Neutrophils (70%): These are the big guys in infection. Generally when someone has an “elevated white count” it’s due to the neutrophils (unless there’s a lymphoma grumbling along). They are the major players in fighting off bacterial infection and the main component in pus.
Lymphocytes (20-60%): These are the B cells, T cells, and Natural Killer (NK) cells. When you’re looking at a blood smear, you can’t tell the difference between them.
T cells: cell-mediated immunity
B cells: humoral (antibody-mediated) immunity
Natural Killer cells: protect against viruses and tumours
Monocytes (3-8%): Mature into macrophages and mast cells, they play a major role in mounting an inflammatory reaction. Macrophages are the “professional antigen presenting cells“, displaying foreign peptides in Class II MHC.
Eosinophils (1-6%): fight against parasitic infections (back in the good old days), now they’re the bane of many people’s existence as they’re involved in asthma and allergies.
Basophils (0.1%): contain many base-loving (hence baso-phil) granules containing histamine