phagocyte oxidase See NADPH oxidase.
phagocytic glycoprotein-1 (Pgp1) See CD44.
phagocytosis The internalization of particulate matter by cells by a process of engulfment, in which the cell membrane surrounds the material, eventually forming an intracellular vesicle (phagosome) containing the ingested material.
phagolysosome Intracellular vesicle formed by the fusion of a phagosome (containing ingested material) and a lysosome, and in which the ingested material is broken down.
phagophore A crescent-shaped double-membrane cytoplasmic structure.
phagosome Intracellular vesicle formed when particulate material is ingested by a phagocyte.
phosphatidylinositol 3-kinase (PI 3-kinase) Enzyme involved in intracellular signaling pathways. It phosphorylates the membrane lipid phosphatidylinositol 3,4-bisphosphate (PIP2) to form phosphatidylinositol 3,4,5-trisphosphate (PIP3), which can recruit signaling proteins containing pleckstrin homology (PH) domains to the membrane.
phosphatidylinositol kinases   Enzymes that phosphorylate the inositol headgroup on membrane lipids to produce phosphorylated derivatives that have a variety of functions in intracellular signaling.
phospholipase C-γ (PLC-γ) Key enzyme in intracellular signaling pathways leading from many different receptors. It is activated by membrane recruitment and tyrosine phosphorylation following receptor ligation, and cleaves membrane inositol phospholipids into inositol trisphosphate and diacylglycerol.
phosphorylation Addition of a phosphate group to a molecule, usually a protein, catalyzed by enzymes called kinases.
phycoerythrin A light harvesting protein pigment made by algae and used in conjunction with ﬂow cytometry, it can also be recognized as a ligand by some γ:δ T-cell receptors.
physiological inflammation The state of the normal healthy intestine, whose wall contains large numbers of effector lymphocytes and other cells. It is thought to be the result of continual stimulation by commensal organisms and food antigens.
pi-cation interactions   Chemical interaction between a cation (e.g., Na+) and the pi-electron system of an aromatic moiety.
pilin An adhesin of Neisseria gonorrhoeae allowing attachment to and infection of epithelial cells of urinary and reproductive tracts.
PIP2   Phosphatidylinositol 3,4-bisphosphate, a membrane-associated phospholipid that is cleaved by phospholipase C-γ to give the signaling molecules diacylglycerol and inositol trisphosphate and is phosphorylated by PI3-kinase to generate PIP3.
PIP3   Phosphatidylinositol 3,4,5-trisphosphate, a membrane-associated phospholipid that can recruit intracellular signaling molecules containing pleckstrin homology (PH) domains to the membrane.
PKR Serine/threonine kinase activated by IFN-α and IFN-β. It phosphorylates the eukaryotic protein synthesis initiation factor eIF-2, inhibiting translation and thus contributing to the inhibition of viral replication.
plasma cells Terminally differentiated activated B lymphocytes. Plasma cells are the main antibody-secreting cells of the body. They are found in the medulla of the lymph nodes, in splenic red pulp, in bone marrow, and in mucosal tissues.
plasmablasts A B cell in a lymph node that already shows some features of a plasma cell.