Optimization of Luminex Cytokine Assay Performance

Cytokines and chemokines are integral signaling molecules playing a critical role in immune responses. These responses help to assess therapeutic effects and understand disease mechanisms and progression. Hence, quantifying these biomolecules is increasingly becoming crucial for studying drug-body interactions at every stage of a drug discovery project. Over the years, several methods have been developed for assessing cytokines during the drug discovery and drug development process. Out of these approaches, ELISA is still the most widely used method for evaluating cytokines and chemokines in biological matrices.

However, ELISA assays are laborious and expensive for assessing large profiles of chemokines and cytokines in biological samples. Hence, newer technologies such as Luminex ELISA multiplex assays are ideal platforms for evaluating and quantifying these biomarkers. Luminex cytokine assays can quantitate multiple cytokines and chemokines in limited sample volumes. However, limited sample volumes and low quantities of cytokines of interest are considerable challenges faced while assessing cytokines and chemokines. Hence, we provide crucial considerations for optimizing the performance of Luminex-based assays. We also highlight aspects of three manufacturer Luminex kits.

Technical elements and standard curve

Some kits, such as the VersaMAP kit, have higher bead aggregation and hence a lower bead count. This discrepancy is partly due to its software setting. However, researchers can use vacuum washing and relatively viscous tissue homogenates to retain sample matrices. Also, using a magnetic plate washer is advantageous while analyzing tissue samples.

Low sample volume is a significant advantage of using Luminex-based assays. Both Bio-Plex and VersaMAP need 50μL samples per well, whereas MILLIPLEX recommends only 25μL per well. Furthermore, MILLIPLEX also provides two additional quality control vials with expected ranges. However, Bio-Plex has the shortest incubation periods, making it faster than VersaMAP and MILLIPLEX. Hence, researchers can select a suitable Luminex kit to enhance assay performance by understanding individual experimental requirements. 

Furthermore, each assay kit has a different dilution for the standard curve, ranging from 3-fold up to 5-fold dilutions. These dilutions are relatively wider than 2-fold ELISA assays and thus provide a broader dynamic assay range. Again, researchers can maximize assay performance by employing wider dilutions to increase the assay wells and decrease the need to retest multiple cytokines. Though considering analyte availability and compatibility is critical for optimizing the performances of Luminex assays.

Adequate optimization of sample processing protocols

Researchers report that manual homogenization and disruption techniques are effective compared to automated methods. This superiority is unexpected but may be due to the relatively large surface area of the Luminex assay beads. The same researchers report that homogenization using a needle leads to sample loss. However, they can easily avoid it through aspiration into the tip of a pipette. Moreover, researchers can further enhance assay performance by avoiding ionic detergent and enzymatic and chemical methods to limit protein degradation.

Most Luminex manufacturers do not use complex study matrices such as tissue homogenates during developing and validating Luminex assays. Hence, researchers must optimize the matrix and extraction buffer during cytokine analysis. Generally, PBS-based buffers are used for cytokine evaluations in ELISA assays.

Conclusion

Even though Luminex assays are the most suitable platforms for analyzing multiple cytokines and chemokines in biological matrices, their sensitive measurements can be challenging. Hence, researchers must embrace the above considerations to optimize the performance of Luminex-based assays.

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By Cary Grant

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