Isolation of baculovirus-derived secreted and full-length beta-amyloid precursor protein

We have expressed two forms of the Alzheimer's beta-amyloid precursor protein (beta APP), the 695-amino acid form (695 beta APP), and the 751-amino acid form (751 beta APP) in a baculovirus system. Both forms were expressed as full-length precursor, and were subsequently processed in vivo to release extracellular secreted proteins. The secreted forms were cleaved from the full-length beta APP in a manner analogous to the cleavage of beta APP during constitutive secretion in mammalian cells (Weidemann, A., K?nig, G., Bunke, D., Fischer, P., Salbaum, J. M., Masters, C. L., Beyreuther, K. (1989) Cell 57, 115-126; Oltersdorf, T., Ward, P. J., Henriksson, T., Beattie, E. C., Neve, R., Lieberburg, I., and Fritz, L. J. (1990) J. Biol. Chem. 265, 4492-4497). High levels of expression of 20-50 mg/liter were achieved. Both full-length and secreted forms of the beta-amyloid precursor proteins were purified using a combination of ion-exchange and immunoaffinity chromatography using a monoclonal antibody directed against beta APP. The 751 beta APP-derived full-length and secreted forms, which contain the Kunitz protease inhibitor domain, were shown to be as active in the inhibition of trypsin as is mammalian-derived secreted beta APP. The availability of purified full-length beta APP from the baculovirus system will be valuable for biochemical and cell biological analyses that may elucidate the mechanism of the inappropriate processing that leads to beta-amyloid formation in Alzheimer's disease.     

The beta2 integrin CD11c distinguishes a subset of cytotoxic pulmonary T cells with potent antiviral effects in vitro and in vivo

Background

The integrin CD11c is known as a marker for dendritic cells and has recently been described on T cells following lymphotropic choriomeningitis virus infection, a systemic infection affecting a multitude of organs. Here, we characterise CD11c bearing T cells in a murine model of localised pulmonary infection with respiratory syncytial virus (RSV).

Methods

Mice were infected intranasally with RSV and expression of β2 integrins and T lymphocyte activation markers were monitored by flow cytometry. On day 8 post RSV infection CD11c⁺ CD8⁺ and CD11c^- CD8⁺ T cells were assessed for cytokine production, cytotoxic activity and migration. Expression of CD11c mRNA in CD8⁺ T cells was assessed by quantitative PCR.

Results

Following RSV infection CD11c⁺ CD8⁺ T cells were detectable in the lung from day 4 onwards and accounted for 45.9 ± 4.8% of CD8⁺ T cells on day 8 post infection, while only few such cells were present in mediastinal lymph nodes, spleen and blood. While CD11c was virtually absent from CD8⁺ T cells in the absence of RSV infection, its mRNA was expressed in CD8⁺ T cells of both naïve and RSV infected mice. CD11c⁺, but not CD11c^-, CD8⁺ T cells showed signs of recent activation, including up-regulation of CD11a and expression of CD11b and CD69 and were recruited preferentially to the lung. In addition, CD11c⁺ CD8⁺ T cells were the major subset responsible for IFNγ production, induction of target cell apoptosis in vitro and reduction of viral titres in vivo.

Conclusion

CD11c is a useful marker for detection and isolation of pulmonary antiviral cytotoxic T cells following RSV infection. It identifies a subset of activated, virus-specific, cytotoxic T cells that exhibit potent antiviral effects in vivo.