White blood cells are a crucial part of our immune system, responsible for defending our bodies against harmful disease. Here, a type of human white blood cell called a natural killer cell (coloured red) comes into contact with a virus-infected cell (shown in blue). When the two cells meet, they have a chemical ‘conversation’ exchanging tiny signalling proteins (yellow dots) between their outer membranes via thin, finger-like structures. Different types of cell display different protein ‘signatures’ on their membranes, and this allows them to communicate and recognise one another. Diseases caused by viruses can alter cell surface proteins, which means white blood cells can recognise infected cells as foe, triggering an immune response. The cells pictured measure only a few thousandths of a millimetre across. To capture these cells in conversation, they must be fixed in formaldehyde, coated with platinum and viewed with an electron microscope.
Written by Emma Stoye
BPoD stands for Biomedical Picture of the Day. Managed by the MRC London Institute of Medical Sciences (the new name for the MRC Clinical Sciences Centre) 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.