Ephrin-B3 binds specifically to B lymphocytes in blood and induces migration.

Eph receptors and ephrin ligands have been shown to be differentially expressed on leucocytes. Here, we show that one member of the ephrin-B subfamily of ephrins, ephrin-B3, specifically binds to B lymphocytes in blood. No binding was observed to T lymphocytes or monocytes. The ephrin-B3 binding receptor on B lymphocytes is so far not identified, but our results here indicate that ephrin-B3 binds to a protein not belonging to the Eph receptor family. Recently, we have shown that ephrin-B3 binds to a sulphated cell surface receptor on HEK293T cells and that this binding can be blocked with heparin. Ephrin-B3 binding to B lymphocytes is partially affected by heparin, and a basic amino acid in the extracellular juxtamembrane region, Arg-188, is here shown to be involved in this binding. The functional consequence of ephrin-B3 binding to B lymphocytes is induced migration, in particular of the memory cells. To conclude, ephrin-B3 binds to B lymphocytes, most likely via a non-classical receptor, and induces migration of the memory B cell subpopulation.

Cooperativity mediated by rationally selected combinations of human monoclonal antibodies targeting the henipavirus receptor binding protein.

Hendra virus and Nipah virus (NiV), members of the Henipavirus (HNV) genus, are zoonotic paramyxoviruses known to cause severe disease across six mammalian orders, including humans. We isolated a panel of human monoclonal antibodies (mAbs) from the B cells of an individual with prior exposure to equine Hendra virus (HeV) vaccine, targeting distinct antigenic sites. The most potent class of cross-reactive antibodies achieves neutralization by blocking viral attachment to the host cell receptors ephrin-B2 and ephrin-B3, with a second class being enhanced by receptor binding. mAbs from both classes display synergistic activity in vitro. In a stringent hamster model of NiV Bangladesh (NiVB) infection, antibodies from both classes reduce morbidity and mortality and achieve synergistic protection in combination. These candidate mAbs might be suitable for use in a cocktail therapeutic approach to achieve synergistic potency and reduce the risk of virus escape.

Mouse ephrinB3 augments T-cell signaling and responses to T-cell receptor ligation.

Ephrins (EFN) are cell-surface ligands of Ephs, the largest family of cell-surface receptor tyrosine kinases. The function of EFNs in the immune system has not been well studied, although some EFNs and Ephs are expressed at high levels on certain leukocytes. We report here that EFNB3 and its receptors (collectively called EFNB3Rs, as EFNB3 binds to multiple EphBs) were expressed in peripheral T cells and monocytes/macrophages, with T cells being the dominant EFNB3+ and EFNB3R+ cell type. Solid-phase EFNB3-Fc in the presence of suboptimal anti-CD3 crosslinking enhanced T-cell responses in terms of proliferation, activation marker expression, interferon-gamma but not interleukin-2 production, and cytotoxic T-cell activity. EFNB3R costimulation in the presence of phorbol 12-myristate 13- acetate was insensitive to cyclosporin A, similar to CD28 costimulation, suggesting they might share a part of the signaling pathway. After crosslinking, T-cell receptor and EFNB3R congregated into aggregated rafts, and this provided a morphological basis for signaling pathways of T-cell receptor and EFNB3R to interact. Solid-phase EFNB3-Fc augmented p38 and p44/42 MAPK activation further downstream of the signaling pathway. These data suggest that EFNB3 is important in T-cell/T-cell and T-cell/antigen-presenting cell collaboration to enhance T-cell activation and function.