Activation and accumulation of B cells in TACI-deficient mice

The tumor necrosis factor (TNF)-related ligand B lymphocyte stimulator (BLyS) binds two TNF receptor family members, transmembrane activator and calcium-modulating and cyclophilin ligand interactor (TACI) and B cell maturation molecule (BCMA). Mice that are transgenic for BLyS show B cell accumulation, activation and autoimmune lupus-like nephritis. The existence of at least two distinct BLyS receptors raises the question of the relative contribution of each to B cell functions. We therefore generated mice that were deficient in TACI. TACI-/- mice showed increased B cell accumulation and marked splenomegaly. Isolated TACI-/- B cells hyperproliferated and produced increased amounts of immunoglobulins in vitro. In vivo antigen challenge resulted in enhanced antigen-specific antibody production. Thus, TACI may play an unexpected inhibitory role in B cell activation that helps maintain immunological homeostasis.

TACI-ligand interactions are required for T cell activation and collagen-induced arthritis in mice

Interactions of the tumor necrosis factor superfamily members B lymphocyte stimulator (BLyS) and a proliferation-inducing ligand (APRIL) with their receptors-transmembrane activator and CAML interactor (TACI) and B cell maturation molecule (BCMA)-on B cells play an important role in the humoral immune response. Whereas BCMA is restricted to B cells, TACI is also expressed on activated T cells; we show here that TACI-Fc blocks the activation of T cells in vitro and inhibits antigen-specific T cell activation and priming in vivo. In a mouse model for rheumatoid arthritis (RA), an autoimmune disease that involves both B and T cell components, TACI-Fc treatment substantially inhibited inflammation, bone and cartilage destruction and disease development. Thus, BLyS and/or APRIL are important not only for B cell function but for T cell-mediated immune responses. Inhibition of these ligands might have therapeutic benefits for autoimmune diseases, such as RA, that involve both B and T cells.

CD62L is required on effector cells for local interactions in the CNS to cause myelin damage in experimental allergic encephalomyelitis

Adhesion molecules are believed to facilitate infiltration of leukocytes into the CNS of mice with experimental allergic encephalomyelitis (EAE). The role of the adhesion molecule CD62L (L-selectin) in the immunopathology of EAE is not known. To study this, we crossed CD62L-deficient mice with myelin basic protein-specific TCR (MBP-TCR) transgenic mice. CD62L-deficient MBP-TCR transgenic mice failed to develop antigen-induced EAE, and, despite the presence of leukocyte infiltration, damage to myelin in the CNS was not seen. EAE could, however, be induced in CD62L-deficient mice upon adoptive transfer of wild-type macrophages. Our results suggest that CD62L is not required for activation of autoimmune CD4 T cells but is important for the final destructive function of effector cells in the CNS and support a novel mechanism whereby CD62L expressed on effector cells is important in mediating myelin damage.

VEGF antagonism reduces edema formation and tissue damage after ischemia/reperfusion injury in the mouse brain

VEGF is mitogenic, angiogenic, and a potent mediator of vascular permeability. VEGF causes extravasation of plasma protein in skin bioassays and increases hydraulic conductivity in isolated perfused microvessels. Reduced tissue oxygen tension triggers VEGF expression, and increased protein and mRNA levels for VEGF and its receptors (Flt-1, Flk-1/KDR) occur in the ischemic rat brain. Brain edema, provoked in part by enhanced cerebrovascular permeability, is a major complication in central nervous system pathologies, including head trauma and stroke. The role of VEGF in this pathology has remained elusive because of the lack of a suitable experimental antagonist. We used a novel fusion protein, mFlt(1-3)-IgG, which sequesters murine VEGF, to treat mice exposed to transient cortical ischemia followed by reperfusion. Using high-resolution magnetic resonance imaging, we found a significant reduction in volume of the edematous tissue 1 day after onset of ischemia in mice that received mFlt(1-3)-IgG. 8-12 weeks after treatment, measurements of the resultant infarct size revealed a significant sparing of cortical tissue. Regional cerebral blood flow was unaffected by the administration of mFlt(1-3)-IgG. These results demonstrate that antagonism of VEGF reduces ischemia/reperfusion-related brain edema and injury, implicating VEGF in the pathogenesis of stroke and related disorders.