These bead-like strings of bacteria (viewed by electron microscopy) are suffering a gruesome end. They are being eaten alive as they sit atop a macrophage, a white blood cell that is our primary defence against bacterial infection. After digesting the invader, the macrophage then moves fragments of broken-down bacteria to its surface. This signals other cells in the immune system to make proteins, which also attack the infection. However, the process is not fool proof. Some pathogens have evolved to evade digestion and reproduce inside the macrophage. Tuberculosis and leishmaniasis, two of the biggest killers in the developing world, both use this trick to duck under the immune system’s radar.
Written by Alice Lighton
BPoD stands for Biomedical Picture of the Day. Managed by the MRC London Institute of Medical Sciences the website aims to engage everyone, young and old, in the wonders of biomedicine. Images are kindly provided for inclusion on this website through the generosity of scientists across the globe.