pathogen
An organism which causes diseases.

perforin
Molecule produced by cytotoxic T-cells and NK cells which, like complement component C9, polymerizes to form a pore in the membrane of the target cell leading to cell death.

peritoneal
Associated with the lining of the abdominal cavity.

phagocyte
Cells, including monocytes/macrophages and neutrophils, which are specialized for the engulfment of cellular and particulate matter.

phagocytosis
The process by which cells engulf material and close it within a vacuole (phagosome) in the cytoplasm.

phagosome
Vacuole in the cytoplasm of a phagocyte.

platelet
Tiny bits of protoplasm found in vertebrate blood; essential for blood clotting.

pluripotency
The potential of a cell to develop into more than one type of mature cell, depending on environment.

polymorphonuclear cells
Small, actively motile white blood cells containing many lysosomes and specializing in phagocytosis.

polypeptide
A chain of peptides, or amino acids, usually less than 100 amino acids long. A polypeptide is formed during the process of translation. One or more polypeptides are required to make a protein.

primary immune response
The relatively weak immune response which occurs upon the first encounter of naïve lymphocytes with a given antigen.

protease
An enzyme that cleaves peptide bonds that link amino acids in protein molecules.

prostaglandins
Acidic lipids derived from arachidonic acid which are able to increase vascular permeability, mediate fever, and can both stimulate and inhibit immunological responses.

protein
A molecule made up of amino acids that are needed for the body to function properly. Proteins are the basis of body structures such as skin and hair and of substances such as enzymes, cytokines, and antibodies.

pseudopodium
The protrusion of an amoeboid cell formed by the extrusion or streaming of the cytoplasm (but still enclosed in the membrane) for the purpose of movement or feeding.

pyrogen
Any substance that can cause a rise in body temperature