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The catabolic enzyme thymidine phosphorylase (TP) plays a crucial role in nucleic acid metabolism by regulating the availability of thymidine. Platelet-derived endothelial cell growth factor (PD-ECGF) is an angiogenic factor that was recently shown to be TP. The angiogenic properties of PD-ECGF/TP are attributable to a reduction of thymidine levels that results in a promotion of endothelial cell proliferation. Early studies showed a higher concentration of TP in macrophages than in parenchymal cells and in neoplastic than in nonneoplastic tissues. We examined the immunohistochemical expression of PD-ECGF/TP in reactive lymphoid tissues (lymph node and tonsil), as well as in a series of 20 cases of Hodgkin's disease and 31 cases of non-Hodgkin's lymphomas. Macrophages, sinus lining cells, and cells with dendritic morphology, of both follicular dendritic and interdigitating reticular cell type, presented a prominent nuclear and cytoplasmic positivity in reactive lymphoid tissue and in malignant lymphomas. Small lymphocytes and the neoplastic population were always negative, whereas endothelial staining was variable and showed no correlation to the type or grade of the lymphomas. In Hodgkin's disease (with the exception of the nodular lymphocyte predominance type) and some cases of high-grade non-Hodgkin's lymphomas, the positive dendritic cells formed a dense meshwork closely surrounding the neoplastic population. Our results suggest that the reported upregulation of PD-ECGF/TP activity in lymphoid malignancies is attributable to the nonneoplastic population, especially to cells of dendritic morphology.

The distribution of TAL-1 protein, an important vascular promoter in mice, has been examined immunohistochemically in a range of human vascular lesions and normal tissues. Formalin-fixed, paraffin-embedded vascular lesions including granulation tissue, haemangiomas, Kaposi's sarcomas, spindle cell haemangioendotheliomas, and angiosarcomas, were examined using a monoclonal antibody to recombinant TAL-1. Endothelial cells in all lesions gave positive immunostaining of variable intensity. Granulation tissue and spindle cell areas of the vascular tumours gave the strongest staining (nuclear and cytoplasmic). The better-differentiated endothelial cells within the tumours and resident well-formed vessels were less positive and some cells were in fact negative. The malignant endothelial cells in angiosarcomas showed less intense positive staining than KS cells. This study has shown TAL-1 protein expression in a range of reactive, benign, and malignant vascular lesions. Protein expression appears to be stronger in the spindle cell areas, perhaps reflecting greater expression in less-differentiated endothelial cells.

Platelet-derived endothelial cell growth factor/thymidine phosphorylase (PD-ECGF/TP) is an enzyme with angiogenic and cell motility properties. Moreover, it is involved in the transformation of fluoropyrimidines into active cytotoxic metabolites. In the present study, the expression of PD-ECGF in normal lung and lung cancer was immunohistochemically evaluated using the P-GF.44C monoclonal antibody. Alveolar and tumoural macrophages were invariably stained and were used as an internal control for assessment of the staining. Alveolar epithelium was always negative, whilst bronchiolar epithelium showed occasional positive reactivity. Normal lung and tumour endothelium was occasionally positive. Positive staining in more than 50 per cent of cells was observed in 23/71 squamous carcinomas (32 per cent), 16/38 (42 per cent) adenocarcinomas, and 2/6 (33 per cent) adenosquamous carcinomas. Differentiated areas and areas of squamous metaplasia were more strongly positive than other tumour areas. All 22 small cell carcinomas and one carcinoid tumour were negative. The present study provides a baseline for future studies in non-small cell lung cancer to correlate PD-ECGF expression with tumour vascularization, prognosis, and response to chemotherapy.