Type I Hypersensitivity

Question 1

The type I hypersensitivity reactions are commonly thought of as_______

Answer 1

allergies

Question 2

Some examples of type I hypersensitivity reactions

Answer 2

hay fever,
allergic asthma,
hives, and
systemic anaphylaxis

Question 3

antigens that trigger type I hypersensitivity

Answer 3

allergens

Question 4

Examples of common allergens include

Answer 4

peanuts, eggs, and pollen

Question 5

short time lag, usually minutes, between exposure to allergen and the onset of clinical
symptoms

Answer 5

distinguishing feature of type I hypersensitivity

Question 6

The first clue about the cause of type I hypersensitivity was provided by

Answer 6

Carl Wilhelm Prausnitz and Heinz Küstner

Question 7

It occurs when serum is transferred from an allergic individual to a non-allergic individual, and the second individual is challenged at a later time with the specific allergen.

Answer 7

passive cutaneous anaphylaxis

Question 8

*least abundant antibody class in the serum, normally accounting for less than 1% of all the immunoglobulins
*not involved in typical immune responses such as complement fixation and opsonization
*unique in its ability to bind to specific receptors on mast cells and basophils
*play a major role in type I hypersensitivity allergic reactions and in defense against parasites

Answer 8

IgE

Question 9

Greek word atopos (meaning “out of place”), refers to an inherited tendency to develop classic allergic responses to naturally occurring inhaled or ingested allergens

Answer 9

Atopy

Question 10

The key immunologic components involved in type I hypersensitivity reactions are

Answer 10

IgE antibody,
mast cells,
basophils, and
eosinophils

Question 11

The response begins when a susceptible individual is exposed to an allergen and produces specific IgE antibody. IgE is primarily synthesized by

Answer 11

B cells and plasma cells in the lymphoid tissue of the respiratory and gastrointestinal tracts, as
well as the lymph nodes

Question 12

The regulation of IgE production appears to be a function of a subset of

Answer 12

T cells called type 2 helper cells (Th2)

Question 13

This Th2 type of response results in production of several cytokines, including

Answer 13

IL-4 and IL-13

Question 14

the IgE antibody attaches to high-affinity receptors called FcεRI, which bind the fragment crystallizable (Fc) region of the epsilon-heavy chain

Answer 14

sensitization phase

Question 15

Large numbers of these receptors are found on mast cells and basophils, with a single cell having as many as ______ such receptors

Answer 15

200,000

Question 16

cells internalize and process allergens from the environment and transport the allergen-MHC class II complex to local lymphoid tissue where synthesis of IgE occurs

Answer 16

Langerhans and dendritic

Question 17

Binding of IgE to cell membranes increases the half-life of the antibody from

Answer 17

2 or 3 days to at least 10 days

Question 18

*principal effector cells of immediate hypersensitivity
*These cells are found throughout the body and in most organs tend to be concentrated around the small blood vessels, the lymphatics, the nerves, and the glandular tissue
*have abundant cytoplasmic granules that store numerous preformed inflammatory mediators
*present in the peripheral blood, where they represent less than 1% of the total white blood cells (WBCs)

Answer 18

Mast cells

Question 19

respond to chemotactic stimuli during inflammation and accumulate in the tissues, where they can persist for a few days

Answer 19

Basophils

Question 20

*adjacent cell-bound IgE molecules are cross-linked by a bivalent or multivalent antigen, causing aggregation of the surface FcεRI receptors
*initiates complex intracellular signaling events involving multiple phosphorylation reactions, an influx of calcium, and secretion of cytokines

Answer 20

activation phase

Question 21

*most abundant preformed mediator
*comprises approximately 10% of the total
weight of the granules in mast cells

Answer 21

histamine

Question 22

These preformed substances are referred to as

Answer 22

primary mediators

Question 23

Other primary mediators include

Answer 23

heparin,
eosinophil chemotactic factor of anaphylaxis (ECF-A),
neutrophil chemotactic factor, and
proteases

Question 24

Release of these substances is responsible for the early-phase symptoms seen in allergic reactions, which occur within ____ ____ minutes
after exposure to the allergen

Answer 24

30 to 60

Question 25

mediators bind to receptors on target organs, most notably the skin, respiratory tract, and gastrointestinal tract, producing symptoms characteristic of an allergic response

Answer 25

chemical

Question 26

The clinical manifestations depend on the target tissue and type of receptors activated. For example, in the skin, local swelling and redness, sometimes referred to as a

Answer 26

wheal-and-flare reaction

Question 27

Contraction of the smooth muscle in the bronchioles may result in

Answer 27

airflow obstruction

Question 28

can cause hypotension or shock

Answer 28

Increased vascular permeability

Question 29

*In addition to immediate release of preformed mediators, mast cells and basophils are triggered to synthesize other reactants from the breakdown of phospholipids in the cell membrane.
*In this phase of the reaction, numerous cells, including eosinophils, neutrophils, Th2 cells, mast cells, basophils, and macrophages, exit the circulation and infiltrate the allergenfilled tissue

Answer 29

late-phase

Question 30

newly formed, or secondary, mediators include

Answer 30

plateletactivating factor (PAF);
prostaglandin (PG) D2;
leukotrienes (LT) B4, C4, D4, and E4; and cytokines

Question 31

secondary, mediators are more potent than the primary mediators and are responsible for a late-phase allergic reaction that can be seen in some individuals __ __ hours after exposure to the antigen

Answer 31

6 to 8

Question 32

play an important role in the late-phase reaction. These cells normally compose 1% to 3% of the circulating WBCs

Answer 32

Eosinophils

Question 33

During allergic reactions, IL-5 and other cytokines released from the Th2 cells stimulate the bone marrow to increase production of eosinophils, and the number in the peripheral blood increases, producing

Answer 33

eosinophilia

Question 34

In individuals with persistent inflammation resulting from the late-phase reaction, such as those with

Answer 34

chronic asthma, tissue remodeling can result