Result Interpretation
0.0- 2.2 pg/mL
Tumor necrosis factor-α (cachectin) and tumor necrosis
factor-β (lymphotoxin) are two closely related proteins that
share sequence homology of 34% in their amino acid sequence. Both
mediators act on their target cells via the same receptors and,
therefore, show similar, but not identical, biological effects.
Under denaturing conditions TNF-α is a 17-kilodalton,
nonglycosylated protein. The biologically active form of TNF-α
is a trimer. Besides this soluble form of TNF-α, a
28-kilodalton membrane-bound form occurs on cell surfaces of
TNF-producing cells, which may serve as a pool for soluble
TNF-α and can be proteolytically cleaved from the cell
surface.
Different cells are shown to produce TNF-α: For example,
macrophages, CD4+ T cells and NK cells after stimulation
with lipopolysaccharides. Additionally, smooth muscle cells,
polymorphonuclear neutrophils, astrocytes and a variety of tumor
cell lines can produce TNF-α. TNF-α acts via two distinct
cell surface receptors, which are called TNF receptor I, and TNF
receptor II. These receptors can be identified on virtually all
cell types except erythrocytes. Besides the cell-bound forms of TNF
receptors, soluble forms are known to be capable of TNF-α
binding. They compete, therefore, with the cell-bound forms and can
inhibit the effects of TNF-α.
Due to the occurrence of TNF-α receptors on nearly all
cells, TNF-α demonstrates a wide variety of biological action.
It has cytolytic and cytostatic effects on tumor cells and shows
chemotactic activity on neutrophils. TNF-α is a growth factor
for fibroblasts and stimulates the synthesis of collagenase and
prostaglandin E2 bone resorption can be induced by
TNF-α because it activates osteoclasts. TNF-α enhances
the proliferation of T cells after stimulation with IL-2. In the
absence of IL-2, TNF-α induces the proliferation and
differentiation of β cells.
TNF-α serum or plasma levels may be elevated in sepsis,
autoimmune diseases, various infectious diseases, and transplant
rejection.
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