Epstein-Barr virus promotes interferon-alpha production by plasmacytoid dendritic cells.

OBJECTIVE: Epstein-Barr virus (EBV) infection has been linked to systemic lupus erythematosus (SLE), as demonstrated by the presence of increased seroprevalence and elevated viral loads, but the mechanism of this linkage has not been elucidated. Increased interferon-alpha (IFNalpha) levels and signatures, which are associated with innate immune responses, have been found in patients with SLE. Plasmacytoid dendritic cells (PDCs) are innate immune cells that mediate viral immunity by producing large quantities of IFNalpha, but the role they play during infection with EBV remains unclear. To address this issue, we investigated the ability of EBV to promote IFNalpha production by PDCs in healthy subjects. METHODS: Human PDCs were sorted and cultured in the presence of EBV, EBV-encoded RNA, and EBV double-stranded DNA. IFNalpha production by PDCs was measured by enzyme-linked immunosorbent assay, with the activation of these cells measured by flow cytometry. RESULTS: We found that EBV DNA and RNA promoted IFNalpha production by human PDCs through engagement of Toll-like receptor 9 (TLR-9) and TLR-7, respectively, with the initial viral recognition by PDCs mediated by binding to class II major histocompatibility complex (MHC) molecules. CONCLUSION: These data demonstrate that class II MHC-specific engagement by virus, with subsequent viral nucleic acid recognition, mediates IFNalpha production by PDCs. Our results suggest that elevated levels of IFNalpha found in SLE patients may be a result of aberrantly controlled chronic viral infection.

Editing antigen presentation: antigen transfer between human B lymphocytes and macrophages mediated by class A scavenger receptors.

B lymphocytes can function independently as efficient APCs. However, our previous studies demonstrate that both dendritic cells and macrophages are necessary to propagate immune responses initiated by B cell APCs. This finding led us to identify a process in mice whereby Ag-specific B cells transfer Ag to other APCs. In this study, we report the ability and mechanism by which human B lymphocytes can transfer BCR-captured Ag to macrophages. The transfer of Ag involves direct contact between the two cells followed by the capture of B cell-derived membrane and/or intracellular components by the macrophage. These events are abrogated by blocking scavenger receptor A, a receptor involved in the exchange of membrane between APCs. Macrophages acquire greater amounts of Ag in the presence of specific B cells than in their absence. This mechanism allows B cells to amplify or edit the immune response to specific Ag by transferring BCR-captured Ag to other professional APCs, thereby increasing the frequency of its presentation. Ag transfer may perpetuate chronic autoimmune responses to specific self-proteins and help explain the efficacy of B cell-directed therapies in human disease.

Transfer of antigen from human B cells to dendritic cells.

The cooperation of B lymphocytes with other antigen presenting cells (APCs) is often necessary in the efficient processing and presentation of antigen. Herein, we describe a mechanism by which B cells physically interact with dendritic cells (DCs) resulting in the transfer of B cell receptor (BCR)-enriched antigen to these APCs. Antigen transfer involves direct contact between the two cells followed by the capture of B cell derived membrane and intracellular components. Strikingly, DCs acquire greater amounts of antigen by transfer from B cells than by endocytosis of free antigen. Blocking scavenger receptor A, a DC surface receptor involved in membrane acquisition, abrogates these events. We propose that antigen transfer from B cells to DCs results in a more focused immunologic response due to the selective editing of Ag by the BCR.

Colonic immune stimulation by targeted oral vaccine.

BACKGROUND: Currently, sufficient data exist to support the use of lactobacilli as candidates for the development of new oral targeted vaccines. To this end, we have previously shown that Lactobacillus gasseri expressing the protective antigen (PA) component of anthrax toxin genetically fused to a dendritic cell (DC)-binding peptide (DCpep) induced efficacious humoral and T cell-mediated immune responses against Bacillus anthracis Sterne challenge. METHODOLOGY/PRINCIPAL FINDING: In the present study, we investigated the effects of a dose dependent treatment of mice with L. gasseri expressing the PA-DCpep fusion protein on intestinal and systemic immune responses and confirmed its safety. Treatment of mice with different doses of L. gasseri expressing PA-DCpep stimulated colonic immune responses, resulting in the activation of innate immune cells, including dendritic cells, which induced robust Th1, Th17, CD4(+)Foxp3(+) and CD8(+)Foxp3(+) T cell immune responses. Notably, high doses of L. gasseri expressing PA-DCpep (10(12) CFU) were not toxic to the mice. Treatment of mice with L. gasseri expressing PA-DCpep triggered phenotypic maturation and the release of proinflammatory cytokines by dendritic cells and macrophages. Moreover, treatment of mice with L. gasseri expressing PA-DCpep enhanced antibody immune responses, including IgA, IgG(1), IgG(2b), IgG(2c) and IgG(3). L. gasseri expressing PA-DCpep also increased the gene expression of numerous pattern recognition receptors, including Toll-like receptors, C-type lectin receptors and NOD-like receptors. CONCLUSION/SIGNIFICANCE: These findings suggest that L. gasseri expressing PA-DCpep has substantial immunopotentiating properties, as it can induce humoral and T cell-mediated immune responses upon oral administration and may be used as a safe oral vaccine against anthrax challenge.

Isoaspartyl post-translational modification triggers anti-tumor T and B lymphocyte immunity.

A hallmark of the immune system is the ability to ignore self-antigens. In attempts to bypass normal immune tolerance, a post-translational protein modification was introduced into self-antigens to break T and B cell tolerance. We demonstrate that immune tolerance is bypassed by immunization with a post-translationally modified melanoma antigen. In particular, the conversion of an aspartic acid to an isoaspartic acid within the melanoma antigen tyrosinase-related protein (TRP)-2 peptide-(181-188) makes the otherwise immunologically ignored TRP-2 antigen immunogenic. Tetramer analysis of iso-Asp TRP-2 peptide-immunized mice demonstrated that CD8+ T cells not only recognized the isoaspartyl TRP-2 peptide but also the native TRP-2 peptide. These CD8+ T cells functioned as cytotoxic T lymphocytes, as they effectively lysed TRP-2 peptide-pulsed targets both in vitro and in vivo. Potentially, post-translational protein modification can be utilized to trigger strong immune responses to either tumor proteins or potentially weakly immunogenic pathogens.