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ulcerative colitis (immunologic colitis) 732 ungulate immunity
activated T cells but only a proportion of resting T cells.
This antibody and antibodies to the high molecular-weight
form of CD45 (CD45R) seem to define complementary,
largely nonoverlapping populations in resting peripheral
T cells demonstrating heterogeneity within the CD4 and
CD8 subsets. The antibody labels most thymocytes, a
subpopulation of resting T cells within both the CD4 and
CD8 subsets, and mature activated T cells. Cells of the
myelomonocytic series (e.g., granulocytes and monocytes)
are also labeled, whereas most normal B and natural killer
(NK) cells are consistently negative. Weak cytoplasmic
staining is, however, seen in cases of centroblastic and
immunoblastic lymphoma.
Ulcerative colitis; crypt abscess.
ulcerative colitis (immunologic colitis)
An ulcerative condition that may involve the entire colon
but does not significantly affect the small intestine.
Neutrophils, plasma cells, and eosinophils infiltrate the
colonic mucosa, followed by ulceration of the surface epithelium,
loss of goblet cells, and formation of crypt abscess.
The etiology is unknown. An immune effector mechanism
is believed to maintain chronic disease. Serum immunoglobulins
and peripheral blood lymphocyte counts are
usually normal. Complexes present in the blood are relatively
small and contain IgG, although no antigen has been
identified. The complexes may be merely aggregates of
immunoglobulin G (IgG). Patients have diarrhea with blood
and mucus in stools. The signs and symptoms are intermittent,
and the severity of colon lesions varies. Lymphocytes
are cytotoxic for colon epithelial cells. Antibodies against
Escherichia coli may cross react with colonic epithelium;
whether such antibodies play a role in etiology and pathogenesis
remains to be proven.
ultracentrifugation
The separation of cell components, including organelles
and molecules, through high-speed centrifugation reaching
6000 rpm with a gravitational force of up to 500,000 g. In
differential velocity centrifugation, a stepwise increase in
gravitational force removes selected components. Following
centrifugation of a cellular homogenate at 600 g for 10
minutes to isolate the nuclei, further spinning at 15,000
g for 5 minutes permits isolation of mitochondria, lysosomes,
and peroxisomes. Respinning at 100,000 g for 1
hour permits isolation through sedimentation of the plasma
membrane, microsomal fraction, endoplasmic reticulum,
and large polyribosomes. Respinning at 300,000 g for 2
hours permits sedimentation of ribosomal subunits and
small polyribosomes. This leaves the cytosol—the soluble
portion of the cytoplasm. Separation can also be achieved
by sucrose density gradient ultracentrifugation. Combining
cesium chloride with the molecules to be analyzed permits
the molecules to migrate to a particular density equivalent.
Ultracentrifugation may function as an analytical method
for identifying proteins that differ in sedimentation coefficient
or as a preparative method to separate proteins based
on their densities and shapes.
ultrafiltration
The passage of solutions or suspensions through membranes
with minute pores of graded sizes.
umbrella effect
The masking, by relatively large amounts of immunoglobulin
G (IgG), of low immunoglobulin light chain concentrations
in early IgM macroglobulinemia and IgA myeloma,
observed in immunoelectrophoresis. Immunofixation
electrophoresis, employing fluorochrome-labeled antibodies,
can resolve this masking effect.
undifferentiated connective tissue disease
A prodromal phase of a collagen vascular or connective
tissue disease during which the principal clinical manifestations
have not yet become apparent.
Ungulate immunity.
ungulate immunity
Ungulates develop immune systems similar to those of
most other mammalian species. The thymus and bone
marrow serve as the sources for generation of T and B
cells, respectively. A feature unique to ruminant ungulates
is the major role played in primary B cell development by
the ileal Peyer’s patch, which is a single structure in the
terminal ileum. Ruminants have a higher proportion of
γδ T cells than other species. Ungulate immunoglobulins
consist of IgG 1, IgG 2, IgM, IgA (serum), IgA (secretory),
and IgE isotypes. IgA antibodies predominate on mucosal
surfaces; mammary glands produce milk that is different
in immunoglobulin content compared to other species. No