MAbs were raised in mice against cultured human endothelial cells (EC) and screened by indirect immunofluorescence for their ability to stain intercellular contacts. One mAb denoted 7B4 was identified which, out of many cultured cell types, specifically decorated cultured human EC. The antigen recognized by mAb 7B4 is bound at the appositional surfaces of cultured EC only as they become confluent and is stably expressed at intercellular boundaries of confluent monolayers. EC recognition specificity was maintained when the antibody was assayed by immuno-histochemistry in tissue sections of many normal and malignant tissues and in blood vessels of different size and type. The antigen recognized by 7B4 was enriched at EC intercellular boundaries similarly in vitro and in situ. In vitro, addition of mAb 7B4 to confluent EC increased permeation of macromolecules across monolayers even without any obvious changes of cell morphology. In addition, when EC permeability was increased by agents such as thrombin, elastase, and TNF/gamma IFN, its distribution pattern at intercellular contact rims was severely altered. mAb 7B4 immunoprecipitated a major protein of 140 kD from metabolically and surface-labeled cultured EC extracts which appeared to be an integral membrane glycoprotein. On the basis of its distribution in cultured cells and in tissues in situ, 7B4 antigen is distinct from other described EC proteins enriched at intercellular contacts. NH2-terminal sequencing of the antigen, immunopurified from human placenta, and sequencing of peptides from tryptic peptide maps revealed identity to the cDNA deduced sequence of a recently identified new member of the cadherin family (Suzuki, S., K. Sano, and H. Tanihara. 1991. Cell Regul. 2:261-270.) These data indicate that 7B4 antigen is an endothelial-specific cadherin that plays a role in the organization of lateral endothelial junctions and in the control of permeability properties of vascular endothelium.

Systemic autoimmune diseases (SADs) are a group of connective tissue diseases with diverse, yet overlapping, symptoms and autoantibody development. The etiology behind SADs is not fully elucidated, but a number of genetic and environmental factors are known to influence the incidence of SADs. Recent findings link dysregulation of Epstein-Barr virus (EBV) with SAD development. EBV causes a persistent infection with a tight latency programme in memory B-cells, which enables evasion of the immune defence. A number of immune escape mechanisms and immune-modulating proteins have been described for EBV. These immune modulating functions make EBV a good candidate for initiation of autoimmune diseases and exacerbation of disease progression. This review focuses on systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), and Sjögren’s syndrome (SS) and sum up the existing data linking EBV with these diseases including elevated titres of EBV antibodies, reduced T-cell defence against EBV, and elevated EBV viral load. Together, these data suggest that uncontrolled EBV infection can develop diverse autoreactivities in genetic susceptible individuals with different manifestations depending on the genetic background and the site of reactivation.

The purified urokinase plasminogen activator receptor (u-PAR) was cleaved into two fragments by mild chymotrypsin treatment. The smaller fragment (apparent Mr 16,000) possessed the ligand-binding capability, as shown by chemical cross-linking analysis. This fragment constituted the NH2-terminal part of the intact receptor, probably including the whole sequence 1-87, and contained N-linked carbohydrate. After detergent phase separation in the Triton X-114 system, the fragment was present in the water phase where its binding activity could be demonstrated in the absence of the rest of the protein. An analysis of internal homology in the amino acid sequence of u-PAR revealed the presence of three repeats of approximately 90 residues each. The ligand-binding fragment corresponds to the first repeat, supporting that this unit is a structurally autonomous domain. Domains homologous with the internal repeats of u-PAR constitute the extracellular part of Ly-6 antigens and of the squid glycoprotein Sgp-2. Like u-PAR, these proteins are attached to the membrane by a glycosyl-phosphatidylinositol anchor. The hydrophilic, ligand-binding u-PAR domain identified in the present study has potential applications in interfering with cell-surface plasmin-mediated proteolysis.

The etiology of SLE is not fully established. SLE is a disease with periods of waning disease activity and intermittent flares. This fits well in theory to a latent virus infection, which occasionally switches to lytic cycle, and EBV infection has for long been suspected to be involved. This paper reviews EBV immunobiology and how this is related to SLE pathogenesis by illustrating uncontrolled reactivation of EBV as a disease mechanism for SLE. Studies on EBV in SLE patients show enlarged viral load, abnormal expression of viral lytic genes, impaired EBV-specific T-cell response, and increased levels of EBV-directed antibodies. These results suggest a role for reactivation of EBV infection in SLE. The increased level of EBV antibodies especially comprises an elevated titre of IgA antibodies, and the total number of EBV-reacting antibody isotypes is also enlarged. As EBV is known to be controlled by cell-mediated immunity, the reduced EBV-specific T-cell response in SLE patients may result in defective control of EBV causing frequent reactivation and expression of lytic cycle antigens. This gives rise to enhanced apoptosis and amplified cellular waste load resulting in activation of an immune response and development of EBV-directed antibodies and autoantibodies to cellular antigens.

The applications of peptides and antibodies to multiple targets have emerged as powerful tools in research, diagnostics, vaccine development, and therapeutics. Antibodies are unique since they, in theory, can be directed to any desired target, which illustrates their versatile nature and broad spectrum of use as illustrated by numerous applications of peptide antibodies. In recent years, due to the inherent limitations such as size and physical properties of antibodies, it has been attempted to generate new molecular compounds with equally high specificity and affinity, albeit with relatively low success. Based on this, peptides, antibodies, and peptide antibodies have established their importance and remain crucial reagents in molecular biology.

Enzyme-linked immunosorbent assay (ELISA) is a validated and sensitive method for detection of human autoantibodies, but may have problems with specificity. Non-specific binding is a well-known problem often observed in tests for autoantibodies, when sera are incubated on plastic surfaces, e.g. an ELISA plate. To understand the mechanisms underlying non-specific immunoglobulin deposition, we here analyse the phenomenon in detail and we propose means of reducing false positive test results caused by non-specific binding. The level of non-specific binding, in sera with suspected autoreactivity, was analysed in non-coated and autoantigen-coated ELISA wells and 4-32% of sera showed a high level of non-specific binding depending on the assay conditions and serum properties. Non-specifically binding sera were found to contain increased concentrations of IgG and other inflammatory mediators. Moreover, non-specific binding could be induced in serum by increasing the concentration of IgG and incubating the serum at 40 °C. This suggests that non-specific binding immunoglobulins can be formed during inflammation with high immunoglobulin levels and elevated temperature. We show that the level of non-specific binding correlates with the IgG concentration and therefore propose that non-specific binding may be interpreted as an informative finding indicative of elevated IgG and inflammation.