CD80 and myalgic encephalomeyelitis/chronic fatigue syndrome: Regarding immune cell phenotypes (Figure 2), elevated levels of CD8+ natural killer T cells as a percentage of T cells and lymphocytes, CD19 on IgD+ CD38- B cells, absolute monocyte count, CD80 on CD62L+ myeloid dendritic cells, activated and secreting CD4 regulatory T cells as a percentage of CD4 regulatory T cells, and CD80 on myeloid dendritic cells were significantly linked to an increased risk of ME/CFS.