Annunziato Francesco

Department of Internal Medicine and DENOTHE Center, University of Florence, Italy

Classically, naive CD4+ T cells have been divided into two main lineages, Th1 and Th2 cells. Th1 cells produce IFN-gamma, the cytokine IL-12 being critical for their differentiation. By contrast, Th2 cells produce IL-4, IL-5, IL-9 and IL-13 and their development is usually started by IL-4 signalling. More recently, a third subset of CD4+ effector T cells which produce IL-17 has been described, which was named as Th17 afterwards. We showed that, in addition to human memory T cells producing IL-17 alone (Th17), there is a number of T cells in both blood and tissues that co-produce IL-17 and IFN-gamma (Th17/Th1). We also found that these two cell types express both RORC and T-bet and that Th17 cells could be shifted to Th1 by the addition of IL-12 suggesting a flexibility of human Th17 cells. We also found that CD161 was one of the most up-regulated genes in human Th17, in comparison with Th1 or Th2, clones. Accordingly, all IL-17-producing cells were found to be included within the CD161+ fraction of adult circulating CD4+ T cells. When CD161+ or CD161- cells were sorted  from UCB naïve CD4+ T cells and activated in presence of IL-1beta plus IL-23, Th17, Th17/Th1 or Th1 cells developed from the CD161+ fraction, whereas CD161- cells could never been induced to differentiate into IL-17- producing cells. Moreover, we found that not only CD4+TCRβ+, but also CD8+TCRβ+, CD4-CD8- TCRβ+, and CD4-CD8- TCR+ circulating lymphocytes that produce IL-17 express the distinctive marker CD161 on their surface. In addition, we demonstrated that CD161 expression identifies also CD8+ and CD4-CD8- UCB T cells that already express RORC and IL-23R mRNAs and that can be induced to differentiate into IL-17-producing cells in the presence of IL-1 and IL-23. Finally, we provided evidence that UCB naïve CD4+CD161- T cells, upon lentivirus-mediated transduction with RORC2, can acquire the ability to express IL-23R, IL-1RI, and CD161, as well as to produce IL-17. Taken together these data allow to conclude that T-cell subsets able to produce IL-17, as well as precursors of IL-17-producing T cells, exhibit surface expression of CD161, and that this feature is strictly RORC2-dependent.

More recently, we investigated the phenotype and function of CD4+ T cells in synovial fluid (SF) of affected joints from children with oligoarticular juvenile idiopathic arthritis (JIA) in order to establish a possible link with disease activity. We found that the numbers of CD4+CD161+ cells, showing either the Th1 or Th17/Th1 phenotype, were  higher in SF than in PB from JIA children. The few Th17 cells from SF of JIA spontaneously shifted in vitro to Th1 cells, whereas Th17 cells from PB of healthy children did it only in presence of SF from JIA patients,  this effect being neutralized by blocking IL-12 activity. Spectratyping and clonotypic analyses showed a similar skewing of the TCR-BV repertoire in both SF-derived CD161+Th17 and CD161+Th1 cells from the same JIA patient. The frequencies of CD4+CD161+ cells, particularly the Th17/Th1 ones, in SF of JIA positively correlated with levels of erythrocyte sedimentation rate and C-reactive protein. These findings suggest that a shifting of CD4+CD161+Th17 cells into Th17/Th1 or Th1 cells in the SF from affected joints of oligoarticular JIA can occur, and indicate that the accumulation of these latter cells correlates with parameters of inflammation, thus supporting the hypothesis that these cells may play a role in  disease activity.

1. Annunziato F, Cosmi L, Santarlasci V, Maggi L, Liotta F, Mazzinghi B, Parente E, Filì L, Ferri S, Frosali F, Giudici F, Romagnani P, Parronchi P, Tonelli F, Maggi E Romagnani S.  Phenotypic and functional features of human Th17 cells. J. Exp. Med. 204: 1849-61, 2007

2. Cosmi L, De Palma R, Santarlasci V, Maggi L, Capone M, Frosali F, Rodolico G, Querci V, Abbate G, Angeli R, Berrino L, Fambrini M, Caproni M, Tonelli F, Lazzeri E, Parronchi P, Liotta F, Maggi E, Romagnani S, Annunziato F. Human interleukin-17-producing cells originate from a CD161+ CD4+ T-cell precursor. J. Exp. Med. 205:1903-16, 2008

3. Santarlasci V, Maggi L, Capone M, Frosali F, Querci V, De Palma R, Liotta F, Cosmi L, Maggi E, Romagnani S, Annunziato F. TGF-beta indirectly favours the development of human Th17 cells by inhibiting Th1 cells. Eur. J. Immunol. 39:207-215, 2009

4. Maggi L, Santarlasci V, Capone M, Pereid A, Frosali F, Querci V, Fambrini M, Liotta F, Levings M,  Maggi E, Cosmi L, Romagnani S, Annunziato F. CD161 is a marker of all human IL-17-producing T-cell subsets and is induced by RORC. Eur. J. Immunol 40:2174-81, 2010

5. Cosmi L, Cimaz R, Maggi L, Santarlasci V, Capone M, Borriello F, Frosali F, Querci V, Simonini G, Barra G, Liotta F, De Palma R, Maggi E, Romagnani S, Annunziato F. CD4+CD161+ T cells showing transient nature of the Th17 phenotype are present in the synovial fluid from patients with juvenile idiopathic arthritis. Arthritis Rheum. 2011 Mar 4. doi: 10.1002/art.30332