Why are eosinophils not a reported granulocyte population on your standard panel?

We and others (e.g. Rahman, Tordesillas and Berin, Cytometry Part A 2016) have seen that eosinophils are difficult to identify with mass cytometry, even when markers specific to eosinophils (such as SIGLEC 8) are included in the panel. During our validation studies, we noted eosinophils tend to bind nonspecifically to some antibodies for which they don’t express the antigen, which can lead to eosinophils being confused for other cell types (e.g. platelets, neutrophils, etc). We also observed that eosinophil population frequencies are more sensitive to storage conditions (e.g. measured eosinophil frequencies drop sharply if blood is stored for 5 hours at room temperature before fixation), whereas other populations are more stable. Therefore, Teiko decided that unless specifically requested by a customer, we use SIGLEC8 as a ‘dump gate’ to remove eosinophils and increase confidence in other granulocyte populations, rather than report on eosinophils themselves.

While heparin treatment before antibody staining can improve eosinophil detection, that same treatment negatively affects performance of several key state marker antibodies (i.e. Ki67, TCF1, FOXP3 and Tbet). Our team of experts can discuss options if you are particularly interested in eosinophil frequencies for your study.

Note that in any case, we cannot report on eosinophil state markers, as their intracellular granules interfere with antibody binding.