In contrast, although expression of the relBE and yefM-yoeB genes was not detectable in the early or middle stages of infection following phagocytosis of M. tuberculosis by human macrophages, expression of genes encoding one of the two RelE toxins, the YoeB toxin, and one of the two RelB antitoxins was apparent in the late infection stage [156]. This evidence concerns the gene RELB and infection.