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The murine B7 (mB7) protein is a potent costimulatory molecule for the T-cell receptor (TCR)-mediated activation of murine CD4+ T cells. We have previously shown that stable mB7-transfected Chinese hamster ovary (CHO) cells but not vector-transfected controls synergize with either anti-CD3 monoclonal antibody-induced or concanavalin A-induced T-cell activation, resulting ultimately in lymphokine production and proliferation. We now have generated a hamster anti-mB7 monoclonal antibody. This reagent recognizes a protein with an apparent molecular mass of 50-60 kDa. The mB7 antigen is expressed on activated B cells and on peritoneal exudate cells (PECs). Antibody blocking experiments demonstrate that mB7 is the major costimulatory molecule expressed by PECs for the activation of murine CD4+ T cells. This suggests an important role for mB7 during immune-cell interactions. We have also surveyed a panel of murine cell lines capable of providing costimulatory activity. Our results indicate that mB7 is the major costimulatory molecule on some but not all cell lines and that there may be additional molecules besides mB7 that can costimulate the activation of murine CD4+ T cells.Stimulation of highly purified murine CD4+ T lymphocytes through the T-cell receptor (TCR) with peptide bound to major histocompatibility complex (MHC) proteins, anti-TCR-CD3 complex monoclonal antibodies (mAbs), or lectins does not lead to cell proliferation or lymphokine secretion. The above activation pathways require a second, costimulatory signal for lymphokine gene expression and proliferation that is provided by an antigen-presenting cell (APC) or by a phorbol ester. This costimulatory signal has been postulated to play a central role in the regulation of T-cell activation and in thymic development (1, 2). Its characterization is therefore of great interest.In the case of interleukin 4 (IL-4)-secreting, Th-2 type CD4+ T cells, the costimulatory signal appears to be IL-1 (3, 4). In contrast, the nature of the costimulatory signal for IL-2-secreting, Th-1 type CD4+ T cells has not yet been definitely identified. We and others have recently shown that the B7 antigen (5) can provide a potent costimulatory signal for IL-2-secreting CD4+ T cells. Transfected cell lines that express human (6, 7) or murine B7 (mB7) (8) can synergize with anti-CD3-or lectin-driven T-cell activation. Furthermore, in the human, a recombinant B7 immunoglobulin fusion protein (7) or mAbs to CD28 (9, 10), a 44-kDa homodimeric T-cell glycoprotein that is a receptor for B7 (11), can augment the proliferation or lymphokine secretion of T cells stimulated with suboptimal doses of anti-CD3 mAbs.In the present report, we describe a hamster-anti-mB7 mAb. With this reagent we have characterized the expression and function of mB7 by normal and transformed cells. Our results indicate that mB7 is the major costimulatory molecule expressed by peritoneal exudate cells (PECs) and by certain cell lines. Our results also raise the possibility that there may be other molecules b...

In recent years, the exposure of human skin to environmental and artificial UV irradiation has increased dramatically. This is due not only to increased solar UV irradiation as a consequence of stratospheric ozone depletion, but also to inappropriate social behaviour with the use of tanning salons still being very popular in the public view. Besides this, leisure activities and a lifestyle that often includes travel to equatorial regions add to the individual annual UV load. In addition to the common long-term detrimental effects such as immunosuppression and skin cancer, the photo-oxidative damage due to energy absorption of UV photons in an oxygenized environment leads to quantitative and qualitative alterations of cells and structural macromolecules of the dermal connective tissue responsible for tensile strength, resilience and stability of the skin. The clinical manifestations of UV/reactive oxygen species (ROS)-induced disturbances result in photoaged skin with wrinkle formation, laxity, leathery appearance as well as fragility, impaired wound healing capacities and higher vulnerability. Strategies to prevent or at least minimize ROS-induced photo-ageing and intrinsic ageing of the skin necessarily include protection against UV irradiation and antioxidant homeostasis.

We demonstrate that the murine B7 (mB7) protein is a potent costimulatory molecule for the activation of resting murine CD4+ T cells through the T-cell receptor (TCR)/CD3 complex. Stable mB7-transfected Chinese hamster ovary cells, but not vector-transfected controls, synergize with anti-CD3 monoclonal antibody and Con A-induced T-cell activation, resulting ultimately in proliferation. mB7 exerted its effect by inducing production of interleukin 2 and expression of the interleukin 2 receptor. Thus, mB7 costimulates T-cell activation through the TCR/CD3 complex by positively modulating the normal pathway of T-cell expansion. In contrast to the pronounced effect of mB7 on the activation of T cells through the TCR/CD3 complex, the mB7-transfected CHO cell line costimulated T-cell activation via the glycosylphosphatidylinositol-anchored proteins Thy-1 and Ly-6A.2 only inefficiently. Finally, the combination of a calcium ionophore and mB7 is not sufficient to cause T-cell proliferation, while the combination of a calcium ionophore and phorbol 12-myristate 13-acetate (PMA) stimulates T cells efficiently. The signals that mB7 and PMA provide for murine T lymphocyte activation are therefore not interchangeable, although both costimulate activation through the TCR/CD3 complex.Stimulation of highly purified CD4+ T lymphocytes with peptide-major histocompatibility complex (MHC) complexes, monoclonal antibodies (mAbs) against T-cell receptor (TCR)/CD3 complexes, lectins, or mAbs against the glycosyl-phosphatidylinositol (GPI)-anchored proteins Thy-1 and Ly-6A.2 does not lead to cell proliferation or lymphokine secretion. The above activation pathways require a second, costimulatory, signal for lymphokine gene expression and proliferation that is provided by an antigen-presenting cell (APC) or by pharmacological reagents such as phorbol 12-myristate 13-acetate (PMA) (1, 2).The nature of the costimulatory signal appears to be dependent upon the subset of CD4+ T cells that is activated. On the basis of their capacity to secrete specific lymphokines, two types of murine CD4+ T-helper cells were defined originally. Th-1 clones synthesize interleukin (IL)-2, interferon y, and lymphotoxin, whereas Th-2 clones secrete IL-4, IL-5, and IL-6 (3). In the case of Th-2 type CD4+ T cells, this costimulatory signal appears to be IL-1 (4). In contrast, the nature of the costimulatory signal for Th-1-type CD4+ T cells is unknown. Recent data in the human system suggest that B7, a 45-to 60-kDa cell surface glycoprotein present on activated B cells and on interferon-y-stimulated monocytes/macrophages (5, 6), may be costimulatory for Th-1 CD4+ T cells. Transfected cell lines that express human B7 or recombinant B7-immunoglobulin fusion protein can synergize with anti-CD3 or phytohemagglutinin-driven T-cell activation (7-9). Furthermore, binding of mAbs to CD28, a 44-kDa homodimeric T-cell glycoprotein that is a receptor for B7 (10), can augment the proliferation or lymphokine secretion of T cells stimulated with suboptimal doses of anti...

The murine B7 (mB7) protein is a potent co-stimulatory molecule for the activation of murine CD4+ T cells. We have previously shown that stable mB7-transfected Chinese hamster ovary (CHO) cells synergize with either anti-CD3 monoclonal antibodies (mAb) or concanavalin A to stimulate T cell activation. In addition, mB7 can synergize with phorbol 12-myristate 13-acetate (PMA) to induce T cell activation in an alternative pathway. In the present report we describe the effects of three immunosuppressive drugs, cyclosporin A (CsA), FK 506, and mycalamide A on mB7-mediated T cell activation. The immunophilin ligands CsA and FK 506 block activation of murine CD4+ T cells by the combination of anti-CD3 mAb and CHO-mB7 cells but do not affect activation by CHO-mB7 cells and PMA. These results support the relevance of pharmacological studies of immunosuppressive compounds in the murine model prior to their application in man. In contrast to the effects of CsA and FK 506, mycalamide A blocks activation of murine CD4+ T cells by anti-CD3 mAb and mB7 as well as activation by mB7 and PMA. On a molar basis, mycalamide A appears to be at least 10-fold more potent than FK 506 which is 100-fold more potent than CsA. Because of its effects on multiple activation pathways and because of its potency, mycalamide A could have considerable therapeutic potential.