CD1 molecules present lipid antigens to T cells. An intriguing subset of human T cells recognize CD1-expressing cells without deliberately added lipids. Frequency, subset distribution, clonal composition, naïve-to-memory dynamic transition of these CD1 selfreactive T cells remain largely unknown. By screening libraries of T-cell clones, generated from CD4 1 or CD4 À CD8 À double negative (DN) T cells sorted from the same donors, and by limiting dilution analysis, we find that the frequency of CD1 self-reactive T cells is unexpectedly high in both T-cell subsets, in the range of 1/10-1/300 circulating T cells. These T cells predominantly recognize CD1a and CD1c and express diverse TCRs. Frequency comparisons of T-cell clones from sorted naïve and memory compartments of umbilical cord and adult blood show that CD1 self-reactive T cells are naïve at birth and undergo an age-dependent increase in the memory compartment, suggesting a naïve/ memory adaptive-like population dynamics. CD1 self-reactive clones exhibit mostly Th1 and Th0 functional activities, depending on the subset and on the CD1 isotype restriction. These findings unveil the unanticipated relevance of self-lipid T-cell response in humans and clarify the basic parameters of the lipid-specific T-cell physiology. IntroductionConventional TCR-a/b 1 T lymphocytes recognize peptides presented by MHC molecules and are key players in the adaptive immune response. Thymic selection maximizes the generation of conventional mature T-cell repertoires specific for foreign Ags while minimizing autoreactivity [1]. A key feature of the adaptive immune response is that newly generated conventional T cells are naïve and acquire an effector/memory phenotype upon Ag encounter [2].There exists also an unconventional population of TCR-a/b 1 T lymphocytes that are restricted for CD1 molecules and recognize self-and microbial lipid antigens [3]. CD1 are non-polymorphic MHC class I-like molecules classified into three groups based on the sequence homology: group 1 comprises CD1a, CD1b and CD1c; group 2 CD1d; group 3 CD1e [4]. The best characterized CD1-restricted T cells are the CD1d-restricted invariant Natural Killer à These authors contributed equally to this work. 602Frontline T (iNKT) cells that express, in humans, an invariant Va24-Ja18 TCR paired with Vb11, together with NK-cell receptors [5][6][7]. iNKT cells can be unequivocally identify through their peculiar TCR: they are overly autoreactive, display an innate-like (constitutive) effector/ memory phenotype already at birth [8], unlike conventional T cells, and are divided in two main and functionally distinct CD4 1 and CD4 À CD8 À double negative (DN) subsets [9,10].A second type of CD1-restricted T lymphocytes does not express the invariant TCR and is mainly restricted for group 1 CD1 [3]. Because of the lack of specific markers, this T-cell type has been investigated using sporadically isolated T-cell clones, which provided fundamental hints on the microbial lipids and lipopeptides Ags recognized by these T cells...

CD1c self-reactive T cells recognize a novel class of self-lipids that are accumulated on leukemia cells.

The variables that influence priming of human naive CD4+ T cells by dendritic cells (DC) were dissected in vitro by analyzing the response to the bacterial superantigen toxicshock syndrome toxin or to alloantigens. We show that under conditions that force DC‐T cell interactions a single DC can prime up to 20 naive T cells. Moreover, the strength of antigenic stimulation, as determined by DC numbers, antigen dose, TCR avidity and duration of DC‐T cell interactions, drives the progressive differentiation of proliferating T cells from a non‐effector CCR7+ stage, to an effector CCR7– stage and, eventually, to cell death. We also show that the proliferating CCR7+ and CCR7– populations share clonotypic sequences, demonstrating that the two cell fates can be generated within a single clone. Taken together these results indicate that the strength of antigenic stimulation regulates T cell progression through thresholds of proliferation, differentiation and death. However, the random nature of DC‐T cell encounters introduces a critical stochastic element in T cell stimulation, which leads to the generation of cells endowed with distinct homing potentials and effector functions within a given T cell clone.

Fluoxetine at 10 and 25 mg/kg increased (167 and 205%, respectively) the extracellular dopamine concentration in the prefrontal cortex, whereas 25 (but not 10) mg/kg citalopram raised (216%) dialysate dopamine. No compound modified dialysate dopamine in the nucleus accumbens. The effect of 25 mg/kg of both compounds on cortical extracellular dopamine was not significantly affected by 300 mg/kg p-chlorophenylalanine (PCPA) (fluoxetine, saline, 235%; PCPA, 230%; citalopram, saline, 179%; PCPA, 181%). PCPA depleted tissue and dialysate serotonin by ϳ90 and 50%, respectively, and prevented the effect of fluoxetine and citalopram on dialysate serotonin (fluoxetine, saline, 246%; PCPA, 110%; citalopram, saline, 155%; PCPA, 96%). Citalopram significantly raised extracellular serotonin from 0.1 to 100 M (251-520%), whereas only 10 and 100 M increased dialysate dopamine (143-231%). Fluoxetine similarly increased extracellular serotonin (98 -336%) and dopamine (117-318%). PCPA significantly reduced basal serotonin and the effects of 100 M fluoxetine (saline, 272%; PCPA, 203%) and citalopram (saline, 345%; PCPA, 258%) on dialysate serotonin but did not modify their effect on dopamine (fluoxetine, saline, 220%; PCPA, 202%; citalopram, saline, 191%; PCPA, 211%). The results clearly show that the effects of fluoxetine and of high concentrations of citalopram on extracellular dopamine do not depend on their effects on serotonin. Key Words: Selective serotonin reuptake inhibitor-Microdialysis-Dopamine-Serotonin-Prefrontal cortex-Nucleus accumbens-p-Chlorophenylalanine.

IntroductionOn recognition of antigenic peptides bound to major histocompatibility complex (MHC) molecules, the T cell receptor (TCR) complex generates essential biochemical signals for T-cell activation. 1 Sensitivity of T cells to TCR-dependent activation is greatly enhanced when CD4 or CD8 proteins are engaged at the same time. 2 These proteins have been referred to as coreceptors, 3 because they are supposed to bind the same MHC molecule engaged by the TCR, and are supposed to drag the associated tyrosine kinase Lck in contact with the TCR-associated CD3 zeta chains to initiate the phosphorylation events leading to T-cell activation. 4 While CD8 binds MHC class I molecules, the CD4 coreceptor binds MHC class II molecules, and augments signaling via the TCR by up to 100-fold. 2 Structure-function studies and crystallographic analysis of CD4-MHC class II complexes indicate that CD4 interacts with its residues on the D1 domain with both ␣2 and ␤2 domains of the MHC class II ␣␤ heterodimer. [5][6][7][8][9] Invariant natural killer T cells (iNKT) cells are a subset of nonconventional T lymphocytes present in most mammalian species studied so far that share several phenotypic features with natural killer cells, such as surface expression of CD161. 10 Human iNKT cells express an invariant V␣24-J␣Q TCR␣ chain paired preferentially with junctionally diverse V␤11D␤J␤ regions. 11,12 This semi-invariant TCR (invTCR) is strikingly conserved in evolution, and recognizes lipids and glycolipids presented by CD1d, a member of the CD1 family of antigen-presenting molecules exhibiting an MHC-class I-like structure. [13][14][15] The invTCR display an exquisite specificity for the xenogeneic glycosphingolipid ␣-GalCer, presented by CD1d, which can be used to selectively activate iNKT cells in vitro and in vivo. 16,17 A number of more physiologic CD1d-restricted antigens recognized by iNKT cells have been recently identified. [18][19][20][21][22][23][24] These include bacterial glycolipids, endogenous glycolipids, tumor-derived glycoplipids, and phospholipids, as well as nonlipidic molecules. iNKT cells can be found in various peripheral organs including spleen, lymph nodes, and liver. Peripheral iNKT cells display a memory activated phenotype and can rapidly secrete large amounts of cytokines including IFN-␥, TNF-␣, IL-4, and IL-13 on antigenic activation. Production of cytokines by activated iNKT cells can play a critical role in the pathogenesis of various infectious, autoimmune, and allergic diseases, as well as in the control of tumor progression 25 (see this reference for a recent review).Mature iNKT cells are either CD4 ϩ , CD8␣␣ ϩ , or CD4 Ϫ CD8 Ϫ double negative (DN). 10 The very low frequency of CD8␣␤ ϩ cells among mature iNKT cells has been related to the early deletion of CD8 ϩ iNKT cells during thymic development, 12,26 presumably caused by high-avidity interactions between TCR/CD8 and self-CD1. Although direct interaction between CD8 and CD1d has not been formally demonstrated, these data suggest that CD8 functions ...