Epithelial and endothelial expression of the green fluorescent protein reporter gene under the control of bovine prion protein (PrP) gene regulatory sequences in transgenic mice.

The expression of the cellular form of the prion protein (PrP(c)) gene is required for prion replication and neuroinvasion in transmissible spongiform encephalopathies. The identification of the cell types expressing PrP(c) is necessary to understanding how the agent replicates and spreads from peripheral sites to the central nervous system. To determine the nature of the cell types expressing PrP(c), a green fluorescent protein reporter gene was expressed in transgenic mice under the control of 6.9 kb of the bovine PrP gene regulatory sequences. It was shown that the bovine PrP gene is expressed as two populations of mRNA differing by alternative splicing of one 115-bp 5' untranslated exon in 17 different bovine tissues. The analysis of transgenic mice showed reporter gene expression in some cells that have been identified as expressing PrP, such as cerebellar Purkinje cells, lymphocytes, and keratinocytes. In addition, expression of green fluorescent protein was observed in the plexus of the enteric nervous system and in a restricted subset of cells not yet clearly identified as expressing PrP: the epithelial cells of the thymic medullary and the endothelial cells of both the mucosal capillaries of the intestine and the renal capillaries. These data provide valuable information on the distribution of PrP(c) at the cellular level and argue for roles of the epithelial and endothelial cells in the spread of infection from the periphery to the brain. Moreover, the transgenic mice described in this paper provide a model that will allow for the study of the transcriptional activity of the PrP gene promoter in response to scrapie infection.

Dermal endothelial cells and keratinocytes produce IL-7 in vivo after human Schistosoma mansoni percutaneous infection.

The parasite Schistosoma mansoni infects its definitive mammalian host through an obligatory cutaneous penetration. In this work, we studied early immune response following migration of larvae through human skin, the first immunocompetent organ encountered by the parasite. For this purpose we used an experimental model of severe combined immunodeficient mice engrafted with human skin and injected with autologous PBL. Six days after percutaneous infection, we observed an infiltration of lymphocytes within the human skin, predominantly composed of CD4+ T cells. Moreover, among the cytokines potentially present in the infected skin, immunohistochemistry analysis revealed an in vivo expression of IL-7 in the epidermal layers and strikingly at the level of vascular endothelium. Using an in vitro coculture system, we showed that the S. mansoni larvae directly trigger IL-7 production by human dermal microvascular endothelial cells but not by keratinocytes. Finally, measurements of IL-7 concentrations in plasma of 187 S. mansoni-infected individuals showed that the youngest, which are also the most infected, displayed the highest IL-7 levels. Together, these findings describe dermal endothelial cells as a novel source of IL-7, a cytokine particularly important in schistosomiasis.

Expression of a Schistosoma mansoni 28-kilodalton glutathione S-transferase in the livers of transgenic mice and its effect on parasite infection.

Schistosomiasis is a debilitating tropical disease for which an effective vaccine is needed. A 28-kDa glutathione S-transferase from Schistosoma mansoni (Sm28GST) has been shown to induce protective immunity. Sm28GST possesses significant sequence identity to mammalian GST isoforms. In order to study self-reactivity in mice immunized with Sm28GST and the concomitant phenomena of immune tolerance and epitope suppression, as well as their consequences for the protective immunity induced by this vaccination, we developed transgenic (Tg) mice that express Sm28GST under the control of a part of the mouse transferrin gene promoter. A study of (P28)Tg mice showed that the expression of Sm28GST was strictly localized in pericentrolobular hepatocytes. No histological change, inflammatory infiltrates, or modification of seric L-aspartate: 2-oxoglutarate aminotransferase concentration was observed over an 18-month period, despite a cross-reactivity between Sm28GST and a mouse molecule of 30 kDa. The immunoglobulin G anti-Sm28GST response of (P28)Tg mice immunized with recombinant Sm28GST was lower (P < 0.001) than that observed in non-(P28)Tg littermates and inversely proportional of Sm28GST liver expression. The response of non-(P28)Tg mouse spleen cells to Sm28GST stimulation was greater (P < 0.01) than that observed with (P28)Tg mouse spleen cells. (P28)Tg mice infected with 40 S. mansoni furcocercariae harbored more worms (P < 0.05) than did non-(P28)Tg control mice. The increase in the level of infection in (P28)Tg mice was reflected in concomitant increases in the numbers of adult worms and schistosome eggs found in livers and intestines after whole-body perfusion at 56 days postinfection, but no relative increase in the fertility of individual female worms was observed. The results obtained argue for the involvement of Sm28GST in reducing levels of infection and support the view that this enzyme has a central role in the maintenance of parasite viability, at least during its migration through host tissues.

Protection of nude rats against Toxoplasma infection by excreted-secreted antigen-specific helper T cells.

In the present work we demonstrate the implication of excreted-secreted antigens in eliciting the protective cell-mediated immunity developed by rats toward Toxoplasma gondii. We first showed that 10(4) specific T cells from T. gondii-infected rats conferred to nude rats the ability to resist an infection by the highly virulent RH strain of T. gondii. In a second series of experiments, the role of excreted-secreted antigens in this protection was demonstrated. After the adoptive transfer to nude rats of various doses (10(3), 10(4), 10(5)) of excreted-secreted antigen-specific helper T cells (propagated in vitro during one month), significant protection toward T. gondii was induced. Moreover, these cells were responsible for a specific antibody response in nude rats, which are normally unable to develop any specific humoral response. The specificity of these antibodies was directed toward different molecules with molecular masses of 104, 97, 57, 39, 30, 21, and 18 kilodaltons; some of these have been previously characterized as major excreted-secreted antigens.