IntroductionDendritic cells (DC) are professional antigen-presenting cells that are critically involved in the initiation of T cell-dependent immune responses as a consequence of their high expression of major histocompatibility complex (MHC) and costimulatory molecules. 1 DC are sparsely distributed throughout the body and, in most tissues, are present in an immature state, showing a high capacity for antigen uptake and processing but unable to stimulate T cells. 1,2 Once activated by inflammatory stimuli or infectious agents, DC undergo a maturation process whose hallmarks are up-regulated expression of costimulatory (CD40, CD80, and CD86) and adhesion (CD54 and CD58) molecules, migration into lymphoid organs, and subsequent acquisition of the capacity to activate quiescent, naïve, and memory lymphocytes. [1][2][3][4] In vitro, DC can be derived from either precursor cells or peripheral blood monocytes 5-8 when the appropriate cytokine signals are provided. Immature monocytederived DC (MDDC) can be obtained from peripheral blood monocytes in the presence of granulocyte-macrophage colonystimulating factor (GM-CSF) and interleukin-4 (IL-4). Addition of lipopolysaccharide (LPS) or tumor necrosis factor ␣ (TNF-␣) leads to the appearance of MDDC with all the morphologic, phenotypic, and functional characteristics of mature DC, 5,6 including de novo expression of CD83, 9 up-regulated expression of adhesion and costimulatory molecules, 1-4,10 loss of mannose-receptor-mediated endocytosis, synthesis and release of IL-12, and enhanced antigen presentation capacity. 11 Thus, in vitro maturation of MDDC represents a useful system for analyzing the molecular and functional changes that take place during acquisition of optimal T-cell-stimulating activity by DC.At least 3 distinct mitogen-activated protein kinase (MAPK) signaling cascades exist in mammals, including the extracellular signal-regulated kinase (ERK), the c-Jun N-terminal kinase (JNK), and the p38 MAPK pathways. 12 These kinases are activated by phosphorylation by distinct upstream MAPK kinases. The ERK signaling cascade regulates cell proliferation and differentiation in response to mitogens and growth factors, whereas the JNK and p38 MAPK pathways are preferentially activated by stress-inducing agents. 12 The availability of specific inhibitors for the ERK and p38 MAPK pathways allows evaluation of their respective involvement in cellular responses to extracellular stimuli. The ERK pathway inhibitors PD98059 13 and U0126 14 prevent activation of mitogenactivated protein kinase kinase (MEK) 1/2, 15 upstream activators of ERK 1/2, whereas the pyridinyl imidazole SB203580 inhibits p38 MAPK activity. 15,16 The intracellular signaling pathways implicated in maturation of MDDC are just beginning to be explored. TNF-␣ stimulation of immature MDDC initiates activation of several MAPKs, including For personal use only. on May 11, 2018. by guest www.bloodjournal.org From ERK 2, stress-activated protein kinase-JNK, and p38 MAPK. 10,17,18 Several reports have suggested t...

E2Fs are important regulators of proliferation, differentiation, and apoptosis. Here we characterize the phenotype of mice deficient in E2F2. We show that E2F2 is required for immunologic self-tolerance. E2F2(-/-) mice develop late-onset autoimmune features, characterized by widespread inflammatory infiltrates, glomerular immunocomplex deposition, and anti-nuclear antibodies. E2F2-deficient T lymphocytes exhibit enhanced TCR-stimulated proliferation and a lower activation threshold, leading to the accumulation of a population of autoreactive effector/memory T lymphocytes, which appear to be responsible for causing autoimmunity in E2F2-deficient mice. Finally, we provide support for a model to explain E2F2's unexpected role as a suppressor of T lymphocyte proliferation. Rather than functioning as a transcriptional activator, E2F2 appears to function as a transcriptional repressor of genes required for normal S phase entry, particularly E2F1.

Studies indicate that metabotropic glutamate receptors (mGluRs) may play a role in spinal sensory transmission. We examined the cellular and subcellular distribution of the mGluR subtype 4a in spinal tissue by means of a specific antiserum and immunocytochemical techniques for light and electron microscopy. A dense plexus of mGluR4a-immunoreactive elements was seen in the dorsal horn, with an apparent accumulation in lamina II. The immunostaining was composed of sparse immunoreactive fibres and punctate elements. No perikaryal staining was seen. Immunostaining for mGluR4a was detected in small to medium-sized cells but not in large cells in dorsal root ganglia. At the electron microscopic level, superficial dorsal horn laminae demonstrated numerous immunoreactive vesicle-containing profiles. Labelling was present in the cytoplasmic matrix, but accretion of immunoreaction product to presynaptic specialisations was commonly observed. Axolemmal labelling was confirmed by using a preembedding immunogold technique, which revealed distinctive deposits of gold immunoparticles along presynaptic thickenings with an average centre-to-centre distance of 41 nm (41.145 +/- 13.59). Immunoreactive terminals often formed synaptic contacts with dendritic profiles immunonegative for mGluR4a. Immunonegative dendritic profiles were observed in apposition to both mGluR4a-immunoreactive and immunonegative terminals. Diffuse immunoperoxidase reaction product was also detected in dendritic profiles, some of which were contacted by mGluR4a-immunoreactive endings, but only occasionally were they observed to accumulate immunoreaction product along the postsynaptic density. Terminals immunoreactive for mGluR4a also formed axosomatic contacts. The present results reveal that mGluR4a subserves a complex spinal circuitry to which the primary afferent system seems to be a major contributor.