Epitope localization of a monoclonal antibody, LO-22, with broad specificity for interferon-alpha subtypes

Antigenic characterization of recombinant, lymphoblastoid, and leukocyte IFN-alpha by monoclonal antibodies

To gain more insight into similarities of different interferon-alpha (IFN-alpha) species, we evaluated neutralization and immunoactivity of a variety of IFN preparations with various monoclonal antibodies (IFN-alpha mAb). Nine IFN-alpha mAb obtained through immunization with recombinant IFN-alpha (rmAb), lymphoblastoid IFN-alpha (LY mAb), and leukocyte IFN-alpha (LE mAb) were tested. The IFN-alpha mAb were evaluated for their ability to neutralize the antiviral activity of 11 recombinant IFN-alpha subtypes, two recombinant IFN-alpha hybrids, and lymphoblastoid and leukocyte IFN-alpha preparations. The same IFN-alpha mAb were also used in immunoblotting, and some of them were used in immunoaffinity chromatography. The results of the neutralization assay reveal that the IFN-alpha mAb significantly differ in their ability to neutralize the individual IFN-alpha species. Interestingly, none of the IFN-alpha mAb was able to neutralize all the IFN-alpha species. In particular, rmAb were unable to neutralize LE-IFN-alpha or LY-IFN-alpha, whereas LE mAb and LY mAb efficiently neutralized rIFN-alpha2. In some cases, the epitopes to which IFN-alpha mAb are directed were identified through the use of synthetic fragments of IFN-alpha2 or by evaluating the selectivity in binding to IFN-alpha subtypes.

Structure-activity of type I interferons

Type I IFNs constitute a family of proteins exhibiting high homology in primary, secondary, and tertiary structures. They interact with the same receptor and transmit signals to cellular nucleus through a similar mechanism, eliciting roughly homogeneous biological activity. Nevertheless, the members of that family, IFN alpha species, IFN beta and IFN omega, due to local differences in the structure sometime show distinct properties. From the reported data it results that even minute changes or differences in the primary sequences could be responsible for a significant variety of biological actions, thus inducing to the hypothesis that Type I IFNs, rather than to be the result of a redundant replication during the evolution play definite roles in the defense of living organisms to foreign agents.

Increased sensitivity of an enzyme immunoassay for human interferon alpha 1 using a mixture of three monoclonal antibodies

A sensitive sandwich ELISA for the quantification of human interferon (IFN)-alpha 1 was designed. The assay employed IFN-alpha 1- specific polyclonal antibody for coating and monoclonal antibodies (mAbs) to IFN-alpha 1 as a second antibody. A major increase in sensitivity of the assay could be achieved, when polyclonal antibody was combined with a mixture of three mAbs binding to different regions of IFN-alpha 1, compared to the combination of a polyclonal antibody with a single mAb. The sensitivity of the established ELISA was close to that of an antiviral IFN-bioassay. The ELISA did not cross-react with IFN-alpha 2, beta, tau or omega. The immunoassay allowed to estimate the content of IFN-alpha 1 in leukocyte IFN-alpha to about 25-50% or to 2-6% in Namalwa IFN-alpha, respectively.

Human natural interferon-alpha producing cells

Interferons (IFNs) are critical components of the host immune system, serving as antiviral agents, immunomodulators and inhibitors of cell growth. Among peripheral blood mononuclear cells, the primary IFN-alpha-producing cell is a light density, HLA-DR+ cell negative for cell surface markers typical for T cells, B cells, monocytes, natural-killer or progenitor cells and has been tentatively termed the 'natural IFN-producing cell' or NIPC. Although present in very low frequency (approximately 1:1000 among peripheral blood mononuclear cells), the NIPC are very potent, with an individual cell able to produce 1-2 IU of IFN. In this review, the characteristics, phenotype, regulation and relationship of NIPC to human disease are discussed.

Application of four anti-human interferon-alpha monoclonal antibodies for immunoassay and comparative analysis of natural interferon-alpha mixtures

Four different mouse monoclonal antibodies to human interferon-alpha (IFN-alpha) were evaluated for application in quantitative and comparative analysis of natural IFN-alpha mixtures. Binding to IFN-alpha subtypes in solution revealed individual reactivity patterns. These patterns changed if the IFN-alpha molecules were immobilized either passively to a surface or bound by another antibody. Also, substitution of a single amino acid in IFN-alpha 2 affected the binding, apparently by altering the conformation. Isoelectric focusing of three natural IFN-alpha preparations from different sources, followed by immunoblotting, resulted in individual patterns with each of the four mAbs and also demonstrated variation in the composition of the IFN-alpha preparations. None of the mAbs was subtype specific, but by combining the different mAbs, and also applying polyclonal anti-human IFN-alpha antibodies, it was possible to design sensitive sandwich ELISAs with broad or more limited IFN-alpha subtype specificity.

Human T cell responses to dengue virus antigens. Proliferative responses and interferon gamma production

The severe complications of dengue virus infections, hemorrhagic manifestations and shock, are more commonly observed during secondary dengue virus infections than during primary infections. It has been speculated that these complications are mediated by cross-reactive host-immune responses. We have begun to analyze human T cell responses to dengue antigens in vitro to explain the possible role of T lymphocytes in the pathogenesis of these complications. Dengue antigens induce proliferative responses of PBMC from dengue antibody-positive donors, but do not induce specific proliferative responses of PBMC from dengue antibody-negative donors. IFN gamma is detected in the culture fluids of dengue-immune PBMC stimulated with dengue antigens. The cells that proliferate in the dengue antigen-stimulated bulk cultures have CD3+, CD4+, CD8-, CD16-, and CD20- phenotypes. Dengue-specific T cell lines were established using limiting dilution techniques. They have CD3+, CD4+, and CD8- phenotypes, and produce IFN gamma in response to dengue antigens. Culture fluids from dengue-immune PBMC stimulated with dengue antigens, which contain IFN gamma, augment dengue virus infection of human monocytes by dengue virus-antibody complexes. These results indicate that PBMC from dengue-immune donors contain CD4+ T cells that proliferate and produce IFN gamma after stimulation with dengue antigens, and suggest that the IFN gamma that is produced by these stimulated dengue-specific T cells may contribute to the pathogenesis of dengue hemorrhagic fever and dengue shock syndrome by increasing the number of dengue virus-infected monocytes in the presence of cross-reactive anti-dengue antibodies.