As EBI is highly important for generation of an

As EBI2 is highly important for generation of an efficient T cell-dependent humoral immune response [[5], [6], [7]] it may be that aberrant expression or other dysregulation of this receptor contributes in B cell pathologies. In line with this, EBI2 expression is down-regulated in diffuse large B-cell lymphomas [12] and chronic lymphocytic leukemia [13] but up-regulated in PTLDs [14]. Interestingly, PTLDs are highly associated with Epstein–Barr virus (EBV) seropositivity which agrees well with the finding that EBV infection of EPI-001 synthesis in vitro results in transformation of these into highly proliferative lymphoblastoids [19]. In both cases, the expression of EBI2 is highly upregulated suggesting that this receptor could play a role in pathogenesis [2,15] putatively in combination with BILF1 [20]. This is also indicated by the observation that the proliferation of B cells over-expressing EBI2 is higher than wt counterparts [16]. Importantly, the proliferation could be blocked by GSK682753A suggesting that targeting EBI2 could be therapeutically beneficial. This may not only be limited to malignant diseases but may also extend to EBV-associated benign conditions such as mononucleosis for which no treatment is currently available.
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Introduction Natural killer (NK) cells provide protection from viral infections or cancer via their cytolytic function and interferon gamma (IFNγ) production. A major clinical goal is to harness these NK cell functions for tumor immunotherapy (Baggio et al., 2017, Johnson and Miller, 2018, Romee et al., 2016). In addition, NK cells have been implicated in the control of HIV infection either directly or by antibody-mediated lysis of infected cells (Bradley et al., 2018, Ramsuran et al., 2018). Although NK cells lack antigen-specific receptors, recent studies indicate that some responses are characterized by expansion and memory, features originally thought to be restricted to adaptive immunity. NK cells with a memory or adaptive phenotype may be particularly effective in cellular therapies targeting tumors or chronic viral infections (Cooper et al., 2018, O’Sullivan et al., 2015). In humans, circulating NK cells encompass two major subsets, known as CD56dim and CD56bright (Freud et al., 2017, Michel et al., 2016). While this distinction is based on relative expression of the cell surface molecule CD56, profound functional differences exist between human NK subsets. CD56dim cells predominate in blood, constituting ∼90% of circulating NK populations. This subset has higher cytotoxic activity than CD56bright cells. Moreover, CD56dim NK cells preferentially express the activating Fc receptor CD16, endowing them with a capacity for antibody-dependent cellular cytotoxicity (ADCC) (Nagler et al., 1989). The CD56dim NK population also encompasses two subsets, CD57− and CD57+, the latter of which has adaptive features and expands in response to human cytomegalovirus (HCMV) infection (O’Sullivan et al., 2015). The minor CD56bright population is more efficient than CD56dim NKs in the production of cytokines, including IFNγ, granulocyte-macrophage colony-stimulating factor (GM-CSF), and tumor necrosis factor alpha (TNF-α) (Freud et al., 2017, Michel et al., 2016). Circulating NK subsets also show considerable differences in homing molecules. CD56bright cells express the chemokine receptor CCR7 and L-selectin, which drive their migration to secondary lymphoid organs (Fehniger et al., 2003). In contrast, CD56dim display a high density of CX3CR1 and CXCR1, which direct them into peripheral tissues. Interleukin (IL)-2 and IL-15 promote activation and proliferation of all NK cells. However, CD56dim express the dimeric low-affinity receptor for IL-2 (CD122-CD132), whereas CD56bright express the trimeric high-affinity IL-2R (CD25-CD122-CD132) (Allan et al., 2017). In addition, the CD56bright population expresses IL-7R and c-Kit, which may contribute to homeostatic proliferation. NK cell activation is controlled by inhibitory receptors specific for MHC class I, with CD56dim selectively expressing the KIR and LILR families, whereas CD56bright display CD94-NKG2A. Phenotypic and functional differences between CD56dim and CD56bright subsets have been extended further by gene arrays and proteomics (Hanna et al., 2004, Wendt et al., 2006).