Cytokine Serum Levels in Healthy Individuals
The correct answer is (e): low serum levels are normally detected in healthy individuals. 1
Why Option (e) is Correct
Cytokines in healthy subjects are detectable but at concentrations near or below the lower limit of detection of standard ELISA assays, where measurement variability is substantially higher. 1
Commercial assays designed for acute inflammatory processes often cannot quantify cytokine levels within the reference range of apparently healthy individuals without modification, as these assays are optimized for the higher concentrations seen in disease states. 1
Research confirms that certain cytokines show constant low serum levels in healthy subjects, while others are not produced at all in physiological conditions. 2
Why the Other Options are Incorrect
Option (a) - Serum level is not related to severity of illness: FALSE
- High cytokine levels directly correlate with disease severity and poor prognosis in multiple conditions. 3
- In non-small cell lung cancer patients, high M-CSF and IL-6 levels correlated significantly with poor survival, demonstrating clear relationship between serum levels and illness severity. 3
Option (b) - Stored intracellularly as preformed molecules: FALSE
- Some cytokines like IL-1 have very short half-lives, indicating they are not stored but rather synthesized de novo upon stimulation. 1
- Samples must be rapidly separated from blood cells and either assayed immediately or frozen to at least -70°C to prevent analyte degradation, which would be unnecessary if cytokines were stable preformed molecules. 1
Option (c) - Produced by a limited number of specific cells: FALSE
- Cytokines are produced by a wide variety of cells including inflammatory cells and structural cells of multiple organ systems. 1
- This broad cellular source contradicts the notion of limited, specific cell production. 1
Option (d) - Most commonly function in an endocrine fashion: FALSE
- Cytokines most commonly function in autocrine and paracrine fashions, not endocrine, with short half-lives and local action patterns supporting this mechanism. 1
- Their short half-lives and rapid degradation make systemic endocrine function impractical. 1
Clinical Implications
- The low baseline levels in healthy individuals make cytokine measurement technically challenging and require highly sensitive assays. 1, 4
- Standardization remains problematic because different monoclonal antibody pairs used in various assays do not permit comparable recognition in individual patient samples. 1
- Individual baseline measurements are more reliable controls than population-based reference ranges, as inter-individual variation exceeds intra-individual variation over time. 5