The use of MAb E-9 raised against tissue-cultured endothelial cells (EC) has shown marked heterogeneity in vascular EC lining the blood vessels of normal and tumour tissues. MAb E-9 is human EC-specific and the protein recognized by it is a homodimer with a molecular mass of 97 kDa. The E-9 protein is resistant to treatment by 3 mM sodium periodate, but is sensitive to 10% trichloroacetic acid and 70% ethanol. E-9 protein has been assigned to a new cluster, CD105, and mapped to human chromosome 9q3. It has approximately 70% homology with type-III cell-surface receptor for transforming growth factor beta (TGF-beta). Recently CD105 has been reported to be the gene in patients with hereditary haemorrhagic telangiectasia. We have examined the effects of radiation on its expression in normal human umbilical-vein endothelial cells (HUVEC) and brain-tumour-derived endothelial cells (BTEC). Irradiation induced dose- and time-dependent up-regulation in the expression of the E-9 protein on the plasma membranes of EC, and also resulted in greater increase in the expression of the E-9 protein in semi-confluent (proliferating) as compared with confluent (non-proliferating) EC. It may well be that, following radiotherapy in cancer patients, E-9 protein is also up-regulated. The presence of increased amounts of E-9 protein in EC makes it an attractive target in the control of angiogenesis, especially after radiotherapy in cancer patients. The time scale involved in the up-regulation of E-9 protein following irradiation has led us to suggest that it may be a secondary event, the primary being the production and release of mitogenic factors (such as basic fibroblast growth factor) from irradiated EC.

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Hybridoma H129 .19 was derived by fusion between spleen cells of a Lou / Ws1 rat immunized with an Lyt-1+,2- anti-I-Ak cytolytic T lymphocyte (CTL) clone and the nonsecreting myeloma X63-Ag8.653. The monoclonal antibody (mAb) H129 .19 (IgG2a, kappa) was selected for its capacity to inhibit the lytic potential of the immunizing clone. H129 .19 identified a monomorphic determinant on a 55 m.w. murine T cell differentiation antigen, which appeared to be homologous to the human T4 molecule in that: 1) H129 .19 reacted with 80% adult thymocytes, with a subset of splenic T cells, and with the interleukin 2 (IL 2)-producing EL4 thymoma; 2) The mAb bound to and inhibited the IL 2 production and the proliferation of various allo- or soluble antigen-reactive T cell clones that recognized restriction or activating determinants on the I-A or I-E molecules, respectively; 3) H129 .19 did not inhibit the proliferation and/or cytolysis of Lyt-2,3+ T cells specific for class I MHC antigen; and 4) Among six anti-Iak CTL clones examined in this study, the mAb H129 .19 reacted with two I-Ak-specific, Lyt-2,3- clones on which it exerted strong cytolysis inhibiting effect at the effector cell level. By contrast, two other anti-I-Ak and two anti-I-Ek CTL clones were found to express the Lyt-2,3+,T4- cell surface phenotype. The cytolytic potential of the latter clones was not inhibited by anti-Lyt-2,3 mAb. These studies strongly suggest that the mouse T4 molecule facilitates the recognition of class II MHC antigen by most but not all T cells.