SUMMARY Tumours of uncertain tissue of origin were investigated by immunohistochemistry on formalin fixed paraffin embedded sections. Two antibodies-PD7/26, an anti common leucocyte antigen, and CAM5.2, an anticytokeratin-recognised most lymphomas and carcinomas, respectively: 88% of these tumours were identified by the two antibodies alone. These antibodies permitted the separation of the cases into groups: positive with CAM5.2, positive with PD7/26, and a third comprising those negative with both. The negative group contained other tumours and a small number of carcinomas and lymphomas; many of the lymphomas were, apparently, of histiocytic origin.Comparison of CAM5.2 with other epithelial markers showed that it was the most effective. Some further classification of the tumours was carried out with a panel of organ and cell specific antibodies: mesotheliomas were recognised by their pattern of reactivity with epithelial markers. Overall, the tumour type was determined in 90% of cases. Immunohistochemistry performed as described can be a potent aid to the diagnostic histopathology of tumours.

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We have compared the adhesion of 51Cr-labeled eosinophils and neutrophils to cultured human umbilical vein endothelial cell (EC) monolayers that have been stimulated with IL-1, TNF, or LPS. Each agent stimulated the adhesion to EC of both eosinophils and neutrophils in a similar dose- and time-dependent manner. F(ab')2 fragments of mAb 1.2B6 (anti-endothelial leukocyte adhesion molecule (ELAM)-1) and mAb 6.5B5 (anti-intercellular adhesion molecule (ICAM)-1) each inhibited partially, and to a similar extent, eosinophil and neutrophil adhesion to EC monolayers prestimulated with TNF (10 ng/ml) for 6 h. Greater inhibition of both eosinophil and neutrophil adhesion was achieved by combining the effects of mAb 1.2B6 with either mAb 6.5B5 or mAb TS1/18 (anti-CD18). These observations indicate that both ELAM-1 and ICAM-1 are involved in the adhesion of eosinophils and neutrophils to EC stimulated with TNF. In order to determine whether these molecules are expressed in vivo during allergen-induced late phase allergic responses in the skin, human skin biopsies were examined at 6 h after Ag or saline challenge with the use of an alkaline phosphatase-staining technique. Both ELAM-1 and ICAM-1 were expressed with greater intensities in Ag-challenged biopsies, suggesting that these molecules may be involved in granulocyte recruitment in vivo. The similarities we have established between mechanisms of eosinophil and neutrophil adhesion to cytokine-stimulated EC suggests that factors other than differential leukocyte-EC adhesion may be responsible for the selective accumulation of eosinophils at sites of allergic inflammation.