= Phagocyte
A \b[phagocyte] is a <biological cell> that takes up particles, such as <bacteria> or cell debris, by <phagocytosis>: the <cell membrane> encloses the material in an intracellular <phagosome>. <Macrophages> and <neutrophils> are important examples. The term describes an uptake capability, rather than a single developmental lineage. Contact with a particle, internalization and destruction of the ingested material are distinct events.
A useful experimental distinction is between <phagocytosis> and production of reactive oxygen compounds. <S. D. Wright> and <S. C. Silverstein> measured <hydrogen peroxide> released by human <granulocytes>, <monocytes> and <macrophages> spreading on surfaces coated with defined recognition molecules. Surfaces carrying <IgG> stimulated peroxide release, whereas surfaces carrying <C3b> or <iC3b> did not appreciably do so. Even when <fibronectin> supported a strong complement-receptor-associated phagocytic response in cultured <monocytes>, measurable peroxide release did not follow.<Receptors for C3b and C3bi promote phagocytosis but not the release of toxic oxygen from human phagocytes by S. D. Wright and S. C. Silverstein>[Abstract and Figure1: ligand-coated surfaces, cultured monocytes and separate uptake/oxidant endpoints.]{ref}
For example, counting ten particle-containing <phagosomes> would establish uptake in the observed <phagocyte>; it would not count ten killed <bacteria>. A killing assay needs a further endpoint, such as recovery of viable organisms. Likewise, a low extracellular peroxide measurement alone does not establish absence of <phagocytosis>. Choosing an endpoint that matches the biological question is essential when comparing <phagocytes>.
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