas with a neuroendocrine component (initially considered as pure ductal tumors), and mixed ductal-endocrine tumors. This pattern of expression in neoplasms recapitulates the normal pattern during the embryonal development of the organ, and may be important for the development of new therapeutic approaches with eventual clinical utility.

Altered intrahepatic hematopoiesis in neonates from women with pregnancy induced hypertension/pre-eclampsia.

AIM: To detect whether preeclampsia influences neonatal intrahepatic hematopoiesis, given that an activation of fetal neutrophils and monocytes during the course of this disorder occurs. EXPERIMENTAL DESIGN: We examined liver samples from 10 neonates of hypertensive/preeclamptic women at 27 to 28 weeks of gestation delivered by a cessarian section. All neonates were placed in incubators but they all died within 24 hours due to immaturity. The control group comprised 10 fetuses of the same gestational age, after voluntary abortion due to a neural defect. Specific antibodies against CD34, glycophorin C, hemoglobins A and F, myeloperoxidase, CD61, CD68, terminal desoxynucleotidyl transferase and the pax-5/B-cell specific activator protein, were used in each sample. RESULTS: Neonates from hypertensive/preeclamptic women, in comparison with controls, showed: a statistically significant reduction of erythropoiesis by 25% (p=0.015); a statistically significant increase of granulopoiesis (p=0.019); a statistically significant increase in the expression of CD68 positive cells of the monocytic lineage (p=0.017); a statistically significant increase in the expression of CD34 progenitor/stem positive cells (p=0.021). No statistically significant differences were observed in both examined groups, concerning megakaryopoiesis and B lymphopoiesis. CONCLUSIONS: Preeclampsia of pregnancy has an impact on neonatal intrahepatic hematopoiesis by increasing granulopoiesis, reducing erythropoiesis and triggering endothelial and stem cell activation. We suggest that these findings reflect a state of persistent inflammation and a loss of red blood cell production possibly contributing to the neonatal morbidity related to this disorder.

Polymorphous low grade adenocarcinoma of the parotid gland. Cytological, histological and immunohistochemical features and review of the literature.

AIM: Polymorphous low grade adenocarcinoma of the salivary glands (PLGA) is a low grade neoplasm that predominantly occurs in the minor salivary glands. In this site is amenable to biopsy and histologic diagnosis. However, experience with cytological findings in these tumors is limited. We describe the cytology of this entity. EXPERIMENTAL DESIGN: Touch imprint cytology of a primary parotid PLGA is specified and correlated with histology. RESULTS: Smears were hypercellular showing branching papillae, sheets and clusters of uniform cells with bland nuclei, dispersed chromatin and no nucleoli. The cells had a scant to moderate amount of eosinophilic cytoplasm. They formed tubular structures containing hyaline globules. CONCLUSIONS: The cytologic differential diagnosis of PLGA includes adenoid cystic carcinoma, pleomorphic adenoma, and monomorphic adenoma. PLGA should be considered in the differential diagnosis of head and neck tumors, where the cytology suggests on of the above mentioned tumors, even when the clinical findings (involvement of a major salivary gland, lymph node metastasis) is not typical of PLGA.

Cytologic differential diagnostic problems in ulcerative cervicitis.

OBJECTIVE: To improve the detection rates in the determination of signs consistent with ulcerative cervicitis against signs of intraepithelial neoplasia, in PAP smears. STUDY DESIGN: We investigated the frequency of establishing a diagnosis of a simple ulcerative cervicitis by histology in a cohort of 58 females with cervical cytology suggestive of intraepithelial neoplasia. RESULTS: There was found a detection rate of 81.58% in the determination of ulcerative cervicitis by cytology and a rate of 100% in the determination of HPV-infection, CIN1, CIN2 and CIN3 respectively. There was no statistically significant difference between cytology and histology in the diagnosis of ultracerative cervicitis (p>0.5, chi-square). CONCLUSIONS: There is an overestimation of the cytological signs in the diagnosis of ulcerative cervicitis 18.42%). There is also an excellent agreement in the diagnosis of HPV-infection and CIN grades (100%) between cytology and histology, discordant with the literature (2.4%-71%).

Malignant mucoepidermoid tumor arising in the accessory parotid gland: a case report.

PURPOSE: The head and neck surgeon's fascination with parotid surgery arises from the gland's spectrum of histopathological presentations, as well as the diversity of its morphological features. A mass arising in the mid-cheek region may often be overlooked as a rare accessory lobe parotid neoplasm. This report serves to revisit the topic of accessory parotid gland neoplasms to emphasize proper management, particularly the surgical aspects, so that consequences of salivary fistula, facial nerve paralysis, and recurrence are avoided. CASE REPORT: We report a case of mucoepidermoid carcinoma which was assessed pre-operatively as arising from the accessory parotid gland of a 11-year-old female. She had complained of a painless and round mass of the left cheek for a duration of 12 months. Sialography, ultrasonography, CT scan and MRI were performed preoperatively. Sialography revealed a small duct separating from the Stensen's duct. CT and MRI showed that the tumor with smooth outline was lying on the masseter muscle and detached from the main parotid gland. The preoperative diagnosis was an accessory parotid gland tumor. The tumor was removed without facial nerve injury via standard parotidectomy incision. The tumor was composed of mucous, intermediate and epidermoid cells. The pathological diagnosis was low-grade mucoepidermoid carcinoma. CONCLUSIONS: Accessory parotid gland neoplasms are rare and may present as innocuous extraparotid mid-cheek masses. A high index of suspicion, prudent diagnostic skills (including fine-needle aspiration [FNA] biopsy followed by computed tomography [CT] imaging), and scrupulous surgical approach (extended parotidectomy-style incision and limited peripheral nerve dissection when possible) are the keys to successful management of these lesions.

Pancreatic-polypeptide in the human pancreas: expression and quantitative variation during development and in ductal adenocarcinoma.

AIM: To determine the immunoreactivity of pancreatic-polypeptide (PP) during the development of the human fetal pancreas and ductal pancreatic adenocarcinoma, given that, PP positive cells were demonstrated either into its embryonic anlage or into pancreatic cancer. METHODS: Tissue sections from 15 pancreatic fetal specimens, and equal number of ductal adenocarcinoma specimens, were assessed. RESULTS: The density of positive cells in the primitive exocrine ductal epithelium and endocrine epithelium was significantly higher than the relevant density in the neoplastic pancreatic tissue of mixed (ductal - endocrine) and pure ductal type (p1 = 0.001, p2 < 0.0005, p3 = 0.046 and p4 < 0.0005 respectively). The above values were estimated during the 10th to 12th week. There was no significant difference in the density of positive cells in the mantle zone of the islets from the 13th to the 24th week, and the neoplastic tissue of mixed (p5 = 0.11) and pure ductal type (p6 = 0.23). CONCLUSION: The immunostaining for PP identifies a subgroup of pancreatic ductal adenocarcinomas with a neuroendocrine component, initially considered as pure ductal tumors, and mixed ductal and neuroendocrine tumors. This pattern of expression in neoplasms recapitulates the normal pattern during the embryonal development of the organ, raising the question of therapeutic efficacy of PP and analogues as potential adjuvant treatment of pancreatic cancer.

Prevalence of CD8/CD4 ratio in the fetal thymic parenchyme in Down's syndrome.

AIM: The maturation of most T-lymphocyte precursors takes place within the meshwork of thymic epithelial cells. Different steps of this process can be defined by immunologic phenotyping. The prothymocytes are positive for the terminal deoxynucleotidyl transferase (TdT) and give rise to cortical thymocytes, which express CD1, CD2, CD3, CD5, and both CD4 and CD8. These CD4 and CD8 double-positive cortical thymocytes differentiate into two lineages: CD4+ or CD8+ lymphocytes of the thymic medulla, by the tenth week of gestation. Our study points towards the determination of the CD8 cytotoxic/suppressor capacity of the fetal thymus in Down's syndrome. EXPERIMENTAL DESIGN: A quantitative comparison of T-lymphocytes (CD3, CD4, and CD8) in the thymic parenchyme in embryos after voluntary abortion during 2nd trimester of gestation and embryos with Down's syndrome, respectively, was performed. RESULTS: Our results showed: 1) A statistically significant depletion in the total number of T-cells (CD3 positive) in the cases of embryos with Down's syndrome over those after voluntary abortion, during the second trimester of gestation (p<0.0001, t-test). 2) A significant difference in the CD8/CD4 ratio in the cases of embryos with Down's syndrome, during the second trimester of gestation which was numerically stronger with the progress of fetal development (20th week: p<0.025; 24th week: p<0.01, chi-square). CONCLUSIONS: The occurrence of increased CD8/CD4 ratio in the cases with Down's syndrome, in the second trimester of gestation, underlines the cytotoxic/suppressor property of the thymus in the affected fetuses.