polymorphonuclear

Polymorphonuclear describes leukocytes with multi-lobed nuclei, a characteristic feature of granulocytes. In humans, the term most often refers to polymorphonuclear neutrophils (PMNs), which are the most abundant type of white blood cell in peripheral blood. Other granulocytes—eosinophils and basophils—also exhibit segmented nuclei, and these cells are sometimes described as polymorphonuclear, though the expression “polymorphonuclear neutrophils” is most common.

Morphology and identification: The nucleus is typically segmented into 2 to 5 lobes linked by slender chromatin strands. The cytoplasm contains granules that vary by subtype: neutrophils have pale granules, eosinophils have red-orange granules, and basophils have dark granules that can obscure the nucleus. The polymorphonuclear arrangement is most readily observed on stained blood smears (e.g., Giemsa or Wright stain) or in tissue sections.

Function: Neutrophils act as first responders to bacterial infection, performing phagocytosis, degranulation, and the formation of neutrophil extracellular traps (NETs). Eosinophils and basophils participate in defense against parasites and in mediating allergic responses, with their own granulocyte-specific functions, but all three can display a polymorphonuclear appearance.

Clinical relevance: The term is used in hematology and pathology to describe the cellular composition of blood and inflammatory exudates. Clinical interpretations often focus on absolute neutrophil counts (neutrophilia or neutropenia) as indicators of infection, inflammation, or immune status.