Glossary P

• p24 antigen: A structural core antigen that is part of HIV
• Pyrosequencing: A DNA sequencing method that relies on the generation of light when nucleotides are added to a growing strand of DNA.
• Paracrine: Secretions such as cytokines that affect only target cells in close proximity
• Paraprotein (M protein): A single immunoglobulin component produced by a malignant clone of lymphoid cells in lymphoproliferative diseases
• Parasite: Microorganism that survives by living off of another organism
• Parasitic: Relationship in which an organism causes harm to its host
• Paratope: An antigen - binding site on an antibody molecule
• Parenteral: Mode of transmission other than through the intestinal tract, most notably bloodborne transmission
• Paroxysmal cold hemoglobinuria: A condition in which patients produce a biphasic autoantibody that binds to red blood cells (RBCs) at cold temperatures and activates complement at 37°C to produce an intermittent hemolysis
• Paroxysmal nocturnal hemoglobinuria (PNH): A disease characterized by complement - mediated hemolysis of erythrocytes resulting from a deficiency of decay - accelerating factor on the red blood cells (RBCs)
• Particle agglutination (PA) test: Agglutination test that uses antigen - coated gel particles or red blood cells to detect antibody to Treponema pallidum
• Passive agglutination: A reaction in which particles coated with antigens not normally found on their surfaces clump together because of their combination with antibody
• Passive immunity: A type of immunity that results from the transfer of antibodies from immunized hosts to a nonimmune individual
• Passive immunodiffusion: A precipitation reaction in a gel in which antigen – antibody combination occurs by means of diffusion
• Passive immunotherapy: Passive immunization of an individual with commercial preparations of antibodies formed by other hosts to prevent or treat a disease
• Pathogen - associated molecular patterns (PAMPs): Structural patterns of carbohydrates, nucleic acids, or bacterial peptides on microorganisms that are recognized by pathogen recognition receptors (PRRs) on the cells of the innate immune system
• Pathogenicity: The inherent capacity of an organism to cause disease
• Pattern recognition receptors (PRRs): Receptors on cells of the innate immune system that bind to PAMPs on pathogenic microorganisms
• Percent panel reactive antibody (%PRA): A calculation that determines the likelihood that a donor and recipient will be incompatible bas ed on HLA frequencies in a large donor population
• Periarteriolar lymphoid sheath (PALS): White pulp of splenic tissue, which is made up of lymphocytes, macrophages, plasma cells, and granulocytes
• Peripheral tolerance: Destruction or repression of lymphocytes in the peripheral lymphoid organs that could respond to self - antigens
• Personal protective equipment (PPE): Items such as gowns, masks, gloves, and face shields used to protect the body from infectious agents
• Phagocytosis: From the Greek word phagein, meaning “cell eating,” the engulfment of cells or particulate matter by neutrophils, macrophages, or other cells
• Postexamination variable: A process that affects the reporting of results and correct interpretation of data
• Precision: The ability to consistently reproduce the same result upon repeated testing of the same sample
• Positive predictive value: The percentage of all positives in a serological test that are true positives
• Polymyositis (PM): A systemic rheumatic autoimmune disorder that involves inflammation of the skeletal muscles
• Precipitation: The combination of soluble antigen with soluble antibody to produce visible insoluble complexes
• Primary antibody response: The initial response to a foreign antigen, characterized by a long lag phase and a slow rise in antibody and consisting of mostly immunoglobulin M (IgM).
• Primary follicle: A cluster of B cells that have not yet been stimulated by antigen
• Primary lymphoid organs: The organs in which lymphocytes mature: these are the bone marrow and the thymus.
• Primary immunodeficiency disease (PID): Inherited diseases in which part of the immune system is absent or dysfunctional
• Poststreptococcal glomerulonephritis: A condition that damages the glomeruli of the kidney, caused by an initial immune response to a streptococcal infection
• Pre - B cell: The stage of development of a B cell where the heavy-chain part of the antibody molecule is present
• Polymorphism: The presence of two or more different genetic compositions (e.g., human leukocyte antigen [HLA] genes) among individuals in a population
• Prostate-specific antigen (PSA): A glycoprotein that is produced specifically by epithelial cells in the prostate gland; PSA is a widely used marker for prostate cancer</flash
• Pro - B cell: A stage in B-cell development in which rearrangement of the genes that code for the heavy-chain region of an antibody molecule occur
• Polymerase chain reaction (PCR): A means of amplifying tiny quantities of nucleic acid using a heat-stable polymerase enzyme and a primer pair that is specific for the DNA sequence desired
• Primary biliary cholangitis (PBC): An autoimmune disease that involves progressive destruction of the intrahepatic bile ducts; formerly known as primary biliary cirrhosis
• Primer: Short sequences of DNA, usually 20 to 30 nucleotides long, used to hybridize specifically to a particular target DNA to help initiate replication of the DNA