Antigen presentation determines the fate of the T memory response in vivo after sublethal gamma-irradiation.

The survival of memory T cells is critical to vaccination strategies for infectious diseases and cancer, whereas their elimination may be crucial for treatment of autoimmune states. We examined the consequences of gamma-irradiation, which induces apoptosis of memory T cells in vitro, on the memory response to MHC class I alloantigen in vivo. Sublethal gamma-irradiation of primed mice eliminated accelerated rejection of skin allografts but failed to induce tolerance. Accelerated rejection was restored in irradiated mice by infusion of bone marrow cells expressing the priming alloantigen on immunostimulatory APCs (dendritic cells), whereas the memory response was not restored by infusion of bone marrow cells expressing the priming alloantigen on nonstimulatory APCs (B cells). Strikingly, irradiated mice infused with nonstimulatory bone marrow APCs exhibited long-term survival or tolerance to skin grafts expressing the priming MHC class I alloantigen. The mechanism of tolerance in this setting is explored.

Induction of antigen-specific hyporesponsiveness by transplantation of hemopoietic cells containing an MHC class I transgene regulated by a lymphocyte-specific promoter.

We explored a novel approach to tolerance induction by the transplantation of bone marrow (BM) cells (BMCs) that themselves do not express a foreign histocompatibility Ag, but which give rise to mature lymphocytes that do so. Lines of transgenic (FVB) mice were generated that contained an MHC class I Dd cDNA regulated by a CD2 promoter. Because the CD2 promoter is lymphocyte-specific and activated relatively late in lymphocyte ontogeny, Dd is expressed on most mature lymphocytes in the periphery but only on developing B cells in the BM of transgenic mice. Transgenic BMCs are tolerogenic and reproducibly engraft in nontransgenic mice using a conditioning regimen that is nonpermissive for the engraftment of conventional (MHC promoter) Dd-transgenic BMCs. Engrafted BMCs generate transgene-expressing lymphocytes and confer a state of Ag-specific hyporesponsiveness on the host that is primarily attributable to a peripheral mechanism. The strategies by which tolerance can be optimized in this system are discussed.

Localization of the forskolin labeling sites to both halves of P-glycoprotein: similarity of the sites labeled by forskolin and prazosin.

An iodinated derivative of forskolin, 6-O-[[2-[3-(4-azido-3-[125I] iodophenyl)propionamido]ethyl]carbamyl]forskolin ([125I]6-AIPP-Fsk), photolabels the multidrug efflux pump P-glycoprotein in membranes prepared from the multidrug-resistant cell lines KB-V1 and KB-C1. The labeling site for [125I]6-AIPP-Fsk was localized by immunoprecipitation of tryptic fragments of P-glycoprotein labeled in KB-C1 membranes. A 6-kDa, photolabeled, tryptic fragment was immunoprecipitated by antiserum raised against residues 348-419 of P-glycoprotein, PEPG9, but not by antisera raised against flanking regions PEPG7 and PEPG11. A peptide that corresponds to residues 343-359 of P-glycoprotein inhibited immunoprecipitation of the 6-kDa fragment by antiserum against PEPG9 but had no effect on the immunoprecipitation of photolabeled fragments by antiserum against PEPG7. A second peptide, corresponding to residues 360-376, had no effect on the immunoprecipitation by antiserum against PEPG9. [125I]6-AIPP-Fsk labels the carboxyl-terminal half of P-glycoprotein, because low molecular mass tryptic fragments were immunoprecipitated by three carboxyl-terminal antisera. Therefore, [125I]6-AIPP-Fsk labels both halves of P-glycoprotein, and labeling in the amino-terminal half can be localized to residues 291-359, which span proposed transmembrane regions 5 and 6. KB-V1 membranes photolabeled with [125I]6-AIPP-Fsk and [125I]iodoarylazidoprazosin were digested with either Staphylococcus aureus V8 protease or chymotrypsin and had similar digestion patterns, suggesting that the two drugs label the same sites on P-glycoprotein.

Interaction of forskolin with the P-glycoprotein multidrug transporter.

Forskolin and 1,9-dideoxyforskolin, an analogue that does not activate adenylyl cyclase, were tested for their ability to enhance the cytotoxic effects of adriamycin in human ovarian carcinoma cells, SKOV3, which are sensitive to adriamycin and express low levels of P-glycoprotein, and a variant cell line, SKVLB, which overexpresses the P-glycoprotein and has the multidrug resistance (MDR) phenotype. Forskolin and 1,9-dideoxyforskolin both increased the cytotoxic effects of adriamycin in SKVLB cells, yet had no effect on SKOV3 cells. Two photoactive derivatives of forskolin have been synthesized, 7-O-[[2-[3-(4-azido-3- [125I]iodophenyl)propionamido]ethyl] carbamyl]-7-deacetylforskolin, 125I-7-AIPP-Fsk, and 6-O-[[2-[3-(4-azido-3- [125I]iodophenyl)propionamido]ethyl]carbamyl]forskolin, 125I-6-AIPP-Fsk, which exhibit specificity for labeling the glucose transporter and adenylyl cyclase, respectively (Morris et al., 1991). Both photolabels identified a 140-kDa protein in membranes from SKVLB cells whose labeling was inhibited by forskolin and 1,9-dideoxyforskolin. There was no specific labeling of proteins in membranes from the SKOV3 cells. The overexpressed 140-kDa protein in SKVLB membranes was identified as the P-glycoprotein by immunoblot analysis and immunoprecipitation using anti-P-glycoprotein antiserum. Total inhibition of photolabeling of the P-glycoprotein was observed with verapamil, nifedipine, diltiazem, and vinbalastine, and partial inhibition was observed with colchicine and cytochalasin B. Forskolin was less effective at inhibiting the photolabeling of the P-glycoprotein than 1,9-dideoxyforskolin or a lipophilic derivative of forskolin. The data are consistent with forskolin binding to the P-glycoprotein analogous to that of other chemosensitizing drugs that have been shown to partially reverse MDR.(ABSTRACT TRUNCATED AT 250 WORDS)