The bacteria that cause tuberculosis are excellent at avoiding destruction by host cells. Indeed, the immune system’s only recourse is to surround infected cells (coloured cyan) with a huddle of immune cells – called a granuloma – in an attempt to prevent the infection spreading. But the bugs have another trick according to research performed in a fish model of the disease: They need oxygen to grow, and as oxygen levels drop (indicated by red staining) at the core of the granuloma, new blood vessels start to infiltrate. These vessels provide not only oxygen for growth but escape routes for the bacteria to spread. It’s very like what goes on inside tumours, where low oxygen levels promote blood vessel infiltration allowing cancer cells to escape (metastasise). So similar are the processes in fact that anti-cancer treatments designed to stop blood vessel growth prevented the spread of bacteria within the infected fish.
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