The mechanisms involved in the pathogenesis of epilepsy, a chronic neurological disorder that affects approximately 1 percent of the world population, are not well understood [1][2][3] . Using a mouse model of epilepsy, we show that seizures induce elevated expression of vascular cell adhesion molecules and enhanced leukocyte rolling and arrest in brain vessels mediated by the leukocyte mucin P-selectin glycoprotein ligand-1 (PSGL-1) and leukocyte integrins α4β1 and αLβ2. Inhibition of leukocytevascular interactions either with blocking antibodies, or in mice genetically deficient in functional PSGL-1, dramatically reduced seizures. Treatment with blocking antibodies following acute seizures prevented the development of epilepsy. Neutrophil depletion also inhibited acute seizure induction and chronic spontaneous recurrent seizures. Blood-brain barrier (BBB) leakage, which is known to enhance neuronal excitability, was induced by acute seizure activity but was prevented by blockade of leukocyte-vascular adhesion, suggesting a pathogenetic link between leukocyte-vascular interactions, BBB damage and seizure generation. Consistent with potential leukocyte involvement in the human, leukocytes were more abundant in brains of epileptics than of controls. Our results Correspondence should be addressed to: P.F.F (E-mail: paolo.fabene@univr.it) or G.C. (E-mail: gabriela.constantin@univr.it). Author contribution G.N.M., D.B., A.C., L.Z., F.S. performed epilepsy experiments, telemetry and open field behavior. M.M., B.R., L.O., S.B., S.A., performed intravital microscopy, in vivo staining for adhesion molecules, adhesion assays and contributed to the obtainment of behavioral data. A.O. provided the human samples. F.M., A.C. and F.O. performed immunohistochemistry on human and animal samples. P.M., E.N. and A.S provided MRI expertise. J.W.H., L.X., J.B.L., R.P.M provided vital reagents and mice. E.C.B contributed experimental suggestions, reagents and assistance with writing. P.F.F and G.C. designed the study, analyzed the data and wrote the paper NIH Public Access suggest leukocyte-endothelial interaction as a potential target for the prevention and treatment of epilepsy.Experimental data from animal models as well as human evidence indicate that seizures can lead to neuronal damage and cognitive impairement 2, 3 . However, the molecular mechanisms leading to seizures and epilepsy are not well understood. Recent data suggests that inflammation may play a role in the pathogenesis of epilepsy 4, 5 . For instance, elevation in inflammatory cytokines are seen in the central nervous system (CNS) and plasma in experimental models of seizures and in clinical cases of epilepsy 4, 5 . Moreover, CNS inflammation is associated with breakdown in the blood-brain barrier (BBB), and BBB leakage has been implicated both in the induction of seizures and in the progression to epilepsy 6-9 . Leukocyte recruitment is a hallmark of and a point of therapeutic intervention in tissue inflammation 10,11 , but a role for leukocyte-endothelia...

We have recently shown that granulocytecolony-stimulating factor (G-CSF)-and interferon-␥ (IFN-␥)-activated human neutrophils accumulate and release remarkable amounts of soluble B-lymphocyte stimulator (BLyS) in vitro. In this study, we provide evidence that neutrophils migrating into skin window exudates (SWEs) developed in healthy volunteers and in patients with rheumatoid arthritis (RA), synthesized, and released BLyS in response to locally produced G-CSF. Accordingly, the concentrations of soluble BLyS in SWEs were significantly more elevated than in serum. Because the levels of SWE BLyS, but not SWE G-CSF, were higher in patients with RA than in healthy subjects, we examined the effect of CXCL8/IL-8, C5a, and other proinflammatory mediators that dramatically accumulate in RA SWEs and in inflamed synovial fluids. We show that CXCL1/GRO␣, CXCL8/IL-8, C5a, immune complexes, tumor necrosis factor-␣ (TNF-␣), leukotriene B 4 , N-formyl-methionyl-leucyl-phenylalanine (fMLP), and lipopolysaccharide (LPS), which by themselves do not induce BLyS de novo synthesis, act as potent secretagogues for BLyS, which is mainly stored in Golgi-related compartments within G-CSF-treated neutrophils, as determined by immunogold electron microscopy. This action is pivotal in greatly amplifying neutrophil-dependent BLyS release in SWEs of patients with RA compared with healthy subjects. IntroductionB-lymphocyte stimulator (BLyS) is a recently identified member of the tumor necrosis factor (TNF) ligand superfamily that is important in B-cell differentiation, survival, and regulation of immunoglobulin production. 1,2 BLyS exists as a type 2 membrane protein and a soluble protein, 3,4 and its expression seems to be mainly, but not exclusively, restricted to cells of myeloid origin, including activated monocytes, macrophages, myeloid dendritic cells, and neutrophils. 5,6 BLyS is also known as BAFF (B-cell activator factor belonging to the TNF family), THANK (TNF homolog activating apoptosis, NF-B, and JNK), and TALL-1 (TNF-and ApoL-related leukocyte-expressed ligand 1), and it exerts its effect by binding to 3 receptors: transmembrane activator and CAML interactor (TACI), B-cell maturation antigen (BCMA), and BAFF receptor (BAFF-R). 1,2 The requirement of BLyS for humoral immune response has been clearly evidenced in mice lacking BLyS, which exhibit profound deficiencies in peripheral B-cell development and maturation and a strong impairment in T cell-dependent and T cellindependent antibody responses. 1,2 On the other hand, studies reported in the literature suggest a role of soluble BLyS in the pathogenesis of autoimmune diseases. For instance, transgenic mice overexpressing soluble BLyS develop a syndrome that has similarities with systemic lupus erythematosus (SLE) in humans. 1,2 Consistent with these observations, elevated serum BLyS levels have been found in patients with SLE and Sjögren syndrome and in patients with rheumatoid arthritis (RA). 1,2 In addition, elevated BLyS levels have been detected in patients with non-Hodgkin ...