What is the first step in the common assay for cytokine detection using flow cytometry?

The first step in the common assay for cytokine detection using flow cytometry is cell collection. This initial step is critical as it involves obtaining the appropriate cells from tissues or blood, which are necessary for analyzing cytokine production. The success of the subsequent steps depends on the quality and quantity of the cells collected. Proper cell collection ensures that there are sufficient viable cells available for fixation, permeabilization, and subsequent staining, which are essential for accurately detecting intracellular cytokines.

Following cell collection, fixation usually occurs to preserve the cellular structure and prepare the cells for staining. After fixation, permeabilization allows antibodies to access intracellular proteins such as cytokines. Lastly, intracellular staining is performed to label those proteins, enabling their detection and quantification using flow cytometry. However, it's important to recognize that these steps build upon the foundational action of collecting cells, making it the critical beginning of the process.