Final answer:
The neutrophil is the most common white blood cell in a vaginal cytology smear, comprising 50-70% of leukocytes and serving as a rapid defense against pathogens.
Step-by-step explanation:
The most common type of white blood cell to be seen when viewing a vaginal cytology smear is neutrophil. Neutrophils are a type of granulocyte that stain with a neutral dye and are especially active against bacteria. They typically comprise 50-70 percent of the total leukocyte count and have a distinctive lobed nucleus. The lobed nucleus may have two to five lobes, with older neutrophils being referred to as polymorphonuclear or 'polys' due to the increasing number of lobes as the cell ages. Neutrophils play a crucial role in providing an early, rapid, and nonspecific defense against invading pathogens.