Broadly, white blood cells are different in key ways from the red blood cells that most of us associate with “blood.” Red blood cells, for one thing, appear red, not white. So there’s that. The two kinds of cells also have fundamentally different contours. Red blood cells look like beautiful circles carved with graceful indentations. White blood cells resemble baseballs covered in spikes. Many of these spikes are receptors. They send and receive signals. These cells are information hubs, and they can be vicious killers.
