Human endothelial cells (ECs) provide costimulatory signals sufficient to activate resting memory T cells to produce IL-2 and IFN-γ, at least in part through CD58-CD2 interactions. Recently, the B7-like molecule, B7-H1 (PD-L1), was described and shown to regulate T cell activation; however, there are conflicting reports on whether it stimulates or inhibits T cell cytokine synthesis. B7-H1 is not expressed constitutively by ECs; however, it is rapidly induced by IFN-γ, and synergistically by IFN-γ and TNF. In inflamed skin, B7-H1 is expressed by a subset of microvessels, and by keratinocytes, but is barely detectable in normal skin. Blocking the interaction of EC-expressed B7-H1 with its T cell ligand, programmed death-1 (PD-1), using a PD-1-Fc fusion protein, or by blocking B7-H1 expression with morpholino antisense oligonucleotides, augments expression of IL-2 and IFN-γ, implicating B7-H1 as a negative regulator of cytokine synthesis. However, signaling through PD-1 does not affect induction of the activation markers CD25 or CD69 on T cells, suggesting that its effects are specific to cytokine synthesis. The suppressive effects of B7-H1 on cytokine expression are proportional to the strength of the primary stimulus, allowing for B7-H1 to determine the level of T cell activation in response to ECs. Our results demonstrate that B7-H1 negatively regulates cytokine synthesis in T cells activated by ECs.

This study demonstrates the in vitro complementation of an RNA replication-defective lesion in poliovirus RNA by providing a replicase/polymerase precursor polypeptide [P3(wt) {wild type}] in trans. The replication-defective mutation was a phenylalanine-to-histidine change (F69H) in the hydrophobic domain of the membrane-associated viral protein 3AB. RNAs encoding wild-type forms of protein 3AB or the P3 precursor polypeptide were cotranslated with full-length poliovirus RNAs containing the F69H mutation in a HeLa cell-free translation/replication assay in an attempt to trans complement the RNA replication defect exhibited by the 3AB(F69H) lesion. Unexpectedly, generation of 3AB(wt) in trans was not able to efficiently complement the defective replication complex; however, cotranslation of the large P3(wt) precursor protein allowed rescue of RNA replication. Furthermore, P3 proteins harboring mutations that resulted in either an inactive polymerase or an inactive proteinase domain displayed differential abilities to trans complement the RNA replication defect. Our results indicate that replication proteins like 3AB may need to be delivered to the poliovirus replication complex in the form of a larger 3AB-containing protein precursor prior to complex assembly rather than as the mature viral cleavage product.

IFN-inducible T cell α chemoattractant (I-TAC) is a recently discovered member of the CXC chemokine family. It is a potent T cell chemoattractant expressed by IFN-γ-treated astrocytes, monocytes, keratinocytes, bronchial epithelial cells, and neutrophils. In this study, we show that I-TAC is also expressed by IFN-γ-treated endothelial cells (EC), both at the mRNA and protein levels. Induction of the I-TAC message is rapid and sustained over 24 h. TNF-α does not induce I-TAC mRNA alone, but does act synergistically with IFN-γ. Blocking Abs to I-TAC, or to its receptor, CXCR3, reduce T cell adhesion to EC monolayers demonstrating that the expressed protein is functional. Finally, the expression of I-TAC by EC is resistant to the immunosuppressive drug cyclosporin A, suggesting that I-TAC may contribute to the chronic immune inflammation characteristic of graft arteriosclerosis.

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