Serotonin N-acetyltransferase (arylalkylamine N-acetyltransferase, AANAT, EC 2.3.1.87) is the first enzyme in the conversion of serotonin to melatonin. Large changes in AANAT activity play an important role in the daily rhythms in melatonin production. Although a single AANAT gene has been found in mammals and the chicken, we have now identified two AANAT genes in fish. These genes are designated AANAT-1 and AANAT-2; all known AANATs belong to the AANAT-1 subfamily. Pike AANAT-1 is nearly exclusively expressed in the retina and AANAT-2 in the pineal gland. The abundance of each mRNA changes on a circadian basis, with retinal AANAT-1 mRNA peaking in late afternoon and pineal AANAT-2 mRNA peaking 6 h later. The pike AANAT-1 and AANAT-2 enzymes (66% identical amino acids) exhibit marked differences in their affinity for serotonin, relative affinity for indoleethylamines versus phenylethylamines and temperature-activity relationships. Two AANAT genes also exist in another fish, the trout. The evolution of two AANATs may represent a strategy to optimally meet tissue-related requirements for synthesis of melatonin: pineal melatonin serves an endocrine role and retinal melatonin plays a paracrine role.Melatonin is synthesized in two vertebrate tissues, the pineal gland and the retina (1-5). Production of melatonin is almost always under control of a circadian clock, with the highest levels occurring at night (6 -10). The pineal gland produces circulating melatonin, which serves as an endocrine signal of the night period. This signal of night length is important in circadian and seasonal physiology (11,12). In contrast, retinal melatonin functions as a paracrine signal within the retina to enhance retinal functioning under low light conditions. This is done by shifting the positions of the rods and cones and regulating the turnover rates of the photoreceptive apparatuses of the rods and cones and surrounding pigment epithelium (5,13,14).The enzyme which controls the circadian pattern of melatonin synthesis (serotonin 3 N-acetylserotonin 3 melatonin) is serotonin N-acetyltransferase (arylalkylamine N-acetyltransferase; AANAT 1 ; E.C. 2.3.1.87) (15). Rhythms in AANAT activity in most vertebrates are driven by circadian clocks; light acts to reset and entrain these clocks. Light also acts independently via a downstream mechanism to turn off AANAT activity by initiating AANAT proteolysis (16).It has been generally thought that a single AANAT gene is expressed in both the pineal gland and retina. AANATs from various species are characterized by three highly conserved peptide sequences (C/c-1, D/c-1, and D/c-2; see Fig. 1) that have been proposed to be involved in arylalkylamine binding (15,17).The single AANAT gene hypothesis is consistent with the results from studies in mammals and the chicken, but not with those from studies in teleosts (bony fishes). Biochemical investigations of the Northern pike indicate that pineal and retinal AANAT have distinctly different affinities toward arylalkylamine substrates and different te...

Acute graft-versus-host disease (GVHD) and leukemic relapse are serious complications of allogeneic stem-cell transplantation (SCT). Recruitment of activated T cells to host target tissues or sites of leukemic infiltration (graft-versusleukemia [GVL]) is likely mediated by chemokine receptor-ligand interactions.We examined the contribution of donor cell CCR1 expression to the development of GVHD and GVL using a well-established murine SCT model (B6 3 B6D2F1) and CCR1-deficient mice (CCR1 ؊/؊ ). Allo-SCT with CCR1 ؊/؊ donor cells significantly reduced systemic and target organ GVHD severity, and CCR1 expression on both T cells and accessory cells contributed to GVHD mortality. Significant GVL activity was preserved following CCR1 ؊/؊ SCT, but the survival advantage diminished with increasing tumor burden. We then explored the effects of CCR1 expression on allo-specific T-cell responses. Although cytolytic effector function was maintained on a per-cell basis, T-cell proliferation and IFN␥ secretion were significantly reduced both in vivo and in vitro. T-cell function was partially dependent on interactions between CCR1 and CCL5.Collectively, these data demonstrate that CCR1 expression on donor cells contributes to the development of both GVHD and GVL, and suggest that CCR1/CCL5 receptorligand interactions modulate allo-specific T-cell responses occurring in this context. IntroductionAllogeneic stem-cell transplantation (allo-SCT) is an important therapeutic option for a variety of malignant and nonmalignant disorders. 1 Acute graft-versus-host disease (GVHD) is the most frequent and serious complication following allo-SCT and continues to limit the broader application of this therapy. 2 In the context of hematologic malignancies, a delicate balance exists between the harmful consequences of GVHD and the beneficial effects incurred when donor T cells attack recipient malignant cells, a process referred to as the graft-versus-leukemia (GVL) effect. 3,4 A better understanding of the mechanisms responsible for these graft-versushost reactions may ultimately allow for directed therapies that promote GVL while reducing GVHD. 5 The pathophysiology of acute GVHD is complex. Experimental and clinical data suggest that host antigen-presenting cells (APCs) present alloantigen to donor T cells and initiate a cascade of events resulting in the development of cytotoxic effectors and the release of inflammatory proteins including cytokines and chemokines. 6 Activated donor leukocytes subsequently traffic to specific host tissues, where they, along with soluble effectors, cause end organ damage and dysfunction.Leukocyte migration is characterized by an orchestrated process involving interactions between white blood cells (WBCs) and endothelial cells that are mediated by adhesion molecules, chemoattractants, and their receptors. Chemokines are a large family of chemotactic cytokines that interact with specific G-proteincoupled chemokine receptors. 7 Chemokines are involved in both the innate and adaptive immune responses, 8 and h...

We investigated whether CTLA4-Ig can reverse established asthma manifestations in a novel murine model of ongoing disease. In BALB/c mice, sensitized to ovalbumin (OVA) without adjuvant, airway inflammation was induced by a first series of OVA aerosol challenges. Murine CTLA4-IgG was then administered, followed by a second series of OVA inhalations. In control-treated mice, two series of OVA challenges induced upregulation of OVA-specific IgE in serum, eosinophils in the bronchoalveolar lavage fluid (BALF), and IL-5 production by lung lymphocytes upon OVA restimulation in vitro, compared with saline-challenged mice. CTLA4-IgG significantly inhibited all of these parameters in OVA-challenged mice. Importantly, mCTLA4-IgG performed better than the gold-standard dexamethasone because this corticosteroid did not inhibit the upregulation of OVA-specific IgE in serum. In a more "severe" ongoing model, induced by sensitization to OVA emulsified in aluminum hydroxide, resulting in airway hyperresponsiveness to methacholine and stronger inflammatory responses, mCTLA4-IgG was less effective in that only the number of eosinophils in the BALF was reduced (P = 0.053), whereas dexamethasone inhibited both BALF eosinophilia and cytokine production by lung lymphocytes. Thus, CTLA4-Ig might be an effective alternative therapy in established allergic asthma, especially in situations of mild disease.

These data clearly demonstrate that T cell co-stimulation via the putative B7-1/B7-2 receptor appears to have no role in the induction of Th2-mediated asthma manifestations in this murine model and, conversely, that CD28 signalling is crucial.