ah! the joys of transcriptional control...

... and the 'shrewdness' of M. tuberculosis! A transcription factor that up-regulates expression of a secretion system required for virulence, is itself secreted by this same system. The resulting reduction of transcription factor molecules in the bacterial cell thus quickly establishes a negative feedback loop, effectively contributing to the 'damping' of M. tuberculosis virulence - which is precisely the special trait that allows this bacterium to persist in the human host for a long time, to go through latency stage(s), and be potentially re-activated later in life.