The CD8αα homodimer, a ligand for the non-classical major histocompatibility complex (MHC) molecule

thymic leukaemia antigen,51 is transiently expressed on CD8αβ+50 T cells that down-regulated the CD8β chain. Studies performed on human blood samples identified CD8αα+ T cells as a particular memory T-cell subset47,48 which is stable over time52 and enriched in antigen-specific T cells. Our data showed that CD8αα+ T cells are not only present in NHPs, buy BYL719 but are also present at higher frequency, in the peripheral circulation of NHPs, and that in HDs and NHPs CD8αα+ T cells were enriched in differentiated T cells compared with CD8αβ+ T cells. The NHP CD8αα+ T cells may therefore also represent a memory T-cell subsets for long-lived antigen-specific immune responses:53 we have previously shown that NHP CD8αα+ T cells, and not CD8αβ+ T cells specifically proliferate in response to molecularly defined Mycobacterium tuberculosis antigens.53 Down-regulation of the CD8β chain may represent a mechanism that lowers the avidity of the TCR to its MHC–peptide Alectinib cost ligand to secure long-term immune cell memory limiting T-cell activation54 and the risk of activation-induced apoptosis.55,56. Two additional T-cell compartments were present in HDs and at a higher frequency in NHPs: CD4+ CD8αα+ and CD4+ CD8αβ+ T cells as reported previously.57–59 Their frequency appeared to be higher in female rhesus monkeys.20

CD4+ CD8+ T cells stained positive for the degranulation marker CD107a. In contrast to a previous report,59 CD4+ CD8αα+ and CD4+ CD8αβ+ T cells in NHPs showed similar frequencies and their maturation/differentiation marker profile reflected the phenotype of the ‘conventional’ CD4+ CD8– T

Selleck Decitabine cells. We postulate that CD4+ CD8+ T cells represent a specialized compartment of CD4+ T cells formed during the different stages of T-cell differentiation, characterized by CD8 expression. Because the CD4+ CD8+ T cells were endowed with effector capacity (CD107a expression) (model Fig. 7); it could be that CD4+ CD8− T cells represent a CD4+ T-cell compartment capable of lysing target cells, the co-expression of CD8 enables intracellular calcium levels to be increased, enhances cytotoxicity and may prevent apoptosis60 upon binding to MHC class I molecules. To examine the role of CD4+ CD8+ T cells, we evaluated IL-17 production in PBMCs from HDs and NHPs in the presence IL-23 and IL-1β.61 Only data from HDs could be analysed because of the low number of IL-17-positive events in NHP PBMCs. CD4+ CD8+ T cells showed a higher, and CD8αα+ T cells a comparable, frequency of IL-17 production, yet a different profile (more polyfunctional IL-17+ TNF-α+ IFN-γ+) as compared with CD4+ (CD8−) T cells. These data support the notion that CD4+ CD8+ T cells appear to represent a distinct CD4+ T-cell memory compartment, in part characterized by IL-17 production.