Assessment of T-cell activation in healthy adults living in Nouna, Burkina Faso (A and B) or Heidelberg, Germany (C and D). Blood samples were stained with anti-CD3-PerCP, anti-CD4-FITC, and anti-CD95-PE (A and C) or anti-CD3-PerCP, anti-CD8-FITC, and anti-CD38-PE (B and D). CD3+ lymphocytes were identified as having low side-scatter characteristics (SSC-Height) with a high staining intensity in the FL3 channel (CD3-PerCP). Panel A and C: Expression of CD95 on CD4+ Tcells showed two distinct populations with different CD95 expression levels (peak 1 = CD4+ CD95dim, peak 2 = CD4+ CD95bright). Panel B and D: Expression of CD38 on CD8+ T-cells was characterized by a single peak on a broad distribution curve of single cell fluorescence intensities. In each histogram plot a marker spanning the region beyond the unstained control signal was used to determine the percentage of marker-positive cells. The median fluorescence intensity (MFI) of each peak representing a specific cell population as well as the median autofluorescence intensity of unstained control cells (MFI-C) was determined using a specific histogram marker positioned over the histogram curve of the population of interest.