Requirement for dendritic cells in the establishment of anti-phospholipid antibodies

Objective: The cross-presentation of cell-associated autoantigens contributes to systemic autoimmune diseases, including systemic lupus erythematosus (SLE). Little is known about the regulation of the immune response against soluble autoantigens targeted in these diseases.

Methods: We immunized the offspring of New Zealand Black and New Zealand White mice (NZB × NZW F₁) with syngeneic dendritic cells (DC) that had macropinocytosed β2-glycoprotein 1 (β₂GPI) during propagation in normal mouse serum or that had phagocytosed apoptotic thymocytes with syngeneic (murine) or xenogeneic (bovine) β₂GPI, which was associated to plasma membrane of the cells. Mice were in parallel immunized with apoptotic thymocytes that had associated the β₂GPI to their membranes in the absence of DC. The development of anti-β₂GPI antibodies and clinical features were monitored.

Results. Apoptotic cells alone, opsonized with β₂GPI, failed to induce anti-β₂GPI autoantibodies or clinical disease. In contrast, autoimmunity developed in the presence of DC. Furthermore, the syngeneic β₂GPI was a more effective antigen than the xenogeneic protein in re-boosted animals.

Conclusions. DC effectively initiate in NZB × NZW F₁ mice self-sustaining autoimmunity against the β₂GPI, either associated to apoptotic cells or macropinocytosed from the serum.     

Anti-endothelial cell IgG antibodies from patients with Wegener's granulomatosis bind to human endothelial cells in vitro and induce adhesion molecule expression and cytokine secretion

Objective. To elucidate the role of antiendothelial cell antibodies (AECA) in vascular inflammation in patients with Wegener's granulomatosis (WG). Methods. IgG fractions from 3 AECA-positive WG patients, IgG from 3 AECA-negative WG patients, and IgG from healthy donors were tested for their ability to: a) bind to endothelial cells and to display complement-dependent or antibody-dependent cellular cytotoxicity, b) modulate cell membrane expression of adhesion molecules, as evaluated by cytofluorometry and by immunoenzymatic assay, and c) induce the secretion of interleukin-1β (IL-1β), IL-6, IL-8, and monocyte chemotactic protein 1 (MCP-1). Results. We found that AECA IgG from WG patients do not display any significant cytotoxicity but are able to up-regulate the expression of E-selectin, intercellular adhesion molecule 1 and vascular cell adhesion molecule 1 and to induce the secretion of IL-1β, IL-6, IL-8, and MCP-1. Conclusion. AECA in patients with WG could play a potential pathogenetic role by activating endothelial cells, and thus facilitating leukocyte recruitment and adhesion to endothelial surfaces, rather than by displaying a cytotoxic activity.     

Immunization of naive BALB/c mice with human β2‐Glycoprotein I breaks tolerance to the murine molecule

Objective

Immunization of naive mice with β₂‐glycoprotein I (β₂GPI) leads to the generation of pathogenic anticardiolipin antibodies associated with clinical manifestations of the antiphospholipid syndrome (APS). The aim of this study was to determine whether immunization of naive mice with human β₂GPI, which shares homology with mouse β₂GPI molecules, breaks tolerance to murine β₂GPI and leads to the generation of anti‐mouse β₂GPI.

Methods

Twenty‐four female BALB/c mice were immunized in the footpads with 10 μg of human β₂GPI. Twelve age‐ and sex‐matched BALB/c mice were immunized in the same manner with Freund's complete adjuvant and served as controls. The reactivity of whole sera, polyclonal IgG, and affinity‐purified anti‐β₂GPI IgG antibodies against human, bovine, and mouse β₂GPI was evaluated by enzyme‐linked immunosorbent assay.

Results

High titers of anti‐human β₂GPI IgG antibodies were detected 1 month after immunization. Progressively increasing titers against murine and bovine β₂GPI were recorded 1–4 months after injection.

Conclusion

Immunization of mice with human β₂GPI resulted in the generation of antibodies reacting with human, bovine, and murine β₂GPI. The loss of tolerance to mouse β₂GPI is attributable to the high interspecies homology of β₂GPI. These results may point to molecular mimicry as a possible cause of APS.