Soluble interleukin 6 receptor in biological fluids from human origin

Area of Science:

• Biochemistry
• Immunology
• Clinical Chemistry

Background:

• Interleukin 6 (IL-6) is a key cytokine in inflammation and immunity.
• The soluble IL-6 receptor (sIL-6R) plays a role in IL-6 signaling.
• Understanding baseline levels of sIL-6R and IL-6 in various bodily fluids is crucial for interpreting disease states.

Purpose of the Study:

• To measure baseline levels of soluble IL-6 receptor (sIL-6R) and IL-6 in human serum, urine, cerebrospinal fluid (CSF), and synovial fluid (SF) under non-pathological conditions.
• To establish reference ranges for sIL-6R in these biological fluids.
• To assess potential interference between sIL-6R and IL-6 assays.

Main Methods:

• Blood, urine, CSF, and SF samples were collected from healthy volunteers and patients with non-pathological conditions.
• Enzyme-linked immunosorbent assays (ELISAs) were employed to quantify sIL-6R and IL-6 concentrations.
• Assay specificity and potential cross-reactivity were evaluated.

Main Results:

• Detectable baseline levels of sIL-6R were found in serum (76.6 ± 19.3 ng/ml), urine (3.7 ± 1.3 ng/ml), CSF (1.6 ± 0.4 ng/ml), and SF (11.6 ± 3.3 ng/ml).
• IL-6 levels were below detectable limits in CSF and SF.
• Serum sIL-6R concentrations were significantly higher than in CSF, urine, and SF.
• Substantial inter-individual variability in baseline sIL-6R concentrations was observed.

Conclusions:

• sIL-6R is present in serum, urine, CSF, and SF in healthy individuals.
• Serum sIL-6R levels are considerably higher compared to other tested biological fluids.
• Significant inter-individual differences in baseline sIL-6R levels necessitate careful interpretation in clinical settings.