No abstract

The CD4 glycoprotein is expressed on T-helper and cytotoxic lymphocytes which are restricted to class II major histocompatibility complex (MHC) antigens on target cells. Antibody inhibition studies imply that CD4 acts to increase the avidity of effector-target cell interactions. These observations have led to the speculation that CD4 binds to a monomorphic class II antigen determinant, thereby augmenting low affinity T-cell receptor-antigen interactions. However, no direct evidence has been presented indicating that CD4 and class II molecules interact. To address this issue, we have used a vector derived from simian virus 40 (SV40) to express a complementary DNA (cDNA) encoding the human CD4 glycoprotein. When CV1 cells expressing large amounts of the CD4 protein at the cell surface are incubated with human B cells bearing MHC-encoded class II molecules, they are bound tightly to the infected monolayer, whereas mutant B cells which lack class II molecules fail to bind. Furthermore, the binding reaction is specifically inhibited by anti-class II and anti-CD4 antibodies. Thus, the CD4 protein, even in the absence of T-cell receptor-antigen interactions, can interact directly with class II antigens to function as a cell surface adhesion molecule.

T lymphocyte selection and lineage commitment in the thymus requires multiple signals. Herein, CD4+ T cell generation required engagement of CD83, a surface molecule expressed by thymic epithelial and dendritic cells. CD83-deficient (CD83-/-) mice had a specific block in CD4+ single-positive thymocyte development without increased CD4+CD8+ double- or CD8+ single-positive thymocytes. This resulted in a selective 75%-90% reduction in peripheral CD4+ T cells, predominantly within the naive subset. Wild-type thymocytes and bone marrow stem cells failed to differentiate into mature CD4+ T cells when transferred into CD83-/- mice, while CD83-/- thymocytes and stem cells developed normally in wild-type mice. Thereby, CD83 expression represents an additional regulatory component for CD4+ T cell development in the thymus.

We have identified a region of the human tumor necrosis factor a (TNF-a) gene promoter that is necessary for maximal constitutive, virus-induced, and lipopolysaccharide (LPS)-induced transcription. This region contains three sites that match an NF-KB binding-site consensus sequence. We show that these three sites specifically bind NF-icB in vitro, yet each of these sites can be deleted from the TNF-a promoter with little effect on the induction of the gene by virus or LPS. Moreover, when multimers of these three sites are placed upstream from a truncated TNF-a promoter, or a heterologous promoter, an increase in the basal level of transcription is observed that is influenced by sequence context and cell type. However, these multimers are not sufficient for virus or LPS induction of either promoter. Thus, unlike other virusand LPS-inducible promoters that contain NF-#cB binding sites, these sites from the TNF-ai promoter are neither required nor sufficient for virus or LPS induction. Comparison of the sequence requirements of virus induction of the human TNF-a gene in mouse L929 and P388D1 cells reveals significant differences, indicating that the sequence requirements for virus induction of the gene are cell 'type-specific. However, the sequences required for virus and LPS induction of the gene in a single cell type, P388D1, overlap.The human tumor necrosis factor a (TNF-a) gene encodes a protein with complex biological activities that include inhibition of viral infection and possible mediation of lipopolysaccharide (LPS)-induced septic shock (reviewed in ref. 1). TNF-a gene transcription is highly inducible by virus and LPS in certain cell types (reviewed in ref.2), while in other cell types, virus alone induces the gene (3). Therefore, TNF-a gene regulation provides a model system for the study of inducible and tissue-specific gene regulation. Here we show that the cloned human TNF-a gene is appropriately regulated by virus and LPS when transiently introduced into cultured murine cells, and we identify promoter sequences that are required for constitutive, virus-induced, and LPSinduced transcription of the gene. We find that the sequences required for LPS and virus induction of TNF-a overlap. However, the minimal sequence requirements of TNF-a mRNA induction by virus are cell type-specific.The 5' flanking sequence of the TNF-a gene contains three sequences with strong similarity to NF-KB binding sites, which are located in regions of the TNF-a promoter that we show are required for maximal levels of constitutive, virusinduced, and LPS-induced transcription. We demonstrate that these sites, K1, K2, and K3, specifically bind to NF-KB. The active form of the transcription factor NF-KB, which can be activated by virus and LPS, is thought to be involved in the transcriptional activation of numerous genes (reviewed in ref. 4). However, K1, K2, and K3 can each be deleted from the TNF-a promoter with little effect on the induction of the gene by virus or LPS. Therefore, virus and LPS induction of the human ...