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T-cell clones generated from both CD4+CD25+ and CD8+CD25+ human thymocytes were assessed for their ability to suppress the proliferative response to allogeneic stimulation of type 1 T-helper (Th1) or type 2 T-helper (Th2) clones derived from autologous CD4+CD25- thymocytes. Both CD4+ and CD8+ T-regulatory (Treg) cells completely suppressed the proliferation of Th1 clones but exhibited significantly lower suppressive activity on the proliferation of Th2 clones. The partial suppressive effect on Th2 cells was further reduced by the addition in culture of interleukin-4 (IL-4), whereas it was increased in the presence of an anti-IL-4 monoclonal antibody (mAb). The suppressive activity on Th2 clones was also completely inhibited by the addition of IL-7, IL-9, and IL-15 but not of IL-2, whereas the suppressive effect on Th1 clones was only reverted by the addition of IL-15. Of note, Th2 clones expressed significantly higher amounts of mRNA for IL-4 receptor (IL-4R) and IL-9R alpha chains than Th1 clones, whereas the expression of mRNA for IL-2R, IL-7R, and IL-15R alpha chains was comparable. Taken together, these findings demonstrate that Th2 cells have a lower susceptibility than Th1 cells to the suppressive activity of human CD25+ regulatory thymocytes, because they are able to produce, and to respond to, growth factors distinct from IL-2, such as IL-4 and IL-9.

CD8+CD25+ cells, which expressed high levels of Foxp3, glucocorticoid-induced tumor necrosis factor receptor (GITR), CCR8, tumor necrosis factor receptor 2 (TNFR2), and cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4) mRNAs, were identified in the fibrous septa and medullary areas of human thymus. Activated CD8+CD25+ thymocytes did not produce cytokines, but most of them expressed surface CTLA-4 and transforming growth factor beta1 (TGF-beta1). Like CD4+CD25+, CD8+CD25+ thymocytes suppressed the proliferation of autologous CD25-T cells via a contact-dependent mechanism. The suppressive activity of CD8+CD25+ thymocytes was abrogated by a mixture of anti-CTLA-4 and anti-TGF-beta1 antibodies and it was mediated by their ability to inhibit the expression of the interleukin 2 receptor alpha chain on target T cells. These results demonstrate the existence of a subset of human CD8+CD25+ thymocytes sharing phenotype, functional features, and mechanism of action with CD4+CD25+ T regulatory cells.

Strong reactivity for interferon-inducible protein 10 (IP-10), monokine induced by interferon gamma (Mig), and interferon-inducible T-cell alpha chemoattractant (I-TAC) was found in epithelial cells mainly localized to the medulla of postnatal human thymus. The CXC chemokine receptor common to the 3 chemokines (CXCR3) was also preferentially expressed in medullary areas of the same thymuses and appeared to be a property of 4 distinct populations: CD3+ T-cell receptor (TCR) alphabeta+ CD8+ single-positive (SP) T cells, TCRgammadelta+ T cells, natural killer (NK)-type cells, and a small subset of CD3+(low) CD4+ CD8+ TCRalphabeta+ double-positive (DP) T cells. IP-10, Mig, and I-TAC showed chemoattractant activity for TCRalphabeta+ CD8+ SP T cells, TCRgammadelta+ T cells, and NK-type cells, suggesting their role in the migration of different subsets of mature thymocytes during human thymus lymphopoiesis.

Human T helper (Th) cells (Th1- or Th2-oriented memory T cells as well as Th1- or Th2-polarized naive T cells) were infected in vitro with an R5-tropic HIV-1 strain (BaL) and assessed for their profile of cytokine production, CCR5 receptor expression, and HIV-1 p24 antigen (p24 Ag) production. Higher p24 Ag production was found in CCR5-negative Th2-like memory T cells than in CCR5-positive Th1-like memory T cells. By contrast, p24 Ag production was higher in Th1-polarized activated naive T cells in the first 4 days after infection. However, p24 Ag production in Th1-polarized T cells became comparable or even lower than the production in Th2-polarized populations later in infection or when the cells were infected with HIV-1BaL after secondary stimulation. The higher levels of p24 Ag production by Th1-polarized naive T cells soon after infection reflected a higher virus entry, as assessed by the single round infection assay using the HIV-chloramphenicol acetyl transferase (HIV-CAT) R5-tropic virus that contains the envelope protein of HIV-1 YU2 strain. The limitation of viral spread in the Th1-polarized populations, despite the initial higher level of T-cell entry of R5-tropic strains, was due to the ability of Th1 cells to produce greater amounts of beta-chemokines than Th2 cells. In fact, an inverse correlation was observed between Th1-polarized naive T cells and Th1-like memory-activated T cells in regards to p24 Ag production and the release of the following CCR5-binding chemokines: regulated on activation normal T expressed and secreted (RANTES), macrophage inflammatory protein-1alpha (MIP-1alpha), and MIP-1beta. Moreover, infection with the HIV-1BaL strain of Th1-polarized T cells in the presence of a mixture of anti-RANTES, anti-MIP-1alpha, and anti-MIP-1beta neutralizing antibodies resulted in a significant increase of HIV-1 expression. These findings suggest that Th1-type responses may favor CD4(+) T-cell infection by R5-tropic HIV-1 strains, but HIV-1 spread in Th1 cells is limited by their ability to produce CCR5-binding chemokines. (Blood. 2000;95:1167-1174)

CD30 is a member of tumor necrosis factor (TNF) receptor superfamily that is expressed by activated T cells in the presence of interleukin-4 (IL-4). Although CD30 can mediate a variety of signals, CD30-deficient mice have impaired negative selection of T cells, suggesting that at least in the context of murine thymus, CD30 is a cell death-mediating molecule. The ligand for CD30 (CD30L) is a membrane-associated glycoprotein related to TNF, which is known to be expressed mainly by activated T cells and other leukocytes. However, the nature of CD30L-expressing cells involved in the interaction with CD30+ thymocytes is unclear. We report here that in postnatal human thymus the great majority of CD30+ cells are double positive (CD4+CD8+), activated, IL-4 receptor-expressing T cells which selectively localize in the medullary areas. Moreover, many medullary epithelial cells and Hassal's corpuscles in the same thymus specimens showed unusually high expression of CD30L in comparison with other lymphoid or nonlymphoid tissues. These findings provide additional information on the nature and localization of CD30+ thymocytes and show that epithelial cells are the major holder of CD30L in the thymic medulla.

CD8+ T-cell clones were generated from peripheral blood mononuclear cells (PBMC) of three human immunodeficiency virus (HIV)-seronegative individuals and six HIV-seropositive individuals and assessed for their cytokine secretion profile, cytolytic potential, and chemokine production. While the great majority of CD8+ T-cell clones generated from HIV-seronegative individuals produced interferon (IFN)-gamma, but not interleukin-4 (IL-4), that is a type 1 cytotoxic (Tc1) profile, high numbers of CD8+ T-cell clones generated from HIV-seropositive individuals produced IL-4 in addition to IFN-gamma or IL-4 alone, thus showing a type 0 cytotoxic (Tc0)- or a type 2 cytotoxic (Tc2) profile, respectively. Tc0/Tc2 cells displayed lower cytolytic activity than Tc1 cells, including a reduced ability to lyse autologous targets pulsed with HIV or HIV peptides. By contrast, the production of chemokines RANTES and macrophage inflammatory protein-1alpha was comparable in Tc1, Tc0, and Tc2 clones irrespective of whether they were derived from HIV-seronegative or HIV-seropositive individuals. When CD8+ T-cell clones were generated from PBMC cultures of HIV-seronegative individuals conditioned with IL-4 plus an anti-IL-12 antibody (Ab), a shift towards the Tc0/Tc2-like profile was observed. Conversely, the addition to PBMC cultures of IL-12 plus an anti-IL-4 Ab shifted the differentiation of CD8+ T cells from HIV-infected individuals towards the Tc1-like profile, whereas IL-12 or anti-IL-4 Ab alone had a lower Tc1-promoting effect. Irradiated PBMC from HIV-infected individuals, used as feeder cells, shifted the differentiation of CD8+ T cells from a healthy HIV-seronegative individual towards the Tc0/Tc2-like profile. On the other hand, a shift towards the Tcl-like profile was noted in CD8+ T-cell clones generated from the skin specimens of two HIV-seropositive patients with Kaposi's sarcoma, successfully treated with IFN-alpha, in comparison to CD8+ clones generated from the same skin areas before treatment. The IFN-alpha-induced Tc1 shift could be prevented by the incubation of skin-infiltrating CD8+ T cells with IL-4 before cloning. Taken together, these data indicate that both defective production of IL-12 and abnormal IL-4 production in bulk PBMC populations of HIV-infected individuals may contribute to the development of high numbers of CD8+ T-cell clones showing a Tc0/Tc2-like phenotype and reduced cytolytic potential against HIV itself. They also suggest that the cytokine profile of CD8+ T-cell clones can be modulated by cytokines (or anticytokine Ab) both in vitro and in vivo.