Nasopharyngeal tonsils (adenoids) contain extrathymic corticothymocytes

Histogenesis of Merkel Cell Carcinoma: A Comprehensive Review

Merkel cell carcinoma (MCC) is a primary neuroendocrine carcinoma of the skin. This neoplasia features aggressive behavior, resulting in a 5-year overall survival rate of 40%. In 2008, Feng et al. identified Merkel cell polyomavirus (MCPyV) integration into the host genome as the main event leading to MCC oncogenesis. However, despite identification of this crucial viral oncogenic trigger, the nature of the cell in which MCC oncogenesis occurs is actually unknown. In fact, several hypotheses have been proposed. Despite the large similarity in phenotype features between MCC tumor cells and physiological Merkel cells (MCs), a specialized subpopulation of the epidermis acting as mechanoreceptor of the skin, several points argue against the hypothesis that MCC derives directly from MCs. Alternatively, MCPyV integration could occur in another cell type and induce acquisition of an MC-like phenotype. Accordingly, an epithelial as well as a fibroblastic or B-cell origin of MCC has been proposed mainly based on phenotype similarities shared by MCC and these potential ancestries. The aim of this present review is to provide a comprehensive review of the current knowledge of the histogenesis of MCC.

TdT expression in germ cell tumours: a possible immunohistochemical cross-reaction and diagnostic pitfall

AIMS

Very recent papers proposed a possible role for the expression of terminal deoxynucleotidyl transferase (TdT) in the tumourigenesis of gonadal and extragonadal germ cell-derived tumours (GCTs). Our multicentric study evaluated the magnitude of the immunoreactivity for TdT in GCTs, encompassing seminoma, dysgerminoma, mature teratoma and mixed GCTs.

METHODS AND RESULTS

The histological series was stained with both monoclonal and polyclonal antibodies, yielding a positivity of 80% of cases with well-defined nuclear reactivity. A significant difference in staining intensity between monoclonal and polyclonal antibodies was observed (p=0.005). However, exploiting western blot and more innovative proteomic approaches, no clear-cut evidence of the TdT protein was observed in the neoplastic tissues of the series.

CONCLUSIONS

Alternatively to the pathogenetic link between TdT expression and GCTs tumourigenesis, we hypothesised the occurrence of a spurious immunohistochemical nuclear cross-reaction, a well-known phenomenon with important implications and a possible source of diagnostic pitfalls in routine practice for pathologists.

Benign TdT-positive cells in pediatric and adult lymph nodes: a potential diagnostic pitfall

Benign terminal deoxynucleotidyl transferase (TdT)-positive cells have been documented in a variety of nonhematopoietic tissues. Scant data are, however, available on their presence in nonneoplastic lymph nodes. This study is aimed to (1) characterize the presence/distribution of benign TdT-positive cells in pediatric and adult reactive lymph nodes and (2) define the phenotype and nature of such elements. This retrospective study considered 141 reactive lymph nodes from pediatric and adult patients without history of neoplastic disease. TdT-positive cells were characterized by immunohistochemical and morphometric analyses, and their presence was correlated with the clinical-pathological features. The nature of TdT-positive cells was investigated by (1) double immunostaining for early lymphoid cell markers and (2) assessment of TdT expression in fetal lymph nodes. Sparse TdT-positive cells were documented in all pediatric cases and in most (76%) adult lymph nodes. TdT-positive cell density was higher in children than adults (15.9/mm² versus 8.6/mm²; P < .05). TdT positivity did not correlate with any clinical or histological parameter, and double immunostaining disclosed a phenotype compatible with early lymphoid precursors (positivity for CD34 and CD10, and variable expression of CD7). A very high TdT-positive cell density (802.4/mm²) was reported in all fetal lymph nodes. In conclusion, TdT-positive cells are a common finding in pediatric and adult lymph nodes. The interstitial distribution and low number of such cells allow for the differential diagnosis with precursor lymphoid neoplasms. The high density in fetal lymph nodes and the phenotype of such cells suggest their belonging to an immature lymphoid subset gradually decreasing with age.

Differential changes in the adenoids and tonsils in Japanese children and teenagers: a cross-sectional study

When adenoids (Ad) and tonsils (Tn) become hypertrophied, craniofacial and general body growth is affected. However, there are no objective explicit criteria for evaluating the size of the Ad and Tn, and their respective growth patterns remain unclear. This study determined the average proportions of the Ad and Tn sizes to the upper airway area at various developmental stages in Japanese individuals. Lateral cephalometric radiographs were obtained from 300 Japanese children and teenagers (150 boys and 150 girls, aged 6–20 years), and the respective proportions of Ad to the nasopharynx (Ad/Np) and Tn to the oropharynx (Tn/Op) in the upper airway were determined. Average and standard deviation (SD) were calculated for each of the 5 age groups: lower primary school, upper primary school, junior high school, senior high school, and young adults. We investigated the correlation between age and growth patterns of Ad and Tn, and determined the average Ad/Np and Tn/Op. There was an age-related decrease in Ad and Tn size, and a significant positive correlation between Ad/Np and Tn/Op values in the upper primary school group. Both Ad/Np and Tn/Op decrease as individuals approach adulthood. However, the growth patterns of the Ad/Np and Tn/Op differ from each other.

TdT-positive Infiltrate in Inflamed Pediatric Kidney: A Potential Diagnostic Pitfall

We encountered a patient with infantile nephrotic syndrome associated with a dense interstitial inflammatory infiltrate and prominent extramedullary hematopoiesis. Immunohistochemical analysis revealed numerous terminal deoxynucleotidyl transferase (TdT)-positive cells, which may raise concern for lymphoblastic lymphoma. Thus, we further characterized a group of pediatric kidneys with inflammation. TdT-positive nuclei were quantitated, and dual immunostains for TdT/CD79a, TdT/CD3, and TdT/CD43 were performed in a subset of cases; flow cytometry was performed in 1 case. TdT-positive nuclei were present in inflamed pediatric kidneys in 40 of 42 patients. TdT counts (average of 3 maximal high-power fields) ranged from 1 to >200, with a mean of 47. The presence and number of TdT-positive nuclei showed a strong association with younger patient age. Extramedullary hematopoiesis was identified in 11/42 patients, all under the age of 1. The presence of extramedullary hematopoiesis did not correlate with TdT count (P=0.158). Dual immunostaining and flow cytometric analysis in 1 case showed weak expression of B-cell markers and favored normal precursor B cells. Although TdT is a common marker of lymphoblastic lymphoma, we have demonstrated that TdT-positive cells may be part of the inflammatory milieu in infant kidneys. Together with cytologic, architectural, and clinical features, these data can help to avoid misinterpretation of involvement by lymphoblastic lymphoma/leukemia.

Flow cytometric characteristics of extrathymic thymocytes in adenoid tissue: A case report and comparison to normal thymus and thymoma

BACKGROUND

Normal thymocyte precursors in secondary lymphoid organs have previously been described. It is important to recognize normal thymocyte precursors by flow cytometry to differentiate them from T-cell lymphoblastic leukemia.

METHODS

A 3-year-old boy status 2 years post-allogenic cardiac transplant underwent adenoidectomy to exclude post-transplant lymphoproliferative disorder. Microscopic, immunohistochemical, and flow cytometry analyses of the adenoid were performed.

RESULTS

By flow cytometry, a population of CD45+(dim)/CD7+(bright)/CD3- cells were observed at 1.0% of lymphocytes. These cells expressed CD10, partial CD34, and exhibited acquisition of CD4 followed by CD8. Within the brighter CD45+ lymphocytes, a population of CD3-/CD4+/CD8+ thymocytes and a similarly sized population of CD4+/CD8+ cells exhibiting acquisition of low-density CD3 were identified. By immunostaining, clusters of TdT+/CD1a+/CD4+/CD8+ T-cells were identified in the interfollicular areas. Compared to normal thymus, thymocytes in the adenoid tissue lacked the classic CD4xCD8 winged differentiation profile but showed a normal early precursor pattern.

CONCLUSIONS

Thymocytes in adenoid show a similar differentiation pattern to thymus and thymoma. However, the classic winged pattern of common thymocyte differentiation may not be readily apparent in thymocytes differentiating outside of the thymus. Recognition of the early thymocyte precursor antigen acquisition profile can be crucial to correct interpretation. © 2017 International Clinical Cytometry Society.

Neonatal infection with species C adenoviruses confirmed in viable cord blood lymphocytes

Credible but conflicting reports address the frequency of prenatal infection by species C adenovirus. This question is important because these viruses persist in lymphoid cells and suppress double-stranded DNA-break repair. Consequently, prenatal adenovirus infections may generate the aberrant clones of lymphocytes that precede development of childhood acute lymphoblastic leukemia (ALL). The present study was designed to overcome technical limitations of prior work by processing cord blood lymphocytes within a day of collection, and by analyzing sufficient numbers of lymphocytes to detect adenovirus-containing cells at the lower limits determined by our previous studies of tonsil lymphocytes. By this approach, adenoviral DNA was identified in 19 of 517 (3.7%) samples, providing definitive evidence for the occurrence of prenatal infection with species C adenoviruses in a significant fraction of neonates predominantly of African American and Hispanic ancestry. Cord blood samples were also tested for the presence of the ETV6-RUNX1 translocation, the most common genetic abnormality in childhood ALL. Using a nested PCR assay, the ETV6-RUNX1 transcript was detected in four of 196 adenovirus-negative samples and one of 14 adenovirus-positive cord blood samples. These findings indicate that this method will be suitable for determining concordance between adenovirus infection and the leukemia-associated translocations in newborns.