IRTA1+ monocytoid B cells in reactive lymphadenitis show a unique topographic distribution and immunophenotype and a peculiar usage and mutational pattern of IgVH genes.

The origin and function of monocytoid B cells (MBCs) are poorly understood. Taking advantage of their strong expression of IRTA1 (a receptor that is also associated with MALT marginal zone B cells), we have comprehensively analysed MBCs in 25 cases of lymphadenitis of different aetiologies, shedding new light on the topographical distribution, immunophenotype and IgV(H) gene usage and mutational profile of this B cell subset. IRTA1(+) MBCs, although predominantly located in the subcapsular and intermediary sinuses, were also observed scattered within germinal centres (GCs) in all lymphadenitis cases examined. The molecular characterization of IgV(H) genes revealed that IRTA1(+) MBCs residing in different areas of the lymph node (subcapsular sinus, intermediary sinuses and GCs) can be clonally related (with intraclonal variation), and that those located in GCs are consistently more mutated and selected for expression of a functional antigen receptor than those located in the sinuses. Moreover, by contrast, IRTA1(+) MBCs in GCs express the memory B cell marker CD27. Finally, in toxoplasmic lymphadenitis, the IRTA1(+) MBC population shows a highly preferential usage of the V(H) genes 3-7 and 3-30 (without any obvious peculiarity in their CDR3s), possibly suggesting that a superantigen expressed by Toxoplasma gondii may be involved in the early activation of this B cell subset.

Cytokeratin-positive interstitial cell neoplasm: a case report and classification issues.

AIMS: Tumours of dendritic/accessory cell origin are rare neoplasms arising in lymph nodes. Among these, tumours derived from cytokeratin-positive interstitial reticulum cells (CIRCs), a subset of fibroblastic reticulum cells, are reported even less frequently. The International Lymphoma Study Group (ILSG) has recently proposed a classification for tumours of histiocytes and accessory dendritic cells in which CIRC tumours are not included. We report a case of a CIRC tumour arising in a submandibular lymph node of a 66-year-old male. METHODS AND RESULTS: The neoplasm was composed of spindle cells with elongated or round nuclei, prominent nucleoli and abundant cytoplasm. These cells were arranged in a diffuse fascicular and vaguely whorled pattern. The tumour cells stained diffusely for S100, vimentin, desmin, lysozyme, and focally for CD68 and cytokeratins 7, 8, 18, CK-AE1 and CK-pool. Electron microscopy was performed for further evaluation on samples taken from the paraffin block; this revealed cytoplasmic projections and rudimentary cell junctions. CONCLUSIONS: Histopathologist should be aware of the existence of tumours deriving from CIRCs, as these cases may be misdiagnosed as metastatic carcinoma. Careful clinical and pathological evaluation is necessary to exclude this possibility.

Thymic hyperplasia and lung carcinomas in a line of mice transgenic for keratin 5-driven HPV16 E6/E7 oncogenes.

Human Papillomavirus type 16 (HPV-16) is the cause of both benign lesions and ano-genital cancers. In HPV-associated cancers the transforming properties of the expressed viral E6 and E7 proteins have been revealed by a number of different assays. We have generated transgenic mice expressing HPV-16 E6/E7 genes under the control of the murine keratin 5 gene promoter, which should confer cell-type specific expression in the basal cells of squamous stratified epithelia. Transgenic mice developed thymic hyperplasia and lung neoplasia with 100% frequency, the thymus showing a size increase at 2 months and reaching the maximum dimension at 6 months, when lung carcinomas appeared. After this time the size of hyperplastic thymi decreased, while malignant formations invaded the mediastinal area. Hepatic metastasis could be also observed in some of the animals at the autopsy and death invariably occurred around 10-11 months of age.