CD4 and tuberculosis: To further understand theunderlying mechanisms of the low frequency of effector T cell activation in thelungs, we quantitated CD4+ effector T cell responses to the peptide25 epitope of M. tuberculosis Ag85B, a secreted protein targeted bya large number of M. tuberculosis-specific CD4+ Tcells [45].Ag85B is targeted by 5 of the 9 novel tuberculosis vaccine candidates currently inclinical trials [46], thus understanding its behavior and responses to it invivo has considerable importance for TB vaccine development.