Which type of leukocyte is classified as a lymphocyte?

Lymphocytes are a type of white blood cell that play a critical role in the immune system, primarily in the body's adaptive immune response. Among the various types of leukocytes, B cells are specifically classified as lymphocytes. B cells are responsible for producing antibodies, which are essential for recognizing and neutralizing pathogens. They also have a role in memory immunity, where they can remember specific pathogens for faster response upon re-exposure.

In contrast, neutrophils are another type of leukocyte that function primarily in the innate immune response, providing the first line of defense against infections, particularly bacterial infections. Macrophages, while also part of the immune response and capable of phagocytosis, are derived from monocytes, not lymphocytes. Eosinophils are primarily involved in combating parasitic infections and play a role in allergic reactions, but they do not belong to the lymphocyte category. Therefore, B cells are the only type of leukocyte mentioned that is classified as a lymphocyte.