The Mtb ESX1 mutant does not exhibit a growth defect in human cells or in vivo in the murine model [5] and this was also determined to be the case in the transwell system by plating out colony forming units (CFU) from 0, 24, 48 and 72 h post-infection plus and minus anti-fractalkine antibody (data not shown). Here, CX3CL1 is linked to infection.