IL4 and disease arising from reactivation of latent virus: A progressive disease may be characterised by high levels of circulating IL-4 and IFN-γ expressing Mtb-specific effector/effector memory T cells and disease resolution by the reduction in circulating IL-4 expressing Mtb-specific T cells, while latent infection may be characterised by high levels of IFN-γ expression with little or no IL-4 secreting Mtb-specific cells.