Biological or Clinical Significance:
Interleukin 6 (IL-6) is a multifunctional cytokine that has a major role in initiation and promulgation of the inflammatory and immune responses.
The biological activities of IL-6 are initiated by binding of the cytokine to a high-affinity receptor complex consisting of two membrane glycoproteins: An 80 kDa component receptor that binds IL-6 with low affinity (IL-6R) and a signal-transducing component of 130 kDa (gp130) that does not bind IL-6 by itself, but is required for high-affinity binding of the IL-6 by the complex.
A soluble form of the IL-6R with a molecular weight of approximately 50 kDa has been found in the urine of healthy adult humans, in the culture medium conditioned by the growth of a human myeloma cell line, in culture supernates from PHA-stimulated human PBMC and HTLV-1-positive T cell lines, and in the serum of HIV-seropositive blood donors. This soluble form of the receptor apparently arises from proteolytic cleavage of membrane-bound IL-6R.
It has been suggested, that pathological states involving elevated levels of IL-6 might also be associated with increased production of soluble IL-6R.
Principle of Test Method:
The IL-6 assay is a solid-phase ELISA that employs the quantitative sandwich enzyme immunoassay principle.