CD69 and bacterial infectious disease: In addition, highest numbers of activated, CD69+ Vγ9/Vδ2 T cells were seen at the earliest time-points post-infection (p.i.) and steadily declined over the following days to the background values seen in HMB-PP− bacterial infections and in non-infected individuals (Fig. 8A), underscoring an immediate as opposed to long-lasting involvement of HMB-PP-responsive γδ T cells in bacterial infections.