Detecting Secreted Analytes from Immune Cells: An Overview of Technologies

The tumor microenvironment is largely shaped by secreted factors and infiltrating immune cells and the nature of this environment can profoundly influence tumor growth and progression. As such, there is an increasing need to identify and quantify secreted factors by tumor cells, tumor-associated cells, and infiltrating immune cells. To meet this need, the dynamic range of immunoassays such as ELISAs and ELISpots have been improved and the scope of reagents commercially available has been expanded. In addition, new bead-based and membrane-based screening arrays have been developed to allow for the simultaneous detection of multiple analytes in one sample. Similarly, the optimization of intracellular staining for flow cytometry now allows for the quantitation of multiple cytokines from either a purified cell population or a complex mixed cell suspension. Herein, we review the rapidly evolving technologies that are currently available to detect secreted analytes. Emphasis is placed on discussing the advantages and disadvantages of these assays and their applications.