Interleukin-17 production by memory CD8+ T cells, displaying a CD27+ CD28+/− CD45RA− phenotype

in humans, was described by Kondo et al.62 CD4+ Tregs are characterized by co-expression of FoxP3 and high levels of CD25.63 We observed comparable frequencies of CD4+ (CD25high FoxP3+) Tregs in PBMCs from HD and NHPs. CD8+ Tregs (CD8+ CD25+ FoxP3+) have been described in humans,64,65 and in rhesus monkeys.66 We show that CD8+ selleck Tregs (CD8+ CD25interm./high FoxP3+) were present in PBMCs from NHPs in higher frequencies compared with HDs. The same was true for other T-cell subsets co-expressing FoxP3 and CD25 with putative regulatory functions, i.e. CD4+ CD25interm FoxP3+, CD4+ CD8+ CD25interm./high FoxP3+. The FoxP3 and CD25 can be induced upon T-cell activation, it is exclusively expressed by Tregs. The observation that NHPs showed a decreased number of bona fide IL-7Rα+ in CD4+ Tregs underlines the fact that differential suppressive functions may be present in NHPs compared with HDs. FoxP3 interacts with the IL-7Rα promoter and facilitates the down-regulation of IL-7Rα in CD4+ CD25bright Tregs;67 negative staining for IL-7Rα was postulated as a marker for human Tregs in concert with CD4, CD25 and FoxP3 analysis.68,69 A low percentage of human Tregs express IL-7Rα and these cells are important in diseases: a recent study showed that

human CD3+ CD4+ CD25+ Tregs, which stain positive for IL-7Rα, exhibit an aberrant functional capacity in patients with autoimmune diseases: they exhibit increased proliferation these and more IFN-γ/IL-2 production compared with the same cells from healthy individuals.70 The number of BGJ398 in vitro IL-7Rα+ expressing CD4+ Tregs was lower in NHPs than in HDs and this may also provide the cellular basis for differential suppressive networks in NHPs. In summary, we showed, using high content flow cytometry, that the cellular immune system in humans and NHPs exhibited high level of communalities, including a unique CD4+ CD8αα/αβ+ T-cell population with cytotoxic potential. Differences

between humans and NHPs reside in immune cell subsets with long-term memory, i.e. in CD8αα+ T cells and in cells with regulatory functions. This may be biologically important in chronic disease models where inflammatory patterns contribute to immune pathology. We would like to thank Meryl Forman, Beckman Coulter (Miami, FL) for her valuable advice concerning antibody selection and the choice of fluorochromes on custom-labelled reagents. The project was funded in part by the AERAS foundation, from Karolinska Institutet, from SIDA, Vetenskaprådet and from the Söderberg Foundation, Sweden. The study was in part financed by the Aeras foundation, by a Marie-Curie Host Fellowship for Early Stage Researchers Training grant to I.M., from Cancerfonden, the Söderberg foundation, SIDA, Vetenskapsrådet and Karolinska Institutet to M.M.