What distinguishes eosinophils from other types of white blood cells?

Eosinophils are distinguished from other types of white blood cells primarily by the presence of granular cytoplasmic contents that stain specifically with eosin, a red dye. This characteristic staining is due to the unique protein composition of the granules, which contain enzymes and toxic proteins used in the immune response, particularly in combating parasitic infections and modulating allergic reactions.

The size and abundance of eosinophils compared to other white blood cells do not play a defining role in their classification; they are generally less numerous than neutrophils and lymphocytes. Additionally, eosinophils are not involved in transporting oxygen—this function is primarily attributed to red blood cells. Lastly, while eosinophils play an important role in the immune response, they are not the primary cells involved in blood clotting; that role is mainly fulfilled by platelets and other factors. Thus, the key distinguishing feature of eosinophils is their eosinophilic granules, which are readily identified by their staining properties.