Perforin-mediated immune regulation is shown as a negative feedback loop. In response to pathogens, DCs prime, or initiate, T-cell responses. T-cell populations expand, differentiate, and direct successful resistance to infection. As cytotoxic CD8⁺ T-cell populations expand, they continue to interact with DCs (presumably in a reiterative fashion) and selectively eliminate those that continue to present infection-related antigens. This selective pruning of DC populations suppresses the principle driver of ongoing T-cell activation and expansion. Defects in this loop lead to the pathological overshooting of immune activation and the disorder known as HLH.