Age dependence of the percentages of CD8+ CD28- T cells in the peripheral blood. (a) The levels of CD8+ CD28- T cells are shown in correlation with age. Regression lines were calculated for patients with ankylosing spondylitis (AS) (●, unbroken line) and healthy controls (○, dashed line). (b) A regression model was applied to determine the possible effects of AS disease and age on the level of peripheral CD8+ CD28- T cells. Receiver operating curves (ROC) and the area under the curve (AUC) were determined for both independent parameters.