A whole blood assay to assess peripheral blood dendritic cell function in response to Toll-like receptor stimulation.

We report a practical technique to assess peripheral blood dendritic cell (DC) maturation and function in whole blood (WB), which requires minimal blood volumes and minimizes ex vivo manipulations of clinical specimens. We determined optimal conditions for flow cytometric analysis of markers of DC maturation, including CCR7, CD25, CD80 and CD83, and of the intracellular cytokines, tumor necrosis factor-alpha (TNF-alpha) and interferon-alpha (IFN-alpha), in both myeloid (mDC) and plasmacytoid (pDC) lineages. We demonstrate concentration-dependent production of these cytokines by DC following short-term stimulation with ligands to Toll-like receptors (TLRs) 2/1, 3, 4, 7, 8 and 9. Kinetic studies revealed maximal TNF-alpha and IFN-alpha protein expression at 2 to 3 h after stimulation with certain TLR ligands. Finally, utilizing cells from a cohort of eight healthy donors, we compared DC responses to TLR activation in WB, freshly isolated peripheral blood mononuclear cells (PBMC) and cryopreserved PBMC. We found that TNF-alpha responses were essentially preserved, but IFN-alpha responses were profoundly diminished or entirely abrogated following cryopreservation. In conclusion, we propose that WB analysis of peripheral DC function is a rapid, reliable and simple method to evaluate TLR function in clinical specimens, which obviates artifact-prone cell purification. The major impact of cryopreservation on some DC responses further strengthens the case for a rapid method that uses fresh blood.

Regulation of acquired immunity by gamma delta T-cell/dendritic-cell interactions.

In humans, innate immune recognition of mycobacteria, including Mycobacterium tuberculosis and Mycobacterium leprae, involves toll-like receptor-2 (TLR-2), expressed on immature dendritic cells (DCs), and the T-cell gammadelta receptor expressed by a subpopulation of T cells that utilize Vdelta2 (Vdelta2 T cells). To investigate modulatory relationships between these host-cell populations in a microbial context, in vitro experiments were performed with human DCs and Vdelta2 T cells stimulated with model TLR-2 ligands and phosphoantigens, respectively. We observed that TLR-2-stimulated DCs enhanced interferon-gamma (IFN-gamma) production by Vdelta2 T cells; conversely, activated Vdelta2 T cells enhanced TLR-2-induced DC maturation via soluble factors including IFN-gamma, which costimulated interleukin-12 (IL-12) p70 secretion by DCs. Exposure of DCs to activated Vdelta2 T cells was critical for Th1 T-cell priming when TLR-2 stimulation was limiting. These results suggest that Vdelta2 T cells may play an adjuvant role in priming protective antimycobacterial immunity when TLR-2 stimulation is lacking, as may occur if the infectious inoculum is small, or if the pathogen is an intrinsically weak activator of DCs.