Immune: A Journey Into the Mysterious System That Keeps You Alive

by Philipp Dettmer

Helper T Cells are able to recognize an antigen only if it is presented in an MHC class II molecule. Or in other words, they eat a wiener only in a hot dog bun. Think of Helper T Cells as really picky eaters—they would NEVER even think to touch and eat a wiener that floats around by itself. No sir, that would be disgusting! Helper T Cells only ever consider eating a wiener if it is nicely presented to them in a hot dog bun. This makes sure that Helper T Cells can’t just get activated by accident because they pick up antigens that float around freely in the blood or lymph. They need to be presented with an antigen that sits in an MHC class II molecule, from an antigen-presenting cell. Only this way does the Helper T Cell have confirmation that there is actual danger and that it should get active!