Radioreceptor binding assays

Cytokines may also be assayed by competitive binding for the receptor between the test material and radiolabeled (usually 12T) ligand. This assay requires availability of cells expressing high levels of the receptor and that optimal conditions of ligand and receptor binding are understood. In addition, nonspecific interference in receptor ligand binding must be excluded by including controls for the media and buffers in the materials to be tested.

The assay involves incubation of iodinated ligand with varying dilutions of test or standard material under optimal conditions which must be predetermined for each receptor ligand pair, possibly at 4° to reduce internalization. This is followed by wash ing to remove excess ligand, solubilization of the ligand receptor complexes and counting in a 7-counter.

Problems intrinsic to this assay are:

• cytokines and their receptors may exist in several forms, e.g. PDGF and PDGF receptor with different binding coefficients;

• cytokines can cross-compete for the same receptor, e.g. IGF1 and ICF2, and MGSF (melanocyte growth-stimulating factor) and IL-8;

• cytokine inhibitors may bind to the cytokine receptor with equal avidity to the cytokine.

See also: Cytokine inhibitors; Cytokine receptors, soluble; Cytokines; Cytokine receptors; Enzyme-linked immunosorbent assay (ELISA); Granulocyte colony stimulating factor (G-CSF); Granulocyte-macrophage colony stimulating factor (GM-CSF); Immunoassays; Interferon 7; Interleukin 1 and its receptors; Interleu-kin 2; Interleukin 3; Interleukin 4; Interleukin 5 and its receptor; Interleukin 6; Interleukin 7 and its receptor; Interleukin 8 and its receptor; Transforming growth factor ß (TGFß); Tumor necrosis factor <*; TNF receptors.

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