640
UNIT FOUR
B cell
Plasma cell
Mast cell
Released IgE
antibodies
IgE receptor
Initial B cell
contact with
allergen
Granule
Allergic
reaction
Histamine
and other
chemicals
Subsequent
contact with
allergen
(a)
1
2
3
5
4
Allergen
Allergen
Plasma cell
secretes
antibodies
Antibodies
attach to
mast cell
Mast cell releases
allergy mediators
(b)
FIGURE 16.22
Immediate-reaction allergy. (
a
) 1. B cells are
activated when they contact an allergen. 2. An activated B cell
dif
erentiates Further into an antibody-secreting plasma cell.
3. Antibodies attach to mast cells. 4. When allergens are encountered,
they combine with the antibodies on the mast cells. 5. The mast cells
release allergy mediators, which cause the symptoms oF the allergy
attack. (
b
) A mast cell releases histamine granules (3,000×).
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