CD274 and airway hyperresponsiveness: Although T cells, plasmacytoid DCs and monocytes represent the major sources for PD-1 and PD-L1 expression during the respiratory chlamydia infection that leads to an airway hyperresponsiveness (AHR) [170], there is no report that documents the role of the PD-1/PD-L1 axis in chlamydia-associated atherosclerosis.