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equilibrium constant 254 erythema nodosum
Epithelium
with
productive
infection
EBV-infected
B cell
B cell pool
with latent
infection
B
B
B
B
E-B virus
particles
B
Circulates
B
B cell
transformed
by EBV
binding to complement receptor 2 (CR2 or CD21). It causes
infectious mononucleosis and establishes a latent infection
of B cells that persists for life and is controlled by T cells.
equilibrium constant
A constant that expresses the state of equilibrium reached
by molecules in a reversible reaction such as A + B = AB.
The equilibrium constant may be expressed as a dissociation
constant, K D = [A][B]/[AB] or an association constant,
K A = [AB]/[A][B].
equilibrium dialysis
A method to ascertain the affinity of an antibody for an
antigen and its valency. Equilibrium dialysis was developed
for the study of primary antibody–hapten interactions. Two
cells are separated by a semipermeable membrane, allowing
the free passage of hapten molecules but not larger antibody
molecules. At time zero (t 0), there is a known concentration
of hapten in cell A and antibody in cell B. Hapten from
cell A will then diffuse across the membrane into cell B
until, at equilibrium, the concentration of free hapten is
the same in both cells A and B; that is, the rate of diffusion
of hapten from cell A to B is the same as that from cell B
to A. Although the concentrations of free hapten are the
B
Release
into
oropharynx
T cell activated
Lytic cycle T
T cell pool
T
with
T
EBV-specific
T memory
T cell activated
Epstein–Barr virus (EBV)–host interaction.
Antigen Antigen + Antibody
Antibody
Antigen
Equilibrium dialysis.
same in both cells, the total amount of hapten in cell B is
greater because some of the hapten is bound to the antibody
molecules. A series of experiments is performed, varying
the starting amount of hapten concentration while keeping
antibody concentration constant.
equivalence (equivalence point)
In a precipitation reaction in vitro, the antigen-to-antibody
ratio at which maximal precipitation takes place. The supernatant
should not contain free antigen or free antibody, as
all of the antigen and antibody molecules react with one
another at equivalence.
equivalence zone
Refer to zone of equivalence.
erbA, erbB
Oncogenes expressing tyrosine kinase activity. They are
similar in structure to the avian erythroblastosis retrovirus.
They code for cell membrane proteins. erbB is expressed
in breast and salivary gland carcinomas and is a truncated
version of epidermal growth factor receptor. Increased copy
numbers of the c-erbB2 (HER2/neu) gene suggest an unfavorable
prognosis for carcinoma of the breast.
ergotype
A T lymphocyte being activated. The injection of antiergotype
T cells blocks full-scale activation of T lymphocytes
and may prevent development of experimental autoimmune
disease in animal models. An example is experimental
allergic encephalomyelitis (EAE), in which antiergotype T
lymphocytes may prevent full T lymphocyte activation.
erp57
A chaperone molecule that participates in the loading of
peptide onto major histocompatibility complex (MHC) class
I molecules in the endoplasmic reticulum.
erythema
Redness of the skin caused by dilatation of blood vessels
lying near the surface.
erythema marginatum
Immune-complex-induced vasculitis in the subcutaneous
tissues associated with rheumatic fever.
erythema multiforme
Skin lesions resulting from subcutaneous vasculitis produced
by immune complexes. They are frequently linked
to drug reactions. A lesion is identified by a red center
encircled by an area of pale edema that is encircled by a
red or erythematous ring. This gives it a target appearance.
Erythema multiforme usually signifies a drug allergy or
may be linked to systemic infection. Lymphocytes and
macrophages infiltrate the lesions. When involvement and
sloughing of the mucous membranes are present, the lesions
are considered quite severe and even life threatening. This
form is called the Stevens–Johnson syndrome.
erythema nodosum
Slightly elevated erythematous nodules that develop on the
shins and sometimes the forearm and head and are very
painful. They represent subcutaneous vasculitis involving
small arteries. The phenomenon is associated with infection
and is produced by antigen–antibody complexes. Erythema
nodosum may be an indicator of inflammatory bowel disease,
histoplasmosis, tuberculosis, sarcoidosis, or leprosy.
It can follow the use of certain drugs. Although claimed in
the past to be due to antigen–antibody deposits in the walls
of small venules, the immunologic mechanism may involve
type IV (delayed-type) hypersensitivity in the small venules.