Ultrastructure of B cells infected with M. smegmatis (MSM) and M. tuberculosis (MTB). a) MSM-infected B cell with abundant internalised bacilli (white arrow) after 1 h of infection. b) MSM-infected B cell after 1 h of infection, which shows the binding of a bacillus to a lamellipodium (black arrow) and the destruction of an intracellular bacillus contained in a vacuole (white arrow). c) MSM-infected B cell at 24 h post-infection, which shows that the cell morphology was recovered and that no internalised bacilli were present, although some swollen mitochondria were still observed (white arrows). d-e) After 1 h of infection, a B cell infected with MTB exhibits a large number of alterations, abundant vacuoles, swollen mitochondria, internalised mycobacteria (white arrow), and “curved vacuoles” (black arrowheads). f) Magnification of a B cell infected with MTB (square), which shows that some of the altered mitochondria are in the process of forming double to multi-membrane vacuoles (autophagy-like vacuoles). g) B cell infected with MTB for 24 h shows intracellular bacilli in vacuoles (white arrows), abundant vacuoles, and an electro-dense cellular nucleus, which suggests strong damage. h) Replicating mycobacteria in spacious vacuole (white arrow) formed in a B cell infected with MTB for 24 h. g) Detail of MTB bacillus in a spacious vacuole after 24 h of B cell infection.