Epstein-Barr virus (EBV)-induced gene 2 (EBI2, aka GPR183) is a G protein-coupled receptor that is required for humoral immune responses and polymorphisms in the receptor have been associated with inflammatory autoimmune diseases1-3. The natural ligand for EBI2 has been unknown. Here we describe identification of 7α, 25-dihydroxycholesterol (5-cholesten-3β, 7α, 25-triol; 7α, 25-OHC) as a potent and selective agonist of EBI2. Functional activation of EBI2 by 7α, 25-OHC and closely related oxysterols was verified by monitoring second messenger readouts and saturable, high affinity radioligand binding. Furthermore we find that 7α, 25-OHC and closely related oxysterols act as chemoattractants for immune cells expressing EBI2 by directing cell migration in vitro and in vivo. A key enzyme required for the generation of 7α, 25-OHC is cholesterol 25-hydroxylase (Ch25h)4. Similar to EBI2 receptor knockout mice, mice deficient in Ch25h fail to position activated B cells within the spleen to the outer follicle and mount a reduced plasma cell response after an immune challenge. This demonstrates that Ch25h generates EBI2 bioactivity in vivo and suggests that the EBI2 − oxysterol signaling pathway plays an important role in the adaptive immune response.

Leukocytes roll along the endothelium of postcapillary venules in response to inf lammatory signals. Rolling under the hydrodynamic drag forces of blood f low is mediated by the interaction between selectins and their ligands across the leukocyte and endothelial cell surfaces. Here we present force-spectroscopy experiments on single complexes of P-selectin and P-selectin glycoprotein ligand-1 by atomic force microscopy to determine the intrinsic molecular properties of this dynamic adhesion process. By modeling intermolecular and intramolecular forces as well as the adhesion probability in atomic force microscopy experiments we gain information on rupture forces, elasticity, and kinetics of the P-selectin͞P-selectin glycoprotein ligand-1 interaction. The complexes are able to withstand forces up to 165 pN and show a chain-like elasticity with a molecular spring constant of 5.3 pN nm ؊1 and a persistence length of 0.35 nm. The dissociation constant (off-rate) varies over three orders of magnitude from 0.02 s ؊1 under zero force up to 15 s ؊1 under external applied forces. Rupture force and lifetime of the complexes are not constant, but directly depend on the applied force per unit time, which is a product of the intrinsic molecular elasticity and the external pulling velocity. The high strength of binding combined with force-dependent rate constants and high molecular elasticity are tailored to support physiological leukocyte rolling.

The paracaspase MALT1 plays an important role in immune receptor-driven signaling pathways leading to NF-κB activation. MALT1 promotes signaling by acting as a scaffold, recruiting downstream signaling proteins, as well as by proteolytic cleavage of multiple substrates. However, the relative contributions of these two different activities to T and B cell function are not well understood. To investigate how MALT1 proteolytic activity contributes to overall immune cell regulation, we generated MALT1 protease-deficient mice (Malt1PD/PD) and compared their phenotype with that of MALT1 knockout animals (Malt1−/−). Malt1PD/PD mice displayed defects in multiple cell types including marginal zone B cells, B1 B cells, IL-10–producing B cells, regulatory T cells, and mature T and B cells. In general, immune defects were more pronounced in Malt1−/− animals. Both mouse lines showed abrogated B cell responses upon immunization with T-dependent and T-independent Ags. In vitro, inactivation of MALT1 protease activity caused reduced stimulation-induced T cell proliferation, impaired IL-2 and TNF-α production, as well as defective Th17 differentiation. Consequently, Malt1PD/PD mice were protected in a Th17-dependent experimental autoimmune encephalomyelitis model. Surprisingly, Malt1PD/PD animals developed a multiorgan inflammatory pathology, characterized by Th1 and Th2/0 responses and enhanced IgG1 and IgE levels, which was delayed by wild-type regulatory T cell reconstitution. We therefore propose that the pathology characterizing Malt1PD/PD animals arises from an immune imbalance featuring pathogenic Th1- and Th2/0-skewed effector responses and reduced immunosuppressive compartments. These data uncover a previously unappreciated key function of MALT1 protease activity in immune homeostasis and underline its relevance in human health and disease.

Interleukin-2 (IL-2) immunotherapy is an attractive approach in treating advanced cancer. However, by binding to its IL-2 receptor α (CD25) subunit, IL-2 exerts unwanted effects, including stimulation of immunosuppressive regulatory T cells (T) and contribution to vascular leak syndrome. We used a rational approach to develop a monoclonal antibody to human IL-2, termed NARA1, which acts as a high-affinity CD25 mimic, thereby minimizing association of IL-2 with CD25. The structure of the IL-2-NARA1 complex revealed that NARA1 occupies the CD25 epitope of IL-2 and precisely overlaps with CD25. Association of NARA1 with IL-2 occurs with 10-fold higher affinity compared to CD25 and forms IL-2/NARA1 complexes, which, in vivo, preferentially stimulate CD8 T cells while disfavoring CD25 T and improving the benefit-to-adverse effect ratio of IL-2. In two transplantable and one spontaneous metastatic melanoma model, IL-2/NARA1 complex immunotherapy resulted in efficient expansion of tumor-specific and polyclonal CD8 T cells. These CD8 T cells showed robust interferon-γ production and expressed low levels of exhaustion markers programmed cell death protein-1, lymphocyte activation gene-3, and T cell immunoglobulin and mucin domain-3. These effects resulted in potent anticancer immune responses and prolonged survival in the tumor models. Collectively, our data demonstrate that NARA1 acts as a CD25-mimobody that confers selectivity and increased potency to IL-2 and warrant further assessment of NARA1 as a therapeutic.