A single complete and infectious virus particle is called a virion.
Missing Word
virion
A virion is one whole virus particle, made of a nucleic acid genome inside a protein capsid and sometimes an envelope. The term refers to the virus in its mature form outside a host cell.
Category: Virus Structure and Replication
Question 2
The outer layer of phospholipid and protein that some viruses, such as influenza and HIV, take from the host cell's membrane is called the envelope.
Missing Word
envelope
The envelope is a membrane layer around the capsid of some viruses, acquired from the host cell as new virus particles leave it. Its glycoproteins help the virus attach to host cells, but it is fragile, so enveloped viruses survive harsh conditions poorly.
Category: Virus Structure and Replication
Question 3
Weakening a virus by growing it under laboratory conditions so it can be used safely in a live vaccine is called attenuation.
Missing Word
attenuation
Attenuation lets the virus adapt to lab conditions through mutations, so it grows in culture but no longer causes disease in the host. The weakened virus still stimulates strong immunity.
Category: Viral Disease Control
Question 4
Hairlike projections called cilia on cells of the upper respiratory tract sweep pathogen-trapping mucus up toward the mouth.
Missing Word
cilia
Cilia beat in coordinated waves that move mucus and the particles caught in it out of the airways. They are part of the physical first line of innate defense.
Category: Innate Immunity
Question 5
The innate response marked by redness, swelling, heat and pain at a site of injury or infection is called inflammation.
Missing Word
inflammation
Inflammation is a localized response in which dilated, leaky capillaries let fluid and white blood cells reach the damaged tissue. The classic signs, including the redness, swelling, heat and pain named here, come from this increased blood flow and fluid leakage.
Category: Innate Immunity
Question 6
Natural killer cells eliminate virus-infected cells by triggering apoptosis, a form of programmed cell death.
Missing Word
apoptosis
Apoptosis is an orderly, programmed self-destruction of a cell. Killing an infected cell this way stops viral replication, and phagocytes then clear away the remains.
Category: Innate Immunity
Question 7
Cytokines acting on the nervous system can raise core body temperature, producing a fever that slows pathogen growth.
Missing Word
fever
A fever is a raised body temperature set by cytokine signals during infection. The higher temperature slows the growth of many pathogens and speeds cellular repair.
Category: Innate Immunity
Question 8
Coating a pathogen with antibodies or complement proteins so that phagocytes engulf it more readily is called opsonization.
Missing Word
opsonization
Opsonization marks a pathogen for destruction. Phagocytes such as macrophages and neutrophils have receptors for these tags, so a coated pathogen is recognized and ingested more efficiently.
Category: Humoral Immunity and Memory
Question 9
Any molecule that stimulates a specific adaptive immune response is called an antigen.
Missing Word
antigen
An antigen is a molecule, often a protein or polysaccharide on a pathogen, that B and T cell receptors can recognize. Not every molecule is antigenic.
Category: Humoral Immunity and Memory
Question 10
Antibodies are Y-shaped proteins, also known as immunoglobulins, that plasma cells secrete into blood and other body fluids.
Missing Word
immunoglobulins
Immunoglobulin is the formal name for an antibody, a protein whose variable regions bind one specific antigen. Antibodies are found in blood, mucus secretions and breast milk.
Category: Humoral Immunity and Memory
Question 11
A maturing lymphocyte that has become able to recognize one specific foreign molecule is described as immunocompetent.
Missing Word
immunocompetent
An immunocompetent lymphocyte carries working receptors for a single target. Its specificity comes from its genes and exists before it ever meets a pathogen.
Category: Cell-Mediated Immunity
Question 12
The spleen is a lymphoid organ that filters blood and houses B cells, T cells, macrophages and dendritic cells.
Missing Word
spleen
The spleen does for the blood what lymph nodes do for lymph: it is where antigen-presenting cells meet lymphocytes and where plasma cells make antibodies against blood-borne pathogens.
Category: Cell-Mediated Immunity
Question 13
Regulatory T cells help maintain immune tolerance by suppressing responses to self molecules and harmless substances such as food proteins.
Missing Word
tolerance
Immune tolerance prevents harmful responses to the body's own molecules and to harmless foreign ones. It depends on removing strongly self-reactive lymphocytes during maturation and on regulatory T cells that dampen responses.
Category: Cell-Mediated Immunity
Question 14
During an allergic reaction, mast cells release histamine, a chemical that dilates blood vessels and causes itching.
Missing Word
histamine
Histamine is an inflammatory chemical stored in mast cells. When an allergen binds antibodies on a sensitized mast cell, histamine is released and causes symptoms such as sneezing, itching and hives.
Category: Immune Disorders
Question 15
An immune protein that mistakenly marks the body's own molecules as foreign is called an autoantibody.
Missing Word
autoantibody
An autoantibody binds self components and drives most autoimmune diseases, such as the attack on acetylcholine receptors in myasthenia gravis or on DNA in lupus.
Category: Immune Disorders