Neutrophils are the most abundant type of white blood cells in humans. They are formed in our bone marrow. They migrate thru blood vessels and get to the site of injury the most quickly. They are filled with microscopic granules, little sacs containing enzymes that digest microorganisms. Think of them as the first responders. They are white and are the predominant cells in pus. (gross, I know...) Humans have two times more neutrophils than lymphocytes.
--Perhaps this is why the tragic flaw of PML in lymphocyte sequestering drugs like Tysabri wasn't discovered until they were administered to humans. The mice never developed PML.
Time to look at cerebral perfusion in human beings.