Classification of Leukocytes

Leukocytes containing cytoplasmic granules are classified as granular, while those with relatively clear cytoplasm are termed agranular.

All granulocytes belong to the myeloid lineage and are further divided into neutrophils, eosinophils, and basophils, all with roughly spherical shapes.

Neutrophils make up 50-70% of all leukocytes. They have small, evenly distributed granules with a polymorphonuclear appearance with two to five nuclear lobes. They primarily phagocytize bacteria.

Next are the eosinophils and basophils with a two-lobed nucleus. Eosinophils have large, digestive enzyme-filled granules used to combat multicellular parasites like flatworms.

In contrast, a dense cloud of histamine-containing granules surrounding the basophil nucleus is involved in allergic reactions.

On the other hand, monocytes from the myeloid lineage and lymphocytes from the lymphoid lineage form the agranulocytes.

Monocytes have a kidney-shaped nucleus with a lysosome-dense cytoplasm. They migrate from the blood to tissue and differentiate into macrophages.

Lastly, the lymphocytes comprise antibody-producing B-cells, T-cells, and natural killer cells. They primarily mount an immune response by direct cell attack or using antibodies.