Memory Th-17 cells specific for C. albicans are persistent in human peripheral blood

Th-17 cells, a new subset of effector CD4+ T cells, have been identified in mice and in humans. In the present study, we show that a high level of IL-17 and a high frequency of IL-17-producing cells were detected by ELISA and ELISPOT assay, respectively, when human PBMCs were stimulated with both anti-CD3 and anti-CD28. Further analysis of IL-17-producing cells by flow cytometry showed that CD4+ T cells were the main contributor to IL-17 production, and IL-17 production could be directly induced by purified CD4+ T cells at the protein and transcriptional levels. Phenotypic analyses revealed that the majority of IL-17-producing CD4+ T cells were memory cells with the expression of CD45RO, CD69, CCR6 and CCR4, and approximately 70% of IL-17-producing CD4+ T cells expressed CCR7. In addition, Th-17 cells were different from Th1, Th2 and Treg cells, because the expression of IL-17, IFN-γ, IL-4 or Foxp3 was restricted to distinct CD4+ T subsets. Importantly, stimulation of PBMCs with heated-inactivated Candida albicans (C. albicans) yeast or hyphae induced IL-17 production at the protein and transcriptional levels. These data suggest that memory Th-17 cells are present in healthy individual PBMCs and some memory Th-17 cells might play an important role in the defense against the infections of fungi such as C. albicans.