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FITC (fluorescein isothiocyanate) 274 flagellin
and macrophages. It represents the primary lymphoid organ.
Fish thymocytes resemble T lineage cells in mammals. The
anterior tip of the kidney consists largely of lymphoreticular
and hematopoietic tissues. It is the principal antibodysynthesizing
tissue. The fish spleen is comprised mostly of
red pulp sinuses; the white pulp is poorly differentiated. The
fish kidney and spleen have melanomacrophage centers.
These may be analogs of germinal centers in mammals.
Fish have T- and B-like lymphocytes. The B-like population
possesses surface immunoglobulin similar to mammalian B
lymphocytes. Although the fish T-like lymphocyte antigen
receptor has not yet been characterized, it is postulated
to be homologous to the mammalian T cell receptor.
Monocytes and macrophages as well as granulocytes that
participate in inflammatory responses have been identified
in fish. Mast cells have not been demonstrated, but a
granulocytic cell with eosinophilic granules that otherwise
resembles a mast cell has been described along with
natural cytotoxic cells. Fish demonstrate both humoral and
cell-mediated immunity, which is temperature-dependent.
Some species respond very slowly immunologically after
antigenic challenge at 4°C yet exhibit a maximal response
at 12°C. The optimal temperature varies from one species
to another. An IgM-like antibody is the only immunoglobulin
class present. It is a tetrameric molecule, and
in some species it is monomeric. Secretory IgM has also
been described. Two types of light chains comparable
to κ and λ light chains of vertebrates and heavy chains
of different molecular masses have been described. The
kinetics of the antibody response in fish resembles that in
higher vertebrates. Fish also demonstrate cell-mediated
immunity that includes production of lymphokines, yet no
fish cytokine has yet been characterized. Fish have shown
evidence for interferon γ, IL1, IL2, colony-stimulating
factor, transforming growth factor β, and tumor necrosis
factor. Immunological memory involving both humoral and
cell-mediated responses has been described. Memory antibody
responses in fish are usually lower than in mammals,
and memory is temperature-dependent. Immunological
tolerance has also been shown in some species. Vaccines
are available to protect fish against the main bacterial and
viral diseases. Three methods of fish vaccination include
injection, immersion, and oral. Injection vaccinations stimulate
protective immunity. Immersion vaccination involves
placing the fish in water containing formalin-killed broth
culture vaccines and immunizing them through immersion
for 1 minute in the vaccine, which enters through the
gills. Vaccine absorption through the hind intestine leads to
protective immunity in certain species.
FITC (fluorescein isothiocyanate)
A widely used fluorochrome for labeling antibody
molecules. It may also be used to label other proteins.
Fluorescein-labeled antibodies are popular because they
appear apple-green under ultraviolet irradiation, permitting
easy detection of antigens of interest in tissues and cells.
FITC fluoresces at 490 and 520 nm. FITC-labeled antibodies
are useful for the demonstration of immune deposits in
both skin and kidney biopsies.
fixed drug eruption
A hypersensitivity reaction to a drug that appears at the
same local site on the body surface regardless of the route
by which the drug is administered. The lesion is a clearly
circumscribed plaque that is reddish-brown or purple and
edematous. It may be covered by a bulla. Common sites of
occurrence include the extremities, hands, and glans penis.
Drugs that may induce this reaction include sulfonamides,
barbiturates, quinine, and tetracycline, among other substances.
There is hydropic degeneration of the basal layer.
FK506
Refer to tacrolimus.
FKBP (FK-binding protein)
An immunophilin protein that binds FK506. A rotamase
enzyme with an amino acid sequence that closely resembles
that of protein kinase C. It serves as a receptor for both
FK506 and rapamycin. Cyclophilins that bind tacrolimus
(FK506) are FK-binding proteins. Refer also to cyclophilins.
MeO
OMe
H
OMe
Fixed drug eruption.
O
OH
O
OMe
OH
flagellar antigen
Epitopes of flagella in an organelle that renders some bacteria
motile. Also called H antigens.
flagellin
A protein that is a principal constituent of bacterial flagella.
It consists of 25- to 60-kDa monomers that are arranged
into helical chains that wind around a central hollow core.
O
O
O
N
Structure of FK506.
O