The Stream Exchange Protocol: A Secure and Lightweight Tool for Decentralized Connection Establishment

With the growing availability and prevalence of internet-capable devices, the complexity of networks and associated connection management increases. Depending on the use case, different approaches in handling connectivity have emerged over the years, tackling diverse challenges in each distinct area. Exposing centralized web-services facilitates reachability; distributing information in a peer-to-peer fashion offers availability; and segregating virtual private sub-networks promotes confidentiality. A common challenge herein lies in connection establishment, particularly in discovering, and securely connecting to peers. However, unifying different aspects, including the usability, scalability, and security of this process in a single framework, remains a challenge. In this paper, we present the Stream Exchange Protocol (SEP) collection, which provides a set of building blocks for secure, lightweight, and decentralized connection establishment. These building blocks use unique identities that enable both the identification and authentication of single communication partners. By utilizing federated directories as decentralized databases, peers are able to reliably share authentic data, such as current network locations and available endpoints. Overall, this collection of building blocks is universally applicable, easy to use, and protected by state-of-the-art security mechanisms by design. We demonstrate the capabilities and versatility of the SEP collection by providing three tools that utilize our building blocks: a decentralized file sharing application, a point-to-point network tunnel using the SEP trust model, and an application that utilizes our decentralized discovery mechanism for authentic and asynchronous data distribution.

SP-A binding sites on bovine alveolar macrophages

Surfactant protein A (SP-A) binding to bovine alveolar macrophages was examined in order to characterize SP-A binding proteins on the cell surface and to isolate putative receptors from these cells that could be obtained in large amounts. Human SP-A, unlabeled or labeled with gold particles, was bound to freshly isolated macrophages and analyzed with ELISA or the transmission electron microscope. Binding of SP-A was inhibited by Ca2+ chelation, by an excess of unlabeled SP-A, or by the presence of 20 mg/ml mannan. We conclude that bovine alveolar macrophages expose binding sites for SP-A that are specific and that depend on Ca2+ and on mannose residues. For isolation of SP-A receptors with homologous SP-A as ligand we isolated SP-A from bovine lung lavage. SDS-PAGE analysis of the purified SP-A showed a protein of 32-36 kDa. Functional integrity of the protein was demonstrated. Bovine SP-A bound to Dynabeads was used to isolate SP-A binding proteins. From the fractionated and blotted proteins of the receptor preparation two proteins bound SP-A in a Ca2+-dependent manner, a 40-kDa protein showing mannose dependency and a 210-kDa protein, showing no mannose sensitivity.

Analysis of major histocompatibility complex class I-restricted hapten recognition by mutation of the V-J joining of T cell receptor alpha chains

Hapten-specific T cell responses are responsible for chemically induced immune disorders. However, the molecular details of hapten interactions with T cell receptors (TCR) are poorly understood. Recent studies of trinitrophenyl (TNP)-specific responses revealed major histocompatibility complex-associated TNP-peptides as dominant epitopes for CD8+ and CD4+ T cells. The present study is based on the observation that two H-2Kb/TNP-specific CTL clones (II/7 and III/1), differing exclusively in two amino acids of their TCR alpha chains, also differed in their carrier specificities for various TNP-peptides. The genes of the two alpha chains and the common beta chain were cloned into expression vectors. Transfection of the TCR alpha chain of clone III/1 into a hybridoma of clone II/7 also transferred the fine specificity of clone III/1, indicating that the small alpha chain variations were indeed responsible for the different carrier specificities. Point mutations bridging the difference between the alpha chains of clones II/7 and III/1 and functional studies of the respective TCR alpha beta transfectants into a TCR-negative hybridoma revealed an unexpected result: the two receptors did not represent examples of structural complementarity for different sets of hapten-peptide conjugates; rather, they resembled two structures of principally similar specificity but of significantly different overall affinity. This was demonstrated more directly by comparing the fine specificities of III/1 transfectants expressing or not expressing the co-receptor CD8: the CD8-negative III/1 transfectant assumed a specificity pattern indistinguishable from that of a CD8-expressing, II/7-derived transfectant. Hence, comparable alterations of antigen recognition may be induced either by subtle TCR alterations or by removal of CD8, i.e. by the presence or absence of a non-polymorphic adhesion molecule.

Purified MHC class I molecules present hapten-conjugated peptides to TNP/H-2Kb-specific T cell hybridomas

Several trinitrophenyl (TNP)-specific mouse cytotoxic T cell (CTL) clones recognize TNP-conjugated peptides in association with class I MHC Kb-molecules. Here we show that CD8+ T cell hybridomas derived from these CTL exhibit the same pattern of antigen-specificity as their parent CTL-clones. These T cell hybridomas reacted with TNBS- or TNP-peptide modified syngeneic target cells, and also with affinity purified, immobilized Kb-molecules preloaded with TNP-peptides. These findings demonstrate most directly that MHC-associated, haptenated peptides create functional antigenic epitopes for TNP-specific CTL. Furthermore, using purified Kb-molecules and a panel of Kb-binding TNP-conjugated peptides, we demonstrated that the epitope density is a critical factor in triggering these T cell hybridomas. Chemical modification of immobilized Kb-layers resulted in poor antigenicity, implying low epitope density and therefore arguing against covalent MHC-haptenization as a major source of T cell antigenic determinants.