Induced sputum: validity of fluid-phase IL-5 measurement

Area of Science:

• Respiratory Medicine
• Immunology
• Biochemistry

Background:

• Interleukin-5 (IL-5) measurement in induced sputum is crucial for asthma assessment.
• The accuracy and validity of current IL-5 measurement techniques in sputum are questionable.

Purpose of the Study:

• To evaluate the validity of sputum IL-5 measurements using spiking experiments.
• To determine the impact of dithiothreitol (DTT) on IL-5 quantification in induced sputum.

Main Methods:

• Induced sputum samples from 26 asthma patients were spiked with IL-5.
• Recovery rates were assessed using immunoassay, with and without albumin.
• Radiolabeled IL-5 recovery was compared between gamma counting and immunoassay.
• The effect of DTT on IL-5 immunoassay was investigated.

Main Results:

• Mean IL-5 recovery via immunoassay was low (26.1%), significantly improved by albumin (47.7%).
• Gamma counting showed high IL-5 recovery (84.8%), unaffected by albumin.
• Dithiothreitol (DTT) did not significantly alter IL-5 immunoassay results.

Conclusions:

• Current immunoassay methods for sputum IL-5 exhibit poor validity.
• Discrepancies suggest immunoassay epitope recognition issues in sputum.
• Interfering substances like proteases or autoantibodies, not DTT, likely impact IL-5 measurement.