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Peripheral lung tissue contains large numbers of T cells, strategically located for immune surveillance at the blood-air interface. Given the intensity of antigenic exposure at this site, it is clear that local T-cell activation events require strict control, in order to maintain tissue homeostasis. How this control is achieved in this unique tissue microenvironment is unknown, and the present study sought to elucidate the process via detailed analysis of the surface phenotypic characteristics of freshly isolated lung T cells. We report below that these cells display typical characteristic of ‘postactivation’, notably elevated basal Ca2+ concentrations, down-modulated T-cell receptors, expression of Ia and ‘late’ activation antigens and concomitant CD4/CD8. However, levels of interleukin-2 receptor and CD2 expression were below those expected of ‘activated’ T-cell populations, and virtually all of the cells were found to be in the G0/G1 phases of the cell cycle. These properties bear a remarkable similarity to those of T cells activated in the presence of endogenous tissue (alveolar) macrophages from the lung (see accompanying paper). We hypothesize that they reflect the in vivo operation of an endogenous macrophage-mediated T-cell anergy-induction process, the function of which is to limit the local clonal expansion of T cells in peripheral lung tissue after in situ activation. [ABSTRACT FROM AUTHOR]

Listeria monocytogenes is a facultative intracellular pathogen that replicates inside mononuclear phagocytes and induces specific cellular immunity. Listeriosis encompasses many clinical syndromes and meningitis is the most frequent clinical manifestation. Human α/β and γ/δ T cells have been shown to respond to L. monocytogenes antigens and to play an important role in resistance against listerial infection. We investigated the nature of listerial ligands and the influence of the major virulence factor, listeriolysin (hly), on the stimulation of human γ/δ T cells from healthy individuals. We found that a listerial somatic protein ligand, which is sensitive to proteinase treatment, stimulated γ/δ T cells in vitro; the majority of Listeria-responsive γ/δ T cells expressed Vγ9Vδ2 T-cell receptor chains and human leucocyte antigen-DR molecules; γ/δ T-cell responses to hly+ and hly- Listeria strains were comparable; L. monocytogenes strains of different virulence stimulated γ/δ T cells equally. Thus, protein components of L. monocytogenes unrelated to virulence activate human γ/δ T cells in vitro. [ABSTRACT FROM AUTHOR]