All moral rights asserted. Recolouring or alteration of the image is prohibited without permission. Coloured scanning electron micrograph (SEM) of a B lymphocyte. Also known as a B cell, this is a type of white blood cell that functions by secreting antibodies. It recognises a specific site (antigen) on the surface of a pathogen or foreign object, which it then binds to before producing antibodies to destroy that antigen. In mammals, B cells mature in the bone marrow. Magnification: x5000 when printed at 12 centimetres wide.