Altered expression of vascular endothelial cell (EC) surface antigens in response to irradiation is one of the early events of radiation-induced damage. Using flow cytometry, we investigated the immunocytochemical reactivity of a blind panel comprising 87 mAbs submitted to the endothelial section of the 6th International Workshop on Human Leukocyte Differentiation Antigens with irradiated and resting human dermal microvascular endothelial (HDME) and EA cell lines. Monolayers of irradiated cells received a single 5 Gy dose of 72 h prior to staining but were otherwise treated the same as resting cells. For comparative purposes we have also examined the immunohistochemical reactivity of the mAb panel with EC in ovarian tumour, Wilms' tumour and human placenta. In the flow cytometry experiments 42 and 44 mAbs stained HDME and EA cells respectively and while no antibody stained irradiated but not unirradiated cells, upregulation was seen for CD31, CD34, CD141 and CD146 in irradiated cells. The upregulation of thrombomodulin (CD141) is noteworthy since it is a marker of EC damage and thus may be a useful reagent in investigations of vascular injury. Comparison with tissue staining showed that 21 mAbs were reactive with at least one tissue but not with either EA or HDME cells. Nine mAbs showed no cross reactivity with tissue and of these one reacted with EA cells only.

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